The ALICE experiment has measured the inclusive J/$\psi$ production in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}} } = 2.76$ TeV down to zero transverse momentum in the rapidity range $2.5 < y < 4$. A suppression of the inclusive J/$\psi$ yield in Pb-Pb is observed with respect to the one measured in pp collisions scaled by the number of binary nucleon-nucleon collisions. The nuclear modification factor, integrated over the 0-80% most central collisions, is $0.545 \pm 0.032 \rm{(stat.)} \pm 0.083 \rm{(syst.)}$ and does not exhibit a significant dependence on the collision centrality. These features appear significantly different from measurements at lower collision energies. Models including J/$\psi$ production from charm quarks in a deconfined partonic phase can describe our data.
Jpsi Nuclear Modification Factor (Raa) measured in Pb-Pb collisions at sqrt(sNN) = 2.76 TeV in 2.5 < y < 4 and pt > 0 GeV/c, as a function of - the average number of participating nucleons (<Npart>), - the average number of participating nucleons (<Npart,w>) weigthed by the average number of binary collisions, - the mid-rapidity charged-particle density measured at pseudo-rapidity eta = 0 dNch,w/deta|eta=0 weigthed by the average number of binary collisions.
Centrality integrated (0%-80%) inclusive Jpsi Nuclear Modification Factor (Raa) measured in Pb-Pb collisions at sqrt(sNN) = 2.76 TeV as a function of rapidity for two transverse momentum ranges.
The production of K$^{*}$(892)$^{0}$ and $\phi$(1020) mesons has been measured in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. K$^{*0}$ and $\phi$ are reconstructed via their decay into charged hadrons with the ALICE detector in the rapidity range $-0.5 < y <0$. The transverse momentum spectra, measured as a function of the multiplicity, have p$_{\mathrm{T}}$ range from 0 to 15 GeV/$c$ for K$^{*0}$ and from 0.3 to 21 GeV/$c$ for $\phi$. Integrated yields, mean transverse momenta and particle ratios are reported and compared with results in pp collisions at $\sqrt{s}$ = 7 TeV and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV. In Pb-Pb and p-Pb collisions, K$^{*0}$ and $\phi$ probe the hadronic phase of the system and contribute to the study of particle formation mechanisms by comparison with other identified hadrons. For this purpose, the mean transverse momenta and the differential proton-to-$\phi$ ratio are discussed as a function of the multiplicity of the event. The short-lived K$^{*0}$ is measured to investigate re-scattering effects, believed to be related to the size of the system and to the lifetime of the hadronic phase.
Average charged particle pseudo-rapidity density, $\langle\mathrm{d}N_{\rm ch}/\mathrm{d}\eta_{\mathrm{lab}}\rangle$, measured at mid-rapidity in visible cross section event classes and average number of colliding nucleons, $\langle\mathrm{N_{coll}}\rangle$. Multiplicity classes are defined using the V0A estimator; values for $\langle\mathrm{d}N_{\rm ch}/\mathrm{d}\eta_{\mathrm{lab}}\rangle$ are corrected for vertexing and trigger efficiency. Since statistical uncertainties are negligible, only total systematic uncertainties are reported.
$p_{\rm T}$-differential yield of (K$^{*0}$ + $\overline{K^{*0}}$)/2 in p-Pb collisions with centre-of-mass energy/nucleon=5.02 TeV (NSD). Additional systematic error: +- 3.1% (normalization).
$p_{\rm T}$-differential yield of (K$^{*0}$ + $\overline{K^{*0}}$)/2 in p-Pb collisions with centre-of-mass energy/nucleon=5.02 TeV (0-20% multiplicity class).
Three- and four-pion Bose-Einstein correlations are presented in pp, p-Pb, and Pb-Pb collisions at the LHC. We compare our measured four-pion correlations to the expectation derived from two- and three-pion measurements. Such a comparison provides a method to search for coherent pion emission. We also present mixed-charge correlations in order to demonstrate the effectiveness of several analysis procedures such as Coulomb corrections. Same-charge four-pion correlations in pp and p-Pb appear consistent with the expectations from three-pion measurements. However, the presence of non-negligible background correlations in both systems prevent a conclusive statement. In Pb-Pb collisions, we observe a significant suppression of three- and four-pion Bose-Einstein correlations compared to expectations from two-pion measurements. There appears to be no centrality dependence of the suppression within the 0-50% centrality interval. The origin of the suppression is not clear. However, by postulating either coherent pion emission or large multibody Coulomb effects, the suppression may be explained.
Mixed charge (- - - +) C4QS, a4QS, c4QS at low KT4 in pp collisions projected against Q4.
Mixed charge (- - - +) C4QS, a4QS, c4QS at high KT4 in pp collisions projected against Q4.
Mixed charge (- - - +) C4QS, a4QS, c4QS at low KT4 in pPb collisions projected against Q4.
We report the measurements of correlations between event-by-event fluctuations of amplitudes of anisotropic flow harmonics in nucleus-nucleus collisions, obtained for the first time using a new analysis method based on multiparticle cumulants in mixed harmonics. This novel method is robust against systematic biases originating from non-flow effects and by construction any dependence on symmetry planes is eliminated. We demonstrate that correlations of flow harmonics exhibit a better sensitivity to medium properties than the individual flow harmonics. The new measurements are performed in Pb-Pb collisions at the centre-of-mass energy per nucleon pair of $\sqrt{s_{_{\rm NN}}}=2.76$ TeV by the ALICE experiment at the Large Hadron Collider (LHC). The centrality dependence of correlation between event-by-event fluctuations of the elliptic, $v_2$, and quadrangular, $v_4$, flow harmonics, as well as of anti-correlation between $v_2$ and triangular, $v_3$, flow harmonics are presented. The results cover two different regimes of the initial state configurations: geometry-dominated (in mid-central collisions) and fluctuation-dominated (in the most central collisions). Comparisons are made to predictions from MC-Glauber, viscous hydrodynamics, AMPT and HIJING models. Together with the existing measurements of individual flow harmonics the presented results provide further constraints on initial conditions and the transport properties of the system produced in heavy-ion collisions.
Centrality dependence of observables SC(4,2) and SC(3,2) in Pb-Pb collisions at 2.76 TeV.
Centrality dependence of normalized observables SC(4,2) and SC(3,2) in Pb-Pb collisions at 2.76 TeV.
Centrality dependence of observables SC(4,2) and SC(3,2) in Pb-Pb collisions at 2.76 TeV, in 0-10% most central collisions.
We report the transverse energy ($E_{\mathrm T}$) measured with ALICE at midrapidity in Pb-Pb collisions at ${\sqrt{s_{\mathrm {NN}}}}$ = 2.76 TeV as a function of centrality. The transverse energy was measured using identified single particle tracks. The measurement was cross checked using the electromagnetic calorimeters and the transverse momentum distributions of identified particles previously reported by ALICE. The results are compared to theoretical models as well as to results from other experiments. The mean $E_{\mathrm T}$ per unit pseudorapidity ($\eta$), $\langle $d$E_{\mathrm T}/$d$\eta \rangle$, in 0-5% central collisions is 1737 $\pm$ 6(stat.) $\pm$ 97(sys.) GeV. We find a similar centrality dependence of the shape of $\langle $d$E_{\mathrm T}/$d$\eta \rangle$ as a function of the number of participating nucleons to that seen at lower energies. The growth in $\langle $d$E_{\mathrm T}/$d$\eta \rangle$ at the LHC ${\sqrt{s_{\mathrm {NN}}}}$ exceeds extrapolations of low energy data. We observe a nearly linear scaling of $\langle $d$E_{\mathrm T}/$d$\eta \rangle$ with the number of quark participants. With the canonical assumption of a 1 fm/$c$ formation time, we estimate that the energy density in 0-5% central Pb-Pb collisions at ${\sqrt{s_{\mathrm {NN}}}}$ = 2.76 TeV is 12.3 $\pm$ 1.0 GeV/fm$^3$\xspace and that the energy density at the most central 80 fm$^2$ of the collision is at least 21.5 $\pm$ 1.7 GeV/fm$^3$. This is roughly 2.3 times that observed in 0-5% central Au-Au collisions at ${\sqrt{s_{\mathrm {NN}}}}$ = 200 GeV.
$\langle $d$E_{\mathrm T}/$d$\eta \rangle / (\langle N_{\mathrm{part}}/2\rangle)$ versus $N_{\mathrm{part}}$, $\langle $d$E_{\mathrm T}/$d$\eta \rangle / (\langle N_{\mathrm{quark}}/2\rangle)$, and $\epsilon\tau$ versus $N_{\mathrm{part}}$ at midrapidity calculated from the tracking detectors,.
$N_{part}$, $N_{quark}$, and area from Glauber calculations.
$\langle $d$E_{\mathrm T}/$d$\eta \rangle$/$\langle $d$N_{\mathrm{ch}}/$d$\eta \rangle$ versus $N_{part}$.
The elliptic, triangular, quadrangular and pentagonal anisotropic flow coefficients for $\pi^{\pm}$, $\mathrm{K}^{\pm}$ and p+$\overline{\mathrm{p}}$ in Pb-Pb collisions at $\sqrt{s_\mathrm{{NN}}} = 2.76$ TeV were measured with the ALICE detector at the Large Hadron Collider. The results were obtained with the Scalar Product method, correlating the identified hadrons with reference particles from a different pseudorapidity region. Effects not related to the common event symmetry planes (non-flow) were estimated using correlations in pp collisions and were subtracted from the measurement. The obtained flow coefficients exhibit a clear mass ordering for transverse momentum ($p_{\mathrm{T}}$) values below $\approx$ 3 GeV/$c$. In the intermediate $p_{\mathrm{T}}$ region ($3 < p_{\mathrm{T}} < 6$ GeV/$c$), particles group at an approximate level according to the number of constituent quarks, suggesting that coalescence might be the relevant particle production mechanism in this region. The results for $p_{\mathrm{T}} < 3$ GeV/$c$ are described fairly well by a hydrodynamical model (iEBE-VISHNU) that uses initial conditions generated by A Multi-Phase Transport model (AMPT) and describes the expansion of the fireball using a value of 0.08 for the ratio of shear viscosity to entropy density ($\eta/s$), coupled to a hadronic cascade model (UrQMD). Finally, expectations from AMPT alone fail to quantitatively describe the measurements for all harmonics throughout the measured transverse momentum region. However, the comparison to the AMPT model highlights the importance of the late hadronic rescattering stage to the development of the observed mass ordering at low values of $p_{\mathrm{T}}$ and of coalescence as a particle production mechanism for the particle type grouping at intermediate values of $p_{\mathrm{T}}$ for all harmonics.
pion <uQ>2 as a function of pT in pp collision.
kaon <uQ>2 as a function of pT in pp collision.
proton <uQ>2 as a function of pT in pp collision.
The elliptic flow of electrons from heavy-flavour hadron decays at mid-rapidity ($|y|$ $<$ 0.7) is measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV with ALICE at the LHC. The particle azimuthal distribution with respect to the reaction plane can be parametrized with a Fourier expansion, where the second coefficient ($v_{\rm 2}$) represents the elliptic flow. The $v_{\rm 2}$ coefficient of inclusive electrons is measured in three centrality classes (0-10%, 10-20% and 20-40%) with the event plane and the scalar product methods in the transverse momentum ($p_{\rm T}$) intervals 0.5-13 GeV/$c$ and 0.5-8 GeV/$c$, respectively. After subtracting the background, mainly from photon conversions and Dalitz decays of neutral mesons, a positive $v_{\rm 2}$ of electrons from heavy-flavour hadron decays is observed in all centrality classes, with a maximum significance of $5.9\sigma$ in the interval $2 <$ $p_{\rm T}$ $<$ 2.5 GeV/$c$ in semi-central collisions (20-40%). The value of $v_{\rm 2}$ decreases towards more central collisions at low and intermediate $p_{\rm T}$ (0.5 $<$ $p_{\rm T}$ $<$ 3 GeV/$c$). The $v_{\rm 2}$ of electrons from heavy-flavour hadron decays at mid-rapidity is found to be similar to the one of muons from heavy-flavour hadron decays at forward rapidity (2.5 $<$ $y$ $<$ 4). The results are described within uncertainties by model calculations including substantial elastic interactions of heavy quarks with an expanding strongly-interacting medium.
Elliptic flow of electrons from heavy flavour hadron decays as a function of transverse momentum at midrapidity in the 0--10% centrality class.
Elliptic flow of electrons from heavy flavour hadron decays as a function of transverse momentum at midrapidity in the 10--20% centrality class.
Elliptic flow of electrons from heavy flavour hadron decays as a function of transverse momentum at midrapidity in the 20--40% centrality class.
The inclusive production of the $\psi$(2S) charmonium state was studied as a function of centrality in p-Pb collisions at the nucleon-nucleon center of mass energy $\sqrt{s_{\rm NN}}$ = 5.02 TeV at the CERN LHC. The measurement was performed with the ALICE detector in the center of mass rapidity ranges $-4.46<y_{\rm cms}<-2.96$ and $2.03<y_{\rm cms}<3.53$, down to zero transverse momentum, by reconstructing the $\psi$(2S) decay to a muon pair. The $\psi$(2S) production cross section $\sigma_{\psi(\rm 2S)}$ is presented as a function of the collision centrality, which is estimated through the energy deposited in forward rapidity calorimeters. The relative strength of nuclear effects on the $\psi$(2S) and on the corresponding 1S charmonium state J/$\psi$ is then studied by means of the double ratio of cross sections $[\sigma_{\psi(\rm 2S)}/\sigma_{\rm J/\psi}]_{\rm pPb}/[\sigma_{\psi(\rm 2S)}/\sigma_{\rm J/\psi}]_{\rm pp}$ between p-Pb and pp collisions, and by the values of the nuclear modification factors for the two charmonium states. The results show a large suppression of $\psi$(2S) production relative to the J/$\psi$ at backward (negative) rapidity, corresponding to the flight direction of the Pb-nucleus, while at forward (positive) rapidity the suppressions of the two states are comparable. Finally, comparisons to results from lower energy experiments and to available theoretical models are presented.
Centrality-differential cross section dsigma_JPsi/dy in the backward and forward rapidity ranges (-4.46<y_cms<-2.96 and 2.03<y_cms<3.53). The first uncertainty is statistical, the second is a systematic one. The third uncertainty is a systematic uncertainty fully correlated over centrality.
Centrality dependence of the Psi(2S)/J/Psi ratio in the backward and forward rapidity ranges (-4.46<y_cms<-2.96 and 2.03<y_cms<3.53). The first uncertainty is statistical, the second is a systematic one. The third systematic uncertainty is fully correlated over centrality.
Centrality dependence of the (Psi(2S)/J/Psi)_pA/(Psi(2S)/J/Psi)_pp double ratio in the backward and forward rapidity range (-4.46<y_cms<-2.96 and 2.03<y_cms<3.53). The first uncertainty is statistical, the second one is a systematic one. The third systematic uncertainty is fully correlated over centrality, but uncorrelated versus rapidity, while the fourth uncertainty is fully correlated over centrality and over rapidity.
The pseudorapidity density of charged particles ($\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta$) at mid-rapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}}$ = 5.02 TeV. It increases with centrality and reaches a value of $1943 \pm 54$ in $|\eta|<0.5$ for the 5% most central collisions. A rise in $\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta$ as a function of $\sqrt{s_{\rm NN}}$ for the most central collisions is observed, steeper than that observed in proton-proton collisions and following the trend established by measurements at lower energy. The centrality dependence of $\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta$ as a function of the average number of participant nucleons, ${\langle N_\mathrm{part} \rangle}$, calculated in a Glauber model, is compared with the previous measurement at lower energy. A constant factor of about 1.2 describes the increase in $\frac{2}{\langle N_\mathrm{part} \rangle}\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta \rangle$ from $\sqrt{s_{\rm NN}}$ = 2.76 TeV to $\sqrt{s_{\rm NN}}$ = 5.02 TeV for all centrality intervals, within the measured range of 0-80% centrality. The results are also compared to models based on different mechanisms for particle production in nuclear collisions.
The values of ${\langle N_\mathrm{part} \rangle}$ obtained with the Glauber model are measured in $|\eta|$ < 0.5 for eleven centrality classes. The statistical error contribution being negligible.
The $\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta$ values measured in $|\eta|$ < 0.5 for eleven centrality classes.
The $\frac{2}{\langle N_\mathrm{part} \rangle}\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta \rangle$ values measured in $|\eta|$ < 0.5 for eleven centrality classes. The statistical error contribution being negligible.
Measurements of charged jet production as a function of centrality are presented for p-Pb collisions recorded at $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector. Centrality classes are determined via the energy deposit in neutron calorimeters at zero degree, close to the beam direction, to minimise dynamical biases of the selection. The corresponding number of participants or binary nucleon-nucleon collisions is determined based on the particle production in the Pb-going rapidity region. Jets have been reconstructed in the central rapidity region from charged particles with the anti-$k_{\rm T}$ algorithm for resolution parameters $R = 0.2$ and $R = 0.4$ in the transverse momentum range 20 to 120 GeV/$c$. The reconstructed jet momentum and yields have been corrected for detector effects and underlying-event background. In the five centrality bins considered, the charged jet production in p-Pb collisions is consistent with the production expected from binary scaling from pp collisions. The ratio of jet yields reconstructed with the two different resolution parameters is also independent of the centrality selection, demonstrating the absence of major modifications of the radial jet structure in the reported centrality classes.
pp reference spectrum, obtained by scaling down the measured charged jets at 7 TeV to 5.02 TeV for R = 0.2 jets.
$p_{\rm T}$-differential production cross section of charged jets in p-Pb collisions at 5.02 TeV for R = 0.2 measured with the ALICE detector, centrality 0-20%.
$p_{\rm T}$-differential production cross section of charged jets in p-Pb collisions at 5.02 TeV for R = 0.2 measured with the ALICE detector, centrality 20-40%.
We have studied J/psi production in pp collisions at $\sqrt{s}=7$ TeV at the LHC through its muon pair decay. The polar and azimuthal angle distributions of the decay muons were measured, and results on the J/$\psi$ polarization parameters $\lambda_{\theta}$ and $\lambda_\phi$ were obtained. The study was performed in the kinematic region 2.5<y<4, 2<$p_{\rm T}$<8 GeV/$c$, in the helicity and Collins-Soper reference frames. In both frames, the polarization parameters are compatible with zero, within uncertainties.
$\lambda_\theta$ as a function of $p_{\rm T}$ for inclusive J/$\psi$, measured in the helicity reference frame.
$\lambda_\phi$ as a function of $p_{\rm T}$ for inclusive J/$\psi$, measured in the helicity reference frame.
$\lambda_\theta$ as a function of $p_{\rm T}$ for inclusive J/$\psi$, measured in the Collins-Soper reference frame.
We present measurements of two-particle correlations with neutral pion trigger particles of transverse momenta $8 < p_{\mathrm{T}}^{\rm trig} < 16~\mathrm{GeV}/c$ and associated charged particles of $0.5 < p_{\mathrm{T}}^{\rm assoc} < 10~\mathrm{GeV}/c$ versus the azimuthal angle difference $\Delta\varphi$ at midrapidity in pp and central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV with ALICE. The new measurements exploit associated charged hadrons down to $0.5~\mathrm{GeV}/c$, which significantly extends our previous measurement that only used charged hadrons above $3~\mathrm{GeV}/c$. After subtracting the contributions of the flow background, $v_2$ to $v_5$, the per-trigger yields are extracted for $|\Delta\varphi|<0.7$ on the near and for $|\Delta\varphi-\pi| < 1.1$ on the away side. The ratio of per-trigger yields in Pb--Pb to those in pp collisions, $I_{\mathrm{AA}}$, is measured on the near and away side for the $0$--$10$\% most central Pb--Pb collisions. On the away side, the per-trigger yields in Pb--Pb are strongly suppressed to the level of $I_{\mathrm{AA}} \approx 0.6$ for $p_{\mathrm{T}}^{\rm assoc} > 3~\mathrm{GeV}/c$, while with decreasing momenta an enhancement develops reaching about $5$ at low $p_{\mathrm{T}}^{\rm assoc}$. On the near side, an enhancement of $I_{\mathrm{AA}}$ between $1.2$ at the highest to $1.8$ at the lowest $p_{\mathrm{T}}^{\rm assoc}$ is observed. The data are compared to parton-energy-loss predictions of the JEWEL and AMPT event generators, as well as to a perturbative QCD calculation with medium-modified fragmentation functions. All calculations qualitatively describe the away-side suppression at high $p_{\mathrm{T}}^{\rm assoc}$. Only AMPT captures the enhancement at low $p_{\mathrm{T}}^{\rm assoc}$, both on the near and away side. However, it also underpredicts $I_{\mathrm{AA}}$ above $5$ GeV/$c$, in particular on the near-side.
Charged-particle associated yields relative to $\pi^{0}$ trigger particles versus $\Delta\varphi$ in pp collisions at $\sqrt{s_{NN}}$=2.76 TeV. The $\pi^{0}$ trigger momentum range is $8< p_{T}^{trig} < 16~GeV/c$, and associated charged particle ranges are $0.5 < p_{T}^{assoc} < 1$, $1 < p_{T}^{assoc} < 2$, $2 < p_{T}^{assoc} < 4$ and $4 < p_{T}^{assoc} < 6~GeV/c$.
Charged-particle associated yields relative to $\pi^{0}$ trigger particles versus $\Delta\varphi$ in Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV. The $\pi^{0}$ trigger momentum range is $8< p_{T}^{trig} < 16~GeV/c$, and associated charged particle ranges are $0.5 < p_{T}^{assoc} < 1$, $1 < p_{T}^{assoc} < 2$, $2 < p_{T}^{assoc} < 4$ and $4 < p_{T}^{assoc} < 6~GeV/c$.
Per-trigger yield modification, $I_{\rm AA}$, on the near side with trigger $\pi^{0}$ particle at $8 < p_{T}^{trig} < 16~GeV/c$ for $0$-$10$$\%$ Pb-Pb collisions at $\sqrt{s_{NN}}$= 2.76 TeV.
The inclusive J/$\psi$ production has been studied in Pn-Pb and pp collisions at the centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}=5.02$ TeV, using the ALICE detector at the CERN LHC. The J/$\psi$ meson is reconstructed, in the centre-of-mass rapidity interval $2.5<y<4$ and in the transverse-momentum range $p_{\rm T}<12$ GeV/$c$, via its decay to a muon pair. In this Letter, we present results on the inclusive J/$\psi$ cross section in pp collisions at $\sqrt{s}=5.02$ TeV and on the nuclear modification factor $R_{\rm AA}$. The latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum $p_{\rm T}$ of the J/$\psi$. The measured $R_{\rm AA}$ values indicate a suppression of the J/$\psi$ in nuclear collisions and are then compared to our previous results obtained in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV. The ratio of the $R_{\rm AA}$ values at the two energies is also computed and compared to calculations of statistical and dynamical models. The numerical value of the ratio for central events (0-10\% centrality) is $1.17 \pm 0.04 {\rm{(stat)}}\pm 0.20 {\rm{(syst)}}$. In central events, as a function of $p_{\rm T}$, a slight increase of $R_{\rm AA}$ with collision energy is visible in the region $2<p_{\rm T}<6$ GeV/$c$. Theoretical calculations provide a good description of the measurements, within uncertainties.
Differential cross section ${\rm d}^2\sigma^{\rm pp}_{{\rm J}/\psi}/{\rm d}y{\rm d}p_{\rm T}$ for inclusive J/$\psi$ cross section in pp collisions at $\sqrt{s}=5.02$ TeV. The first uncertainty is statistical, the second is the uncorrelated systematic, while the third one is a $p_{\rm T}$-correlated systematic uncertainty.
The nuclear modification factor for inclusive J/$\psi$ production, as a function of centrality, at $\sqrt{s_{\rm NN}}=5.02$ TeV. The widths of the centrality classes used are 2% from 0 to 12%, then 3% up to 30% and 5% for more peripheral collisions. The first uncertainty is statistical, the second is the uncorrelated systematic, while the third one is a centrality-correlated systematic uncertainty.
Centrality dependence (with 10% width centrality classes) of the inclusive J/$\psi$ $R_{\rm AA}$ for $0.3<p_{\rm T}<8$ GeV/$c$. The first uncertainty is statistical, the second is the uncorrelated systematic, while the third one is a centrality-correlated systematic uncertainty.
At sufficiently high temperature and energy density, nuclear matter undergoes a transition to a phase in which quarks and gluons are not confined: the Quark-Gluon Plasma (QGP) [1]. Such an extreme state of strongly-interacting QCD (Quantum Chromo-Dynamics) matter is produced in the laboratory with high-energy collisions of heavy nuclei, where an enhanced production of strange hadrons is observed [2-6]. Strangeness enhancement, originally proposed as a signature of QGP formation in nuclear collisions [7], is more pronounced for multi-strange baryons. Several effects typical of heavy-ion phenomenology have been observed in high-multiplicity proton-proton (pp) collisions [8,9]. Yet, enhanced production of multi-strange particles has not been reported so far. Here we present the first observation of strangeness enhancement in high-multiplicity pp collisions. We find that the integrated yields of strange and multi-strange particles relative to pions increases significantly with the event charged-particle multiplicity. The measurements are in remarkable agreement with p-Pb collision results [10,11] indicating that the phenomenon is related to the final system created in the collision. In high-multiplicity events strangeness production reaches values similar to those observed in Pb-Pb collisions, where a QGP is formed.
$K^{0}_{S}$ transverse momentum spectrum: V0M Class I (pp at $\sqrt{s}=7$ TeV).
$K^{0}_{S}$ transverse momentum spectrum: V0M Class II (pp at $\sqrt{s}=7$ TeV).
$K^{0}_{S}$ transverse momentum spectrum: V0M Class III (pp at $\sqrt{s}=7$ TeV).
Electrons from heavy-flavour hadron decays (charm and beauty) were measured with the ALICE detector in Pb-Pb collisions at a centre-of-mass of energy $\sqrt{s_{\rm NN}}=2.76$ TeV. The transverse momentum ($p_{\rm T}$) differential production yields at mid-rapidity were used to calculate the nuclear modification factor $R_{\rm AA}$ in the interval $3<p_{\rm T}< 18$ GeV/$c$. The $R_{\rm AA}$ shows a strong suppression compared to binary scaling of pp collisions at the same energy (up to a factor of 4) in the 10% most central Pb-Pb collisions. There is a centrality trend of suppression, and a weaker suppression (down to a factor of 2) in semi-peripheral (50-80%) collisions is observed. The suppression of electrons in this broad $p_{\rm T}$ interval indicates that both charm and beauty quarks lose energy when they traverse the hot medium formed in Pb-Pb collisions at LHC.
Pb-Pb collision centrality 0-10%.
Pb-Pb collision centrality 10-20%.
Pb-Pb collision centrality 20-30%.
We present measurements of the elliptic ($\mathrm{v}_2$), triangular ($\mathrm{v}_3$) and quadrangular ($\mathrm{v}_4$) anisotropic azimuthal flow over a wide range of pseudorapidities ($-3.5< \eta < 5$). The measurements are performed with Pb-Pb collisions at $\sqrt{s_{\text{NN}}} = 2.76$ TeV using the ALICE detector at the Large Hadron Collider (LHC). The flow harmonics are obtained using two- and four-particle correlations from nine different centrality intervals covering central to peripheral collisions. We find that the shape of $\mathrm{v}_n(\eta)$ is largely independent of centrality for the flow harmonics $n=2-4$, however the higher harmonics fall off more steeply with increasing $|\eta|$. We assess the validity of extended longitudinal scaling of $\mathrm{v}_2$ by comparing to lower energy measurements, and find that the higher harmonic flow coefficients are proportional to the charged particle densities at larger pseudorapidities. Finally, we compare our measurements to both hydrodynamical and transport models, and find they both have challenges when it comes to describing our data.
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The production of charged pions, kaons and (anti)protons has been measured at mid-rapidity ($-0.5 y 0$) in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV using the ALICE detector at the LHC. Exploiting particle identification capabilities at high transverse momentum ($p_{\rm T}$), the previously published $p_{\rm T}$ spectra have been extended to include measurements up to 20 GeV/$c$ for seven event multiplicity classes. The $p_{\rm T}$ spectra for pp collisions at $\sqrt{s}=7$ TeV, needed to interpolate a pp reference spectrum, have also been extended up to 20 GeV/$c$ to measure the nuclear modification factor ($R_{\rm pPb}$) in non-single diffractive p-Pb collisions. At intermediate transverse momentum ($2 p_{\rm T} 10$\,GeV/$c$) the proton-to-pion ratio increases with multiplicity in p-Pb collisions, a similar effect is not present in the kaon-to-pion ratio. The $p_{\rm T}$ dependent structure of such increase is qualitatively similar to those observed in pp and heavy-ion collisions. At high $p_{\rm T}$ ($>10$ GeV/$c$), the particle ratios are consistent with those reported for pp and Pb-Pb collisions at the LHC energies. At intermediate $p_{\rm T}$ the (anti)proton $R_{\rm pPb}$ shows a Cronin-like enhancement, while pions and kaons show little or no nuclear modification. At high $p_{\rm T}$ the charged pion, kaon and (anti)proton $R_{\rm pPb}$ are consistent with unity within statistical and systematic uncertainties.
pT-differential invariant yield of charged pions in p-Pb collisions with centre-of-mass energy/nucleon=5.02 TeV, measured for different V0A multiplicity classes. The first uncertainty is statistical, the second one is the total systematic uncertainty, while the third one is the uncorrelated systematic uncertainty which is multiplicity dependent.
pT-differential invariant yield of charged pions in p-Pb collisions with centre-of-mass energy/nucleon=5.02 TeV, measured for NSD events. The first uncertainty is statistical, the second one is the total systematic uncertainty, while the third one is the uncorrelated systematic uncertainty which is multiplicity dependent.
pT-differential invariant yield of charged kaons in p-Pb collisions with centre-of-mass energy/nucleon=5.02 TeV, measured for different V0A multiplicity classes. The first uncertainty is statistical, the second one is the total systematic uncertainty, while the third one is the uncorrelated systematic uncertainty which is multiplicity dependent.
The production cross sections of the prompt charmed mesons D$^0$, D$^+$, D$^{*+}$ and D$_s$ were measured at mid-rapidity in p-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}=5.02$ TeV with the ALICE detector at the LHC. D mesons were reconstructed from their decays D$^0\rightarrow{\rm K}^-\pi^+$, D$^+\rightarrow{\rm K}^-\pi^+\pi^+$, D$^{*+}\rightarrow D^0\pi^+$, D$_s^+\rightarrow\phi\pi^+\rightarrow{\rm K}^-{\rm K}^+\pi^+$, and their charge conjugates. The $p_{\rm T}$-differential production cross sections were measured at mid-rapidity in the interval $1<p_{\rm T}<24$ GeV/$c$ for D$^0$, D$^+$ and D$^{*+}$ mesons and in $2<p_{\rm T}<12$ GeV/$c$ for D$_s$ mesons, using an analysis method based on the selection of decay topologies displaced from the interaction vertex. The production cross sections of the D$^0$, D$^+$ and D$^{*+}$ mesons were also measured in three $p_{\rm T}$ intervals as a function of the rapidity $y_{\rm cms}$ in the centre-of-mass system in $-1.26<y_{\rm cms}<0.34$. In addition, the prompt D$^0$ cross section was measured in pp collisions at $\sqrt{s}=7$ TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV down to $p_{\rm T}=0$ using an analysis technique that is based on the estimation and subtraction of the combinatorial background, without reconstruction of the D$^0$ decay vertex. The nuclear modification factor $R_{\rm pPb}(p_{\rm T})$, defined as the ratio of the $p_{\rm T}$-differential D-meson cross section in p-Pb collisions and that in pp collisions scaled by the mass number of the Pb nucleus, was calculated for the four D-meson species and found to be compatible with unity within experimental uncertainties. The results are compared to theoretical calculations that include cold-nuclear-matter effects and to transport model calculations incorporating the interactions of charm quarks with an expanding deconfined medium.
pT-differential cross section of inclusive Dzero mesons in pp collisions at sqrt{sNN}=7 TeV in the rapidity interval |y|<0.5. Branching ratio of D0->Kpi : 0.0388.
pT-differential cross section of prompt Dzero mesons in pp collisions at sqrt{sNN}=7 TeV in the rapidity interval |y|<0.5. Branching ratio of D0->Kpi : 0.0388. Data points for pt<2 GeV/c from analysis "without vertexing". Data points for pt>2 GeV/c from the analysis "with vertexing" taken from JHEP 1201 (2012) 128 (http://hepdata.cedar.ac.uk/view/ins944757) and corrected for the updated BR value.
First column: production cross sections per unit of rapidity for prompt D0 mesons, inclusive D0 mesons (no feed-down subtraction) and charm quarks at mid-rapidity in pp collisions at 7 TeV. For D0 mesons, the second (sys) error is from the luminosity uncertainty, the third (sys) error is from the branching-ratio uncertainties. For charm quarks, the second (sys) error is from the luminosity uncertainty, the third (sys) error is from the Fragmentation Function uncertainties, the fourth (sys) error is from the rapidity shapes of D0 mesons and single charm quarks. Second column: total production cross sections, extrapolated to the full phase space, for prompt D0 mesons and charm quarks. For D0 mesons, the second (sys) error is the from the extrapolation uncertainty, the third from the luminosity uncertainty and the fourth from the branching-ratio uncertainties. For charm quarks, the second (sys) error is from the extrapolation, the third is from the luminosity uncertainty and the fourth is from the Fragmentation Function uncertainties. Third column: value of <pT> of prompt D0 mesons. The first uncertainty is statistical, the second is the systematic uncertainty.
The production of muons from heavy flavour decays is measured at forward rapidity in proton-proton collisions at $\sqrt{s} = 7$ TeV collected with the ALICE experiment at the LHC. The analysis is carried out on a data sample corresponding to an integrated luminosity $L_{\rm int} = 16.5$ nb$^{-1}$. The transverse momentum and rapidity differential production cross sections of muons from heavy flavour decays are measured in the rapidity range 2.5 < y < 4, over the transverse momentum range 2 < $p_{\rm T}$ < 12 GeV/$c$. The results are compared to predictions based on perturbative QCD calculations.
pT-differential production cross section of muons from heavy flavour decays, in the rapidity range 2.5<y<4.
y-differential production cross section of muons from heavy flavour decays, in the range 2<pT<12 GeV/C.
pT-differential production cross section of muons from heavy flavour decays, in the rapidity range 2.5<y<2.8.
We present measurements of Underlying Event observables in pp collisions at $\sqrt{s}$ = 0.9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum $p_{\rm T, LT}$ in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different $p_{\rm T}$ thresholds: 0.15, 0.5 and 1.0 GeV/$c$. In the Transverse region we observe an increase in the multiplicity of a factor 2-3 between the lower and higher collision energies, depending on the track $p){\rm T}$ threshold considered. Data are compared to Pythia 6.4, Pythia 8.1 and Phojet. On average, all models considered underestimate the multiplicity and summed $p_{\rm T}$ in the Transverse region by about 10-30%.
Number density as a function of the leading charged-particle PT at a centre-mass-energy of 900 GeV for events having charged-particle PT > 0.15 GeV. The data is shown for the three azimuthal regions.
Number density as a function of the leading charged-particle PT at a centre-mass-energy of 7000 GeV for events having charged-particle PT > 0.15 GeV. The data is shown for the three azimuthal regions.
Number density as a function of the leading charged-particle PT at a centre-mass-energy of 900 GeV for events having charged-particle PT > 0.5 GeV. The data is shown for the three azimuthal regions.
The effect of event background fluctuations on charged particle jet reconstruction in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV has been measured with the ALICE experiment. The main sources of non-statistical fluctuations are characterized based purely on experimental data with an unbiased method, as well as by using single high $p_{\rm T}$ particles and simulated jets embedded into real Pb-Pb events and reconstructed with the anti-$k_{\rm T}$ jet finder. The influence of a low transverse momentum cut-off on particles used in the jet reconstruction is quantified by varying the minimum track $p_{\rm T}$ between 0.15 GeV/$c$ and 2 GeV/$c$. For embedded jets reconstructed from charged particles with $p_{\rm T} > 0.15$ GeV/$c$, the uncertainty in the reconstructed jet transverse momentum due to the heavy-ion background is measured to be 11.3 GeV/$c$ (standard deviation) for the 10% most central Pb-Pb collisions, slightly larger than the value of 11.0 GeV/$c$ measured using the unbiased method. For a higher particle transverse momentum threshold of 2 GeV/$c$, which will generate a stronger bias towards hard fragmentation in the jet finding process, the standard deviation of the fluctuations in the reconstructed jet transverse momentum is reduced to 4.8-5.0 GeV/$c$ for the 10% most central events. A non-Gaussian tail of the momentum uncertainty is observed and its impact on the reconstructed jet spectrum is evaluated for varying particle momentum thresholds, by folding the measured fluctuations with steeply falling spectra.
DeltaPT of random cones in the 10% most central events for three types of random cone probes with a minimum track PT of 0.15 GeV. (1) sampling all the events, (2) avoiding overlap with the leading jet candidate in the event and (3) after randomizing the (ETA,PHI) direction of the tracks hence destroying any correlations.
DeltaPT of random cones in the 10% most central events for three regions with a minimum track PT of 0.15 GeV. (1) the in-plane orientation where the angle between the reconstructed event plane and the random cone axis is < 30 degrees, (2) the out-of plane orientation where this angle is > 60 degrees and (3) the intermediate region where this angle is between 30 and 60 degrees.
Dependence of the standard deviation on the uncorrected charged particle multiplicity. As in figure 2 the data are given for three different random cone probes: (1) sampling all the events, (2) avoiding overlap with the leading jet candidate in the event and (3) after randomizing the (ETA,PHI) direction of the tracks hence destroying any correlations.
The W and Z boson production was measured via the muonic decay channel in proton-lead collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at the Large Hadron Collider with the ALICE detector. The measurement covers backward ($-4.46 < y_{\rm cms} < -2.96$) and forward ($2.03 < y_{\rm cms} < 3.53$) rapidity regions, corresponding to Pb-going and p-going directions, respectively. The Z-boson production cross section, with dimuon invariant mass of $60<m_{\mu\mu}<120$ GeV/$c^2$ and muon transverse momentum ($p_{\rm T}^\mu$) larger than 20 GeV/$c$, is measured. The production cross section and charge asymmetry of muons from W-boson decays with $p_{\rm T}^\mu>10$ GeV/$c$ are determined. The results are compared to theoretical calculations both with and without including the nuclear modification of the parton distribution functions. The W-boson production is also studied as a function of the collision centrality: the cross section of muons from W-boson decays is found to scale with the average number of binary nucleon-nucleon collisions within uncertainties.
Z-boson production cross section in the dimuon decay channel at backward and forward rapidities measured in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The first uncertainty is statistical, the second is systematic.
Cross section of $\mu^{+}$ from W$^{+}$ boson decay at backward and forward rapidities measured in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The first uncertainty is statistical, the second is systematic.
Cross section of $\mu^{-}$ from W$^{-}$ boson decay at backward and forward rapidities measured in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The first uncertainty is statistical, the second is systematic.
The production of beauty hadrons was measured via semi-leptonic decays at mid-rapidity with the ALICE detector at the LHC in the transverse momentum interval $1<p_{\rm T}<8$ GeV/$c$ in minimum-bias p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV and in $1.3<p_{\rm T}<8$ GeV/$c$ in the 20% most central Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV. The pp reference spectra at $\sqrt{s}=5.02$ TeV and $\sqrt{s}=2.76$ TeV, needed for the calculation of the nuclear modification factors $R_{\rm pPb}$ and $R_{\rm PbPb}$, were obtained by a pQCD-driven scaling of the cross section of electrons from beauty-hadron decays measured at $\sqrt{s}=7$ TeV. In the $p_{\rm T}$ interval $3<p_{\rm T}<8$ GeV/$c$ a suppression of the yield of electrons from beauty-hadron decays is observed in Pb-Pb compared to pp collisions. Towards lower $p_{\rm T}$, the $R_{\rm PbPb}$ values increase with large systematic uncertainties. The $R_{\rm pPb}$ is consistent with unity within systematic uncertainties and is well described by theoretical calculations that include cold nuclear matter effects in p-Pb collisions. The measured $R_{\rm pPb}$ and these calculations indicate that cold nuclear matter effects are small at high transverse momentum also in Pb-Pb collisions. Therefore, the observed reduction of $R_{\rm PbPb}$ below unity at high $p_{\rm T}$ may be ascribed to an effect of the hot and dense medium formed in Pb-Pb collisions.
Invariant cross section of electrons from beauty-hadron decays as a function of transverse momentum in minimum-bias p--Pb collisions in the rapidity interval $-1.06 < y_{\rm cms} < 0.14$. The systematic uncertainties do not include an additional p--Pb normalisation uncertainty of 3.7%.
Invariant yield of electrons from beauty-hadron decays as a function of transverse momentum in 20% most central Pb--Pb collisions.
Nuclear modification factor $R_{\text{pA}}$ of electrons from beauty-hadron decays as a function of transverse momentum for minimum-bias p--Pb collisions in the rapidity interval $-1.06 < y_{\rm cms} < 0.14$. The systematic uncertainties do not include a global normalisation uncertainty of 5.1%.
The production of muons from heavy-flavour hadron decays in p-Pb collisions at $\sqrt{{\textit s}_{\rm NN}}=5.02$ TeV was studied for $2 < p_{\rm T} < 16$ GeV/$c$ with the ALICE detector at the CERN LHC. The measurement was performed at forward (p-going direction) and backward (Pb-going direction) rapidity, in the ranges of rapidity in the center-of-mass system (cms) $2.03<y_{\rm cms}<3.53$ and $-4.46<y_{\rm cms}<-2.96$, respectively. The production cross sections and nuclear modification factors are presented as a function of transverse momentum ($p_{\rm T}$). At forward rapidity, the nuclear modification factor is compatible with unity while at backward rapidity, in the interval $2.5<p_{\rm T}<3.5$ GeV/$c$, it is above unity by more than 2$\sigma$. The ratio of the forward-to-backward production cross sections is also measured in the overlapping interval $2.96 < \vert y_{\rm cms} \vert < 3.53$ and is smaller than unity by 3.7$\sigma$ in $2.5<p_{\rm T}<3.5$ GeV/$c$. The data are described by model calculations including cold nuclear matter effects.
pT-differential production cross section of heavy-flavour decay muons at forward rapidity (proton-going side) and backward rapidity (Pb-going side)
pT-differential nuclear modification factor of heavy-flavour decay muons at forward rapidity (proton-going side)
pT-differential nuclear modification factor of heavy-flavour decay muons at backward rapidity (Pb-going side)
We report the first results of elliptic ($v_2$), triangular ($v_3$) and quadrangular flow ($v_4$) of charged particles in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV with the ALICE detector at the CERN Large Hadron Collider. The measurements are performed in the central pseudorapidity region $|\eta|<0.8$ and for the transverse momentum range $0.2<p_{\rm T}<5$ GeV/$c$. The anisotropic flow is measured using two-particle correlations with a pseudorapidity gap greater than one unit and with the multi-particle cumulant method. Compared to results from Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV, the anisotropic flow coefficients $v_{2}$, $v_{3}$ and $v_{4}$ are found to increase by ($3.0\pm0.6$)%, ($4.3\pm1.4$)% and ($10.2\pm3.8$)%, respectively, in the centrality range 0-50%. This increase can be attributed mostly to an increase of the average transverse momentum between the two energies. The measurements are found to be compatible with hydrodynamic model calculations. This comparison provides a unique opportunity to test the validity of the hydrodynamic picture and the power to further discriminate between various possibilities for the temperature dependence of shear viscosity to entropy density ratio of the produced matter in heavy-ion collisions at the highest energies.
Centrality dependence of $v_2$, with two- and multi-particle correlations, integrated over the $p_{\rm T}$ range 0.2 < $p_{\rm T}$ < 5.0 GeV/$c$, at $\sqrt{s_{\rm NN}}$ = 5.02 TeV.
Centrality dependence of $v_2$, with two- and multi-particle correlations, integrated over the $p_{\rm T}$ range 0.2 < $p_{\rm T}$ < 5.0 GeV/$c$, at $\sqrt{s_{\rm NN}}$ = 5.02 TeV.
Centrality dependence of $v_3$ and $v_4$, with two-particle correlations, integrated over the $p_{\rm T}$ range 0.2 < $p_{\rm T}$ < 5.0 GeV/c, at $\sqrt{s_{\rm NN}}$ = 5.02 TeV.
The azimuthal correlations of D mesons and charged particles were measured with the ALICE detector in pp collisions at $\sqrt{s}=7$ TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV at the Large Hadron Collider. D$^0$, D$^+$, and D$^{*+}$ mesons and their charge conjugates with transverse momentum $3<p_{\rm T}<16$ GeV/$c$ and rapidity in the nucleon-nucleon centre-of-mass system $|y_{\rm cms}|<0.5$ (pp collisions) and $-0.96<y_{\rm cms}<0.04$ (p-Pb collisions) were correlated to charged particles with $p_{\rm T}>0.3$ Gev/$c$. The properties of the correlation peak induced by the jet containing the D meson, described in terms of the yield of charged particles in the peak and peak width, are compatible within uncertainties between the two collision systems, and described by Monte-Carlo simulations based on the PYTHIA, POWHEG and EPOS 3 event generators.
Comparison of the azimuthal-correlation distributions of D mesons and charged particles obtained for D$^0$, D$^{+}$ and D$^{*+}$ mesons for $5 < p_{\rm T} < 8$ GeV/$c$, charged particles $p_{\rm T} > 1$ GeV/$c$, in pp collisions at $\sqrt{s} = 7$ TeV. Rapidity range for the D mesons is $|y^{\rm D}_{\rm cms}| < 0.5$. Correlations are integrated for $|\Delta\eta|=|\eta_{\rm ch}-\eta_{\rm D}| < 1$. The azimuthal-correlation distributions are reported in the range $0 < \Delta\varphi < \pi$.
Comparison of the azimuthal-correlation distributions of D mesons and charged particles obtained for D$^0$, D$^{+}$ and D$^{*+}$ mesons for $8 < p_{\rm T} < 16$ GeV/$c$, charged particles $p_{\rm T} > 1$ GeV/$c$, in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV. Rapidity range for the D mesons is $-0.96 < y^{\rm D}_{\rm cms} < 0.04$. Correlations are integrated for $|\Delta\eta|=|\eta_{\rm ch}-\eta_{\rm D}| < 1$. The azimuthal-correlation distributions are reported in the range $0 < \Delta\varphi < \pi$.
Azimuthal correlation of D mesons (${\rm D}^{0}$, ${\rm D}^{+}$, ${\rm D}^{*+}$ average) with $3 < p_{\rm T} < 5~{\rm GeV}/c$ and $|y_{\rm cms}| < 0.5$ and charged particles with $p_{\rm T} > 0.3~{\rm GeV}/c$ for $|\Delta\eta| = |\eta_{\rm ch}-\eta_{\rm D}| < 1$ measured in pp collisions at $\sqrt{s} = 7~{\rm TeV}$.
We present results on transverse momentum ($p_{\rm T}$) and rapidity ($y$) differential production cross sections, mean transverse momentum and mean transverse momentum square of inclusive J/$\psi$ and $\psi(2S)$ at forward rapidity ($2.5<y<4$) as well as $\psi(2S)$-to-J/$\psi$ cross section ratios. These quantities are measured in pp collisions at center of mass energies $\sqrt{s}=5.02$ and 13 TeV with the ALICE detector. Both charmonium states are reconstructed in the dimuon decay channel, using the muon spectrometer. A comprehensive comparison to inclusive charmonium cross sections measured at $\sqrt{s}=2.76$, 7 and 8 TeV is performed. A comparison to non-relativistic quantum chromodynamics and fixed-order next-to-leading logarithm calculations, which describe prompt and non-prompt charmonium production respectively, is also presented. A good description of the data is obtained over the full $p_{\rm T}$ range, provided that both contributions are summed. In particular, it is found that for $p_{\rm T}>15$ GeV/$c$ the non-prompt contribution reaches up to 50% of the total charmonium yield.
Differential production cross sections of $J/\psi$ as a function of $p_{\rm T}$.
Differential production cross sections of $J/\psi$ as a function of rapidity.
Differential production cross sections of $\psi(2S)$ as a function of $p_{\rm T}$.
A measurement of beauty hadron production at mid-rapidity in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{\rm NN}}=5.02$ TeV is presented. The semi-inclusive decay channel of beauty hadrons into J/$\psi$ is considered, where the J/$\psi$ mesons are reconstructed in the dielectron decay channel at mid-rapidity down to transverse momenta of 1.3 GeV/$c$. The ${\rm {b\overline{b}}}$ production cross section at mid-rapidity, ${\rm d}\sigma_{\rm {b\overline{b}}}/{\rm d} y$, and the total cross section extrapolated over full phase space, $\sigma_{\rm {b\overline{b}}}$, are obtained. This measurement is combined with results on inclusive J/$\psi$ production to determine the prompt J/$\psi$ cross sections. The results in p-Pb collisions are then scaled to expectations from pp collisions at the same centre-of-mass energy to derive the nuclear modification factor $R_{\rm pPb}$, and compared to models to study possible nuclear modifications of the production induced by cold nuclear matter effects. $R_{\rm pPb}$ is found to be smaller than unity at low $p_{\rm T}$ for both J/$\psi$ coming from beauty hadron decays and prompt J/$\psi$.
Fraction of non-prompt J/$\psi$ in pp collisions at $\sqrt{s_{NN}}$ = 5.02 TeV for different $p_{\rm T}$ ranges, as determined with a procedure of interpolation from measurments at other energies. It is not a direct measurment.
Fraction of non-prompt J/$\psi$ in pPb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV for different $p_{\rm T}$ ranges.
Fraction of non-prompt J/$\psi$ in pPb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV for different $p_{\rm T}$ ranges.
We report a precise measurement of the J/$\psi$ elliptic flow in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector at the LHC. The J/$\psi$ mesons are reconstructed at mid-rapidity ($|y| < 0.9$) in the dielectron decay channel and at forward rapidity ($2.5<y<4.0$) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow $v_2$ of the J/$\psi$ is studied as a function of transverse momentum and centrality. A positive $v_2$ is observed in the transverse momentum range $2 < p_{\rm T} < 8$ GeV/$c$ in the three centrality classes studied and confirms with higher statistics our earlier results at $\sqrt{s_{\rm NN}} = 2.76$ TeV in semi-central collisions. At mid-rapidity, the J/$\psi$ $v_2$ is investigated as a function of transverse momentum in semi-central collisions and found to be in agreement with the measurements at forward rapidity. These results are compared to transport model calculations. The comparison supports the idea that at low $p_{\rm T}$ the elliptic flow of the J/$\psi$ originates from the thermalization of charm quarks in the deconfined medium, but suggests that additional mechanisms might be missing in the models.
Transverse momentum dependence of inclusive J/$\psi$ $v_2$ at $\sqrt{s_{\rm NN}}=5.02$ TeV for the 20-40% centrality class (forward rapidity). The first uncertainty (stat) is statistical, the second (sys,uncorrel) is the uncorrelated systematic, while the third one (sys,correl) is a $p_{\rm T}$-correlated systematic uncertainty.
Transverse momentum dependence of inclusive J/$\psi$ $v_2$ at $\sqrt{s_{\rm NN}}=5.02$ TeV for the 20-40% centrality class (mid-rapidity). The first uncertainty (stat) is statistical, the second (sys,uncorrel) is the uncorrelated systematic, while the third one (sys,correl) is a $p_{\rm T}$-correlated systematic uncertainty.
Transverse momentum dependence of inclusive J/$\psi$ $v_2$ at $\sqrt{s_{\rm NN}}=5.02$ TeV for the 5-20% centrality class (forward rapidity). The first uncertainty (stat) is statistical, the second (sys,uncorrel) is the uncorrelated systematic, while the third one (sys,correl) is a $p_{\rm T}$-correlated systematic uncertainty.
The measurement of two-particle angular correlations is a powerful tool to study jet quenching in a $p_{\mathrm{T}}$ region inaccessible by direct jet identification. In these measurements pseudorapidity ($\Delta\eta$) and azimuthal ($\Delta\varphi$) differences are used to extract the shape of the near-side peak formed by particles associated to a higher $p_{\mathrm{T}}$ trigger particle ($1 < p_{\mathrm{T, trig}} <$ 8 GeV/c). A combined fit of the near-side peak and long-range correlations is applied to the data allowing the extraction of the centrality evolution of the peak shape in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV. A significant broadening of the peak in the $\Delta\eta$ direction at low $p_{\mathrm{T}}$ is found from peripheral to central collisions, which vanishes above 4 GeV/c, while in the $\Delta\varphi$ direction the peak is almost independent of centrality. For the 10% most central collisions and $1 < p_{\mathrm{T, assoc}} <$ 2 GeV/c, $1 < p_{\mathrm{T, trig}} <$ 3 GeV/c a novel feature is observed: a depletion develops around the centre of the peak. The results are compared to pp collisions at the same centre of mass energy and to AMPT model simulations. The comparison to the investigated models suggests that the broadening and the development of the depletion is connected to the strength of radial and longitudinal flow.
Variance of the near-side jet peak from a generalized Gaussian fit.
Variance of the near-side jet peak from a generalized Gaussian fit.
Variance of near-side peak in the 0-10% centrality bin divided by the variance of the near-side peak in the 50-80% centrality bin.
We report measurements of the inclusive J/$\psi$ yield and average transverse momentum as a function of charged-particle pseudorapidity density ${\rm d}N_{\rm ch}/{\rm d}\eta$ in p-Pb collisions at $\sqrt{s_{\rm NN}}= 5.02$ TeV with ALICE at the LHC. The observables are normalised to their corresponding averages in non-single diffractive events. An increase of the normalised J/$\psi$ yield with normalised ${\rm d}N_{\rm ch}/{\rm d}\eta$, measured at mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward rapidity, a saturation of the relative yield is observed for high charged-particle multiplicities. The normalised average transverse momentum at forward and backward rapidities increases with multiplicity at low multiplicities and saturates beyond moderate multiplicities. In addition, the forward-to-backward nuclear modification factor ratio is also reported, showing an increasing suppression of J/$\psi$ production at forward rapidity with respect to backward rapidity for increasing charged-particle multiplicity.
Relative yield of inclusive J/psi mesons as a function of relative charged-particle pseudorapidity density for forward rapidities 2.03 < y_cms < 3.53 (p-going direction).
Relative yield of inclusive J/psi mesons as a function of relative charged-particle pseudorapidity density for backward rapidities -4.46 < y_cms < -2.96 (Pb-going direction).
Relative yield of inclusive J/psi mesons as a function of relative charged-particle pseudorapidity density for central rapidities -1.37 < y_cms < 0.43.
The correlations between event-by-event fluctuations of anisotropic flow harmonic amplitudes have been measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV with the ALICE detector at the LHC. The results are reported in terms of multiparticle correlation observables dubbed Symmetric Cumulants. These observables are robust against biases originating from nonflow effects. The centrality dependence of correlations between the higher order harmonics (the quadrangular $v_4$ and pentagonal $v_5$ flow) and the lower order harmonics (the elliptic $v_2$ and triangular $v_3$ flow) is presented. The transverse momentum dependence of correlations between $v_3$ and $v_2$ and between $v_4$ and $v_2$ is also reported. The results are compared to calculations from viscous hydrodynamics and A Multi-Phase Transport ({AMPT}) model calculations. The comparisons to viscous hydrodynamic models demonstrate that the different order harmonic correlations respond differently to the initial conditions and the temperature dependence of the ratio of shear viscosity to entropy density ($\eta/s$). A small average value of $\eta/s$ is favored independent of the specific choice of initial conditions in the models. The calculations with the AMPT initial conditions yield results closest to the measurements. Correlations between the magnitudes of $v_2$, $v_3$ and $v_4$ show moderate $p_{\rm T}$ dependence in mid-central collisions. Together with existing measurements of individual flow harmonics, the presented results provide further constraints on the initial conditions and the transport properties of the system produced in heavy-ion collisions.
Centrality dependence of observables SC(5,2) in Pb-Pb collisions at 2.76 TeV.
Centrality dependence of observables SC(5,2) in Pb-Pb collisions at 2.76 TeV.
Centrality dependence of observables SC(5,3) in Pb-Pb collisions at 2.76 TeV.
The azimuthal anisotropy coefficient $v_2$ of prompt D$^0$, D$^+$, D$^{*+}$ and D$_s^+$ mesons was measured in mid-central (30-50% centrality class) Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} = 5.02$ TeV, with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decays at mid-rapidity, $|y|<0.8$, in the transverse momentum interval $1<p_{\rm T}<24$ GeV/$c$. The measured D-meson $v_2$ has similar values as that of charged pions. The D$_s^+$ $v_2$, measured for the first time, is found to be compatible with that of non-strange D mesons. The measurements are compared with theoretical calculations of charm-quark transport in a hydrodynamically expanding medium and have the potential to constrain medium parameters.
$v_2$ vs. $p_{\rm T}$ of $D^0$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$=5.02 TeV in the centrality class 30-50% in the rapidity interval |$y$|<0.8. The second (sys) error is the systematic uncertainty from the B feed-down contribution. The first (sys) error is the systematic uncertainty from the other sources.
$v_2$ vs. $p_{\rm T}$ of $D^+$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$=5.02 TeV in the centrality class 30-50% in the rapidity interval |$y$|<0.8. The second (sys) error is the systematic uncertainty from the B feed-down contribution. The first (sys) error is the systematic uncertainty from the other sources.
$v_2$ vs. $p_{\rm T}$ of $D^{*+}$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$=5.02 TeV in the centrality class 30-50% in the rapidity interval |$y$|<0.8. The second (sys) error is the systematic uncertainty from the B feed-down contribution. The first (sys) error is the systematic uncertainty from the other sources.
The production cross sections of the prompt charmed mesons ${\rm D^0}$, ${\rm D^+}$, ${\rm D^{*+}}$ and ${\rm D_s^+}$ were measured at mid-rapidity in proton-proton collisions at a centre-of-mass energy $\sqrt{s}=7$ TeV with the ALICE detector at the Large Hadron Collider (LHC). D mesons were reconstructed from their decays ${\rm D}^0 \to {\rm K}^-\pi^+$, ${\rm D}^+\to {\rm K}^-\pi^+\pi^+$, ${\rm D}^{*+} \to {\rm D}^0 \pi^+$, ${\rm D_s^{+}\to \phi\pi^+\to K^-K^+\pi^+}$, and their charge conjugates. With respect to previous measurements in the same rapidity region, the coverage in transverse momentum ($p_{\rm T}$) is extended and the uncertainties are reduced by a factor of about two. The accuracy on the estimated total $\rm c\overline c$ production cross section is likewise improved. The measured $p_{\rm T}$-differential cross sections are compared with the results of three perturbative QCD calculations.
$p_{\rm T}$-differential cross section of prompt $\rm{D}^{0}$ mesons in pp collisions at $\sqrt{s_{\rm{NN}}}$=7 TeV in the rapidity interval $|y|$<0.5. Branching ratio of $\rm{D}^{0}\rightarrow K\pi$ : 0.0393.
$p_{\rm T}$-differential cross section of prompt $\rm{D^{+}}$ mesons in pp collisions at $\sqrt{s_{\rm{NN}}}$=7 TeV in the rapidity interval $|y|$<0.5. Branching ratio of $\rm D^{+-}\rightarrow K{\rm{\pi}}{\rm{\pi}}$ : 0.0946.
$p_{\rm T}$-differential cross section of prompt $\rm D^{*}$ mesons in pp collisions at $\sqrt{s_{\rm{NN}}}$=7 TeV in the rapidity interval $|y|$<0.5. Branching ratio of $\rm{D}^{*+}\rightarrow \rm{D}^{0}\pi\rightarrow K\pi\pi$ : 0.0266.
Two-particle angular correlations were measured in pp collisions at $\sqrt{s} = 7$ TeV for pions, kaons, protons, and lambdas, for all particle/anti-particle combinations in the pair. Data for mesons exhibit an expected peak dominated by effects associated with mini-jets and are well reproduced by general purpose Monte Carlo generators. However, for baryon-baryon and anti-baryon--anti-baryon pairs, where both particles have the same baryon number, a near-side anti-correlation structure is observed instead of a peak. This effect is interpreted in the context of baryon production mechanisms in the fragmentation process. It currently presents a challenge to Monte Carlo models and its origin remains an open question.
$\Delta\eta$ integrated projections of correlation functions for combined pairs of $\rm pp+\overline{p}\overline{p}$, $\rm p\Lambda+\overline{p}\overline{\Lambda}$, and $\Lambda\Lambda+\overline{\Lambda}\overline{\Lambda}$.
$\Delta\eta$ integrated projections of correlation functions for combined pairs of $\rm p\overline{p}$, $\rm p\overline{\Lambda}+\overline{p}\Lambda$, and $\Lambda\overline{\Lambda}$.
$\Delta\eta$ integrated projections of correlation functions for combined pairs of $\rm pp+\overline{p}\overline{p}$ for two transverse momentum intervals (a) $0.5 < p_{\rm T} < 1.25$ GeV/$c$ and (b) $1.25 < p_{\rm T} < 2.5$ GeV/$c$.
The production of the charm-strange baryon $\Xi_{\rm c}^0$ is measured for the first time at the LHC via its semileptonic decay into e$^+\Xi^-\nu_{\rm e}$ in pp collisions at $\sqrt{s}=7$ TeV with the ALICE detector. The transverse momentum ($p_{\rm T}$) differential cross section multiplied by the branching ratio is presented in the interval 1 $<$ $p_{\rm T}$ $<$ 8 GeV/$c$ at mid-rapidity, $|y|$ $<$ 0.5. The transverse momentum dependence of the $\Xi_{\rm c}^0$ baryon production relative to the D$^0$ meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured cross-section ratio.
Inclusive $\Xi_{\rm c}^{0}$ $p_{\rm T}$ differential cross section multiplied by the branching ratio into the semileptonic decay for $|y|<0.5$.
Ratio of the $p_{\rm T}$ differential cross sections of $\Xi_{\rm c}^{0}$ baryons (multiplied by the branching ratio into the semileptonic decay) and D$^{0}$ mesons for $|y|<0.5$.
The production of Z$^0$ bosons at large rapidities in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV is reported. Z$^0$ candidates are reconstructed in the dimuon decay channel (${\rm Z}^0 \rightarrow \mu^+\mu^-$), based on muons selected with pseudo-rapidity $-4.0<\eta<-2.5$ and $p_{\rm T}>20$ GeV/$c$. The invariant yield and the nuclear modification factor, $R_{\rm AA}$, are presented as a function of rapidity and collision centrality. The value of $R_{\rm AA}$ for the 0-20% central Pb-Pb collisions is $0.67 \pm 0.11 \, \mbox{(stat.)} \, \pm 0.03 \, \mbox{(syst.)} \, \pm 0.06 \, \mbox{(corr. syst.)}$, exhibiting a deviation of $2.6 \sigma$ from unity. The results are well-described by calculations that include nuclear modifications of the parton distribution functions, while the predictions using vacuum PDFs deviate from data by $2.3\sigma$ in the 0-90% centrality class and by $3\sigma$ in the 0-20% central collisions.
Invariant yield of Z$^{0}$ production in 2.5 < y < 4.0 divided by the average nuclear overlap function in the 0-90% centrality class. The first uncertainty is statistical, the second is systematic.
Nuclear modification factor of Z$^{0}$ production in 2.5 < y < 4.0 in the 0-90% centrality class. The first uncertainty is statistical, the second is systematic.
Invariant yield of Z$^{0}$ production in 2.5 < y < 4.0 divided by the average nuclear overlap function as a function of rapidity in the 0-90% centrality class. The first uncertainty is statistical, the second is the uncorrelated systematic and the third is the correlated systematic.
We report on the measurement of the inclusive J/$\psi$ polarization parameters in pp collisions at a center of mass energy $\sqrt{s} = 8$ TeV with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.23 pb$^{-1}$. J/$\psi$ resonances are reconstructed in their di-muon decay channel in the rapidity interval $2.5 < y < 4.0$ and over the transverse-momentum interval $2 < p_{\rm T} < 15$ GeV/$c$. The three polarization parameters ($\lambda_\theta$, $\lambda_\varphi$, $\lambda_{\theta\varphi}$) are measured as a function of $p_{\rm T}$ both in the helicity and Collins-Soper reference frames. The measured J/$\psi$ polarization parameters are found to be compatible with zero within uncertainties, contrary to expectations from all available predictions. The results are compared with the measurement in pp collisions at $\sqrt{s} = 7$ TeV.
ALICE inclusive J/psi polarization parameters lambda_theta in the Collins-Soper frame as a function of p_T in pp collisions at sqrt{s} = 8 TeV in the rapidity interval 2.5 < y < 4.0. The error bars represent the total uncertainties.
ALICE inclusive J/psi polarization parameters lambda_phi in the Collins-Soper frame as a function of p_T in pp collisions at sqrt{s} = 8 TeV in the rapidity interval 2.5 < y < 4.0. The error bars represent the total uncertainties.
ALICE inclusive J/psi polarization parameters lambda_thetaphi in the Collins-Soper frame as a function of p_T in pp collisions at sqrt{s} = 8 TeV in the rapidity interval 2.5 < y < 4.0. The error bars represent the total uncertainties.
Measurements of anisotropic flow coefficients with two- and multi-particle cumulants for inclusive charged particles in Pb-Pb collisions at $\sqrt{{\textit s}_\text{NN}} = 5.02$ and 2.76 TeV are reported in the pseudorapidity range $|\eta| < 0.8$ and transverse momentum $0.2 < p_\text{T} < 50$ GeV/$c$. The full data sample collected by the ALICE detector in 2015 (2010), corresponding to an integrated luminosity of 12.7 (2.0) $\mu$b$^{-1}$ in the centrality range 0-80%, is analysed. Flow coefficients up to the sixth flow harmonic ($v_6$) are reported and a detailed comparison among results at the two energies is carried out. The $p_\text{T}$ dependence of anisotropic flow coefficients and its evolution with respect to centrality and harmonic number $n$ are investigated. An approximate power-law scaling of the form $v_n(p_\text{T}) \sim p_\text{T}^{n/3}$ is observed for all flow harmonics at low $p_\text{T}$ ($0.2 < p_\text{T} < 3$ GeV/$c$). At the same time, the ratios $v_n/v_m^{n/m}$ are observed to be essentially independent of $p_\text{T}$ for most centralities up to about $p_\text{T} = 10$ GeV/$c$. Analysing the differences among higher-order cumulants of elliptic flow ($v_2$), which have different sensitivities to flow fluctuations, a measurement of the standardised skewness of the event-by-event $v_2$ distribution $P(v_2)$ is reported and constraints on its higher moments are provided. The Elliptic Power distribution is used to parametrise $P(v_2)$, extracting its parameters from fits to cumulants. The measurements are compared to different model predictions in order to discriminate among initial-state models and to constrain the temperature dependence of the shear viscosity to entropy-density ratio.
$v_2\{2,|\Delta\eta| > 1.\}$ as a function of centrality for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
$v_2\{4\}$ as a function of centrality for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
$v_3\{2,|\Delta\eta| > 1.\}$ as a function of centrality for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
The transverse momentum distributions of the strange and double-strange hyperon resonances ($\Sigma(1385)^{\pm}$, $\Xi(1530)^{0}$) produced in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV were measured in the rapidity range $-0.5< y_{\rm{CMS}}<0$ for event classes corresponding to different charged-particle multiplicity densities, $\langle{\rm d}N_{\rm{ch}}/{\rm d}\eta_{\rm{lab}}\rangle$. The mean transverse momentum values are presented as a function of $\langle{\rm d}N_{\rm{ch}}/{\rm d}\eta_{\rm{lab}}\rangle$, as well as a function of the particle masses and compared with previous results on hyperon production. The integrated yield ratios of excited to ground-state hyperons are constant as a function of $\langle{\rm d}N_{\rm{ch}}/{\rm d}\eta_{\rm{lab}}\rangle$. The equivalent ratios to pions exhibit an increase with $\langle{\rm d}N_{\rm{ch}}/{\rm d}\eta_{\rm{lab}}\rangle$, depending on their strangeness content.
Average charged particle pseudo-rapidity density, $\langle\rm{d}N_{\rm{ch}}/\rm{d}\eta_{\rm{lab}}\rangle$, measured at mid-rapidity in visible cross section event classes. Multiplicity classes are defined using the V0A estimator; values for $\langle\rm{d}N_{\rm{ch}}/\rm{d}\eta_{\rm{lab}}\rangle$ are corrected for vertexing and trigger efficiency. Since statistical uncertainties are negligible, only total systematic uncertainties are reported.
Average charged particle pseudo-rapidity density, $\langle\rm{d}N_{\rm{ch}}/\rm{d}\eta_{\rm{lab}}\rangle$, measured at mid-rapidity in visible cross section event classes. Multiplicity classes are defined using the V0A estimator; values for $\langle\rm{d}N_{\rm{ch}}/\rm{d}\eta_{\rm{lab}}\rangle$ are corrected for vertexing and trigger efficiency. Since statistical uncertainties are negligible, only total systematic uncertainties are reported.
$p_{\rm{T}}$-differential yield of $\Sigma^{*+}$ in p-Pb collisions with centre-of-mass energy/nucleon=5.02 TeV (NSD).
We present a measurement of azimuthal correlations between inclusive J/$\psi$ and charged hadrons in p-Pb collisions recorded with the ALICE detector at the CERN LHC. The J/$\psi$ are reconstructed at forward (p-going, 2.03 $<$ y $<$ 3.53) and backward (Pb-going, $-$4.46 $<$ y $<$ $-$2.96) rapidity via their $\mu^+\mu^-$ decay channel, while the charged hadrons are reconstructed at mid-rapidity ($|\eta|$ $<$ 1.8). The correlations are expressed in terms of associated charged-hadron yields per J/$\psi$ trigger. A rapidity gap of at least 1.5 units is required between the trigger J/$\psi$ and the associated charged hadrons. Possible correlations due to collective effects are assessed by subtracting the associated per-trigger yields in the low-multiplicity collisions from those in the high-multiplicity collisions. After the subtraction, we observe a strong indication of remaining symmetric structures at $\Delta\varphi$ $\approx$ 0 and $\Delta\varphi$ $\approx$ $\pi$, similar to those previously found in two-particle correlations at middle and forward rapidity. The corresponding second-order Fourier coefficient ($v_2$) in the transverse momentum interval between 3 and 6 GeV/$c$ is found to be positive with a significance of about 5$\sigma$. The obtained results are similar to the J/$\psi$ $v_2$ coefficients measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV, suggesting a common mechanism at the origin of the J/$\psi$ $v_2$.
$v_2^{J/\psi}${2,sub} in bins of $p_T^{J/\psi}$ for p-Pb collisions in proton-going direction at $\sqrt{s_{NN}}$ = 5.02 TeV. The quoted global systematic uncertainties correspond to the combined statistical and systematic uncertainties of the measured $v_2^{tracklet}$ coefficient. The results are obtained by subtracting associated per-trigger yields in low-multiplicity (40-100% V0M) collisions from the yields in high-multiplicity (0-20% V0M) collisions.
$v_2^{J/\psi}${2,sub} in bins of $p_T^{J/\psi}$ for p-Pb collisions in Pb-going direction at $\sqrt{s_{NN}}$ = 5.02 TeV. The quoted global systematic uncertainties correspond to the combined statistical and systematic uncertainties of the measured $v_2^{tracklet}$ coefficient. The results are obtained by subtracting associated per-trigger yields in low-multiplicity (40-100% V0M) collisions from the yields in high-multiplicity (0-20% V0M) collisions.
$v_2^{J/\psi}${2,sub} in bins of $p_T^{J/\psi}$ for p-Pb collisions in proton-going direction at $\sqrt{s_{NN}}$ = 8.16 TeV. The quoted global systematic uncertainties correspond to the combined statistical and systematic uncertainties of the measured $v_2^{tracklet}$ coefficient. The results are obtained by subtracting associated per-trigger yields in low-multiplicity (40-100% V0M) collisions from the yields in high-multiplicity (0-20% V0M) collisions.
This letter presents the first measurement of jet mass in Pb-Pb and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV and 5.02 TeV, respectively. Both the jet energy and the jet mass are expected to be sensitive to jet quenching in the hot Quantum Chromodynamics (QCD) matter created in nuclear collisions at collider energies. Jets are reconstructed from charged particles using the anti-$k_{\rm T}$ jet algorithm and resolution parameter $R = 0.4$. The jets are measured in the pseudorapidity range $|\eta_{\rm{jet}}|<0.5$ and in three intervals of transverse momentum between 60 GeV/$c$ and 120 GeV/$c$. The measurement of the jet mass in central Pb-Pb collisions is compared to the jet mass as measured in p-Pb reference collisions, to vacuum event generators, and to models including jet quenching. It is observed that the jet mass in central Pb-Pb collisions is consistent within uncertainties with p-Pb reference measurements. Furthermore, the measured jet mass in Pb-Pb collisions is not reproduced by the quenching models considered in this letter and is found to be consistent with PYTHIA expectations within systematic uncertainties.
Jet mass distribution in pPb collisions at cme 5020 GeV, pT,jet ch = 60-80 GeV/c
Jet mass distribution in pPb collisions at cme 5020 GeV, pT,jet ch = 80-100 GeV/c
Jet mass distribution in pPb collisions at cme 5020 GeV, pT,jet ch = 100-120 GeV/c
Invariant differential yields of deuterons and anti-deuterons in pp collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV and the yields of tritons, $^{3}$He nuclei and their anti-nuclei at $\sqrt{s}$ = 7 TeV have been measured with the ALICE detector at the LHC. The measurements cover a wide transverse momentum ($p_{\text{T}}$) range in the rapidity interval $|y|<0.5$, extending both the energy and the $p_{\text{T}}$ reach of previous measurements up to 3 GeV/$c$ for $A=2$ and 6 GeV/$c$ for $A=3$. The coalescence parameters of (anti-)deuterons and $^{3}\overline{\text{He}}$ nuclei exhibit an increasing trend with $p_{\text{T}}$ and are found to be compatible with measurements in pA collisions at low $p_{\text{T}}$ and lower energies. The integrated yields decrease by a factor of about 1000 for each increase of the mass number with one (anti-)nucleon. Furthermore, the deuteron-to-proton ratio is reported as a function of the average charged particle multiplicity at different center-of-mass energies.
Invariant differential yield of deuterons and antideuterons in inelastic pp collisions at $\sqrt{s}$ = 0.9 TeV. The uncertainties of $_{-0.8}^{+2.2}$% due to the extrapolation to inelastic pp collisions are not included in the systematic uncertainties.
Invariant differential yield of deuterons and antideuterons in inelastic pp collisions at $\sqrt{s}$ = 2.76 TeV. The uncertainties of $_{-2.8}^{+5.2}$% due to the extrapolation to inelastic pp collisions are not included in the systematic uncertainties.
Invariant differential yield of deuterons and antideuterons in inelastic pp collisions at $\sqrt{s}$ = 7 TeV. The uncertainties of $_{-2.0}^{+5.0}$% due to the extrapolation to inelastic pp collisions are not included in the systematic uncertainties.
We present the first ever measurements of femtoscopic correlations between the K$^0_{\rm S}$ and K$^{\rm \pm}$ particles. The analysis was performed on the data from Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding via the $a_0(980)$ resonance. The extracted kaon source radius and correlation strength parameters for K$^0_{\rm S}$K$^{\rm -}$ are found to be equal within the experimental uncertainties to those for K$^0_{\rm S}$K$^{\rm +}$. Comparing the results of the present study with those from published identical-kaon femtoscopic studies by ALICE, mass and coupling parameters for the $a_0$ resonance are constrained. Our results are also compatible with the interpretation of the $a_0$ having a tetraquark structure over that of a diquark.
Raw K0s K+ correlation function for all kT bin
Raw K0s K+ correlation function for kT < 0.675 GeV/c bin
Raw K0s K+ correlation function for kT > 0.675 GeV/c bin
Neutral pion and $\eta$ meson production in the transverse momentum range 1 < $p_{T}$ < 20 GeV/$c$ have been measured at mid-rapidity by the ALICE experiment at the Large Hadron Collider (LHC) in central and semi-central Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. These results were obtained using the photon conversion method as well as the PHOS and EMCal detectors. The results extend the upper $p_{T}$ reach of the previous ALICE $\pi^{0}$ measurements from 12 GeV/$c$ to 20 GeV/$c$ and present the first measurement of $\eta$ meson production in heavy-ion collisions at the LHC. The $\eta/\pi^{0}$ ratio is similar for the two centralities and reaches at high $p_{T}$ a plateau value of 0.457 $\pm$ 0.013$^{stat}$ $\pm$ 0.018$^{syst}$. A suppression of similar magnitude for $\pi^{0}$ and $\eta$ meson production is observed in Pb-Pb collisions with respect to their production in pp collisions scaled by the number of binary nucleon-nucleon collisions. We discuss the results in terms of NLO pQCD predictions and hydrodynamic models. The measurements show a stronger suppression with respect to what was observed at lower center-of-mass energies in the $p_{T}$ range 6 < $p_{T}$ < 10 GeV/$c$. At $p_{T}$ < 3 GeV/$c$, hadronization models describe the $\pi^{0}$ results while for the $\eta$ some tension is observed.
Invariant yields of the $\pi^{0}$ meson in the centrality class 0-10% in Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV at mid-rapidity.
Invariant yields of the $\pi^{0}$ meson in the centrality class 20-50% in Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV at mid-rapidity.
Invariant yields of the $\eta$ meson in the centrality class 0-10% in Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV at mid-rapidity.
Transverse-momentum ($p_{\rm T}$) differential yields of electrons from semileptonic heavy-flavour hadron decays have been measured in the most central (0-10%) and in semi-central (20-40%) Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV. The corresponding production cross section in pp collisions has been measured at the same energy with substantially reduced systematic uncertainties with respect to previously published results. The modification of the yield in Pb-Pb collisions with respect to the expectation from an incoherent superposition of nucleon-nucleon collisions is quantified at mid-rapidity ($|y|$ $<$ 0.8) in the $p_{\rm T}$ interval 0.5-3 GeV/$c$ via the nuclear modification factor, $R_{\rm AA}$. This paper extends the $p_{\rm T}$ reach of the $R_{\rm AA}$ measurement towards significantly lower values with respect to a previous publication. In Pb-Pb collisions the $p_{\rm T}$-differential measurements of yields at low $p_{\rm T}$ are essential to investigate the scaling of heavy-flavour production with the number of binary nucleon-nucleon collisions. Heavy-quark hadronization, a collective expansion and even initial-state effects, such as the nuclear modification of the Parton Distribution Functions, are also expected to have a significant effect on the measured distribution.
Cross section of electron from heavy-flavour hadron decays in pp collisions at 2.76 TeV; additional systematic uncertainty: ± 1.9% (normalization/luminosity uncertainty) not shown.
Spectra of electron from heavy-flavour hadron decays in 0-10% centrality class.
Spectra of electron from heavy-flavour hadron decays in 20-40% centrality class.
We present the first azimuthally differential measurements of the pion source size relative to the second harmonic event plane in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon pair of $\sqrt{s_{\rm NN}}=2.76$ TeV. The measurements have been performed in the centrality range 0-50% and for pion pair transverse momenta $0.2 < k_{\rm T} < 0.7$ GeV/$c$. We find that the $R_{\rm side}$ and $R_{\rm out}$ radii, which characterize the pion source size in the directions perpendicular and parallel to the pion transverse momentum, oscillate out of phase, similar to what was observed at the Relativistic Heavy Ion Collider (RHIC). The final-state source eccentricity, estimated via $R_{\rm side}$ oscillations, is found to be significantly smaller than the initial-state source eccentricity, but remains positive; indicating that even after a stronger expansion in the in-plane direction, the pion source at the freeze-out is still elongated in the out-of-plane direction. The 3+1D hydrodynamic calculations are in qualitative agreement with observed centrality and transverse momentum $R_{\rm side}$ oscillations, but systematically underestimate the oscillation magnitude.
The azimuthal dependence of $R_{out}^{2}$ as a function of $\Delta\varphi=\varphi_{\mathrm{pair}}-\Psi_{\mathrm EP,2}$ for the centrality 20--30% and different $k_{\mathrm{T}}$ ranges.
The azimuthal dependence of $R_{out}^{2}$ as a function of $\Delta\varphi=\varphi_{\mathrm{pair}}-\Psi_{\mathrm EP,2}$ for the centrality 20--30% and different $k_{\mathrm{T}}$ ranges.
The azimuthal dependence of $R_{out}^{2}$ as a function of $\Delta\varphi=\varphi_{\mathrm{pair}}-\Psi_{\mathrm EP,2}$ for the centrality 20--30% and different $k_{\mathrm{T}}$ ranges.
In two-particle angular correlation measurements, jets give rise to a near-side peak, formed by particles associated to a higher $p_{\mathrm{T}}$ trigger particle. Measurements of these correlations as a function of pseudorapidity ($\Delta\eta$) and azimuthal ($\Delta\varphi$) differences are used to extract the centrality and $p_{\mathrm{T}}$ dependence of the shape of the near-side peak in the $p_{\mathrm{T}}$ range $1 < p_{\mathrm{T}} <$ 8 GeV/c in Pb-Pb and pp collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV. A combined fit of the near-side peak and long-range correlations is applied to the data and the peak shape is quantified by the variance of the distributions. While the width of the peak in the $\Delta\varphi$ direction is almost independent of centrality, a significant broadening in the $\Delta\eta$ direction is found from peripheral to central collisions. This feature is prominent for the low $p_{\mathrm{T}}$ region and vanishes above 4 GeV/c. The widths measured in peripheral collisions are equal to those in pp in the $\Delta\varphi$ direction and above 3 GeV/c in the $\Delta\eta$ direction. Furthermore, for the 10\% most central collisions and $1 < p_{\mathrm{T, assoc}} <$ 2 GeV/c, $1 < p_{\mathrm{T, trig}} <$ 3 GeV/c a departure from a Gaussian shape is found: a depletion develops around the centre of the peak. The results are compared to AMPT model simulations as well as other theoretical calculations indicating that the broadening and the development of the depletion is connected to the strength of radial and longitudinal flow.
Variance of the near-side jet peak from a generalized Gaussian fit.
Variance of the near-side jet peak from a generalized Gaussian fit.
Variance of near-side peak in the 0-10% centrality bin divided by the variance of the near-side peak in the 50-80% centrality bin.
First results on K/$\pi$, p/$\pi$ and K/p fluctuations are obtained with the ALICE detector at the CERN LHC as a function of centrality in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV. The observable $\nu_{\rm dyn}$, which is defined in terms of the moments of particle multiplicity distributions, is used to quantify the magnitude of dynamical fluctuations of relative particle yields and also provides insight into the correlation between particle pairs. This study is based on a novel experimental technique, called the Identity Method, which allows one to measure the moments of multiplicity distributions in case of incomplete particle identification. The results for p/$\pi$ show a change of sign in $\nu_{\rm dyn}$ from positive to negative towards more peripheral collisions. For central collisions, the results follow the smooth trend of the data at lower energies and $\nu_{\rm dyn}$ exhibits a change in sign for p/$\pi$ and K/p.
Beam-energy dependence of nu_dyn.
Beam-energy dependence of nu_dyn.
Beam-energy dependence of nu_dyn.
Comprehensive results on the production of unidentified charged particles, $\pi^{\pm}$, $\rm{K}^{\pm}$, $\rm{K}^{0}_{S}$, $\rm{K}$*(892)$^{0}$, $\rm{p}$, $\overline{\rm{p}}$, $\phi$(1020), $\Lambda$, $\overline{\Lambda}$, $\Xi^{-}$, $\overline{\Xi}^{+}$, $\Omega^{-}$ and $\overline{\Omega}^{+}$ hadrons in proton-proton (pp) collisions at $\sqrt{s}$ = 7 TeV at midrapidity ($|y| < 0.5$) as a function of charged-particle multiplicity density are presented. In order to avoid auto-correlation biases, the actual transverse momentum ($p_{\rm{T}}$) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a function of multiplicity, the corresponding ratios of strange hadrons to pions show a significant enhancement that increases with increasing strangeness content. Furthermore, all identified particle to pion ratios are shown to depend solely on charged-particle multiplicity density, regardless of system type and collision energy. The evolution of the spectral shapes with multiplicity and hadron mass shows patterns that are similar to those observed in p-Pb and Pb-Pb collisions at LHC energies. The obtained $p_{\rm{T}}$ distributions and yields are compared to expectations from QCD-based pp event generators as well as to predictions from thermal and hydrodynamic models. These comparisons indicate that traces of a collective, equilibrated system are already present in high-multiplicity pp collisions.
Transverse momentum spectra of charged particles in V0M I multiplicity class
Transverse momentum spectra of charged particles in V0M II multiplicity class
Transverse momentum spectra of charged particles in V0M III multiplicity class
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