The longitudinal spin transfer, $D_{LL}$, from high energy polarized protons to $\Lambda$ and $\bar{\Lambda}$ hyperons has been measured for the first time in proton-proton collisions at $\sqrt{s} = 200 \mathrm{GeV}$ with the STAR detector at RHIC. The measurements cover pseudorapidity, $\eta$, in the range $|\eta| < 1.2$ and transverse momenta, $p_\mathrm{T}$, up to $4 \mathrm{GeV}/c$. The longitudinal spin transfer is found to be $D_{LL}= -0.03\pm 0.13(\mathrm{stat}) \pm 0.04(\mathrm{syst})$ for inclusive $\Lambda$ and $D_{LL} = -0.12 \pm 0.08(\mathrm{stat}) \pm 0.03(\mathrm{syst})$ for inclusive $\bar{\Lambda}$ hyperons with $<\eta> = 0.5$ and $<p_\mathrm{T}> = 3.7 \mathrm{GeV}/c$. The dependence on $\eta$ and $p_\mathrm{T}$ is presented.
The spin transfer $D_{LL}$ to (a) $\Lambda$ and (b) $\bar{\Lambda}$ hyperons produced at positive pseudorapidity with respect to the polarized proton beam from $MB$, $JP$, and $HT$ data versus hyperon transverse momenta $p_{T}$. The sizes of the statistical and systematic uncertainties are indicated by the vertical bars and bands, respectively. For clarity, the HT data points have been shifted slightly in $p_{T}$. The dotted vertical lines indicate the $p_{T}$ intervals in the analysis of HT and JP data.
The spin transfer $D_{LL}$ to (a) $\Lambda$ and (b) $\bar{\Lambda}$ hyperons produced at positive pseudorapidity with respect to the polarized proton beam from $MB$, $JP$, and $HT$ data versus hyperon transverse momenta $p_{T}$. The sizes of the statistical and systematic uncertainties are indicated by the vertical bars and bands, respectively. For clarity, the HT data points have been shifted slightly in $p_{T}$. The dotted vertical lines indicate the $p_{T}$ intervals in the analysis of HT and JP data.
The spin transfer $D_{LL}$ to (a) $\Lambda$ and (b) $\bar{\Lambda}$ hyperons produced at positive pseudorapidity with respect to the polarized proton beam from $MB$, $JP$, and $HT$ data versus hyperon transverse momenta $p_{T}$. The sizes of the statistical and systematic uncertainties are indicated by the vertical bars and bands, respectively. For clarity, the HT data points have been shifted slightly in $p_{T}$. The dotted vertical lines indicate the $p_{T}$ intervals in the analysis of HT and JP data.
The cross section for the process e + e − → multihadrons has been measured at the highest PETRA energies. We measure R (the total cross section in units of the point-like e + e - → μ + μ - cross section) to be 2.9 ± 0.7, 4.0 ± 0.5, 4.6 ± 0.4 and 4.2 ± 0.6 at s of 22, 27.7, 30 and 31.6 GeV, respectively. The observed average multiplicity, together with existing low energy data, indicate a rapid increase in multiplicity with increasing energy.
We present the first measurements of femtoscopic correlations between the K$^0_{\rm S}$ and K$^{\rm \pm}$ particles in pp collisions at $\sqrt{s}=7$ TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding solely 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$^{\rm +}$. Results of the present study are compared with those from identical-kaon femtoscopic studies also performed with pp collisions at $\sqrt{s}=7$ TeV by ALICE and with a K$^0_{\rm S}$K$^{\rm \pm}$ measurement in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV. Combined with the Pb-Pb results, our pp analysis is found to be compatible with the interpretation of the $a_0(980)$ having a tetraquark structure instead of that of a diquark.
Raw K0s K+ correlation function for all kT
Raw K0s K+ correlation function for kT < 0.85 GeV/c
Raw K0s K+ correlation function for kT > 0.85 GeV/c
Measurements of energy weighted angular correlations in electron positron annihilations at c.m. energies of 22 GeV and 34 GeV are presented.
We have measured the form factor ratios r_V = V(0)/A_1(0) and r_2 = A_2(0)/A_1(0) for the decay D_s^+ -> phi ell^+ nu_ell, phi -> K^+ K^-, using data from charm hadroproduction experiment E791 at Fermilab. Results are based on 144 signal and 22 background events in the electron channel and 127 signal and 34 background events in the muon channel. We combine the measurements from both lepton channels to obtain r_V = 2.27 +- 0.35 +- 0.22 and r_2 = 1.57 +- 0.25 +- 0.19.
The average transverse momentum $\langle p_{\rm T}\rangle$ versus the charged-particle multiplicity $N_{\rm ch}$ was measured in p-Pb collisions at a collision energy per nucleon-nucleon pair $\sqrt{s_{\rm NN}}=5.02$ TeV and in pp collisions at collision energies of $\sqrt{s}=0.9$, 2.76, and 7 TeV in the kinematic range $0.15<p_{\rm T}<10.0$ GeV/$c$ and $|\eta|<0.3$ with the ALICE apparatus at the LHC. These data are compared to results in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV at similar charged-particle multiplicities. In pp and p-Pb collisions, a strong increase of $\langle p_{\rm T}\rangle$ with $N_{\rm ch}$ is observed, which is much stronger than that measured in Pb-Pb collisions. For pp collisions, this could be attributed, within a model of hadronizing strings, to multiple-parton interactions and to a final-state color reconnection mechanism. The data in p-Pb and Pb-Pb collisions cannot be described by an incoherent superposition of nucleon-nucleon collisions and pose a challenge to most of the event generators.
The average transverse momentum as a function of multiplicity of charged particles having transverse momentum in the range 0.15-10 GeV/c and |eta| < 0.3 produced from P-P collisions at a centre-of mass energy/nucleon of 0.9 TeV.
The average transverse momentum as a function of multiplicity of charged particles having transverse momentum in the range 0.15-10 GeV/c and |eta| < 0.3 produced from P-P collisions at a centre-of mass energy/nucleon of 2.76 TeV.
The average transverse momentum as a function of multiplicity of charged particles having transverse momentum in the range 0.15-10 GeV/c and |eta| < 0.3 produced from P-P collisions at a centre-of mass energy/nucleon of 7 TeV.
The production of the $\rho$(770)${^{0}}$ meson has been measured at mid-rapidity $(|y|<0.5)$ in pp and centrality differential Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV with the ALICE detector at the Large Hadron Collider. The particles have been reconstructed in the $\rho$(770)$\rightarrow\pi^{+}\pi^{-}$ decay channel in the transverse momentum ($p_{T}$) range $0.5-11$ GeV/$c$. A centrality dependent suppression of the ratio of the integrated yields $2\rho$(770)$^{0}/(\pi^{+}+\pi^{-})$ is observed. The ratio decreases by $\sim40\%$ from pp to central Pb-Pb collisions. A study of the $p_{T}$-differential $2\rho$(770)$^{0}/(\pi^{+}+\pi^{-})$ ratio reveals that the suppression occurs at low transverse momenta, $p_{T}<2$ GeV/$c$. At higher momentum, particle ratios measured in heavy-ion and pp collisions are consistent. The observed suppression is very similar to that previously measured for the $K^{*}$(892)$^{0}/K$ ratio and is consistent with EPOS3 predictions that may imply that rescattering in the hadronic phase is a dominant mechanism for the observed suppression.
Reconstructed mass of $\rho^{0}$ meson in pp collisions at $\sqrt{s}=2.76~{\rm TeV}$.
Reconstructed mass of $\rho^{0}$ meson in 0-20$\%$ central Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76~{\rm TeV}$.
Reconstructed mass of $\rho^{0}$ meson in 20-40$\%$ central Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76~{\rm TeV}$.
Charged-particle spectra at midrapidity are measured in Pb-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair $\sqrt{s_{\rm NN}}$ = 5.02 TeV and presented in centrality classes ranging from most central (0-5%) to most peripheral (95-100%) collisions. Possible medium effects are quantified using the nuclear modification factor ($R_{\rm AA}$) by comparing the measured spectra with those from proton-proton collisions, scaled by the number of independent nucleon-nucleon collisions obtained from a Glauber model. At large transverse momenta ($8<p_{\rm T}<20$ GeV/$c$), the average $R_{\rm AA}$ is found to increase from about $0.15$ in 0-5% central to a maximum value of about $0.8$ in 75-85% peripheral collisions, beyond which it falls off strongly to below $0.2$ for the most peripheral collisions. Furthermore, $R_{\rm AA}$ initially exhibits a positive slope as a function of $p_{\rm T}$ in the $8$-$20$ GeV/$c$ interval, while for collisions beyond the 80% class the slope is negative. To reduce uncertainties related to event selection and normalization, we also provide the ratio of $R_{\rm AA}$ in adjacent centrality intervals. Our results in peripheral collisions are consistent with a PYTHIA-based model without nuclear modification, demonstrating that biases caused by the event selection and collision geometry can lead to the apparent suppression in peripheral collisions. This explains the unintuitive observation that $R_{\rm AA}$ is below unity in peripheral Pb-Pb, but equal to unity in minimum-bias p-Pb collisions despite similar charged-particle multiplicities.
Nuclear modification factor RAA versus pT for charged particles at midrapidity in 0-5% central Pb-Pb collisions at 5.02 TeV
Nuclear modification factor RAA versus pT for charged particles at midrapidity in 5-10% central Pb-Pb collisions at 5.02 TeV
Nuclear modification factor RAA versus pT for charged particles at midrapidity in 10-15% central Pb-Pb collisions at 5.02 TeV
The $p_{\rm T}$-differential production cross sections of the prompt charmed mesons $D^0$, $D^+$, $D^{*+}$ and $D_{\rm s}^{+}$ and their charge conjugate in the rapidity interval $-0.96 < y_{\rm cms} < 0.04$ were measured in p-Pb collisions at a centre-of-mass energy $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector at the LHC. The nuclear modification factor $R_{\rm pPb}$, quantifying the D-meson yield in p-Pb collisions relative to the yield in pp collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15-20% uncertainties with unity in the transverse momentum interval $1 < p_{\rm T} < 24$ GeV/$c$. No significant difference among the $R_{\rm pPb}$ of the four D-meson species is observed. The results are described within uncertainties by theoretical calculations that include initial-state effects. The measurement adds experimental evidence that the modification of the momentum spectrum of D mesons observed in Pb-Pb collisions with respect to pp collisions is due to strong final-state effects induced by hot partonic matter.
pT-differential cross section of prompt D0 mesons measured in p-Pb collisions in the rapidity interval -0.96<y_cms<0.04.
pT-differential cross section of prompt D+ mesons measured in p-Pb collisions in the rapidity interval -0.96<y_cms<0.04.
pT-differential cross section of prompt D*+ mesons measured in p-Pb collisions in the rapidity interval -0.96<y_cms<0.04.
In high-energy collisions, the spatio-temporal size of the particle production region can be measured using the Bose-Einstein correlations of identical bosons at low relative momentum. The source radii are typically extracted using two-pion correlations, and characterize the system at the last stage of interaction, called kinetic freeze-out. In low-multiplicity collisions, unlike in high-multiplicity collisions, two-pion correlations are substantially altered by background correlations, e.g. mini-jets. Such correlations can be suppressed using three-pion cumulant correlations. We present the first measurements of the size of the system at freeze-out extracted from three-pion cumulant correlations in pp, p-Pb and Pb-Pb collisions at the LHC with ALICE. At similar multiplicity, the invariant radii extracted in p-Pb collisions are found to be 5-15% larger than those in pp, while those in Pb-Pb are 35-55% larger than those in p-Pb. Our measurements disfavor models which incorporate substantially stronger collective expansion in p-Pb as compared to pp collisions at similar multiplicity.
Mixed charge C3 and c3 in pp collisions projected against 1 of a mixed-charge pair invariant relative momentum.
Same charge C3 and c3 in pp collisions projected against Q3.
Same charge C3 and c3 in p Pb collisions projected against Q3.
We report the measured transverse momentum ($p_{\rm T}$) spectra of primary charged particles from pp, p-Pb and Pb-Pb collisions at a center-of-mass energy $\sqrt{s_{\rm NN}} = 5.02$ TeV in the kinematic range of $0.15<p_{\rm T}<50$ GeV/$c$ and $|\eta|< 0.8$. A significant improvement of systematic uncertainties motivated the reanalysis of data in pp and Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV, as well as in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV, which is also presented. Spectra from Pb-Pb collisions are presented in nine centrality intervals and are compared to a reference spectrum from pp collisions scaled by the number of binary nucleon-nucleon collisions. For central collisions, the $p_{\rm T}$ spectra are suppressed by more than a factor of 7 around 6-7 GeV/$c$ with a significant reduction in suppression towards higher momenta up to 30 GeV/$c$. The nuclear modification factor $R_{\rm pPb}$, constructed from the pp and p-Pb spectra measured at the same collision energy, is consistent with unity above 8 GeV/$c$. While the spectra in both pp and Pb-Pb collisions are substantially harder at $\sqrt{s_{\rm NN}} = 5.02$ TeV compared to 2.76 TeV, the nuclear modification factors show no significant collision energy dependence. The obtained results should provide further constraints on the parton energy loss calculations to determine the transport properties of the hot and dense QCD matter.
Transverse momentum spectra of charged particles in PbPb collisions in nine centrality classes.
Transverse momentum spectra of charged particles in PbPb collisions in nine centrality classes.
Transverse momentum spectra of charged particles in pPb collisions.
The centrality dependence of the charged-particle multiplicity density at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor 2 from peripheral (70-80%) to central (0-5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions.
The dependence of the charged particle multiplicity density on the number of participants in the collisions.
The production of K$^{*}(892)^{0}$ and $\phi(1020)$ mesons in proton-proton (pp) and lead-lead (Pb-Pb) collisions at $\sqrt{s_\mathrm{NN}} =$ 2.76 TeV has been analyzed using a high luminosity data sample accumulated in 2011 with the ALICE detector at the Large Hadron Collider (LHC). Transverse momentum ($p_{\mathrm{T}}$) spectra have been measured for K$^{*}(892)^{0}$ and $\phi(1020)$ mesons via their hadronic decay channels for $p_{\mathrm{T}}$ up to 20 GeV/$c$. The measurements in pp collisions have been compared to model calculations and used to determine the nuclear modification factor and particle ratios. The K$^{*}(892)^{0}$/K ratio exhibits significant reduction from pp to central Pb-Pb collisions, consistent with the suppression of the K$^{*}(892)^{0}$ yield at low $p_{\mathrm{T}}$ due to rescattering of its decay products in the hadronic phase. In central Pb-Pb collisions the $p_{\mathrm{T}}$ dependent $\phi(1020)/\pi$ and K$^{*}(892)^{0}$/$\pi$ ratios show an enhancement over pp collisions for $p_{\mathrm{T}}$ $\sim$3 GeV/$c$, consistent with previous observations of strong radial flow. At high $p_{\mathrm{T}}$, particle ratios in Pb-Pb collisions are similar to those measured in pp collisions. In central Pb-Pb collisions, the production of K$^{*}(892)^{0}$ and $\phi(1020)$ mesons is suppressed for $p_{\mathrm{T}}> 8$ GeV/$c$. This suppression is similar to that of charged pions, kaons and protons, indicating that the suppression does not depend on particle mass or flavor in the light quark sector.
Invariant yield of K$^{*0}$ meson normalized to the number of inelastic pp collisions at $\sqrt{s}=2.76~{\rm TeV}$.
Invariant yield of $\phi$ meson normalized to the number of inelastic pp collisions at $\sqrt{s}=2.76~{\rm TeV}$.
Invariant yield of K$^{*0}$ meson for 0-5$\%$ centrality in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76~{\rm TeV}$.
The production of (anti-)deuteron and (anti-)$^{3}$He nuclei in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV has been studied using the ALICE detector at the LHC. The spectra exhibit a significant hardening with increasing centrality. Combined blast-wave fits of several particles support the interpretation that this behavior is caused by an increase of radial flow. The integrated particle yields are discussed in the context of coalescence and thermal-statistical model expectations. The particle ratios, $^3$He/d and $^3$He/p, in Pb-Pb collisions are found to be in agreement with a common chemical freeze-out temperature of $T_{\rm chem} \approx 156$ MeV. These ratios do not vary with centrality which is in agreement with the thermal-statistical model. In a coalescence approach, it excludes models in which nucleus production is proportional to the particle multiplicity and favors those in which it is proportional to the particle density instead. In addition, the observation of 31 anti-tritons in Pb-Pb collisions is reported. For comparison, the deuteron spectrum in pp collisions at $\sqrt{s} = 7$ TeV is also presented. While the p/$\pi$ ratio is similar in pp and Pb-Pb collisions, the d/p ratio in pp collisions is found to be lower by a factor of 2.2 than in Pb-Pb collisions.
Anti-deuteron over deuteron ratio versus pT per nucleon for various centrality classes for Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV.
Anti-deuteron over deuteron ratio versus pT per nucleon for various centrality classes for Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV.
Invariant transverse momentum distribution of deuteron for various centrality classes for Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV.
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
The measurement of azimuthal correlations of charged particles is presented for Pb-Pb collisions at $\sqrt{s_{\rm NN}}=$ 2.76 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}=$ 5.02 TeV with the ALICE detector at the CERN Large Hadron Collider. These correlations are measured for the second, third and fourth order flow vector in the pseudorapidity region $|\eta|<0.8$ as a function of centrality and transverse momentum $p_{\rm T}$ using two observables, to search for evidence of $p_{\rm T}$-dependent flow vector fluctuations. For Pb-Pb collisions at 2.76 TeV, the measurements indicate that $p_{\rm T}$-dependent fluctuations are only present for the second order flow vector. Similar results have been found for p-Pb collisions at 5.02 TeV. These measurements are compared to hydrodynamic model calculations with event-by-event geometry fluctuations in the initial state to constrain the initial conditions and transport properties of the matter created in Pb-Pb and p-Pb collisions.
$v_2\{2\}$ with $|\eta| > 0.0$ for centrality class 0-5\% in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV.
$v_2\{2\}$ with $|\eta| > 0.0$ for centrality class 5-10\% in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV.
$v_2\{2\}$ with $|\eta| > 0.0$ for centrality class 10-20\% in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV.
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.
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.
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 $K^{+} + K^{-}$ in V0M multiplicity class II
Unidentified particle spectral modification in V0M Class IX pp collisions.
$\pi^{+}+\pi^{-}$ spectral modification in V0M Class IX pp collisions.
The yields of the K*(892)$^{0}$ and $\Phi$(1020) resonances are measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV through their hadronic decays using the ALICE detector. The measurements are performed in multiple centrality intervals at mid-rapidity (|$y$|<0.5) in the transverse-momentum ranges 0.3 < $p_{\rm T}$ < 5 GeV/$c$ for the K*(892)$^{0}$ and 0.5 < $p_{\rm T}$ < 5 GeV/$c$ for the $\Phi$(1020). The yields of K*(892)$^{0}$ are suppressed in central Pb-Pb collisions with respect to pp and peripheral Pb-Pb collisions (perhaps due to rescattering of its decay products in the hadronic medium), while the longer lived $\Phi$(1020) meson is not suppressed. These particles are also used as probes to study the mechanisms of particle production. The shape of the $p_{\rm T}$ distribution of the $\Phi$(1020) meson, but not its yield, is reproduced fairly well by hydrodynamic models for central Pb-Pb collisions. In central Pb-Pb collisions at low and intermediate $p_{\rm T}$, the p/$\Phi$(1020) ratio is flat in $p_{\rm T}$, while the p/$\pi$ and $\Phi$(1020)/$\pi$ ratios show a pronounced increase and have similar shapes to each other. These results indicate that the shapes of the $p_{\rm T}$ distributions of these particles in central Pb-Pb collisions are determined predominantly by the particle masses and radial flow. Finally, $\Phi$(1020) production in Pb-Pb collisions is enhanced, with respect to the yield in pp collisions and the yield of charged pions, by an amount similar to the $\Lambda$ and $\Xi$.
Transverse-momentum distributions of (K*(892)0 + anti-K*(892)0)/2 in Pb-Pb collisions at sqrt(sNN)=2.76 TeV, centrality 0.0-20.0%.
Transverse-momentum distributions of (K*(892)0 + anti-K*(892)0)/2 in Pb-Pb collisions at sqrt(sNN)=2.76 TeV, centrality 20.0-40.0%.
Transverse-momentum distributions of (K*(892)0 + anti-K*(892)0)/2 in Pb-Pb collisions at sqrt(sNN)=2.76 TeV, centrality 40.0-60.0%.
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.
The ALICE collaboration at the CERN LHC reports novel measurements of jet substructure in pp collisions at $\sqrt{s}$= 7 TeV and central Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV. Jet substructure of track-based jets is explored via iterative declustering and grooming techniques. We present the measurement of the momentum sharing of two-prong substructure exposed via grooming, the $z_{\rm{g}}$, and its dependence on the opening angle, in both pp and Pb-Pb collisions. We also present the first measurement of the distribution of the number of branches obtained in the iterative declustering of the jet, which is interpreted as the number of its hard splittings. In Pb-Pb collisions, we observe a suppression of symmetric splittings at large opening angles and an enhancement of splittings at small opening angles relative to pp collisions, with no significant modification of the number of splittings. The results are compared to predictions from various Monte Carlo event generators to test the role of important concepts in the evolution of the jet in the medium such as color coherence.
Fully corrected $z_{\rm g}$ distribution in pp collisions for $40 \leq p_{\rm T,jet}^{\rm ch} < 60$ GeV/{\it c} and for $R=0.4$.
Ratio of fully corrected $z_{\rm g}$ distribution in pp collisions for $40 \leq p_{\rm T,jet}^{\rm ch} < 60$ GeV/{\it c} and predictions from PYTHIA 6 Perugia 11 simulations.All for $R=0.4$.
Ratio of fully corrected $z_{\rm g}$ distribution in pp collisions for $40 \leq p_{\rm T,jet}^{\rm ch} < 60$ GeV/{\it c} and predictions from PYTHIA 6 Perugia+POWHEG simulations. All for $R=0.4$.
Measurements of inclusive and direct photon production at mid-rapidity in pp collisions at $\sqrt{s}=2.76$ and 8 TeV are presented by the ALICE experiment at the LHC. The results are reported in transverse momentum ranges of $0.4<p_{T}<10$ GeV/$c$ and $0.3<p_{T}<16$ GeV/$c$, respectively. Photons are detected with the electromagnetic calorimeter~(EMCal) and via reconstruction of e$^+$e$^-$ pairs from conversions in the ALICE detector material using the central tracking system. For the final measurement of the inclusive photon spectra the results are combined in the overlapping $p_{T}$ interval of both methods. Direct photon spectra, or their upper limits at 90% C.L. are extracted using the direct photon excess ratio $R_{\gamma}$, which quantifies the ratio of inclusive photons over decay photons generated with a decay-photon simulation. An additional hybrid method, combining photons reconstructed from conversions with those identified in the EMCal, is used for the combination of the direct photon excess ratio $R_{\gamma}$, as well as the extraction of direct photon spectra or their upper limits. While no significant signal of direct photons is seen over the full $p_{T}$ range, $R_{\gamma}$ for $p_{T}>7$ GeV/$c$ is at least one $\sigma$ above unity and consistent with expectations from next-to-leading order pQCD calculations.
Double Ratio RGAMMA in inelastic pp collisions at center-of-mass energy 2.76 TeV. RGAMMA is the ratio of inclusive GAMMA to decay GAMMA.
Double Ratio RGAMMA in inelastic pp collisions at center-of-mass energy 8 TeV. RGAMMA is the ratio of inclusive GAMMA to decay GAMMA.
Invariant differential cross section of inclusive GAMMA produced in inelastic pp collisions at center-of-mass energy 2.76 TeV, the uncertainty of $\sigma_{MB}$ of 2.5% is not included in the systematic error. Values are given in the center of the PT bin.
We report on the production of inclusive $\Upsilon$(1S) and $\Upsilon$(2S) in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV at the LHC. The measurement is performed with the ALICE detector at backward ($-4.46< y_{{\rm cms}}<-2.96$) and forward ($2.03< y_{{\rm cms}}<3.53$) rapidity down to zero transverse momentum. The production cross sections of the $\Upsilon$(1S) and $\Upsilon$(2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of $\Upsilon$(1S). A suppression of the inclusive $\Upsilon$(1S) yield in p-Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon-nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects.
Inclusive UPSI(1S) production cross section as a function of rapidity in p-Pb collisions at sqrt(s_NN) = 5.02 TeV. The data was collected in 2013 with two beam configurations, p-Pb and Pb-p with integrated luminosities of 5.0 nb-1 and 5.8 nb-1, respectively.
Inclusive UPSI(1S) production cross section as a function of rapidity in p-Pb collisions at sqrt(s_NN) = 5.02 TeV. The data was collected in 2013 with two beam configurations, p-Pb and Pb-p with integrated luminosities of 5.0 nb-1 and 5.8 nb-1, respectively.
Inclusive UPSI(2S) production cross section as a function of rapidity in p-Pb collisions at sqrt(s_NN) = 5.02 TeV. The data was collected in 2013 with two beam configurations, p-Pb and Pb-p with integrated luminosities of 5.0 nb-1 and 5.8 nb-1, respectively.
The transverse momentum ($p_{\rm T}$) spectrum and nuclear modification factor ($R_{\rm AA}$) of reconstructed jets in 0-10% and 10-30% central Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV were measured. Jets were reconstructed from charged and neutral particles, utilizing the ALICE tracking detectors and Electromagnetic Calorimeter (EMCal), with the anti-$k_{\rm T}$ jet algorithm with a resolution parameter of R=0.2. The jet $p_{\rm T}$ spectra are reported in the pseudorapidity interval of $|{\eta}_{\rm jet}|<0.5$ for $40<p_{\rm T,jet}<120$ GeV/$c$ in 0-10% and for $30<p_{\rm T,jet}<100$ GeV/$c$ in 10-30% collisions. Reconstructed jets were required to contain a leading charged particle with $p_{\rm T}>5$ GeV/$c$ to suppress jets constructed from the combinatorial background in Pb-Pb collisions. The effect of the leading charged particle requirement has been studied in both pp and Pb-Pb collisions and has been shown to have negligible effects on the $R_{\rm AA}$ within the uncertainties of the measurement. The nuclear modification factor is obtained by dividing the jet spectrum measured in Pb-Pb by that in pp collisions scaled by the number of independent nucleon-nucleon collisions estimated using a Glauber model. $R_{\rm AA}$ is found to be $0.28\pm0.04$ in 0-10% and $0.35\pm0.04$ in 10-30% collisions, independent of $p_{\rm T,jet}$ within the uncertainties of the measurement. The observed suppression is in fair agreement with expectations from two model calculations with different approaches to jet quenching.
The spectra of $R=0.2$ jets with a leading track requirement of $5$ GeV/$c$ in inelastic pp collisions at $\sqrt{s}=2.76$ TeV.
The spectra of $R=0.2$ jets with a leading track requirement of $5$ GeV/$c$ in 0-10% and 10-30% most central Pb-Pb collisions scaled by 1/$N_{\mathrm{coll}}$ at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV.
Ratio of the jet spectrum with a leading track $p_{\mathrm{T}}$ > 5 GeV/$c$ over the inclusive jet spectrum for $R=0.2$ in pp collisions at $\sqrt{s}=2.76$ TeV.
The measurement of the deuteron and anti-deuteron production in the rapidity range $-1 < y < 0$ as a function of transverse momentum and event multiplicity in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss $\rm{d}E/\rm{d}x$ and via their time-of-flight. Their production in p-Pb collisions is compared to pp and Pb-Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb-Pb collisions at high multiplicities. The mean transverse momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and $\Lambda$ particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p-Pb collisions. In addition, the production of the rare $^{3}{\rm{He}}$ and $^{3}\bar{\rm He}$ nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window $-1 < y < 0$ and the $p_{\rm{T}}$-integrated yield d$N$/d$y$ is extracted. It is found that the yields of protons, deuterons, and $^{3}{\rm{He}}$, normalised by the spin degeneracy factor, follow an exponential decrease with mass number.
Transverse momentum distribution of $^{3}\overline{\mathrm{He}}$ for all non single diffractive (NSD) p-Pb collisions.
Transverse momentum distribution of $^{3}\mathrm{He}$ for all non single diffractive (NSD) p-Pb collisions.
Integrated yield of nuclei produced in NSD p-Pb collisions normalised by the spin degeneracy factor as a function of the mass number
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 the charged-particle pseudorapidity density in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\,\mathrm{Te\kern-.25exV}$ in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from $-3.5$ to $5$, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0-5%) collisions we find $21\,400\pm 1\,300$ while for the most peripheral (80-90%) we find $230\pm 38$. This corresponds to an increase of $(27\pm4)\%$ over the results at $\sqrt{s_{\mathrm{NN}}}=2.76\,\mathrm{Te\kern-.25exV}$ previously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations --- none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies.
Charged-particle pseudorapidity density for ten centrality classes over a broad $\eta$ range in Pb-Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=5.02\,\mathrm{TeV}$. Boxes around the points reflect the total uncorrelated systematic uncertainties, while the filled squares on the right reflect the correlated systematic uncertainty (evaluated at $\eta=0$). Statistical errors are generally insignificant and smaller than the markers. Also shown is the reflection of the $3.5<\eta<5$ values around $\eta=0$ (open circles). The line corresponds to fits of the difference between two Gaussians centred at $\eta=0$ ($f_{\text{GG}}$) [PLB754.373] to the data.
Charged-particle pseudorapidity density at midrapidity in most perihperhal (80-90%) Pb-Pb collisions at $\sqrt{s_{\scriptscriptstyle\mathrm{NN}}}=5.02\,\mathrm{TeV}$.
Estimation of $\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}y$ for in the most central Pb-Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=5.02\,\mathrm{TeV}$. Also shown is a fit of Gaussian distribution to the data.
We report the measurement of a new observable of jet quenching in central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV, based on the semi-inclusive rate of charged jets recoiling from a high transverse momentum (high-$p_{\rm T}$) charged hadron trigger. Jets are measured using collinear-safe jet reconstruction with infrared cutoff for jet constituents of 0.15 GeV/$c$, for jet resolution parameters $R = 0.2$, 0.4 and 0.5. Underlying event background is corrected at the event-ensemble level, without imposing bias on the jet population. Recoil jet spectra are reported in the range $20<p_\mathrm{T,jet}^\mathrm{ch}<100$ GeV/$c$. Reference distributions for pp collisions at $\sqrt{s} = 2.76$ TeV are calculated using Monte Carlo and NLO pQCD methods, which are validated by comparing with measurements in pp collisions at $\sqrt{s} = 7$ TeV. The recoil jet yield in central Pb-Pb collisions is found to be suppressed relative to that in pp collisions. No significant medium-induced broadening of the intra-jet energy profile is observed within 0.5 radians relative to the recoil jet axis. The angular distribution of the recoil jet yield relative to the trigger axis is found to be similar in central Pb-Pb and pp collisions, with no significant medium-induced acoplanarity observed. Large-angle jet deflection, which may provide a direct probe of the nature of the quasi-particles in hot QCD matter, is explored.
Per trigger normalized raw recoil jet yield in hadron trigger bin of {8,9} GeV. The recoil jet yield is measured at delta phi=pi \pm 0.6 with respect to the trigger hadron and with R=0.4 and with minimum constituent cutoff of 0.15 GeV. The measurement is performed in 0-10% most central Pb-Pb collisions at $sqrt{s_{NN}}=2.76$ TeV.
Per trigger normalized raw recoil jet yield in hadron trigger bin of {20,50} GeV. The recoil jet yield is measured at delta phi=pi \pm 0.6 with respect to the trigger hadron and with R=0.4 and with minimum constituent cutoff of 0.15 GeV. The measurement is performed in 0-10% most central Pb-Pb collisions at $sqrt{s_{NN}}=2.76$ TeV.
Per trigger normalized raw recoil jet yield in hadron trigger bin of {8,9} GeV. The recoil jet yield is measured at delta phi=pi \pm 0.6 with respect to the trigger hadron and with R=0.2 and with minimum constituent cutoff of 0.15 GeV. The measurement is performed in 0-10% most central Pb-Pb collisions at $sqrt{s_{NN}}=2.76$ TeV.
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 transverse momentum ($p_{\mathrm T}$) distribution of primary charged particles is measured at midrapidity in minimum-bias p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector at the LHC in the range $0.15<p_{\mathrm T}<50$ GeV/$c$. The spectra are compared to the expectation based on binary collision scaling of particle production in pp collisions, leading to a nuclear modification factor consistent with unity for $p_{\mathrm T}$ larger than 2 GeV/$c$, with a weak indication of a Cronin-like enhancement for $p_{\rm T}$ around 4 GeV/$c$. The measurement is compared to theoretical calculations and to data in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV.
Transverse momentum distributions of charged particles in minimum-bias (NSD) p-Pb collisions for different pseudorapidity ranges.
The histogram represents the reference spectrum (cross section scaled by the nuclear overlap function, T(pPb)) in inelastic pp collisions, determined in |eta(cms)| < 0.8.
The nuclear modification factor of charged particles as a function of transverse momentum, measured in minimum-bias (NSD) p-Pb collisions at sqrt(sNN) = 5.02 TeV in two pseudorapidity ranges, |eta(cms)| < 0.3 and -1.3 < eta(cms) < 0.3.
The production of prompt D$_s^+$ mesons was measured for the first time in collisions of heavy nuclei with the ALICE detector at the LHC. The analysis was performed on a data sample of Pb-Pb collisions at a centre-of-mass energy per nucleon pair, $\sqrt{s_{\rm NN}}$, of 2.76 TeV in two different centrality classes, namely 0-10% and 20-50%. D$_s^+$ mesons and their antiparticles were reconstructed at mid-rapidity from their hadronic decay channel D$_s^+\rightarrow\phi\pi^+$, with $\phi\rightarrow$K$^-$K$^+$, in the transverse momentum intervals $4< p_{\rm T}<12$ GeV/$c$ and $6< p_{\rm T}<12$ GeV/$c$ for the 0-10% and 20-50% centrality classes, respectively. The nuclear modification factor $R_{\rm AA}$ was computed by comparing the $p_{\rm T}$-differential production yields in Pb-Pb collisions to those in proton-proton (pp) collisions at the same energy. This pp reference was obtained using the cross section measured at $\sqrt{s}= 7$ TeV and scaled to $\sqrt{s}= 2.76$ TeV. The $R_{\rm AA}$ of D$_s^+$ mesons was compared to that of non-strange D mesons in the 10% most central Pb-Pb collisions. At high $p_{\rm T}$ ($8< p_{\rm T}<12$ GeV/$c$) a suppression of the D$_s^+$-meson yield by a factor of about three, compatible within uncertainties with that of non-strange D mesons, is observed. At lower $p_{\rm T}$ ($4< p_{\rm T}<8$ GeV/$c$) the values of the D$_s^+$-meson $R_{\rm AA}$ are larger than those of non-strange D mesons, although compatible within uncertainties. The production ratios D$_s^+$/D$^0$ and D$_s^+$\D$^+$ were also measured in Pb-Pb collisions and compared to their values in proton-proton collisions.
$p_{\rm T}$-differential yield of prompt D$_s^+$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$=2.76 TeV in the centrality class 0-10% in the rapidity interval |y|<0.5. Branching ratio of D$_s^+$->$\phi\pi^+$->$K^+K^-\pi^+$ : 0.0224. 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.
$p_{\rm T}$-differential yield of prompt D$_s^+$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$=2.76 TeV in the centrality class 20-50% in the rapidity interval |y|<0.5. Branching ratio of D$_s^+$->$\phi\pi^+$->$K^+K^-\pi^+$ : 0.0224. 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.
Nuclear modification factor $R_{\rm AA}$ of D$_s^+$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$=2.76 TeV in the centrality class 0-10% in |y| < 0.5 as a function of $p_{\rm T}$.
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.
$\Xi^{-}+\bar{\Xi}^{+}$ transverse momentum spectrum: V0M Class II (pp at $\sqrt{s}=7$ TeV).
$2K^{0}_{S}/(\pi^{+}+\pi^{-})$ ratio for pp collisions at $\sqrt{s}=7$ TeV as a function of the average charged particle multiplicity density at midrapidity.
$(\Lambda+\bar{\Lambda})/(\pi^{+}+\pi^{-})$ ratio for pp collisions at $\sqrt{s}=7$ TeV as a function of the average charged particle multiplicity density at midrapidity.
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 multiplicity dependence of electron production from heavy-flavour hadron decays as a function of transverse momentum was measured in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV using the ALICE detector at the LHC. The measurement was performed in the centre-of-mass rapidity interval $-1.07 < y_{\rm cms} < 0.14$ and transverse momentum interval 2 $< p_{\rm T} <$ 16 GeV/$c$. The multiplicity dependence of the production of electrons from heavy-flavour hadron decays was studied by comparing the $p_{\rm T}$ spectra measured for different multiplicity classes with those measured in pp collisions ($Q_{\rm pPb}$) and in peripheral p-Pb collisions ($Q_{\rm CP}$). The $Q_{\rm pPb}$ results obtained are consistent with unity within uncertainties in the measured $p_{\rm T}$ interval and event classes. This indicates that heavy-flavour decay electron production is consistent with binary scaling and independent of the geometry of the collision system. Additionally, the results suggest that cold nuclear matter effects are negligible within uncertainties, in the production of heavy-flavour decay electrons at midrapidity in p-Pb collisions.
$p_{\rm T}$-differential invariant cross section of electrons from heavy-flavour hadron decays in p--Pb collisions
$p_{\rm T}$-differential invariant cross section of electrons from heavy-flavour hadron decays in p--Pb collisions in 0--20\% centrality
$p_{\rm T}$-differential invariant cross section of electrons from heavy-flavour hadron decays in p--Pb collisions in 20--40\% centrality
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.
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.
The measurement of prompt D-meson production as a function of multiplicity in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV with the ALICE detector at the LHC is reported. D$^0$, D$^+$ and D$^{*+}$ mesons are reconstructed via their hadronic decay channels in the centre-of-mass rapidity range $-0.96< y_{\mathrm{cms}}<0.04$ and transverse momentum interval $1<p_{\rm T}<24$ GeV/$c$. The multiplicity dependence of D-meson production is examined by either comparing yields in p-Pb collisions in different event classes, selected based on the multiplicity of produced particles or zero-degree energy, with those in pp collisions, scaled by the number of binary nucleon-nucleon collisions (nuclear modification factor); as well as by evaluating the per-event yields in p-Pb collisions in different multiplicity intervals normalised to the multiplicity-integrated ones (relative yields). The nuclear modification factors for D$^0$, D$^+$ and D$^{*+}$ are consistent with one another. The D-meson nuclear modification factors as a function of the zero-degree energy are consistent with unity within uncertainties in the measured $p_{\rm T}$ regions and event classes. The relative D-meson yields, calculated in various $p_{\rm T}$ intervals, increase as a function of the charged-particle multiplicity. The results are compared with the equivalent pp measurements at $\sqrt{s}=7$ TeV as well as with EPOS~3 calculations.
Average $Q_{\rm pPb}$ of D$^{0}$, D$^{+}$ and D*$^{+}$ mesons for the sum of particles and antiparticles in several multiplicity and PT(D) intervals for p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV as a function of the multiplicity at central rapidity evaluated with the ZNA estimator. The values are reported together with their uncertainties, which are quoted as statistical followed by systematic uncertainties. Normalisation uncertainty is not quoted and amounts to $\pm 0.07$, $\pm 0.05$, $\pm 0.07$ and $\pm 0.08$ for the 0-20%, 20-40%, 40-60% and 60-100% intervals, respectively.
Average $Q_{\rm pPb}$ of D$^{0}$, D$^{+}$ and D*$^{+}$ mesons for the sum of particles and antiparticles in several multiplicity and PT(D) intervals for p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV as a function of the multiplicity at central rapidity evaluated with the CL1 estimator. The values are reported together with their uncertainties, which are quoted as statistical followed by systematic uncertainties. Normalisation uncertainty is not quoted and amounts to $\pm 0.05$, $\pm 0.05$, $\pm 0.07$ and $\pm 0.23$ for the 0-20%, 20-40%, 40-60% and 60-100% intervals, respectively.
Average $Q_{\rm pPb}$ of D$^{0}$, D$^{+}$ and D*$^{+}$ mesons for the sum of particles and antiparticles in several multiplicity and PT(D) intervals for p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV as a function of the multiplicity at central rapidity evaluated with the V0A estimator. The values are reported together with their uncertainties, which are quoted as statistical followed by systematic uncertainties. Normalisation uncertainty is not quoted and amounts to $\pm 0.05$, $\pm 0.05$, $\pm 0.06$ and $\pm 0.22$ for the 0-20%, 20-40%, 40-60% and 60-100% intervals, respectively.
In this Letter, the ALICE Collaboration presents the first measurements of the charged-particle multiplicity density, $\rm{d}N_{\rm{ch}}/\rm{d}\eta$, and total charged-particle multiplicity, $N_{\rm{ch}}^{\rm{tot}}$, in Xe-Xe collisions at a centre-of-mass energy per nucleon--nucleon pair of $\sqrt{s_{\rm NN}}$ = 5.44 TeV. The measurements are performed as a function of collision centrality over a wide pseudorapidity range of $-3.5 < \eta < 5$. The values of $\rm{d}N_{\rm{ch}}/\rm{d}\eta$ at mid-rapidity and $N_{\rm{ch}}^{\rm{tot}}$ for central collisions, normalised to the number of nucleons participating in the collision ($N_{\rm{part}}$) as a function of $\sqrt{s_{\rm NN}}$, follow the trends established in previous heavy-ion measurements. The same quantities are also found to increase as a function of $N_{\rm{part}}$, and up to the 10% most central collisions the trends are the same as the ones observed in Pb-Pb at a similar energy. For more central collisions, the Xe-Xe scaled multiplicities exceed those in Pb-Pb for a similar $N_{\rm{part}}$. The results are compared to phenomenological models and theoretical calculations based on different mechanisms for particle production in nuclear collisions. All considered models describe the data reasonably well within 20%.
Charged-particle pseudorapidity density for 12 centrality classes over a broad $\eta$ range in Xe--Xe collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44\,\mathrm{TeV}$. Statistical errors are generally insignificant.
Charged-particle pseudorapidity density for 12 centrality classes over a broad $\eta$ range in Xe--Xe collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44\,\mathrm{TeV}$. Statistical errors are generally insignificant.
Values of $2/\langle N_\mathrm{part} \rangle \langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle$ and $2/\langle N_\mathrm{part} \rangle N^\mathrm{tot}_\mathrm{ch}$ in Xe--Xe collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44\,\mathrm{TeV}$ for the top 5$\%$ central collisions.
The production of the strange and double-strange baryon resonances ($\Sigma(1385)^{\pm}$, $\Xi(1530)^{0}$) has been measured at mid-rapidity ($\left | y \right |<0.5$) in proton-proton collisions at $\sqrt{s}$ = 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the $\phi(1860)$ pentaquark, decaying in the $\Xi\pi$ channel, has been carried out but no evidence is seen.
Inelastic baryon yields, d2N/(dydpT), per pT interval per unit rapidity for Sigma(1385)+- in INEL pp collisions at sqrts 7 TeV in |y| < 0.5.
Inelastic baryon yields, d2N/(dydpT), per pT interval per unit rapidity for Xi(1530)0 in INEL pp collisions at sqrts 7 TeV in |y| < 0.5.
Mean pT as function of the mass for particles measured with the ALICE detector in INEL pp collisions at sqrts 7 TeV in |y| < 0.5.
Measurements of multi-particle azimuthal correlations (cumulants) for charged particles in p-Pb and Pb-Pb collisions are presented. They help address the question of whether there is evidence for global, flow-like, azimuthal correlations in the p-Pb system. Comparisons are made to measurements from the larger Pb-Pb system, where such evidence is established. In particular, the second harmonic two-particle cumulants are found to decrease with multiplicity, characteristic of a dominance of few-particle correlations in p-Pb collisions. However, when a $|\Delta \eta|$ gap is placed to suppress such correlations, the two-particle cumulants begin to rise at high-multiplicity, indicating the presence of global azimuthal correlations. The Pb-Pb values are higher than the p-Pb values at similar multiplicities. In both systems, the second harmonic four-particle cumulants exhibit a transition from positive to negative values when the multiplicity increases. The negative values allow for a measurement of $v_{2}\{4\}$ to be made, which is found to be higher in Pb-Pb collisions at similar multiplicities. The second harmonic six-particle cumulants are also found to be higher in Pb-Pb collisions. In Pb-Pb collisions, we generally find $v_{2}\{4\} \simeq v_{2}\{6\}\neq 0$ which is indicative of a Bessel-Gaussian function for the $v_{2}$ distribution. For very high-multiplicity Pb-Pb collisions, we observe that the four- and six-particle cumulants become consistent with 0. Finally, third harmonic two-particle cumulants in p-Pb and Pb-Pb are measured. These are found to be similar for overlapping multiplicities, when a $|\Delta\eta| > 1.4$ gap is placed.
No description provided.
We report the first measurement of the net-charge fluctuations in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV, measured with the ALICE detector at the CERN Large Hadron Collider. The dynamical fluctuations per unit entropy are observed to decrease when going from peripheral to central collisions. An additional reduction in the amount of fluctuations is seen in comparison to the results from lower energies. We examine the dependence of fluctuations on the pseudorapidity interval, which may account for the dilution of fluctuations during the evolution of the system. We find that the fluctuations at LHC are smaller compared to the measurements at the Relativistic heavy Ion Collider (RHIC), and as such, closer to what has been theoretically predicted for the formation of Quark-Gluon Plasma (QGP).
The measured NU(+-DYN) as a function of the centrality of the collisions, expressed as the number of participating nucleons, for two values of midrapidity range.
NU(+-DYN), corrected for charge conservation and finite acceptance effects, as a function of the centrality of the collisions, expressed as the number of participating nucleons, for two values of midrapidity range.
The measured and corrected NU(+-DYN) in P P collisions for two values of midrapidity range.
The first measurement of e$^+$e$^-$ pair production at mid-rapidity ($|\eta_{{\rm e}}|$ $<$ 0.8) in pp collisions at $\sqrt{s} = 7$ TeV with ALICE at the LHC is presented. The dielectron production is studied as a function of the invariant mass ($m_{\rm ee}$ $<$ 3.3 GeV/$c^{2}$), the pair transverse momentum ($p_{\rm T,ee}$ $<$ 8 GeV/$c$), and the pair transverse impact parameter (DCA$_{{\rm ee}}$), i.e., the average distance of closest approach of the reconstructed electron and positron tracks to the collision vertex, normalised to its resolution. The results are compared with the expectations from a cocktail of known hadronic sources and are well described when PYTHIA is used to generate the heavy-flavour contributions. In the low-mass region (0.14 $<$ $m_{\rm ee}$ $<$ 1.1 GeV/$c^{2}$), prompt and non-prompt e$^+$e$^-$ sources can be separated via the DCA$_{\rm ee}$. In the intermediate-mass region (1.1 $<$ $m_{\rm ee}$ $<$ 2.7 GeV/$c^{2}$), a double-differential fit to the data in $m_{\rm ee}$ and $p_{\rm T,ee}$ and a fit of the DCA$_{\rm ee}$ distribution allow the total ${\rm c\overline c}$ and ${\rm b\overline b}$ cross sections to be extracted. Two different event generators, PYTHIA and POWHEG, can reproduce the shape of the two-dimensional $m_{\rm ee}$ and $p_{\rm T,ee}$ spectra, as well as the shape of the DCA$_{\rm ee}$ distribution, reasonably well. However, differences in the ${\rm c\overline c}$ and ${\rm b\overline b}$ cross sections are observed when using the generators to extrapolate to full phase space. Finally, the ratio of inclusive to decay photons is studied via the measurement of virtual direct photons in the transverse-momentum range 1 $<$ $p_{\rm T}$ $<$ 8 GeV/$c$. This is found to be unity within the statistical and systematic uncertainties and consistent with expectations from next-to-leading order perturbative quantum chromodynamic calculations.
Inclusive $e^+e^-$ cross section in pp collisions at $\sqrt{s}$ = 7 TeV in the ALICE acceptance as a function of $m_{\rm ee}$.
Inclusive $e^+e^-$ cross section in pp collisions at $\sqrt{s}$ = 7 TeV in the ALICE acceptance as a function of $p_{\rm T,ee}$ for $m_{\rm ee}$ < 0.14 GeV/$c^{2}$.
Inclusive $e^+e^-$ cross section in pp collisions at $\sqrt{s}$ = 7 TeV in the ALICE acceptance as a function of $\rm DCA_{ee}$ for 0.08 < $m_{\rm ee}$ < 0.14 GeV/$c^{2}$.
A comprehensive survey of event-by-event fluctuations of charged hadron multiplicity in relativistic heavy ions is presented. The survey covers Au+Au collisions at sqrt(s_NN) = 62.4 and 200 GeV, and Cu+Cu collisions sqrt(s_NN) = 22.5, 62.4, and 200 GeV. Fluctuations are measured as a function of collision centrality, transverse momentum range, and charge sign. After correcting for non-dynamical fluctuations due to fluctuations in the collision geometry within a centrality bin, the remaining dynamical fluctuations expressed as the variance normalized by the mean tend to decrease with increasing centrality. The dynamical fluctuations are consistent with or below the expectation from a superposition of participant nucleon-nucleon collisions based upon p+p data, indicating that this dataset does not exhibit evidence of critical behavior in terms of the compressibility of the system. An analysis of Negative Binomial Distribution fits to the multiplicity distributions demonstrates that the heavy ion data exhibit weak clustering properties.
The uncorrected multiplicity distributions of charged hadrons with 0.2 < $p_T$ < 2.0 GeV/$c$ for 200 GeV Au+Au collisions.
The uncorrected multiplicity distributions of charged hadrons with 0.2 < $p_T$ < 2.0 GeV/$c$ for 200 GeV Au+Au collisions.
The uncorrected multiplicity distributions of charged hadrons with 0.2 < $p_T$ < 2.0 GeV/$c$ for 200 GeV Au+Au collisions.
The $p_{\rm T}$-differential production cross section of prompt $\Lambda_{\rm c}^+$ charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at $\sqrt{s} = 7$ TeV and in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at midrapidity. The $\Lambda_{\rm c}^+$ and ${\overline{\Lambda}}_{\rm c}^-$ were reconstructed in the hadronic decay modes $\Lambda_{\rm c}^+\rightarrow {\rm p}{\rm K^-}\pi^+$, $\Lambda_{\rm c}^+\rightarrow {\rm p}{\rm K_{\rm S}^0}$ and in the semileptonic channel $\Lambda_{\rm c}^+\rightarrow {\rm e^+}\nu_{\rm e}\Lambda$ (and charge conjugates). The measured values of the $\Lambda_{\rm c}^+/{\rm D_0}$ ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and $p_{\rm T}$ intervals, where the $\Lambda_{\rm c}^+$ production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the $\Lambda_{\rm c}^+$ nuclear modification factor, $R_{\rm pPb}$, is also presented. The $R_{\rm pPb}$ is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium.
Prompt $\Lambda_{\rm {c}}^{+}$ baryon $p_{\rm {T}}$-differential cross section (average among different decay modes and analyses) in pp collisions at $\sqrt{s} = 7$ TeV in the rapidity interval $|y|<0.5$.
Prompt $\Lambda_{\rm {c}}^{+}$ baryon $p_{\rm {T}}$-differential cross section (average among different decay modes and analyses) in p-Pb collisions at $\sqrt{s_{\rm {NN}}} = 5.02$ TeV in the rapidity interval $-0.96 \lt y \lt 0.04$.
The $\Lambda_{\rm {c}}^{+}$/${\rm D}^{0}$ ratio measured in pp collisions at $\sqrt{s} = 7$ TeV in the rapidity interval $|y|<0.5$ as a function of $p_{\rm {T}}$.
A measurement of dijet correlations in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV with the ALICE detector is presented. Jets are reconstructed from charged particles measured in the central tracking detectors and neutral energy deposited in the electromagnetic calorimeter. The transverse momentum of the full jet (clustered from charged and neutral constituents) and charged jet (clustered from charged particles only) is corrected event-by-event for the contribution of the underlying event, while corrections for underlying event fluctuations and finite detector resolution are applied on an inclusive basis. A projection of the dijet transverse momentum, $k_{\rm Ty} = p_\rm{T,jet}^\rm{ch+ne} \; \rm{sin}(\Delta\varphi_{\rm{dijet}})$ with $\Delta\varphi_{\rm{dijet}}$ the azimuthal angle between a full and charged jet and $p_\rm{T,jet}^\rm{ch+ne}$ the transverse momentum of the full jet, is used to study nuclear matter effects in p-Pb collisions. This observable is sensitive to the acoplanarity of dijet production and its potential modification in p-Pb collisions with respect to pp collisions. Measurements of the dijet $k_{\rm Ty}$ as a function of the transverse momentum of the full and recoil charged jet, and the event multiplicity are presented. No significant modification of $k_{\rm Ty}$ due to nuclear matter effects in p-Pb collisions with respect to the event multiplicity or a PYTHIA8 reference is observed.
Dijet |k_{T,y}| distributions in p-Pb collisions in the 0-40% V0A multiplicity event class.
Dijet |k_{T,y}| distributions in p-Pb collisions in the 0-40% V0A multiplicity event class.
Dijet |k_{T,y}| distributions in p-Pb collisions in the 0-40% V0A multiplicity event class.
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.
$p_{\rm T}$-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%.
$p_{\rm T}$-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 40-60%.
We report on the measurement of the inclusive $\Upsilon$(1S) production in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV carried out at forward rapidity ($2.5<y<4$) and down to zero transverse momentum using its $\mu^{+}\mu^{-}$ decay channel with the ALICE detector at the Large Hadron Collider. A strong suppression of the inclusive $\Upsilon$(1S) yield is observed with respect to pp collisions scaled by the number of independent nucleon-nucleon collisions. The nuclear modification factor, for events in the 0-90$\%$ centrality range, amounts to $0.30\pm0.05{\rm (stat)}\pm0.04{\rm (syst)}$. The observed $\Upsilon$(1S) suppression increases with the centrality of the collision and is more pronounced than in corresponding mid-rapidity measurements. Our results are compared with model calculations, which are found to underestimate the measured suppression and fail to reproduce its rapidity dependence.
Inclusive Upsilon (1S) Nuclear Modification Factor (Raa) measured in Lead-Lead collisions at sqrt(sNN) = 2.76 TeV in 2.5 < y < 4 and pt > 0 GeV, as a function of the average number of participating nucleons (<Npart>). Data have been collected in 2011 and the integrated luminosity is ~ 70 inverse microbarn.
Inclusive Upsilon (1S) Nuclear Modification Factor (Raa) measured in Lead-Lead collisions at sqrt(sNN) = 2.76 TeV in 2.5 < y < 4 and pt > 0 GeV, as a function of the rapidity. Data have been collected in 2011 and the integrated luminosity is ~ 70 inverse microbarn.
Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV, and Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC. Dynamical fluctuations indicative of correlated particle emission are observed in all systems. The results in pp collisions show little dependence on collision energy. The Monte Carlo event generators PYTHIA and PHOJET are in qualitative agreement with the data. Peripheral Pb-Pb data exhibit a similar multiplicity dependence as that observed in pp. In central Pb-Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb--Pb are in qualitative agreement with previous measurements in Au-Au at lower collision energies and with expectations from models that incorporate collective phenomena.
Relative fluctuation $\sqrt{C_m}/M(p_{\rm T})_m$ as a function of $\langle {\rm d}N_{\rm ch}/{\rm d}\eta \rangle$ in pp collisions at $\sqrt{s}$ = 0.9 TeV.
Relative fluctuation $\sqrt{C_m}/M(p_{\rm T})_m$ as a function of $\langle {\rm d}N_{\rm ch}/{\rm d}\eta \rangle$ in pp collisions at $\sqrt{s}$ = 2.76 TeV.
Relative fluctuation $\sqrt{C_m}/M(p_{\rm T})_m$ as a function of $\langle {\rm d}N_{\rm ch}/{\rm d}\eta \rangle$ in pp collisions at $\sqrt{s}$ = 7 TeV.
The multi-strange baryon yields in Pb--Pb collisions have been shown to exhibit an enhancement relative to pp reactions. In this work, $\Xi$ and $\Omega$ production rates have been measured with the ALICE experiment as a function of transverse momentum, ${p_{\rm T}}$, in p-Pb collisions at a centre-of-mass energy of ${\sqrt{s_{\rm NN}}}$ = 5.02 TeV. The results cover the kinematic ranges 0.6 GeV/$c<{p_{\rm T}} <$7.2 GeV/$c$ and 0.8 GeV/$c<{p_{\rm T}}<$ 5 GeV/$c$, for $\Xi$ and $\Omega$ respectively, in the common rapidity interval -0.5 $<{y_{\rm CMS}}<$ 0. Multi-strange baryons have been identified by reconstructing their weak decays into charged particles. The ${p_{\rm T}}$ spectra are analysed as a function of event charged-particle multiplicity, which in p-Pb collisions ranges over one order of magnitude and lies between those observed in pp and Pb-Pb collisions. The measured ${p_{\rm T}}$ distributions are compared to the expectations from a Blast-Wave model. The parameters which describe the production of lighter hadron species also describe the hyperon spectra in high multiplicity p-Pb. The yield of hyperons relative to charged pions is studied and compared with results from pp and Pb-Pb collisions. A statistical model is employed, which describes the change in the ratios with volume using a canonical suppression mechanism, in which the small volume causes a species-dependent relative reduction of hadron production. The calculations, in which the magnitude of the effect depends on the strangeness content, show good qualitative agreement with the data.
Mean pT of XI- in p-Pb collisions with centre-of-mass energy/nucleon=5.02 TeV for each V0A multiplicity event class.
Mean pT of XIBAR+ in p-Pb collisions with centre-of-mass energy/nucleon=5.02 TeV for each V0A multiplicity event class.
Mean pT of OMEGA- in p-Pb collisions with centre-of-mass energy/nucleon=5.02 TeV for each V0A multiplicity event class.
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