Angular correlations between heavy-flavour decay electrons and charged particles at mid-rapidity ($|\eta| < 0.8$) are measured in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The analysis is carried out for the 0-20% (high) and 60-100% (low) multiplicity ranges. The jet contribution in the correlation distribution from high-multiplicity events is removed by subtracting the distribution from low-multiplicity events. An azimuthal modulation remains after removing the jet contribution, similar to previous observations in two-particle angular correlation measurements for light-flavour hadrons. A Fourier decomposition of the modulation results in a positive second-order coefficient ($v_{2}$) for heavy-flavour decay electrons in the transverse momentum interval $1.5 < p_{\rm{T}} < 4$ GeV/$c$ in high-multiplicity events, with a significance larger than $5\sigma$. The results are compared with those of charged particles at mid-rapidity and of inclusive muons at forward rapidity. The $v_2$ measurement of open heavy-flavour particles at mid-rapidity in small collision systems could provide crucial information to help interpret the anisotropies observed in such systems.
$V_{2\Delta}^{HFe-ch}$ in bins of $p_T$ for p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. Charged particles are selected on the range $ 0.3 < p_T^{ch} < 2$ GeV/$c$. The results are obtained by subtracting associated per-trigger correlation distribution in low-multiplicity (60-100% V0A) collisions from the correlation distribution in high-multiplicity (0-20% V0A) collisions.
Baselines in high-multiplicity collisions ($b_{\rm HM}$) and low-multiplicity collisions ($b_{\rm LM}$) in bins of $p_T$ for p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. The values were obtained using the Zero Yield at Minimum (ZYAM) method.
$v_2^{HFe}$ in bins of $p_T$ for p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. The systematic and statistical uncertainties correspond to the combined uncertainties of the $V_{2\Delta}^{HFe-ch}$ and of the charged particle $v_2$. The results are obtained by subtracting associated per-trigger correlation distribution in low-multiplicity (60-100% V0A) collisions from the correlation distribution in high-multiplicity (0-20% V0A) collisions.
The elliptic flow of inclusive and direct photons was measured at mid-rapidity in two centrality classes 0-20% and 20-40% in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV by ALICE. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the detector material with the $e^{+}e^{-}$ pairs reconstructed in the central tracking system. The results of the two methods were combined and the direct photon elliptic flow was extracted in the transverse momentum range $0.9 < p_{\rm T} < 6.2$ GeV/$c$. A comparison to RHIC data shows a similar magnitude of the measured direct-photon elliptic flow. Hydrodynamic and transport model calculations are systematically lower than the data, but are found to be compatible.
Ratio V2{GAMMA,INCLUSIVE,PCM}/V2{GAMMA,INCLUSIVE,COMBINED} as function of $p_\text{T}$, collision centrality 0-20%, for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.
Ratio V2{GAMMA,INCLUSIVE,PHOS}/V2{GAMMA,INCLUSIVE,COMBINED} as function of $p_\text{T}$, collision centrality 20-40%, for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.
V2{GAMMA,DECAY} as function of $p_\text{T}$, collision centrality 0-20%, for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.
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.
The elliptic ($v_2$), triangular ($v_3$), and quadrangular ($v_4$) flow coefficients of $\pi^{\pm}$, ${\rm K}^{\pm}$, ${\rm p+\overline{p}}$, ${\Lambda+\overline{\Lambda}}$, ${\rm K}^{\rm 0}_{\rm S}$, and the $\phi$-meson are measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. Results obtained with the scalar product method are reported for the rapidity range $\vert y \vert <$ 0.5 as a function of transverse momentum, $p_\text{T}$, at different collision centrality intervals between 0-70%, including ultra-central (0-1%) collisions for $\pi^{\pm}$, ${\rm K}^{\pm}$, and ${\rm p+\overline{p}}$. For $p_\text{T} < 3$ GeV$\kern-0.05em/\kern-0.02em c$, the flow coefficients exhibit a particle mass dependence. At intermediate transverse momenta ($3
anisotropic flow as a function of transverse momentum for Pb-Pb collisions at sqNN = 5.02 TeV.
anisotropic flow as a function of transverse momentum for Pb-Pb collisions at sqNN = 5.02 TeV.
anisotropic flow as a function of transverse momentum for Pb-Pb collisions at sqNN = 5.02 TeV.
Inclusive $\Upsilon$(1S) and $\Upsilon$(2S) production have been measured in Pb-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair $\sqrt{s_{_{\rm NN}}}=5.02$ TeV, using the ALICE detector at the CERN LHC. The $\Upsilon$ mesons are reconstructed in the centre-of-mass rapidity interval $2.5
Inclusive $\Upsilon$(1S) $R_{\rm AA}$ and Pb-Pb yields for the centrality, transverse-momentum and rapidity ranges 0-90%, $0<p_{\rm T}<15$ GeV/$c$ and $2.5<y<4$, respectively. Statistical and systematic uncertainties are reported. (The yield is not normalized to the kinematic intervals).
Inclusive $\Upsilon$(1S) $R_{\rm AA}$ and Pb-Pb yields as a function of collision centrality. The transverse-momentum and rapidity ranges are $0<p_{\rm T}<15$ GeV/$c$ and $2.5<y<4$, respectively. Statistical and systematic uncertainties are reported. A global systematic uncertainty of 7.7% (4.9%) affects all the $R_{\rm AA}$ (yield) values. (The yields are not normalized to the kinematic intervals).
Inclusive $\Upsilon$(1S) $R_{\rm AA}$ and Pb-Pb yields as a function of transverse momentum. The centrality and rapidity ranges are 0-90% and $2.5<y<4$, respectively. Statistical and systematic uncertainties are reported. A global systematic uncertainty of 2.7% (2.3%) affects all the $R_{\rm AA}$ (yield) values.
The measurement of dielectron production is presented as a function of invariant mass and transverse momentum ($p_{\rm T}$) at midrapidity ($|y_{\rm e}|<0.8$) in proton-proton (pp) collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at $\sqrt{s}=7$ TeV or 13 TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: ${\rm d}\sigma_{\rm c\bar{c}}/{\rm d}y|_{y=0}=974\pm138(\rm{stat.})\pm140(\rm{syst.})~\mu{\rm b}$ and ${\rm d}\sigma_{\rm b\bar{b}}/{\rm d}y|_{y=0}=79\pm14(\rm{stat.})\pm11(\rm{syst.})~\mu{\rm b}$ using PYTHIA simulations and ${\rm d}\sigma_{\rm c\bar{c}}/{\rm d}y|_{y=0}=1417\pm184(\rm{stat.})\pm204(\rm{syst.})~\mu{\rm b}$ and ${\rm d}\sigma_{\rm b\bar{b}}/{\rm d}y|_{y=0}=48\pm14(\rm{stat.})\pm7(\rm{syst.})~\mu{\rm b}$ for POWHEG. These values, whose uncertainties are fully correlated between the two generators, are consistent with extrapolations from lower energies. The different results obtained with POWHEG and PYTHIA imply different kinematic correlations of the heavy-quark pairs in these two generators. Furthermore, comparisons of dielectron spectra in inelastic events and in events collected with a trigger on high charged-particle multiplicities are presented in various $p_{\rm T}$ intervals. The differences are consistent with the already measured scaling of light-hadron and open-charm production at high charged-particle multiplicity as a function of $p_{\rm T}$. Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations.
The dielectron cross section in inelastic pp collisions at $\sqrt{s}$ = 13 TeV as a function of invariant mass for $p_{\rm T,ee}$ < 6.0 GeV/$c$.
The dielectron cross section in inelastic pp collisions at $\sqrt{s}$ = 13 TeV as a function of pair transverse momentum for $m_{\rm ee}$ < 0.14 GeV/$c^{2}$.
The dielectron cross section in inelastic pp collisions at $\sqrt{s}$ = 13 TeV as a function of pair transverse momentum for 0.14 < $m_{\rm ee}$ < 0.7 GeV/$c^{2}$.
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.
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.
Values of $2/\langle N_\mathrm{part} \rangle \langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle$ and $2/\langle N_\mathrm{part} \rangle N^\mathrm{tot}_\mathrm{ch}$ as a function of $\langle N_\mathrm{part} \rangle$ in Xe--Xe collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44\,\mathrm{TeV}$.
Transverse momentum ($p_{\rm T}$) spectra of charged particles at mid-pseudorapidity in Xe-Xe collisions at $\sqrt{s_{\rm NN}}$ = 5.44 TeV measured with the ALICE apparatus at the Large Hadron Collider are reported. The kinematic range $0.15 < p_{\rm T} < 50$ GeV/$c$ and $|\eta| < 0.8$ is covered. Results are presented in nine classes of collision centrality in the 0-80% range. For comparison, a pp reference at the collision energy of $\sqrt{s}$ = 5.44 TeV is obtained by interpolating between existing \pp measurements at $\sqrt{s}$ = 5.02 and 7 TeV. The nuclear modification factors in central Xe-Xe collisions and Pb-Pb collisions at a similar center-of-mass energy of $\sqrt{s_{\rm NN}}$ = 5.02 TeV, and in addition at 2.76 TeV, at analogous ranges of charged particle multiplicity density $\left\langle\rm{d}N_{\rm ch}/\rm{d}\eta\right\rangle$ show a remarkable similarity at $p_{\rm T}> 10$ GeV/$c$. The comparison of the measured $R_{\rm AA}$ values in the two colliding systems could provide insight on the path length dependence of medium-induced parton energy loss. The centrality dependence of the ratio of the average transverse momentum $\left\langle p_{\rm{T}}\right\rangle$ in Xe-Xe collisions over Pb-Pb collision at $\sqrt{s}$ = 5.02 TeV is compared to hydrodynamical model calculations.
Transverse momentum spectra of charged particles in XeXe collisions in nine centrality classes.
Interpolated pp reference spectrum and invariant cross section.
Nuclear modification factor for XeXe. Additional systematic error: 0-5 pct data: +6.1 pct -6.1 pct 5-10 pct data: +6.6 pct -6.6 pct 10-20 pct data: +7.4 pct -7.4 pct 20-30 pct data: +9.8 pct -9.8 pct 30-40 pct data: +11.5 pct -11.5 pct 40-50 pct data: +12.9 pct -12.9 pct 50-60 pct data: +13.8 pct -13.8 pct 60-70 pct data: +14.0 pct -14.0 pct 70-80 pct data: +12.9 pct -12.9 pct
A measurement of $J/\psi$ and $\psi(2\mathrm{S})$ production is presented. It is based on a data sample from Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV and $pp$ collisions at $\sqrt{s}$ = 5.02 TeV recorded by the ATLAS detector at the LHC in 2015, corresponding to an integrated luminosity of $0.42\mathrm{nb}^{-1}$ and $25\mathrm{pb}^{-1}$ in Pb+Pb and $pp$, respectively. The measurements of per-event yields, nuclear modification factors, and non-prompt fractions are performed in the dimuon decay channel for $9 < p_{T}^{\mu\mu} < 40$ GeV in dimuon transverse momentum, and $-2.0 < y_{\mu\mu} < 2.0$ in rapidity. Strong suppression is found in Pb+Pb collisions for both prompt and non-prompt $J/\psi$, as well as for prompt and non-prompt $\psi(2\mathrm{S})$, increasing with event centrality. The suppression of prompt $\psi(2\mathrm{S})$ is observed to be stronger than that of $J/\psi$, while the suppression of non-prompt $\psi(2\mathrm{S})$ is equal to that of the non-prompt $J/\psi$ within uncertainties, consistent with the expectation that both arise from \textit{b}-quarks propagating through the medium. Despite prompt and non-prompt $J/\psi$ arising from different mechanisms, the dependence of their nuclear modification factors on centrality is found to be quite similar.
Per-event-yield of prompt jpsi production in 5.02 TeV PbPb collision data as a function of pT for three different centrality slices in the rapidity range |y| < 2.
Per-event-yield of non-prompt jpsi production in 5.02 TeV PbPb collision data as a function of pT for three different centrality slices in the rapidity range |y| < 2.
Non-prompt fraction of jpsi production in 5.02 TeV PbPb collision data as a function of pT for three different centrality slices in the rapidity range |y| < 2.
The PHENIX collaboration presents first measurements of low-momentum ($0.4
Direct photon spectra(Physical Review C87, 054907 (2013)) normalized by $(dN_{ch}/d\eta)^{1.25}$ for in p+p at $\sqrt{s_{NN}}$= 200 GeV.
Direct photon spectra(Physics Letters B94, 106 (1980)) normalized by $(dN_{ch}/d\eta)^{1.25}$ for in p+p at $\sqrt{s_{NN}}$= 62.4 GeV.
Direct photon spectra(Nucl. Part. Phys. 23, A1 (1997) and Sov. J. Nucl. Phys. 51, 836 (1990)) normalized by $(dN_{ch}/d\eta)^{1.25}$ for in p+p at $\sqrt{s_{NN}}$= 63 GeV.
Forum