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.
The first measurements of anisotropic flow coefficients $v_{\rm{n}}$ for mid-rapidity charged particles in Xe-Xe collisions at $\sqrt{s_{\rm{NN}}} = 5.44$ TeV are presented. Comparing these measurements to those from Pb-Pb collisions at $\sqrt{s_{\rm{NN}}} = 5.02$ TeV, $v_{2}$ is found to be suppressed for mid-central collisions at the same centrality, and enhanced for central collisions. The values of $v_{3}$ are generally larger in Xe-Xe than in Pb-Pb at a given centrality. These observations are consistent with expectations from hydrodynamic predictions. When both $v_{2}$ and $v_{3}$ are divided by their corresponding eccentricities for a variety of initial state models, they generally scale with transverse density when comparing Xe-Xe and Pb-Pb, with some deviations observed in central Xe-Xe and Pb-Pb collisions. These results assist in placing strong constraints on both the initial state geometry and medium response for relativistic heavy-ion collisions.
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.
The production of muons from heavy-flavour hadron decays in p-Pb collisions at $\sqrt{{\textit s}_{\rm NN}}=5.02$ TeV was studied for $2 < p_{\rm T} < 16$ GeV/$c$ with the ALICE detector at the CERN LHC. The measurement was performed at forward (p-going direction) and backward (Pb-going direction) rapidity, in the ranges of rapidity in the center-of-mass system (cms) $2.03<y_{\rm cms}<3.53$ and $-4.46<y_{\rm cms}<-2.96$, respectively. The production cross sections and nuclear modification factors are presented as a function of transverse momentum ($p_{\rm T}$). At forward rapidity, the nuclear modification factor is compatible with unity while at backward rapidity, in the interval $2.5<p_{\rm T}<3.5$ GeV/$c$, it is above unity by more than 2$\sigma$. The ratio of the forward-to-backward production cross sections is also measured in the overlapping interval $2.96 < \vert y_{\rm cms} \vert < 3.53$ and is smaller than unity by 3.7$\sigma$ in $2.5<p_{\rm T}<3.5$ GeV/$c$. The data are described by model calculations including cold nuclear matter effects.
pT-differential production cross section of heavy-flavour decay muons at forward rapidity (proton-going side) and backward rapidity (Pb-going side)
pT-differential nuclear modification factor of heavy-flavour decay muons at forward rapidity (proton-going side)
pT-differential nuclear modification factor of heavy-flavour decay muons at backward rapidity (Pb-going side)
The production of the charm-strange baryon $\Xi_{\rm c}^0$ is measured for the first time at the LHC via its semileptonic decay into e$^+\Xi^-\nu_{\rm e}$ in pp collisions at $\sqrt{s}=7$ TeV with the ALICE detector. The transverse momentum ($p_{\rm T}$) differential cross section multiplied by the branching ratio is presented in the interval 1 $<$ $p_{\rm T}$ $<$ 8 GeV/$c$ at mid-rapidity, $|y|$ $<$ 0.5. The transverse momentum dependence of the $\Xi_{\rm c}^0$ baryon production relative to the D$^0$ meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured cross-section ratio.
Inclusive $\Xi_{\rm c}^{0}$ $p_{\rm T}$ differential cross section multiplied by the branching ratio into the semileptonic decay for $|y|<0.5$.
Ratio of the $p_{\rm T}$ differential cross sections of $\Xi_{\rm c}^{0}$ baryons (multiplied by the branching ratio into the semileptonic decay) and D$^{0}$ mesons for $|y|<0.5$.
We report on the measurement of the inclusive J/$\psi$ polarization parameters in pp collisions at a center of mass energy $\sqrt{s} = 8$ TeV with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.23 pb$^{-1}$. J/$\psi$ resonances are reconstructed in their di-muon decay channel in the rapidity interval $2.5 < y < 4.0$ and over the transverse-momentum interval $2 < p_{\rm T} < 15$ GeV/$c$. The three polarization parameters ($\lambda_\theta$, $\lambda_\varphi$, $\lambda_{\theta\varphi}$) are measured as a function of $p_{\rm T}$ both in the helicity and Collins-Soper reference frames. The measured J/$\psi$ polarization parameters are found to be compatible with zero within uncertainties, contrary to expectations from all available predictions. The results are compared with the measurement in pp collisions at $\sqrt{s} = 7$ TeV.
ALICE inclusive J/psi polarization parameters lambda_theta in the Collins-Soper frame as a function of p_T in pp collisions at sqrt{s} = 8 TeV in the rapidity interval 2.5 < y < 4.0. The error bars represent the total uncertainties.
ALICE inclusive J/psi polarization parameters lambda_phi in the Collins-Soper frame as a function of p_T in pp collisions at sqrt{s} = 8 TeV in the rapidity interval 2.5 < y < 4.0. The error bars represent the total uncertainties.
ALICE inclusive J/psi polarization parameters lambda_thetaphi in the Collins-Soper frame as a function of p_T in pp collisions at sqrt{s} = 8 TeV in the rapidity interval 2.5 < y < 4.0. The error bars represent the total uncertainties.
Inclusive J/$\psi$ production is studied in p-Pb interactions at a centre-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\rm NN}}=8.16$ TeV, using the ALICE detector at the CERN LHC. The J/$\psi$ meson is reconstructed, via its decay to a muon pair, in the centre-of-mass rapidity intervals $2.03<y_{\rm {cms}}<3.53$ and $-4.46<y_{\rm {cms}}<-2.96$, where positive and negative $y_{\rm {cms}}$ refer to the p-going and Pb-going direction, respectively. The transverse momentum coverage is $p_{\rm T}<20$ GeV/$c$. In this paper, $y_{\rm cms}$- and $p_{\rm T}$-differential cross sections for inclusive J/$\psi$ production are presented, and the corresponding nuclear modification factors $R_{\rm pPb}$ are shown. Forward results show a suppression of the J/$\psi$ yield with respect to pp collisions, concentrated in the region $p_{\rm T}\lesssim 5$ GeV/$c$. At backward rapidity no significant suppression is observed. The results are compared to previous measurements by ALICE in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV and to theoretical calculations. Finally, the ratios $R_{\rm FB}$ between forward- and backward-$y_{\rm {cms}}$ $R_{\rm pPb}$ values are shown and discussed.
The y-differential inclusive JPsi cross section obtained in p-Pb and Pb-p collisions. The first uncertainty is statistical, the second one is the uncorrelated systematic uncertainty, while the third one is the global uncertainty common to p-Pb and Pb-p results.
The pt-differential inclusive JPsi cross section obtained in Pb-p collisions. The first uncertainty is statistical, the second one is the uncorrelated systematic uncertainty, while the third one is the global uncertainty common to p-Pb and Pb-p results.
The pt-differential inclusive JPsi nuclear modification factor obtained in p-Pb. The first uncertainty is statistical, the second one is the uncorrelated systematic uncertainty, while the third one is the global uncertainty common to p-Pb and Pb-p results.
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/$c^{2}$.
The invariant differential cross sections for inclusive $\pi^{0}$ and $\eta$ mesons at midrapidity were measured in pp collisions at $\sqrt{s}=2.76$ TeV for transverse momenta $0.4<p_{\rm T}<40$ GeV/$c$ and $0.6<p_{\rm T}<20$ GeV/$c$, respectively, using the ALICE detector. This large range in $p_{\rm T}$ was achieved by combining various analysis techniques and different triggers involving the electromagnetic calorimeter (EMCal). In particular, a new single-cluster, shower-shape based method was developed for the identification of high-$p_{\rm T}$ neutral pions, which exploits that the showers originating from their decay photons overlap in the EMCal. The measured cross sections are found to exhibit a similar power-law behavior with an exponent of about $6.3$. Next-to-leading-order perturbative QCD calculations differ from the measured cross sections by about $30$% for the $\pi^0$, and between $30$-$50$% for the $\eta$ meson, while generator-level simulations with PYTHIA 8.2 describe the data to better than $10$-$30$%, except at $p_{\rm T}<1$ GeV/$c$. The new data can therefore be used to further improve the theoretical description of $\pi^{0}$ and $\eta$ meson production.
Invariant differential yields of $\pi^0$ produced in inelastic pp collisions at center-of-mass energy 2.76 TeV, the normalization uncertainties of 5.7% are not included in the systematic error.
Invariant differential yields of $\eta$ produced in inelastic pp collisions at center-of-mass energy 2.76 TeV, the normalization uncertainties of 5.7% are not included in the systematic error.
Invariant differential cross section of $\pi^0$ 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.
We present results on transverse momentum ($p_{\rm T}$) and rapidity ($y$) differential production cross sections, mean transverse momentum and mean transverse momentum square of inclusive J/$\psi$ and $\psi(2S)$ at forward rapidity ($2.5<y<4$) as well as $\psi(2S)$-to-J/$\psi$ cross section ratios. These quantities are measured in pp collisions at center of mass energies $\sqrt{s}=5.02$ and 13 TeV with the ALICE detector. Both charmonium states are reconstructed in the dimuon decay channel, using the muon spectrometer. A comprehensive comparison to inclusive charmonium cross sections measured at $\sqrt{s}=2.76$, 7 and 8 TeV is performed. A comparison to non-relativistic quantum chromodynamics and fixed-order next-to-leading logarithm calculations, which describe prompt and non-prompt charmonium production respectively, is also presented. A good description of the data is obtained over the full $p_{\rm T}$ range, provided that both contributions are summed. In particular, it is found that for $p_{\rm T}>15$ GeV/$c$ the non-prompt contribution reaches up to 50% of the total charmonium yield.
Differential production cross sections of $J/\psi$ as a function of $p_{\rm T}$.
Differential production cross sections of $J/\psi$ as a function of rapidity.
Differential production cross sections of $\psi(2S)$ as a function of $p_{\rm T}$.
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