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 $2.5<y<4$ and in the transverse-momentum range $p_{\rm T}<15$ GeV/$c$, via their decays to muon pairs. In this Letter, we present results on the inclusive $\Upsilon$(1S) nuclear modification factor $R_{\rm AA}$ as a function of collision centrality, transverse momentum and rapidity. The $\Upsilon$(1S) and $\Upsilon$(2S) $R_{\rm AA}$, integrated over the centrality range 0-90%, are $0.37 \pm 0.02 {\rm{(stat)}}\pm 0.03 {\rm{(syst)}}$ and $0.10 \pm 0.04 {\rm{(stat)}}\pm 0.02 {\rm{(syst)}}$, respectively, leading to a ratio $R_{\rm{AA}}^{\Upsilon(\rm2S)}/R_{\rm{AA}}^{\Upsilon(\rm1S)}$ of $0.28\pm0.12\text{(stat)}\pm0.06\text{(syst)}$. The observed $\Upsilon$(1S) suppression increases with the centrality of the collision and no significant variation is observed as a function of transverse momentum and rapidity.
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.
Inclusive J/$\psi$ production is studied in Xe-Xe interactions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}}= 5.44$ TeV, using the ALICE detector at the CERN LHC. The J/$\psi$ meson is reconstructed via its decay into a muon pair, in the centre-of-mass rapidity interval $2.5<y<4$ and down to zero transverse momentum. In this Letter, the nuclear modification factors $R_{\rm AA}$ for inclusive J/$\psi$, measured in the centrality range 0-90% as well as in the centrality intervals 0-20% and 20-90% are presented. The $R_{\rm AA}$ values are compared to previously published results for Pb-Pb collisions at $\sqrt{s_{\rm NN}}= 5.02$ TeV and to the calculation of a transport model. A good agreement is found between Xe-Xe and Pb-Pb results as well as between data and the model.
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
$\phi$ meson measurements provide insight into strangeness production, which is one of the key observables for the hot medium formed in high-energy heavy-ion collisions. ALICE measured $\phi$ production through its decay in muon pairs in Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 2.76 TeV in the intermediate transverse momentum range $2 < p_{\rm T} < 5$ GeV/$c$ and in the rapidity interval $2.5<y<4$. The $\phi$ yield was measured as a function of the transverse momentum and collision centrality. The nuclear modification factor was obtained as a function of the average number of participating nucleons. Results were compared with the ones obtained via the kaon decay channel in the same $p_{\rm T}$ range at midrapidity. The values of the nuclear modification factor in the two rapidity regions are in agreement within uncertainties.
phi yield as a function of $p_\mathrm{T}$ at forward rapidity in pp collisions.
phi yield as a function of $p_\mathrm{T}$ at forward rapidity in Pb-Pb collisions for 0-40\% centrality.
phi yield as a function of $p_\mathrm{T}$ at forward rapidity in Pb-Pb collisions for 40-90\% centrality (scaled by 3 in the figure).
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.
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 production of Z$^0$ bosons at large rapidities in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV is reported. Z$^0$ candidates are reconstructed in the dimuon decay channel (${\rm Z}^0 \rightarrow \mu^+\mu^-$), based on muons selected with pseudo-rapidity $-4.0<\eta<-2.5$ and $p_{\rm T}>20$ GeV/$c$. The invariant yield and the nuclear modification factor, $R_{\rm AA}$, are presented as a function of rapidity and collision centrality. The value of $R_{\rm AA}$ for the 0-20% central Pb-Pb collisions is $0.67 \pm 0.11 \, \mbox{(stat.)} \, \pm 0.03 \, \mbox{(syst.)} \, \pm 0.06 \, \mbox{(corr. syst.)}$, exhibiting a deviation of $2.6 \sigma$ from unity. The results are well-described by calculations that include nuclear modifications of the parton distribution functions, while the predictions using vacuum PDFs deviate from data by $2.3\sigma$ in the 0-90% centrality class and by $3\sigma$ in the 0-20% central collisions.
Invariant yield of Z$^{0}$ production in 2.5 < y < 4.0 divided by the average nuclear overlap function in the 0-90% centrality class. The first uncertainty is statistical, the second is systematic.
Nuclear modification factor of Z$^{0}$ production in 2.5 < y < 4.0 in the 0-90% centrality class. The first uncertainty is statistical, the second is systematic.
Invariant yield of Z$^{0}$ production in 2.5 < y < 4.0 divided by the average nuclear overlap function as a function of rapidity in the 0-90% centrality class. The first uncertainty is statistical, the second is the uncorrelated systematic and the third is the correlated systematic.
Electrons from heavy-flavour hadron decays (charm and beauty) were measured with the ALICE detector in Pb-Pb collisions at a centre-of-mass of energy $\sqrt{s_{\rm NN}}=2.76$ TeV. The transverse momentum ($p_{\rm T}$) differential production yields at mid-rapidity were used to calculate the nuclear modification factor $R_{\rm AA}$ in the interval $3<p_{\rm T}< 18$ GeV/$c$. The $R_{\rm AA}$ shows a strong suppression compared to binary scaling of pp collisions at the same energy (up to a factor of 4) in the 10% most central Pb-Pb collisions. There is a centrality trend of suppression, and a weaker suppression (down to a factor of 2) in semi-peripheral (50-80%) collisions is observed. The suppression of electrons in this broad $p_{\rm T}$ interval indicates that both charm and beauty quarks lose energy when they traverse the hot medium formed in Pb-Pb collisions at LHC.
Pb-Pb collision centrality 0-10%.
Pb-Pb collision centrality 10-20%.
Pb-Pb collision centrality 20-30%.
The inclusive J/$\psi$ production has been studied in Pn-Pb and pp collisions at the centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}=5.02$ TeV, using the ALICE detector at the CERN LHC. The J/$\psi$ meson is reconstructed, in the centre-of-mass rapidity interval $2.5<y<4$ and in the transverse-momentum range $p_{\rm T}<12$ GeV/$c$, via its decay to a muon pair. In this Letter, we present results on the inclusive J/$\psi$ cross section in pp collisions at $\sqrt{s}=5.02$ TeV and on the nuclear modification factor $R_{\rm AA}$. The latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum $p_{\rm T}$ of the J/$\psi$. The measured $R_{\rm AA}$ values indicate a suppression of the J/$\psi$ in nuclear collisions and are then compared to our previous results obtained in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV. The ratio of the $R_{\rm AA}$ values at the two energies is also computed and compared to calculations of statistical and dynamical models. The numerical value of the ratio for central events (0-10\% centrality) is $1.17 \pm 0.04 {\rm{(stat)}}\pm 0.20 {\rm{(syst)}}$. In central events, as a function of $p_{\rm T}$, a slight increase of $R_{\rm AA}$ with collision energy is visible in the region $2<p_{\rm T}<6$ GeV/$c$. Theoretical calculations provide a good description of the measurements, within uncertainties.
Differential cross section ${\rm d}^2\sigma^{\rm pp}_{{\rm J}/\psi}/{\rm d}y{\rm d}p_{\rm T}$ for inclusive J/$\psi$ cross section in pp collisions at $\sqrt{s}=5.02$ TeV. The first uncertainty is statistical, the second is the uncorrelated systematic, while the third one is a $p_{\rm T}$-correlated systematic uncertainty.
The nuclear modification factor for inclusive J/$\psi$ production, as a function of centrality, at $\sqrt{s_{\rm NN}}=5.02$ TeV. The widths of the centrality classes used are 2% from 0 to 12%, then 3% up to 30% and 5% for more peripheral collisions. The first uncertainty is statistical, the second is the uncorrelated systematic, while the third one is a centrality-correlated systematic uncertainty.
Centrality dependence (with 10% width centrality classes) of the inclusive J/$\psi$ $R_{\rm AA}$ for $0.3<p_{\rm T}<8$ GeV/$c$. The first uncertainty is statistical, the second is the uncorrelated systematic, while the third one is a centrality-correlated systematic uncertainty.
We report on the first measurement of an excess in the yield of J/$\psi$ at very low transverse momentum ($p_{\rm T}< 0.3$ GeV/$c$) in peripheral hadronic Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV, performed by ALICE at the CERN LHC. Remarkably, the measured nuclear modification factor of J/$\psi$ in the rapidity range $2.5<y<4$ reaches about 7 (2) in the $p_{\rm T}$ range 0-0.3 GeV/$c$ in the 70-90% (50-70%) centrality class. The J/$\psi$ production cross section associated with the observed excess is obtained under the hypothesis that coherent photoproduction of J/$\psi$ is the underlying physics mechanism. If confirmed, the observation of J/$\psi$ coherent photoproduction in Pb-Pb collisions at impact parameters smaller than twice the nuclear radius opens new theoretical and experimental challenges and opportunities. In particular, coherent photoproduction accompanying hadronic collisions may provide insight into the dynamics of photoproduction and nuclear reactions, as well as become a novel probe of the Quark-Gluon Plasma.
J/$\psi$ nuclear modification factor $R_{\rm AA}$ as a function of the mean number of participant nucleons $\langle N_{\rm{part}}\rangle$, the first error is statistical, the second error is systematic uncorrelated in $p_{\rm T}$ and centrality, the third error is systematic correlated in $p_{\rm T}$ but not in centrality, the fourth error is systematic correlated in centrality but not in $p_{\rm T}$ and the fifth error is systematic correlated in $p_{\rm T}$ and centrality.
J/$\psi$ nuclear modification factor $R_{\rm AA}$ as a function of the mean number of participant nucleons $\langle N_{\rm{part}}\rangle$, the first error is statistical, the second error is systematic uncorrelated in $p_{\rm T}$ and centrality, the third error is systematic correlated in $p_{\rm T}$ but not in centrality, the fourth error is systematic correlated in centrality but not in $p_{\rm T}$ and the fifth error is systematic correlated in $p_{\rm T}$ and centrality.
J/$\psi$ nuclear modification factor $R_{\rm AA}$ as a function of the mean number of participant nucleons $\langle N_{\rm{part}}\rangle$, the first error is statistical, the second error is systematic uncorrelated in $p_{\rm T}$ and centrality, the third error is systematic correlated in $p_{\rm T}$ but not in centrality, the fourth error is systematic correlated in centrality but not in $p_{\rm T}$ and the fifth error is systematic correlated in $p_{\rm T}$ and centrality.
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