The first measurements of the production of muons and electrons from heavy-flavour hadron decays in Xe-Xe collisions at $\sqrt{s_{\rm NN}}$ = 5.44 TeV, using the ALICE detector at the LHC, are reported. The measurement of the nuclear modification factor $R_{\rm AA}$ is performed as a function of transverse momentum $p_{\rm T}$ in several centrality classes at forward rapidity ($2.5 < y <4$) and midrapidity ($\vert y \vert < 0.8$) for muons and electrons from heavy-flavour hadron decays, respectively. A suppression by a factor up to about 2.5 compared to the binary-scaled pp reference is observed in central collisions at both central and forward rapidities. The $R_{\rm AA}$ of muons from heavy-flavour hadron decays is compared to previous measurements in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. When the nuclear modification factors are compared in the centrality classes 0-10% for Xe-Xe collisions and 10-20% for Pb-Pb collisions, which have similar charged-particle multiplicity density, a similar suppression, with $R_{\rm AA} \sim 0.4$ in the $p_{\rm T}$ interval $4 < p_{\rm T} < 8$ GeV/$c$, is observed. The comparison of the measured $R_{\rm AA}$ values in the two collision systems brings new insights on the properties of the quark-gluon plasma by investigating the system-size and path-length dependence of medium-induced parton energy loss. The results of muons and electrons from heavy-flavour hadron decays provide new constraints to model calculations.
Transverse momentum differential production of muons from heavy-flavour hadron decays at forward rapidity in Xe-Xe collisions at 5.44 TeV.
Transverse momentum differential production of muons from heavy-flavour hadron decays at forward rapidity in Xe-Xe collisions at 5.44 TeV.
Transverse momentum differential production of muons from heavy-flavour hadron decays at forward rapidity in Xe-Xe collisions at 5.44 TeV.
Measurements of the production of muons from heavy-flavour hadron decays in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = $5.02$ and $2.76$ TeV using the ALICE detector at the LHC are reported. The nuclear modification factor $R_{\rm AA}$ at $\sqrt{s_{\rm NN}}$ = 5.02 TeV is measured at forward rapidity ($2.5 < y <4$) as a function of transverse momentum $p_{\rm T}$ in central, semi-central, and peripheral collisions over a wide $p_{\rm T}$ interval, $3 < p_{\rm T} < 20$ GeV/$c$, in which muons from beauty-hadron decays are expected to take over from charm as the dominant source at high $p_{\rm T}$ ($p_{\rm T} > 7$ GeV/$c$). The $R_{\rm AA}$ shows an increase of the suppression of the yields of muons from heavy-flavour hadron decays with increasing centrality. A suppression by a factor of about three is observed in the $10\%$ most central collisions. The $R_{\rm AA}$ at $\sqrt{s_{\rm NN}}$ = 5.02 is similar to that at 2.76 TeV. The precise $R_{\rm AA}$ measurements have the potential to distinguish between model predictions implementing different mechanisms of parton energy loss in the high-density medium formed in heavy-ion collisions. They place important constraints for the understanding of the heavy-quark interaction with the hot and dense QCD medium.
$p_{\rm T}$-differential yield of muons from heavy-flavour hadron decays at forward rapidity ($2.5 < y < 4$) for central (0--10%) and semi-central (20--40%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV.
$p_{\rm T}$-differential yield of muons from heavy-flavour hadron decays at forward rapidity ($2.5 < y < 4$) for peripheral (60--80%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV.
$p_{\rm T}$-differential yield of muons from heavy-flavour hadron decays at forward rapidity ($2.5 < y < 4$) for central (0--10%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV.
The production of $\Upsilon$ mesons in Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}$ = 5 TeV is measured with the muon spectrometer of the ALICE detector at the LHC. The yields as well as the nuclear modification factors are determined in the forward rapidity region $2.5<y<4.0$, as a function of rapidity, transverse momentum and collision centrality. The results show that the production of the $\Upsilon$(1S) meson is suppressed by a factor of about three with respect to the production in proton-proton collisions. For the first time, a significant signal for the $\Upsilon$(2S) meson is observed at forward rapidity, indicating a suppression stronger by about a factor 2-3 with respect to the ground state. The measurements are compared with transport, hydrodynamic, comover and statistical hadronisation model calculations.
Rapidity-differential yield of $\Upsilon(1\mathrm{S}) \rightarrow \mu^{+}\mu^{-}$ divided by the average nuclear overlap function $\langle T_{\mathrm{AA}} \rangle$ for the 0–90% centrality interval ($\langle T_{\mathrm{AA}} \rangle$ = 6.28 $\pm$ 0.06 mb$^{-1}$).
Rapidity-differential yield of $\Upsilon(2\mathrm{S}) \rightarrow \mu^{+}\mu^{-}$ divided by the average nuclear overlap function $\langle T_{\mathrm{AA}} \rangle$ for the 0–90% centrality interval ($\langle T_{\mathrm{AA}} \rangle$ = 6.28 $\pm$ 0.06 mb$^{-1}$).
$p_{\mathrm{T}}$-differential yield of $\Upsilon(1\mathrm{S}) \rightarrow \mu^{+}\mu^{-}$ divided by the average nuclear overlap function $\langle T_{\mathrm{AA}} \rangle$ for the 0–90% centrality interval ($\langle T_{\mathrm{AA}} \rangle$ = 6.28 $\pm$ 0.06 mb$^{-1}$).
The inclusive J/$\psi$ meson production in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision of $\sqrt{s_{\rm NN}}$ = 5.02 TeV at midrapidity ($|y|$ < 0.9) is reported by the ALICE Collaboration. The measurements are performed in the dielectron decay channel, as a function of event centrality and J/$\psi$ transverse momentum $p_{\rm T}$, down to $p_{\rm T}$ = 0 GeV/$c$. The J/$\psi$ mean transverse momentum $\langle p_{\rm T} \rangle$ and $r_{\rm AA}$ ratio, defined as $\langle p^{\rm 2}_{\rm T} \rangle_{\rm PbPb}/\langle p^{\rm 2}_{\rm T} \rangle_{\rm pp}$, are evaluated. Both observables show a centrality dependence decreasing towards central (head-on) collisions. The J/$\psi$ nuclear modification factor $R_{\rm AA}$ exhibits a strong $p_{\rm T}$ dependence with a large suppression at high $p_{\rm T}$ and an increase to unity for decreasing $p_{\rm T}$. When integrating over the measured momentum range $p_{\rm T}$ < 10 GeV/$c$, the J/$\psi$ $R_{\rm AA}$ shows a weak centrality dependence. Each measurement is compared with results at lower center-of-mass energies and with ALICE measurements at forward rapidity, as well as to theory calculations. All reported features of the J/$\psi$ production at low $p_{\rm T}$ are consistent with a dominant contribution to the J/$\psi$ yield originating from charm quark (re)combination.
Transverse momentum dependence of the inclusive J/$\psi$ yields in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at midrapidity in the centrality intervals 0$-$20%, 20$-$40%, and 40$-$90%.
Inclusive J/$\psi$ $\langle p_{\rm T} \rangle$ in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at midrapidity as a function of the mean number of participant nucleons.
Inclusive J/$\psi$ $r_{\rm AA} = \langle p^{2}_{\rm T} \rangle_{\rm PbPb} / \langle p^{2}_{\rm T} \rangle_{\rm pp}$ in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at midrapidity as a function of the mean number of participant nucleons. The correlated systematic uncertainty due to the pp reference is not included and amounts to 4.7%, shown as the red box around unity in the paper figure.
The differential invariant yield as a function of transverse momentum ($p_\mathrm{T}$) of electrons from semileptonic heavy-flavour hadron decays was measured at midrapidity in central (0-10%), semi-central (30-50%) and peripheral (60-80%) lead-lead (Pb-Pb) collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\text{ TeV}$ in the $p_{\mathrm{T}}$ intervals 0.5-26 GeV/$c$ (0-10% and 30-50%) and 0.5-10 GeV/$c$ (60-80%). The production cross section in proton-proton (pp) collisions at $\sqrt{s}=5.02$ TeV was measured as well in $0.5<p_\mathrm{T}<10$ GeV/$c$ and it lies close to the upper band of perturbative QCD calculation uncertainties up to $p_\mathrm{T}=5$ GeV/$c$ and close to the mean value for larger $p_\mathrm{T}$. The modification of the electron yield with respect to what is expected for an incoherent superposition of nucleon-nucleon collisions is evaluated by measuring the nuclear modification factor $R_{\mathrm{AA}}$. The measurement of the $R_{\mathrm{AA}}$ in different centrality classes allows in-medium energy loss of charm and beauty quarks to be investigated. The $R_{\mathrm{AA}}$ shows a suppression with respect to unity at intermediate $p_\mathrm{T}$, which increases while moving towards more central collisions. Moreover, the measured $R_{\mathrm{AA}}$ is sensitive to the modification of the parton distribution functions (PDF) in nuclei, like nuclear shadowing, which causes a suppression of the heavy-quark production at low $p_\mathrm{T}$ in heavy-ion collisions at LHC.
HFe cross section in pp
HFe cross section in Pb-Pb, 0-10 centrality
HFe cross section in Pb-Pb, 30-50 centrality
The inclusive J/$\psi$ production in Pb-Pb collisions at the center-of-mass energy per nucleon pair $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV, measured with the ALICE detector at the CERN LHC, is reported. The J/$\psi$ meson is reconstructed via the dimuon decay channel at forward rapidity ($2.5<y<4$) down to zero transverse momentum. The suppression of the J/$\psi$ yield in Pb-Pb collisions with respect to binary-scaled pp collisions is quantified by the nuclear modification factor ($R_{\rm{AA}}$). The $R_{\rm{AA}}$ at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV is presented and compared with previous measurements at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV as a function of the centrality of the collision, and of the J/$\psi$ transverse momentum and rapidity. The inclusive J/$\psi$ $R_{\rm{AA}}$ shows a suppression increasing toward higher $p_{\rm{T}}$, with a steeper dependence for central collisions. The modification of the J/$\psi$ average $p_{\rm{T}}$ and $p_{\rm{T}}^{2}$ is also studied. Comparisons with the results of models based on a transport equation and on statistical hadronization are also carried out.
Transverse momentum dependence (in 0-90% centrality class) of the inclusive J/$\psi$ $R_{\rm AA}$. The first uncertainty is statistical, the second is the uncorrelated systematic, while the third one is a $p_{\rm T}$-correlated systematic uncertainty.
The minimum and maximum variations for the $R_{\rm AA}$ of prompt J/$\psi$ with respect to the $R_{\rm AA}$ values of inclusive J/$\psi$ reported in Table 1. The variations correspond to two extreme hypotheses on the unknown contribution of non-prompt J/$\psi$.
Transverse momentum dependence (in 0-90% centrality class) of the ratio of the inclusive J/$\psi$ $R_{\rm AA}$ at $\sqrt{s_{NN}}$= 5.02 and 2.76 TeV. The first uncertainty is statistical, the second is the uncorrelated systematic, while the third one is a $p_{\rm T}$-correlated systematic uncertainty.
A measurement of the production of prompt $\Lambda_{\rm c}^{+}$ baryons in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02 $ TeV with the ALICE detector at the LHC is reported. The $\Lambda_{\rm c}^{+}$ and $\overline{\Lambda}_{\rm c}^{-}$ were reconstructed at midrapidity ($|y| < 0.5$) via the hadronic decay channel $\Lambda_{\rm c}^{+}\rightarrow {\rm p} {\rm K}_{\rm S}^{0}$ (and charge conjugate) in the transverse momentum and centrality intervals $6 < p_{\rm T} <12$ GeV/$c$ and 0-80%. The $\Lambda_{\rm c}^{+}$/D$^0$ ratio, which is sensitive to the charm quark hadronisation mechanisms in the medium, is measured and found to be larger than the ratio measured in minimum-bias pp collisions at $\sqrt{s} = 7$ TeV and in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02 $ TeV. In particular, the values in p-Pb and Pb-Pb collisions differ by about two standard deviations of the combined statistical and systematic uncertainties in the common $p_{\rm T}$ interval covered by the measurements in the two collision system. The $\Lambda_{\rm c}^{+}$/D$^0$ ratio is also compared with model calculations including different implementations of charm quark hadronisation. The measured ratio is reproduced by models implementing a pure coalescence scenario, while adding a fragmentation contribution leads to an underestimation. The $\Lambda_{\rm c}^{+}$ nuclear modification factor, $R_{\rm AA}$, is also presented. The measured values of the $R_{\rm AA}$ of $\Lambda_{\rm c}^{+}$, D$_{\rm s}$ and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy $(R_{\rm AA}^{{\rm D}^{0}}<R_{\rm AA}^{{\rm D}_{\rm s}}<R_{\rm AA}^{\Lambda_{\rm c}^{+}})$, conceivable with a contribution of recombination mechanisms to charm hadron formation in the medium.
$\Lambda_{\rm {c}}^{+}$/${\rm D}^{0}$ ratio in 0-80% most central Pb-Pb collisions at $\sqrt{s_{\rm {NN}}} = 5.02$ TeV in the transverse momentum interval 6 < $p_{\rm {T}}$ < 12 GeV/${\it {c}}$
The nuclear modification factor $R_\mathrm{AA}$ of prompt $\Lambda_{\rm {c}}^{+}$ baryons in 0-80% most central Pb-Pb collisions at $\sqrt{s_{\rm {NN}}} = 5.02$ TeV in the transverse momentum interval 6 < $p_{\rm {T}}$ < 12 GeV/${\it {c}}$
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
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