Centrality dependence of the charged-particle multiplicity density at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV

J. Adam , I. Belikov (1) , J.C. Hamon (1) , B. Hippolyte (1) , C. Kuhn (1) , A. Maire (1) , L. Molnar (1) , F. Rami (1) , C. Roy (1) , A. Baldisseri (2) , H. Borel (2) , J. Castillo Castellanos (2) , J.L. Charvet (2) , V.J.G. Feuillard (2, 3) , A. Lardeux (4) , H. Pereira Da Costa (2) , A. Rakotozafindrabe (2) , Laurent Aphecetche (4) , B. Audurier (4) , Guillaume Batigne (4) , B. Erazmus (4) , Magali Estienne (4) , Marie Germain (4) , J. Martin Blanco (4) , Gines Martinez Garcia (4) , L. Massacrier (4) , D.A. Moreira De Godoy (4) , A. Morreale (4) , Philippe Pillot (4) , L. Ronflette (4) , Y. Schutz (4) , Alexandre Shabetai (4) , Diego Stocco (4) , M. Wang (4) , J. Zhu (4) , R. Vernet (5) , C. Cheshkov (6) , B. Cheynis (6) , L. Ducroux (6) , J.-Y. Grossiord (6) , B. Teyssier (6) , R. Tieulent (6) , A. Uras (6) , G. Conesa Balbastre (7) , J. Faivre (7) , C. Furget (7) , R. Guernane (7) , C. Silvestre (7) , A. Vauthier (7) , Z. Conesa Del Valle (8) , I. Das (8) , B. Espagnon (8) , C. Hadjidakis (8) , I. Lakomov (8) , C. Suire (8) , J. D. Tapia Takaki (8) , M. Tarhini (8) , L. Valencia Palomo (8, 3) , V. Barret (3) , N. Bastid (3) , A. Batista Camejo (3) , P. Crochet (3) , P. Dupieux (3) , S. Li (3) , X. Lopez (3) , F. Manso (3) , S. Porteboeuf-Houssais (3) , P. Rosnet (3) , B. Vulpescu (3)

1 IPHC - Institut Pluridisciplinaire Hubert Curien
2 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
3 LPC - Laboratoire de Physique Corpusculaire - Clermont-Ferrand
4 SUBATECH - Laboratoire SUBATECH Nantes
5 CC-IN2P3 - Centre de Calcul de l'IN2P3
6 IPNL - Institut de Physique Nucléaire de Lyon
7 LPSC - Laboratoire de Physique Subatomique et de Cosmologie
8 IPNO - Institut de Physique Nucléaire d'Orsay

The pseudorapidity density of charged particles ($\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta$) at mid-rapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}}$ = 5.02 TeV. It increases with centrality and reaches a value of $1943 \pm 54$ in $|\eta|<0.5$ for the 5% most central collisions. A rise in $\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta$ as a function of $\sqrt{s_{\rm NN}}$ for the most central collisions is observed, steeper than that observed in proton-proton collisions and following the trend established by measurements at lower energy. The centrality dependence of $\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta$ as a function of the average number of participant nucleons, ${\langle N_\mathrm{part} \rangle}$, calculated in a Glauber model, is compared with the previous measurement at lower energy. A constant factor of about 1.2 describes the increase in $\frac{2}{\langle N_\mathrm{part} \rangle}\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta \rangle$ from $\sqrt{s_{\rm NN}}$ = 2.76 TeV to $\sqrt{s_{\rm NN}}$ = 5.02 TeV for all centrality intervals, within the measured range of 0-80% centrality. The results are also compared to models based on different mechanisms for particle production in nuclear collisions.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Physique des Hautes Energies - Expérience [hep-ex]

J. Adam, I. Belikov, J.C. Hamon, B. Hippolyte, C. Kuhn, et al.. Centrality dependence of the charged-particle multiplicity density at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. Physical Review Letters, 2016, 116, pp.222302 ⟨10.1103/PhysRevLett.116.222302⟩. ⟨in2p3-01247070⟩