Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV

J. Adam , J.C. Hamon (1) , B. Hippolyte (1) , C. Kuhn (1) , A. Maire (1) , C. Roy (1) , Y. Schutz (1, 2) , S. Senyukov (1) , V. Barret (3) , N. Bastid (3) , A. Batista Camejo (3) , P. Crochet (3) , P. Dupieux (3) , V.J.G. Feuillard (3) , X. Lopez (3) , F. Manso (3) , S. Porteboeuf-Houssais (3) , P. Rosnet (3) , Laurent Aphecetche (2) , B. Audurier (2) , Guillaume Batigne (2) , B. Erazmus (2) , A. Francisco (2) , Marie Germain (2) , Gines Martinez Garcia (2) , L. Molnar (2) , A. Morreale (2) , Philippe Pillot (2) , L. Ronflette (2) , Alexandre Shabetai (2) , Diego Stocco (2) , . J. Zhu (2) , C. Cheshkov (4) , B. Cheynis (4) , L. Ducroux (4) , B. Teyssier (4) , R. Tieulent (4) , A. Uras (4) , R. Vernet (5) , G. Conesa Balbastre (6) , J. Faivre (6) , C. Furget (6) , R. Guernane (6) , C. Silvestre (6) , A. Vauthier (6) , H. Yokoyama (6) , Z. Conesa Del Valle (7) , I. Das (7) , B. Espagnon (7) , C. Hadjidakis (7) , I. Lakomov (7) , C. Suire (7) , J. D. Tapia Takaki (7) , M. Tarhini (7) , L. Valencia Palomo (7)

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

We present the charged-particle pseudorapidity density in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\,\mathrm{Te\kern-.25exV}$ in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from $-3.5$ to $5$, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0-5%) collisions we find $21\,400\pm 1\,300$ while for the most peripheral (80-90%) we find $230\pm 38$. This corresponds to an increase of $(27\pm4)\%$ over the results at $\sqrt{s_{\mathrm{NN}}}=2.76\,\mathrm{Te\kern-.25exV}$ previously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations --- none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

J. Adam, J.C. Hamon, B. Hippolyte, C. Kuhn, A. Maire, et al.. Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. Physics Letters B, 2017, 772, pp.567-577. ⟨10.1016/j.physletb.2017.07.017⟩. ⟨in2p3-01425241⟩