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

Abstract : 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.
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Journal articles
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http://hal.in2p3.fr/in2p3-01247070
Contributor : Sylvie Flores <>
Submitted on : Tuesday, December 22, 2015 - 8:31:10 AM
Last modification on : Tuesday, November 19, 2019 - 2:46:37 AM

### Citation

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, American Physical Society, 2016, 116, pp.222302 ⟨10.1103/PhysRevLett.116.222302⟩. ⟨in2p3-01247070⟩

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