System Size and Centrality Dependence of Charged Hadron Transverse Momentum Spectra in $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ Collisions at $\sqrt{{s}_{NN}}=62.4$ and 200 GeV

System Size and Centrality Dependence of Charged Hadron Transverse Momentum Spectra in $Au + Au$ and $Cu + Cu$ Collisions at $\sqrt{s_{N N}} = 62.4$ and 200 GeV

B. Alver et al.

Phys. Rev. Lett. 96, 212301 – Published 30 May 2006

Abstract

We present transverse momentum distributions of charged hadrons produced in $Cu + Cu$ collisions at $\sqrt{s_{N N}} = 62.4$ and 200 GeV. The spectra are measured for transverse momenta of $0.25 < p_{T} < 5.0 GeV / c$ at $\sqrt{s_{N N}} = 62.4 GeV$ and $0.25 < p_{T} < 7.0 GeV / c$ at $\sqrt{s_{N N}} = 200 GeV$ , in a pseudorapidity range of $0.2 < η < 1.4$ . The nuclear modification factor $R_{A A}$ is calculated relative to $p + p$ data at both collision energies as a function of collision centrality. At a given collision energy and fractional cross section, $R_{A A}$ is observed to be systematically larger in $Cu + Cu$ collisions compared to $Au + Au$ . However, for the same number of participating nucleons, $R_{A A}$ is essentially the same in both systems over the measured range of $p_{T}$ , in spite of the significantly different geometries of the $Cu + Cu$ and $Au + Au$ systems.