# Quark Matter 2014 - XXIV International Conference on Ultrarelativistic Nucleus-Nucleus Collisions

19-24 May 2014
Europe/Zurich timezone

## Charged particle transverse momentum spectra measured at mid-rapidity by STAR in the RHIC Beam Energy Scan

20 May 2014, 16:30
2h

### spectrum

Board: A-10
Poster QCD at High Temperature and/or Density

### Speaker

Stephen Horvat (STAR)

### Description

Quenching of high transverse momentum ($p_{\mathrm{T}}$) charged hadrons can be measured by the nuclear modification factor, which compares binary collision-scaled $p_{\mathrm{T}}$ spectra from central heavy-ion collisions to a reference spectrum, either proton-proton ($R_{\mathrm{AA}}$) or peripheral heavy-ion collisions ($R_{\mathrm{CP}}$), by taking their ratio. At $\sqrt{s_{\mathrm{NN}}}\ge$ 62.4 GeV the nuclear modification factor at high $p_{\mathrm{T}}$ is observed to be suppressed, i.e. less than unity, which is consistent with quenching. Measurements by STAR of charged hadron $R_{\mathrm{CP}}$($\sqrt{s_{ \mathrm{NN}}}$, $p_{\mathrm{T}}$) for $\sqrt{s_{ \mathrm{NN}}}$ = 7.7 - 200GeV show a smooth transition from strong enhancement of high $p_{\mathrm{T}}$ charged hadrons at $\sqrt{s_{ \mathrm{NN}}}$ = 7.7 GeV to strong suppression at $\sqrt{s_{ \mathrm{NN}}}$ = 200 GeV. These data will be compared with the event generators UrQMD, HIJING and AMPT. RHIC's broad range of collision systems and energies allow us to test the assumptions of the event generators; facilitating the investigation of the relative contributions from processes that lead to suppression and enhancement in heavy-ion collisions as a function of $\sqrt{s_{ \mathrm{NN}}}$.
On behalf of collaboration: STAR

### Primary author

Stephen Horvat (STAR)

 Slides