Transverse Momentum Spectra in Au+Au and d+Au Collisions at s NN − − − − √ =200 GeV and the Pseudorapidity Dependence of High p T Suppression
Abstract
We present spectra of charged hadrons from Au+Au and d+Au collisions at
s
NN
−
−
−
−
√
=200
GeV measured with the BRAHMS experiment at RHIC. The spectra for different collision centralities are compared to spectra from
p+
p
¯
collisions at the same energy scaled by the number of binary collisions. The resulting ratios (nuclear modification factors) for central Au+Au collisions at
η=0
and
η=2.2
evidence a strong suppression in the high
p
T
region (
>
2 GeV/c). In contrast, the d+Au nuclear modification factor (at
η=0
) exhibits an enhancement of the high
p
T
yields. These measurements indicate a high energy loss of the high
p
T
particles in the medium created in the central Au+Au collisions. The lack of suppression in d+Au collisions makes it unlikely that initial state effects can explain the suppression in the central Au+Au collisions.