Transverse momentum spectra in Au+Au and d+Au collisions at s**(1/2) = 200-GeV and the pseudorapidity dependence of high p(T) suppression

We present spectra of charged hadrons from Au + Au and d + Au collisions at s N N = 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.