Evidence of final-state suppression of high-p

Transverse momentum spectra of charged hadrons with p T < 6 GeV/c have been measured near mid-rapidity (0.2 < η < 1.4) by the PHOBOS experiment at RHIC in Au + Au and d + Au collisions at ${\sqrt{s_{_{NN}}}~= \rm {200~GeV}}$. The spectra for different collision centralities are compared to ${p + \bar{p}}$ collisions at the same energy. The resulting nuclear modification factor for central Au + Au collisions shows evidence of strong suppression of charged hadrons in the high-p T region (>2 GeV/c). In contrast, the d + Au nuclear modification factor exhibits no suppression of the high-p T yields. These measurements suggest a large energy loss of the high-p T particles in the highly interacting medium created in the central Au + Au collisions. The lack of suppression in d + Au collisions suggests that it is unlikely that initial state effects can explain the suppression in the central Au + Au collisions. PACS: 25.75.-