Proton and anti-proton production in the forward region of d+Au collisions at RHIC from the color glass condensate

Abstract

The power-law tail of high-pt pi^\pm spectra observed in forward d+Au collisions at RHIC can be attributed to the power-law decrease of the dipole forward scattering amplitude appearing in the color glass condensate (CGC) approach. Forward particle production probes the small-x gluon distribution of the target nucleus where its anomalous dimension is rather flat (gamma = 0.6 \sim 0.8) for moderately high pt (\lsim 5 GeV), and where the leading-twist DGLAP approximation is not valid. In the same framework, we examine p and \bar{p} production using baryon fragmentation functions parameterized in the Lund fragmentation scheme. This provides a good description of the forward \bar{p} spectrum while it underestimates the p data by as much as a factor of 2 \sim 3 at pt \lsim 4 GeV. Part of this anomalous baryon excess can be attributed to surviving constituent diquarks from the deuteron projectile. Thus, the contribution from diquark scattering may play an essential role for forward baryon formation.