engleski

Rapidity and species dependence of particle production at large transverse momentum for d+Au collisions at √sNN = 200 GeV

We determine rapidity asymmetry in the production of charged pions, protons, and antiprotons for large transverse momentum (pT) for d+Au collisions at sNN‾‾‾‾√=200 GeV. The rapidity asymmetry is defined as the ratio of particle yields at backward rapidity (Au beam direction) to those at forward rapidity (d beam direction). The identified hadrons are measured in the rapidity regions ∣∣y∣∣<0.5 and 0.5<∣∣y∣∣<1.0 for the pT range 2.5<pT<10GeV/c. We observe significant rapidity asymmetry for charged pion and proton+antiproton production in both the rapidity regions. The asymmetry is larger for 0.5<∣∣y∣∣<1.0 than for ∣∣y∣∣<0.5 and is almost independent of particle type. The measurements are compared to various model predictions employing multiple scattering, energy loss, nuclear shadowing, saturation effects, and recombination and also to a phenomenological parton model. We find that asymmetries are sensitive to model parameters and show model preference. The rapidity dependence of π−/π+ and p⎯⎯/p ratios in peripheral d+Au and forward neutron-tagged events are used to study the contributions of valence quarks and gluons to particle production at high pT.

rapidity; species; STAR

STAR Collaboration.