Suppression of back-to-back hadron pairs at forward rapidity in d+Au Collisions at sqrt(s_NN)=200 GeV

TL;DR

This study measures back-to-back hadron pair production at forward rapidity in d+Au and p+p collisions at 200 GeV, revealing significant suppression in d+Au collisions linked to high-density cold nuclear matter effects.

Contribution

It provides the first detailed measurement of forward rapidity hadron pair suppression in d+Au collisions at RHIC, highlighting cold nuclear matter effects at low parton momentum fractions.

Findings

Back-to-back hadron pairs are suppressed by a factor of 10 in d+Au compared to p+p.

Suppression increases with nuclear thickness, p_T, and rapidity.

Results suggest high gluon densities cause cold nuclear matter effects.

Abstract

Back-to-back hadron pair yields in d+Au and p+p collisions at sqrt(s_NN)=200 GeV were measured with the PHENIX detector at the Relativistic Heavy Ion Collider. Rapidity separated hadron pairs were detected with the trigger hadron at pseudorapidity |eta|<0.35 and the associated hadron at forward rapidity (deuteron direction, 3.0<eta<3.8). Pairs were also detected with both hadrons measured at forward rapidity; in this case the yield of back-to-back hadron pairs in d+Au collisions with small impact parameters is observed to be suppressed by a factor of 10 relative to p+p collisions. The kinematics of these pairs is expected to probe partons in the Au nucleus with low fraction x of the nucleon momenta, where the gluon densities rise sharply. The observed suppression as a function of nuclear thickness, p_T, and eta points to cold nuclear matter effects arising at high parton densities.