Cold nuclear matter physics at forward rapidities from d+Au collisions in PHENIX

TL;DR

This paper reports on di-hadron pair production measurements in d+Au collisions at RHIC, revealing significant suppression of back-to-back correlations at forward rapidities, which may indicate gluon saturation effects in the gold nucleus.

Contribution

It provides the first detailed di-hadron correlation measurements at forward rapidities in d+Au collisions, exploring potential gluon saturation phenomena at very low parton momentum fractions.

Findings

Back-to-back di-hadron correlations are suppressed in d+Au compared to p+p.

Suppression increases with nuclear path length.

Suppression correlates with lower parton x in the nucleus.

Abstract

We present measurements by the PHENIX experiment at RHIC of di-hadron pair production in \dAu collisions where the particles in the pair are varied across a wide range of pseudorapidity, out to $\eta = 3.8$. With di-hadrons, varying the $p_T$ and rapidity of the particles in the di-hadron pair allows studying any effects as a function of partonic $x$ in the nucleus. These di-hadron measurements might probe down to parton momentum fractions x $\sim$ $10^{-3}$ in the gold nucleus, where the interesting possibility of observing gluon saturation effects at RHIC is the greatest. Our measurements show that the correlated yield of back-to-back pairs in \dAu collisions is suppressed by up to an order of magnitude relative to \pp collisions, and increases with greater nuclear path thickness and with a selection for lower x in the Au nucleus.