Forward azimuthal correlations in 200 GeV p+p and d+Au collisions at STAR

TL;DR

This paper investigates forward particle correlations in 200 GeV proton-proton and deuteron-gold collisions at STAR to explore low-x gluon saturation and the transition from dilute to dense gluon states.

Contribution

It presents new measurements of forward+near-forward azimuthal correlations, providing insights into the gluon density transition at low-x in heavy-ion collisions.

Findings

Suppression of back-to-back correlations in d+Au indicates dense gluon states.

Forward+near-forward correlations probe intermediate x regions.

Results support the Color Glass Condensate model predictions.

Abstract

Forward particle production and correlation measurements at RHIC can probe low-$x$ gluons. The suppression observed in back-to-back forward $\pi^{0}$+forward $\pi^{0}$ correlations at STAR in central d+Au collisions at STAR is consistent with a prediction of the Color Glass Condensate (CGC) calculation, indicating the gold nucleus probed at such low-$x$ is in a dense gluon state. The forward $\pi^{0}$ + near-forward jet-like cluster azimuthal correlations in 200 GeV p+p and d+Au collisions at STAR are studied, which are sensitive to the intermediate x region between forward+mid-rapidity correlations and forward+forward correlations. Together with the other measurements from STAR, which probe different regions of x, forward+near-forward di-hadron correlations can provide information to understand how sharp is the transition from dilute parton gas to dense gluon state.