On the Dihadron Angular Correlations in Forward $pA$ collisions

TL;DR

Forward dihadron angular correlations in pA are highly sensitive to gluon saturation but are shaped by both saturation and parton shower effects. The authors implement a hybrid dilute-dense factorization with Sudakov resummation in b_perp space and use a GBW-based small-x UGD to model saturation, deriving expressions for quark- and gluon-initiated channels. Their Sudakov-enhanced framework jointly describes RHIC pp and dAu data and provides predictions for pA, highlighting the interplay between x_g, p_T, and saturation strength. This approach yields a practical baseline for pp and a quantitative path to identifying saturation signals in pA measurements at RHIC.

Abstract

Dihadron angular correlations in forward $pA$ collisions have been considered as one of the most sensitive observables to the gluon saturation effects. In general, both parton shower effects and saturation effects are responsible for the back-to-back dihadron angular de-correlations. With the recent progress in the saturation formalism, we can incorporate the parton shower effect by adding the corresponding Sudakov factor in the saturation framework. In this paper, we carry out the first detailed numerical study in this regard, and find a very good agreement with previous RHIC $pp$ and $dAu$ data. This study can help us to establish a baseline in $pp$ collisions which contains little saturation effects, and further make predictions for dihadron angular correlations in $pAu$ collisions, which will allow to search for the signal of parton saturation.

Figures (3)

• Figure 1: Normalized forward dihadron angular correlation compared with the experimental data measure by STAR collaboration Braidot:2010ig. Both the leading and associate hadrons are in the forward rapidity region ($2.5<y<4$). The pedestal has not been taken into account in the theoretical curves for the $dAu$ collisions.
• Figure 2: Normalized forward and near-forward dihadron angular correlation comparing with the experimental data measure by STAR collaboration Li:2011we. The trigger $\pi^0$ is in the forward rapidity region ($2.5<y<4$) and the associate $\pi^0$ is in the near forward rapidity region ($1.1<y<1.9$).
• Figure 3: Prediction for normalized forward dihadron ($\pi^0$) angular correlation in the forward rapidity region ($2.6<y<4.2$) in pp and minimal bias pAu collisions at $\sqrt{s}=200$ GeV. The first $p_T$ bin is for the trigger $\pi^0$, while the second bin is for the associate $\pi^0$.