Measurement of emission angle anisotropy via long-range angular correlations with high $p_T$ hadrons in $d$$+$Au and $p$$+$$p$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV

TL;DR

This study investigates angular correlations of high-$p_T$ hadrons in $d$+Au and $p$+$p$ collisions, revealing a ridge-like structure in $d$+Au that depends on collision centrality, similar to flow phenomena in heavy-ion collisions.

Contribution

First observation of a ridge-like azimuthal correlation structure in $d$+Au collisions at high $p_T$, showing centrality dependence and similarity to hydrodynamic flow in heavy-ion collisions.

Findings

Ridge-like structure observed in $d$+Au in the Au-going direction.

No ridge observed in $p$+$p$ or $d$-going direction.

Ridge strength correlates with collision centrality.

Abstract

We present measurements of two-particle angular correlations between high-transverse-momentum ($2<p_T<11$ GeV/$c$) $\pi^0$ observed at midrapidity ($|\eta|<0.35$) and particles produced either at forward ($3.1<\eta<3.9$) or backward ($-3.7<\eta<-3.1$) rapidity in $d$$+$Au and $p$$+$$p$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The azimuthal angle correlations for particle pairs with this large rapidity gap in the Au-going direction exhibit a ridge-like structure that persists up to $p_T{\approx}6$ GeV/$c$ and which strongly depends on collision centrality, which is a similar characteristic to the hydrodynamical particle flow in A+A collisions. The ridge-like structure is absent in the $d$-going direction as well as in $p$$+$$p$ collisions, in the transverse-momentum range studied. The results indicate that the ridge-like structure is shifted in the Au-going direction toward more central collisions, similar to the charged-particle pseudorapidity distributions.