Di-Jet Imbalance Measurements at $\sqrt{s_{NN}} = 200$ GeV at STAR

TL;DR

This paper presents the first measurements of di-jet momentum imbalance in Au+Au and p+p collisions at RHIC, revealing significant imbalance in heavy-ion collisions that can be balanced by including soft particles at specific jet resolution parameters.

Contribution

It introduces novel di-jet imbalance measurements at RHIC and demonstrates how soft particle inclusion restores momentum balance at certain jet resolution scales.

Findings

Greater momentum imbalance in heavy-ion collisions compared to p+p.

Soft particle inclusion restores momentum balance at R=0.4.

Balance is not restored at R=0.2.

Abstract

We report the first di-jet transverse momentum asymmetry measurements from Au+Au and p+p collisions at RHIC. The two highest-energy back-to-back jets reconstructed from fragments with transverse momenta above 2 GeV/c display a significantly stronger momentum imbalance in heavy-ion collisions than in the p+p reference. When re-examined with correlated soft particles included, we observe that these di-jets then exhibit a unique new feature -- momentum balance is restored to that observed in p+p for a jet resolution parameter of R=0.4, while re-balancing is not attained with a smaller value of R=0.2.