Measurement of Two-Point Energy Correlators Within Jets in $pp$ Collisions at $\sqrt{s}$ = 200 GeV at STAR

TL;DR

This paper presents the first measurement of the two-point Energy Correlator (EEC) within jets in proton-proton collisions at 200 GeV at RHIC, providing insights into jet substructure and serving as a baseline for heavy-ion studies.

Contribution

It introduces the first experimental measurement of the EEC in RHIC $pp$ collisions and compares results with PYTHIA predictions, expanding jet substructure analysis methods.

Findings

EEC distribution varies with jet transverse momentum.

Results align with PYTHIA-8 predictions within uncertainties.

Provides baseline for future heavy-ion collision studies.

Abstract

Jet substructure is a powerful tool to probe the time evolution of a parton shower. However, many of the analysis methods used to extract splitting formation times from jet substructure, such as Soft Drop grooming and the Lund plane, focus on the hardest radiation of the jet. A complementary observable with growing theoretical and experimental interest, the 2-point Energy Correlator (EEC), re-contextualizes jet substructure study by using the distribution of angular distance of all combinations of two final state particles within a jet. This distribution is weighted by the product of the fractions of jet energy that each of the constituents carry, and thus is infrared-and-collinear safe. The EEC can reveal the separation between two distinct regimes: effects originating from free hadrons at small opening angles and from perturbative fragmentation of quarks and gluons at large opening angles. In these proceedings, the first measurement of the EEC at RHIC is presented, using the data taken at $\sqrt{s}$ = 200 GeV $pp$ collisions by STAR. The EEC will be shown for several full jet transverse momentum selections and compared to predictions from the PYTHIA-8 Detroit tune. This study is useful as a baseline for comparisons to future studies in heavy-ion collisions, which will provide information about how the quark-gluon plasma interacts with the jet across different angular scales.