Parton splitting scales of reclustered large-radius jets in high-energy nuclear collisions

TL;DR

This paper presents a theoretical study of large-radius jet structures in high-energy nuclear collisions, comparing model predictions with ATLAS data, and exploring how medium effects modify jet substructure and splitting scales.

Contribution

It introduces a novel analysis of reclustered large-radius jets and their splitting scales in Pb+Pb collisions, highlighting medium suppression effects and substructure modifications.

Findings

Medium suppression of large-radius jets exceeds that of smaller jets.

Jet substructure alterations significantly impact the splitting scale dependence.

Numerical results show modifications in splitting angle and fraction in nuclear medium.

Abstract

We carry out the first theoretical investigation on yields and the hardest parton splitting of large-radius jets reclustered from small radius ($R=0.2$) anti-$k_t$ jets in Pb+Pb collisions, and confront them with the recent ATLAS measurements.The Linear Boltzmann Transport (LBT) model is employed for jet propagation and jet-induced medium excitation in the hot-dense medium. We demonstrate that, with their complex structures, the medium suppression of the reclustered large radius jets at $R=1$ is larger than that of inclusive $R=0.4$ jets defined conventionally. The large radius jet constituents are reclustered with the $k_t$ algorithm to obtain the splitting scale $\sqrt{d_{12}}$, which characterizes the transverse momentum scale for the hardest splitting in the jet. The large-radius jet production as a function of the splitting scale $\sqrt{d_{12}}$ of the hardest parton splitting is overall suppressed in Pb+Pb relative to p+p collisions due to the reduction of jets yields. A detailed analyses show that the alterations of jet substructures in Pb+Pb also make significant contribution to the splitting scale $\sqrt{d_{12}}$ dependence of the nuclear modification factor $R_{AA}$. Numerical results for the medium modifications of the jet splitting angle $\Delta R_{12}$ and the splitting fraction $z$ are also presented.