Measurements of jet quenching using semi-inclusive hadron+jet distributions in pp and central Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV

TL;DR

This paper presents precise measurements of charged-particle jet distributions recoiling from high-$p_T$ hadrons in pp and Pb-Pb collisions at 5.02 TeV, providing insights into jet quenching and medium interactions in quark-gluon plasma.

Contribution

It introduces a data-driven background correction method enabling detailed recoil jet measurements over a broad $p_T$ and jet radius range in heavy-ion collisions.

Findings

Recoil jet yields show suppression in Pb-Pb compared to pp.

Jet broadening observed in Pb-Pb collisions.

Results agree with jet quenching theoretical models.

Abstract

The ALICE Collaboration reports measurements of the semi-inclusive distribution of charged-particle jets recoiling from a high transverse momentum (high $p_{\rm T}$) charged hadron, in pp and central Pb$-$Pb collisions at center-of-mass energy per nucleon$-$nucleon collision $\sqrt{s_{\rm NN}}=5.02$ TeV. The large uncorrelated background in central Pb$-$Pb collisions is corrected using a data-driven statistical approach, which enables precise measurement of recoil jet distributions over a broad range in $p_{\rm T,ch\,jet}$ and jet resolution parameter $R$. Recoil jet yields are reported for $R=0.2$, 0.4, and 0.5 in the range $7 < p_{\rm T,ch\, jet} < 140$ GeV$/c$ and $\pi/2<\Delta\varphi<\pi$, where $\Delta\varphi$ is the azimuthal angular separation between hadron trigger and recoil jet. The low $p_{\rm T,ch\,jet}$ reach of the measurement explores unique phase space for studying jet quenching, the interaction of jets with the quark-gluonnplasma generated in high-energy nuclear collisions. Comparison of $p_{\rm T,ch\,jet}$ distributions from pp and central Pb$-$Pb collisions probes medium-induced jet energy loss and intra-jet broadening, while comparison of their acoplanarity distributions explores in-medium jet scattering and medium response. The measurements are compared to theoretical calculations incorporating jet quenching.