# Jet shape modifications at the LHC energies by JEWEL

## TL;DR

This study investigates how jet shapes are modified in proton-proton and lead-lead collisions at various energies, revealing medium effects that influence jet fragmentation and spreading, with new parameters proposed for detailed analysis.

## Contribution

The paper introduces a differential jet shape parameter $D_{girth}$ and provides a comprehensive analysis of jet shape modifications across different collision energies and systems, highlighting medium effects.

## Key findings

- Medium effects dominate jet shape modifications regardless of energy.
- Jet fragmentation is significantly enhanced at very low $z<0.02$.
- Wave-like distributions in jet shape parameters are observed and differ between $pp$ and $Pb+Pb$ collisions.

## Abstract

Jet shape measurements are strongly suggested to explore the microscopic evolution mechanism of parton-medium interaction in ultra-relativistic heavy-ion collisions. In this paper, jet shape modifications are quantified by fragmentation function $F(z)$, relative momentum $p_{T}^{rel}$, density of charged particles $\rho(r)$, jet angularity $girth$, jet momentum dispersion $p_{T}^{Disp}$ and $LeSub$ for proton-proton collisions at $900GeV$, $5.02TeV$, $7TeV$ and $13TeV$, as well as for lead-lead collisions at $2.76TeV$ and $5.02TeV$. A differential jet shape parameters $D_{girth}$ is proposed and studied at smaller-radius jet $r<0.3$. The results indicate that medium effect is dominant for jet shape modifications, which is less dependent on center of mass energy. The jet fragmentation is enhanced significantly at very low $z<0.02$ and fragmented jet constituents are spread to larger jet-radius linearly for $p_{T}^{rel}<1$. The waveform attenuate phenomena is observed in $p_{T}^{rel}$, $girth$ and $D_{girth}$ distributions. The comparison results on $D_{girth}$ from $pp$ to $Pb+Pb$ where the wave-like distribution in $pp$ collision is ahead of $Pb+Pb$ collisions in small jet-radius intervals, is interesting to hint the medium effect.