# Parton energy loss in pp collisions at very high multiplicity

## TL;DR

This study uses PYTHIA8 simulations to explore how high-multiplicity pp collisions at 13 TeV affect jet and underlying event spectra, revealing potential parton energy loss phenomena at extreme multiplicities.

## Contribution

It introduces a novel analysis of parton energy loss effects in high-multiplicity pp collisions using PYTHIA8, reaching multiplicities not yet tested experimentally.

## Key findings

- Spectra are affected by event multiplicity, indicating energy density dependence.
- Partons appear to suffer energy loss at very high multiplicities.
- Energy loss is compensated by increased event multiplicity.

## Abstract

We present the results for the evolution of transverse momentum spectra for the jetty and underlying parts of events as a function of multiplicity in pp collisions at 13 TeV measured at midrapidity ($\left|\eta\right|<0.8$) using PYTHIA8 event generator. The main characteristic of the approach is that it reaches to extreme multiplicities not yet explored by the experiments. We demonstrate that the behavior of both the underlying and hard components are affected by the multiplicity of the events i.e. the energy density. The behavior of the spectra at very high multiplicities suggests that the partons suffer energy loss compensated by an increase in the multiplicity of events.