# Jet Quenching at RHIC and LHC and the Fragmentation Function in Vacuum

## TL;DR

The paper clarifies that the parton to hadron fragmentation function in QCD cannot be simply separated into vacuum and medium parts in non-equilibrium conditions, impacting jet quenching studies at RHIC and LHC.

## Contribution

It demonstrates that the fragmentation function is inherently non-perturbative and cannot be decomposed into vacuum and medium components in non-equilibrium QCD.

## Key findings

- Fragmentation function is non-perturbative in QCD.
- Cannot decompose fragmentation function into vacuum and medium parts.
- Implications for jet quenching analysis at RHIC and LHC.

## Abstract

The value of the parton to hadron fragmentation function in QCD in vacuum (for example from proton-proton collisions at high energy colliders) is directly/indirectly used in the literature to study the jet quenching and the hadron production from quark-gluon plasma at RHIC and LHC. In this paper we show that this is not possible because, unlike the perturbative propagator in non-equilibrium QCD, the parton to hadron fragmentation function is a non-perturbative quantity in QCD and hence it is not possible to decompose the fragmentation function in non-equilibrium QCD into the vacuum part and the medium part.