Resolution Effects in the Hybrid Strong/Weak Coupling Model

TL;DR

This paper introduces a screening length parameter in a hybrid jet quenching model to account for the plasma's inability to resolve fine substructure, affecting jet shape and fragmentation predictions.

Contribution

The study proposes a new resolution length parameter in the hybrid model, bridging weak and strong coupling calculations, to better simulate jet quenching effects.

Findings

Introducing a nonzero resolution length modifies jet shapes and fragmentation functions.

The effects of the resolution length are small but influence particle survival probabilities.

The model's predictions are consistent with minimal impact on missing-$p_T$ observables.

Abstract

Within the context of a hybrid strong/weak coupling model of jet quenching, we study the consequences of the fact that the plasma produced in a heavy ion collision cannot resolve the substructure of a collimated parton shower propagating through it with arbitrarily fine spatial resolution. We introduce a screening length parameter, $L_{\rm res}$, proportional to the inverse of the local temperature in the plasma, estimating a range for the value of the proportionality constant via comparing weakly coupled QCD calculations and holographic calculations appropriate in strongly coupled plasma. We then modify the hybrid model so that when a parton in a jet shower splits, its two offspring are initially treated as unresolved, and are only treated as two separate partons losing energy independently after they are separated by a distance $L_{\rm res}$. This modification delays the quenching of partons with intermediate energy, resulting in the survival of more hadrons in the final state with $p_T$ in the several GeV range. We analyze the consequences of different choices for the value of the resolution length, $L_{\rm res}$, and demonstrate that introducing a nonzero $L_{\rm res}$ results in modifications to the jet shapes and jet fragmentations functions, as it makes it more probable for particles carrying a small fraction of the jet energy at larger angles from the jet axis to survive their passage through the quark-gluon plasma. These effects are, however, small in magnitude, something that we confirm via checking for effects on missing-$p_T$ observables.