Jet axes and universal transverse-momentum-dependent fragmentation

TL;DR

This paper introduces a new transverse-momentum-dependent fragmentation function for jets that is universal, free of rapidity divergences, and insensitive to soft radiation recoil, with applications in heavy-ion physics and boosted resonance identification.

Contribution

It proposes a novel TMD fragmentation function for jets that is process-independent and factorizes boundary effects, advancing understanding of jet substructure.

Findings

The observable is insensitive to soft radiation recoil.

The new TMD fragmentation function does not involve rapidity divergences.

The results are applicable to sub-jets and have potential in heavy-ion and resonance studies.

Abstract

We study the transverse momentum spectrum of hadrons in jets. By measuring the transverse momentum with respect to a judiciously chosen axis, we find that this observable is insensitive to (the recoil of) soft radiation. Furthermore, for small transverse momenta we show that the effects of the jet boundary factorize, leading to a new transverse-momentum-dependent (TMD) fragmentation function. In contrast to the usual TMD fragmentation functions, it does not involve rapidity divergences and is universal in the sense that it is independent of the type of process and number of jets. These results directly apply to sub-jets instead of hadrons. We discuss potential applications, which include studying nuclear modification effects in heavy-ion collisions and identifying boosted heavy resonances.