Number density interpretation of dihadron fragmentation functions

TL;DR

This paper introduces a quantum field-theoretic definition of dihadron fragmentation functions that ensures they can be interpreted as number densities, providing a clearer physical understanding and consistent evolution equations.

Contribution

It offers a new formal definition of dihadron fragmentation functions that satisfy sum rules and have a number density interpretation, enhancing their physical and theoretical clarity.

Findings

Definition satisfies sum rules

Extended DiFFs are confirmed as number densities

Derived evolution equations for DiFFs

Abstract

We present a new quantum field-theoretic definition of fully unintegrated dihadron fragmentation functions (DiFFs) as well as a generalized version for $n$-hadron fragmentation functions. We demonstrate that this definition allows certain sum rules to be satisfied, making it consistent with a number density interpretation. Moreover, we show how our corresponding so-called extended DiFFs that enter existing phenomenological studies are number densities and also derive their evolution equations. Within this new framework, DiFFs extracted from experimental measurements will have a clear physical meaning.