# Invariant-mass and fractional-energy dependence of inclusive production of di-hadrons in $e^+e^-$ annihilation at $\sqrt{s}=$ 10.58 GeV

## TL;DR

This paper measures the inclusive production cross sections of di-hadrons in electron-positron collisions at 10.58 GeV, providing data crucial for understanding fragmentation functions and spin-dependent phenomena.

## Contribution

It presents the first detailed measurement of di-hadron fragmentation functions as a function of invariant mass and fractional energy at Belle, aiding spin physics studies.

## Key findings

- Di-hadron cross sections as a function of energy and invariant mass
- Evidence supporting di-hadron origin from the same initial parton
- Baseline data for spin-dependent fragmentation analyses

## Abstract

The inclusive cross sections for di-hadrons of charged pions and kaons ($e^+e^- \rightarrow hhX$) in electron-positron annihilation are reported. They are obtained as a function of the total fractional energy and invariant mass for any di-hadron combination in the same hemisphere as defined by the thrust event-shape variable and its axis. Since same-hemisphere di-hadrons can be assumed to originate predominantly from the same initial parton, di-hadron fragmentation functions are probed. These di-hadron fragmentation functions are needed as an unpolarized baseline in order to quantitatively understand related spin-dependent measurements in other processes and to apply them to the extraction of quark transversity distribution functions in the nucleon. The di-hadron cross sections are obtained from a $655\,{\rm fb}^{-1}$ data sample collected at or near the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider.