Measurement of azimuthal asymmetries in inclusive charged dipion production in $e^+e^-$ annihilations at $\sqrt{s}$ = 3.65 GeV

TL;DR

This paper reports the measurement of azimuthal asymmetries in charged pion production from electron-positron collisions at 3.65 GeV, providing insights into the Collins fragmentation function and quark transversity.

Contribution

First measurement of azimuthal asymmetries at this energy, contributing valuable data for understanding spin-dependent fragmentation and nucleon structure.

Findings

Nonzero asymmetries observed increasing with pion momentum

Results align with existing semi-inclusive deep inelastic scattering data

Data serve as inputs for global transversity analyses

Abstract

We present a measurement of the azimuthal asymmetries of two charged pions in the inclusive process $e^+e^-\rightarrow \pi\pi X$ based on a data set of 62 $\rm{pb}^{-1}$ at the center-of-mass energy $\sqrt{s}=3.65$ GeV collected with the BESIII detector. These asymmetries can be attributed to the Collins fragmentation function. We observe a nonzero asymmetry, which increases with increasing pion momentum. As our energy scale is close to that of the existing semi-inclusive deep inelastic scattering experimental data, the measured asymmetries are important inputs for the global analysis of extracting the quark transversity distribution inside the nucleon and are valuable to explore the energy evolution of the spin-dependent fragmentation function.