Measurement of Azimuthal Asymmetries in Inclusive Production of Hadron Pairs in e+e- Annihilation at Belle

TL;DR

This paper reports the first measurement of azimuthal asymmetries in charged pion pairs produced in e+e- annihilation at Belle, providing evidence of the Collins effect and quark transverse polarization.

Contribution

It presents a novel experimental observation of azimuthal asymmetries linked to the Collins effect at Belle, using two reconstruction methods on a large data sample.

Findings

Significant azimuthal asymmetries observed for charged pion pairs.

Asymmetries attributed to transverse polarization of primordial quarks.

Measurement performed at a center-of-mass energy of 10.52 GeV.

Abstract

The Collins effect connects transverse quark spin with a measurable azimuthal dependence in the yield of hadronic fragments around the quark's momentum vector. Using two different reconstruction methods we observe statistically significant azimuthal asymmetries for charged pion pairs in e+e- annihilation at a center-of-mass energy of 10.52 GeV, which can be attributed to a transverse polarization of the primordial quarks. The measurement was performed using a sample of 79 million hadronic events collected with the Belle detector.