Observation of Transverse Spin-Dependent Azimuthal Correlations of Charged Pion Pairs in $p^\uparrow+p$ at $\sqrt{s}=200$ GeV

TL;DR

This paper reports the first direct measurement of quark transversity distributions in proton-proton collisions by observing transverse spin-dependent azimuthal correlations of charged pion pairs at RHIC, with significant signals at high transverse momentum.

Contribution

It introduces a novel method to measure quark transversity in p+p collisions through azimuthal correlations, testing the universality of spin-dependent distributions.

Findings

Significant azimuthal correlations observed at high transverse momentum.

First direct measurement of transversity in proton-proton collisions.

Results consistent with expectations from spin physics theories.

Abstract

We report the observation of transverse polarization-dependent azimuthal correlations in charged pion pair production with the STAR experiment in $p^\uparrow+p$ collisions at RHIC. These correlations directly probe quark transversity distributions. We measure signals in excess of five standard deviations at high transverse momenta, at high pseudorapidities eta>0.5, and for pair masses around the mass of the rho-meson. This is the first direct transversity measurement in p+p collisions. Comparing the results to data from lepton-nucleon scattering will test the universality of these spin-dependent quantities.