Transverse spin-dependent azimuthal correlations of charged pion pairs measured in $p^↑ + p$ collisions at $\sqrt{s}$=500 GeV

Abstract

The transversity distribution, which describes transversely polarized quarks in transversely polarized nucleons, is a fundamental component of the spin structure of the nucleon, and is only loosely constrained by global fits to existing semi-inclusive deep inelastic scattering (SIDIS) data. In transversely polarized $p^↑ + p$ collisions it can be accessed using transverse polarization dependent fragmentation functions which give rise to azimuthal correlations between the polarization of the struck parton and the final state scalar mesons. This letter reports on spin dependent di-hadron correlations measured by the STAR experiment. The new dataset corresponds to 25 pb$^{−1}$ integrated luminosity of $p^↑ + p$ collisions at $\sqrt{s}$=500 GeV, an increase of more than a factor of ten compared to our previous measurement at $\sqrt{s}$= 200 GeV. Non-zero asymmetries sensitive to transversity are observed at a $Q^2$ of several hundred GeV and are found to be consistent with the former measurement and a model calculation. We expect that these data will enable an extraction of transversity with comparable precision to current SIDIS datasets but at much higher momentum transfers where subleading effects are suppressed.