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

We report the observation of transverse polarization-dependent azimuthal correlations in charged pion pair production with the STAR experiment in p↑+p collisions at RHIC. These correlations directly probe quark transversity distributions. We measure signals in excess of 5 standard deviations at high transverse momenta, at high pseudorapidities η > 0.5, and for pair masses around the mass of the ρ 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.