Constraining Quark Transversity through Collins Asymmetry Measurements in Mid-Rapidity Jets in p^↑p Collisions at STAR

Quantitative insights have been obtained from past measurements of the Collins asymmetry in e⁺ e⁻ collisions and deep-inelastic lepton-nucleon scattering. Further constraints can be added from measurements of the azimuthal asymmetry of leading charged pions in jets produced by transversely polarized proton collisions. This asymmetry can be expressed as a convolution of the quark transversity (δq(xQ²)), the Collins fragmentation function (Δ^N D(z)) and a hard-scattering spin-transfer coefficient. Previous measurements constrain Δ^N D(z), potentially allowing an independent extraction of δ_q(x,Q²). We present progress toward asymmetry measurements from √s = 200 GeV transversely polarized (∼58%) proton collision data collected at the Solenoidal Tracker at RHIC (STAR), with full azimuthal coverage at mid-rapidity (|η| < 1). A vailable data give a statistical precision of σ ∼ 0.01, for average quark momentum fraction ⟨x⟩ ∼ 0.2, at each of four intervals of the hadron-jet momentum fraction z over 0.1 < z < 0.6.