Measurements of Transverse Spin Dependent 𝝅+𝝅− Azimuthal Correlation Asymmetry and Unpolarized2 𝝅+𝝅− Cross-Section in 𝒑 𝒑 Collisions at STAR

The transversity distribution function, h₁q(x), encapsulates the transverse spin structure of the proton at the leading twist, where x represents the longitudinal momentum fraction carried by the quark q. The extraction of h₁q(x) poses a formidable challenge due to its chiral-odd nature. Measurements of final-state di-hadron pairs in transversely polarized proton-proton (p^↑ p) collisions directly probe the collinear quark transversity via coupling with a chiral-odd interference fragmentation function, IFF. This coupling results in an experimentally measurable azimuthal correlation asymmetry, AUT. The asymmetry originates from the interplay between the spin orientation of the fragmenting quark and the resulting di-hadron in the final state. Thus, precise knowledge of unpolarized di-hadron fragmentation functions (FFs) is necessary to achieve a model-independent extraction of the transversity from these measurements. These FFs can be constrained by measuring the unpolarized di-hadron cross-section in $pp$ collisions. We report the preliminary results on the AUT for π⁺π⁻ pairs using p^↑ p data collected by the STAR experiment at a center-of-mass energy (√s) of 200 GeV in 2015. Additionally, we report preliminary results of the unpolarized π⁺π⁻ cross section using $pp$ data at √s = 200 GeV collected in 2012. These datasets probe the valance quark region ($0.1 < x < 0.3$) at Q² of the order of ~ 100 GeV².