Speaker
Description
Transverse Single Spin Asymmetry (AN ) is an azimuthal or left-right asymmetry observed in the distribution of final-state scattered particles produced in transversely polarized proton-proton (pp) collisions. This asymmetry arises from fundamental Transverse Momentum Dependent (TMD) and Twist-3 mechanisms involving the interplay between transverse momentum and spin of the participating partons and hadrons. Previous measurements of AN for neutral pions (π0) at mid-rapidity ( |η| < 1) indicate that it is consistent with zero; however, at forward rapidities (3.3 < η < 5.5), significantly larger values have been observed. Consequently, measurements in the intermediate rapidity range (1.0 < η < 2.0) are crucial for providing a comprehensive understanding of AN and the underlying physics processes. The STAR EndCap Electromagnetic Calorimeter (EEMC) with a full azimuthal coverage across the pseudorapidity range of 1.09 ≤ η ≤ 2.00 is significant for such measurements. This talk will present the preliminary results of AN for π0 using the EEMC from STAR Run 2015 transversely polarized p↑p collisions at the center-of-mass energy of 200 GeV and with an integrated luminosity of 52 pb−1. Additionally, the status of the same analysis from STAR Run 2017, at the center-of-mass
energy of 510 GeV and with an integrated luminosity of 350 pb−1, higher than Run 2015 will be presented.