Speaker
Description
Nuclear dependence of Single Transverse Spin Asymmetry (STSA) in pp and pA collisions is still a standing mystery. Recent results by PHENIX (A^(−1/3)) [1]
and STAR (A^0) [2] collaborations posses strikingly different nuclear scaling which suggest that the dominant underlying mechanism for STSA may vary with
the kinematics of the collision. In the forward regime, where the gluon saturation effects become important, and where the collisions are described in the
so-called hybrid formalism [3], two contributions to STSA in pp and pA collisions have been found [4,5]. In [5], the phase required for STSA comes from the
imaginary part of twist-3 fragmentation function (FF) with the polarized projectile described with Transversity parton distribution function and the unpolarized
target with real part of Dipole distribution, Pomeron. We have found a new contribution to STSA [Benić, Vivoda in preparation] which comes from the
combination of the real part of genuine twist-3 FF and the imaginary part of dipole distribution, Odderon. The Odderon mechanism to STSA is known to generate
significant nuclear dependance [6] and we expect that this approach could shine a new light at RHIC data [1,2]. Also, this contribution will give us some insight
into the real part of the twist-3 FF which has not yet been constrained by global fits [7]. In this talk I will first provide a formula for polarized cross section and
then discuss our numerical results for STSA [Benić, Vivoda in preparation].
References:
[1] C. Aidala et. al. (PHENIX Collaboration), Phys. Rev. Lett. 123, 122001 (2019).
[2] J. Adam et. al. (STAR Collaboration), Phys. Rev. D 103, 072005 (2021).
[3] A. Schafer and J. Zhou, Phys. Rev. D 90, 034016 (2014), 1404.5809.
[4] Y. Hatta, B.-W. Xiao, S. Yoshida and F. Yuan, Phys. Rev. D 94, 054013 (2016).
[5] Y. Hatta, B.-W. Xiao, S. Yoshida and F. Yuan, Phys. Rev. D 95, 014008 (2017).
[6] Y. V. Kovchegov and M. D. Sievert, Phys. Rev. D 86, 034028 (2012), [Erratum: Phys.Rev.D 86, 079906 (2012)].
[7] L. Gamberg et al. (Jefferson Lab Angular Momentum (JAM) Collaboration), Phys. Rev. D 106, 034014 (2022).
