Transverse Spin Dependent Azimuthal Correlations of Charged Pion Pairs in Polarized pp Collisions at √s = 200 GeV
(Preliminary Results)

Figure 1: A_UT vs M_inv in forward (eta > 0 )(red) and backward (eta < 0) (blue) pseudorapidity regions in five p_T bins. The average p_T increases from left to right and from top to bottom, the value of which is shown on the top right corner of each panel. Higher asymmetries are observed in forward region and the signals are more prominent in higher p_T bins. Forward asymmetries peak around M_inv ≈ 0.8 GeV/c², close to the rho-meson mass (M_inv  ≈ 0.775 GeV/c^₂ ). Backward asymmetries are relatively small, which are mostly from unpolarized beam. Systematic uncertainty includes the particle identification and trigger bias combined.

Figure 2: A_UT vs p_T in forward (eta > 0 )(red) and backward (eta < 0) (blue) regions in five M_inv bins. The average M_inv increases from left to right and  from top to bottom, the value of which is shown on the top left corner of each panel. Higher asymmetries are observed in forward region and the signals are more prominent in M_inv bins close to M_inv ≈ 0.775 GeV/c². Backward asymmetries are small, but non-zero, at higher pT, which is mostly from the unpolarized beam. Systematic uncertainty includes particle identification and trigger bias combined.

 Figure 3: A_UT vs Eta  integrated over M_inv and p_T (top panel). < x >, average of x1 and x2, and < z >, average of z1 and z2, in the same eta bins from simulation (bottom panel). x increases from 0.1 to 0.22 from negative to positive eta regions. z shows slight dependence in forward and backward pseudorapidity region separately, but overall, it is averaged out to be  ≈ 0.46. Forward asymmetries are large, where we have access to higher x. Small backward asymmetries, which is mainly from the unpolarized beam, corresponds to the lower x region. Systematic uncertainty includes the particle identification and trigger bias combined.

 Figure 4: A_UT vs M_inv in highest p_T bin (top panel) and < x > and < z > in corresponding M_inv bins (bottom panel). Although slight fluctuations, x is consistent to  ≈ 0.2, over all M_inv bins, however, z increases with the increase in M_inv. This shows strong correlation between A_UT and z.

Figure 5: STAR A_UT vs M_inv in  eta > 0 region integrated over p_T, compared with the theory at √s = 200 GeV. The uncertainty band of the theory curve is obtained with the bootstrap method based on 600 replicas at 90% confidence level (Radici et. al.).

Watch DIS Presentation: 

www.youtube.com/watch

Updates: 

12/20/2022
1. Analysis note updated. Data table includes the bin ranges as well.
updated note: IFFPrelmNote_Updated.pdf