Transverse Spin-Dependent Azimuthal Correlations of Charged Pion Pairs in $p^{uparrow}p$ collisions at $sqrt{s} = 510$ GeV at STAR

The transverse polarization of quarks within a transversely polarized nucleon, $h^q_1(x)$, can only be accessed through processes involving its coupling with another chiral-odd function, such as the spin-dependent interference fragmentation function (IFF) in polarized proton-proton collisions. The coupling of $h^q_1(x)$ and IFF leads to a measurable azimuthal correlation asymmetry ($A_{UT}$) of di-hadron pairs in the final state. In previous work, the STAR experiment at RHIC measured a non-zero $A_{UT}$ using polarized proton-proton ($p^uparrow p$) collision data collected in 2011 at $sqrt s = 500$ GeV, with an integrated luminosity of 25 pb$^{-1}$. The precise determination of $A_{UT}$, in conjunction with the measurement of the cross section of unpolarized di-hadron pairs, can help constrain the $h^q_1(x)$ in global analyses. In 2017, the STAR experiment collected a dataset of approximately 350 pb$^{-1}$ from $p^uparrow p$ collisions at $sqrt s = 510$ GeV. This new dataset will significantly enhance the statistical accuracy of the $A_{UT}$ measurement. In this presentation, we will provide an update on the analysis of the $A_{UT}$ measurement for pion pairs in the mid-pseudorapidity region from the STAR 2017 $p^uparrow p$ dataset.