Transverse Spin Dependent Azimuthal Correlations of Charged hadron Pairs in $p^\uparrow p$ Collisions at $\sqrt s = 200$ GeV at STAR

Transversity,  $h_1^{q}(x)$, a leading twist parton distribution function, describes the transverse spin distribution of quarks in a transversely polarized proton. It is a fundamental component of nucleon spin structure and is loosely constrained by global fits. As a chiral odd function, $h_1^{q}(x)$ can only be accessed when coupled with another chiral odd partner, such as interference fragmentation function (IFF). This coupling of $h_1^{q}(x)$ and IFF leads to a measurable azimuthal correlation asymmetry ($A_{UT}$) of hadron pairs in final state. The STAR experiment at RHIC has measured non-zero $A_{UT}$ for $\pi^+\pi^-$ in polarized proton-proton ($p^\uparrow p$) collision, using data from 2006 and 2015 at $\sqrt{s} = 200$ GeV and from 2011 and 2017 at $\sqrt{s} = 500/510$ GeV.  The precise determination of $A_{UT}$, along with unpolarized di-hadron cross section in $p^\uparrow p$ collisions, can aid in constraining $h_1^{q}(x)$ in global analysis. 

Measurements of di-hadron $A_{UT}$ and cross section with other hadron species provide additional flavor sensitivity; measurements with $K^+K^-$ provide access to $h_1^{q}(x)$ of strange quarks. We will present an update on $A_{UT}$ for hadron pairs based on 2015 $p^\uparrow p$ dataset at $\sqrt{s} = 200$ GeV in the mid-pseudorapidity region $(|\eta|<1)$.