Transverse Spin Dependent Azimuthal Correlations of Charged Pion Pairs in $p^{\uparrow}+p$ Collisions at $\sqrt s = 200$ GeV

The transversity distribution function, $h^{q}_{1}(x)$, a leading twist parton density which describes the distributions of transversely polarized quarks inside transversely polarized hadrons, is a fundamental component of the spin structure of the nucleon, and is loosely constrained by global fits. Being chiral odd, $h^{q}_{1}$ can be accessed only when it is coupled with another chiral-odd partner, such as transverse spin-dependent fragmentation function. This gives rise to the azimuthal correlation between the polarization of the struck quarks and the final state scalar mesons, called transverse single-spin asymmetry (TSSA), that directly measures quark transversity distribution. The STAR experiment at RHIC has previously measured TSSA using polarized proton-proton collision data from 2006 at $\sqrt s = 200$ GeV and 2011 at $\sqrt s = 500$ GeV. Both measurements reported nonzero asymmetries which are sensitive to $h^{q}_{1}$. We will present an update on the recent TSSA analysis using data from 2015 polarized proton-proton collisions at $\sqrt s = 200$ GeV, $\sim 30$ times larger sample than that from 2006, in the mid pseudorapidity region ($| \eta |< 1$) for exclusive charged pion pairs ($\pi^{+}\pi^{-}$) in the final state.