Speaker
Description
The transversity distribution function, $h^{q}_{1}(x)$, a leading twist parton distribution function, is a fundamental component of the spin structure of the nucleon. $h^{q}_{1}(x)$ describes the distributions of transversely polarized quarks inside a transversely polarized nucleon, where x is the longitudinal8momentum fraction of the proton carried by quark q. It is loosely constrained by global fits. Being chiral odd, $h^{q}_{1}(x)$ can be accessed only when it is coupled with another chiral-odd partner, such as the spin-dependent Collins fragmentation function (FF) or the interference fragmentation function (IFF), which serves as a quark polarimeter. In transversely polarized proton-proton ($p^\uparrow p$) collisions, the resulting azimuthal correlation between the spin of the fragmenting quark and the final state single charged hadron in jets (involving Collins FF) or di-hadron (involving IFF) can be measured, which are sensitive to quark transversity. The STAR experiment at RHIC has previously measured IFF asymmetries for $\pi^+\pi^-$ pairs using $p^\uparrow p$ collision data from 2006 at $\sqrt{s}$= 200 GeV ($\int L dt$ = 1.8 $pb^{-1}$) and from 2011 at $\sqrt{s}$= 500 GeV ($\int L dt$ = 25 $pb^{-1}$) and Collins asymmetries for charged pions within jets from 2011 at $\sqrt{s}$= 500 GeV. Non-zero IFF and Collins asymmetries were reported which are consistent with predictions based on global analyses of $e^+ e^-$ and SIDIS data. In 2012 and 2015, STAR collected $\sim$ 14 $pb^{-1}$ $\sim$ 48 $pb^{-1}$ of $p^\uparrow p$ data at $\sqrt{s}$ = 200 GeV, respectively. These datasets provide the most precise measurements of the Collins and IFF asymmetries in $p^\uparrow p$ collisions at $\sqrt{s}$= 200 GeV to date, especially at the quark momentum fractions 0.1< x <0.4. We will present preliminary results for Collins asymmetries of identified pions, kaons, and protons in jets based on 2012 and 2015 $p^\uparrow p$ datasets and the status update for IFF asymmetries based on 2015 $p^\uparrow p$ dataset at $\sqrt{s}$= 200 GeV.
