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\title{Transverse Spin Physics Programs at STAR}
\author{Jae D. Nam, for the STAR collaboration}
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The unique capability of the Relativistic Heavy Ion Collider (RHIC) to collide transversely polarized protons, accompanied by the excellent coverage and particle identification provided by the Solenoidal Tracker at RHIC (STAR) detector, provides an ideal testing ground for rich and diverse spin physics programs.


This overview talk will encompass recent highlights from the STAR experiment with transversely polarized $pp$ collisions produced in RHIC.
The asymmetric production of $W^\pm/Z$ bosons with respect to the transverse proton polarization provides insights into the transverse partonic motion in the initial state and tests the non-universality of the Sivers mechanism.
Spin-dependent shifts in the azimuthal separation between two jets in a dijet event can be used to extract the initial state parton transverse momenta.
Additionally, the asymmetric production of charged hadrons within a jet can be used to probe quark transversity, and investigate the evolution, universality and factorization breaking of the Collins mechanism in the transverse momentum dependent formalism.
The asymmetric production of hadron pairs provides an independent measurement of quark transversity in the collinear framework.
Measurements of asymmetries in diffractive processes investigate the contribution of these processes to the unexpectedly large asymmetry found in the forward ($2.5 < \eta < 4$) regime.


Finally, prospects for the recent STAR data-taking periods, with enhanced forward tracking and calorimetry delivered by the STAR forward upgrade, will be discussed.






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With large acceptance and excellent particle identification, STAR has facilitated a variety of exciting measurements covering a wide range of physics topics.
The versatility and precision of the STAR detector, accompanied by the unique capability of RHIC to collide polarized hadrons at various energies, has opened new avenues for investigations of the proton spin structure.


% WZ
Calorimetry at STAR allows reconstruction of $W^{\pm}/Z$ bosons by tagging their decay electron.
Measurements of the reconstructed $W^{\pm}$ in longitudinally polarized collisions probe asymmetric anti-quark helicity distributions in the proton sea.
In transversely polarized collisions, the $W^{\pm}/Z$ bosons probe the sea-quark Sivers function and contribute to tests of the predicted sign change.


% Jets
Jets can be reconstructed based on additional information provided by the STAR tracking system.
The longitudinal double-spin asymmetry, $A_{LL}$, in inclusive jet and dijet production at STAR provides the first evidence of a positive gluon polarization with partonic momentum fraction $x > 0.05$.
The tilt of the dijet opening angle in transversely polarized collisions provides a direct access to the first Mellin momentum of the Sivers function.% and avoids the spin-correlated fragmentation contributions.



% Jets+hadron
With the excellent particle identification at STAR, one can pick out hadrons within a jet.
$A_{LL}$ of jets that are tagged with a $\pi^{\pm}$ provides additional examinations of the sign of gluon helicity.
Novel measurements of azimuthal distributions of identified hadrons in jets in transversely polarized collisions directly probe the collinear quark transversity via coupling to transverse momentum dependent (TMD) Collins fragmentation function.

% Hadrons
The identified hadrons, without being tagged to a jet, provide additional probes of the proton spin structure.
Azimuthal correlation between hadron pairs and the proton spin direction provides a complementary extraction of transversity via coupling to dihadron interference fragmentation function.
Longitudinal and transverse spin transfers to $\Lambda(\bar{\Lambda})$ hyperons allow access to much unknown $s(\bar{s})$ helicity and transversity, respectively.


%These measurements shed lights on Sivers function, quark transversity and spin-dependent fragmentation functions in both collinear and TMD formalism.



In this talk, an overview of spin physics at STAR will be presented. 
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