Speaker
Description
Spontaneous polarization of $\Lambda/\bar{\Lambda}$ hyperon in unpolarized hadron-hadron reactions has been observed experimentally for nearly half a century and still eludes a definitive explanation. Recently significant transverse polarization of $\Lambda/\bar{\Lambda}$ was observed by the Belle experiment in unpolarized $e^{+}e^{-}$ annihilation, along the normal direction to the plane defined by the thrust axis and the $\Lambda$ momentum. A possible origin is the effect arising from polarizing fragmentation functions (PFFs), which describe the production of polarized hadrons from the fragmentation of an unpolarized parton. Presented in this talk is a status update on measurement of the polarization of $\Lambda$/$\bar{\Lambda}$ transverse to the plane defined by the jet and $\Lambda$ momentum in unpolarized $pp$ collisions collected at the STAR experiment at the center-of-mass energy of $\sqrt{s}$ = 200 GeV, with an integrated luminosity of 104 $\mathrm{pb}^{-1}$. This is the first measurement in $pp$ collisions and can provide important constraints on the PFFs. The utilized data sample is the largest collected by the STAR detector at RHIC for this collision system and energy.
