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Updated on Wed, 2024-09-25 09:20. Originally created by gty on 2024-09-13 22:04.

Paper title: measurement of transverse polarization of Λ(Λ ̅) within jet in pp collisions at STAR

PAs: Taoya Gao, Jinlong Zhang, Qinghua Xu, Yi Yu

Target Journal: Phys. Rev. L

Abstracts:

It is well-known that $\Lambda$ spontaneous polarization in unpolarized hadron-hadron reactions has been a puzzle for about five decades. Meanwhile, the polarizing Fragmentation Functions(PFFs), which describe an unpolarized parton fragments into polarized hadrons, are perceived as one possible origin. Recently, significant transverse polarization of $\Lambda/\bar{\Lambda}$ was observed by the Belle experiment in unpolarized $e^{+}e^{-}$ annihilation, along the axis normal to the plane defined by the thrust axis and the $\Lambda$ momentum.

In this paper, we present the first measurement of transverse polarization of $\Lambda$ within reconstructed jet in unpolarized $pp$ collisions at the center-of-mass energy of $\sqrt{s}$ = 200 GeV, using data collected by the STAR detector of RHIC. It is observed that $\Lambda$ and $\bar{\Lambda}$ transverse polarizations have a significant on jet $p_T$. Additionally, $z$ and $j_T$ dependence of $\Lambda$ polarization are studied for different jet $p_T$ ranges, where $z$ denotes the fraction of jet momentum carried by $\Lambda$ and $j_T$ means transverse momentum of $\Lambda$ relative to the jet axis. The results could provide important constraints for PFFs and demonstrate the measurement of PFFs via $\Lambda$ inside reconstructed jet is feasible.

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