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Measurements of $Λ$ and $\bar Λ$ polarization in longitudinally polarized proton-proton collisions at $\sqrt s$ =200 GeV at STAR

Qinghua Xu
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Abstract

Preliminary results for the longitudinal polarization of $Λ$ and ${\bar Λ}$ hyperons in longitudinally polarized proton-proton collisions at $\sqrt s$ = 200 GeV are presented. The $Λ$($\bar Λ$) candidates are reconstructed at mid-rapidity ($|η|<1$) with the time projection chamber of the STAR experiment at RHIC, using 0.5 pb$^{-1}$ collected in 2003 and 2004 with beam polarizations of up to 45%. Their mean longitudinal momentum fraction $x_F$ is about 8 $\times$$10^{-3}$ and their mean transverse momentum $p_T$ is about 1.5 GeV. The analysis uses asymmetries of counts for different spin states of the colliding proton beams and does not require detailed knowledge of the detector acceptance. The preliminary $Λ$(${\bar Λ}$) polarization values are consistent with zero within their statistical uncertainties of 0.05.

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Qinghua Xu. 2005-12-22. Measurements of $Λ$ and $\bar Λ$ polarization in longitudinally polarized proton-proton collisions at $\sqrt s$ =200 GeV at STAR. https://doi.org/10.1063/1.2220191

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