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

Abstract

Preliminary results for the longitudinal polarization of $\Lambda$ and $\bar{\Lambda }$ hyperons in longitudinally polarized proton-proton collisions at $\sqrt{s}$ = 200 GeV are presented. The $\Lambda$($\bar{\Lambda }$) candidates are reconstructed at mid-rapidity ($|\eta |<1$) 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 $\Lambda$($\bar{\Lambda }$) polarization values are consistent with zero within their statistical uncertainties of 0.05.

arXiv comment4 pages, 2 eps figures. Talk presented at the Particles and Nuclei International Conference (PANIC05), October 24-28, 2005 Santa Fe, USA

Cited by in corpus (4)

• Longitudinal polarization of hyperon and anti-hyperon in semi-inclusive deep-inelastic scattering
• Anti-Hyperon polarization in high energy pp collisions with polarized beams
• Multiparticle production and initial quasi-temperature from proton induced carbon collisions at $p_{Lab}=31$ GeV/$c$
• Longitudinal spin transfer of Lambda and anti-Lambda in polarized pp collisions at \sqrt s=200 GeV at STAR