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تسجيل مستخدم جديدMeasurements of $Lambda$ and $bar Lambda$ polarization in longitudinally polarized proton-proton collisions at $sqrt s$ =200 GeV at STAR
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Qinghua Xu
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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.
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This contribution reports on a proof-of-principle measurement of the longitudinal spin transfer $D_{LL}$ in inclusive $Lambda$ and $bar Lambda$ production in polarized proton-proton collisions at a center of mass energy $sqrt{s}$ = 200 GeV. The data
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The longitudinal spin transfer $D_{LL}$ to $Lambda$ and $bar{Lambda}$ hyperons produced in high-energy polarized proton--proton collisions is expected to be sensitive to the helicity distribution functions of strange quarks and anti-quarks of the pro
ton, and to longitudinally polarized fragmentation functions. We report an improved measurement of $D_{LL}$ from data obtained at a center-of-mass energy of $sqrt{s}$ = 200 GeV with the STAR detector at RHIC. The data have an approximately twelve times larger figure-of-merit than prior results and cover $|eta|<$ 1.2 in pseudo-rapidity with transverse momenta $p_T$ up to 6 GeV/c. In the forward scattering hemisphere at largest $p_T$, the longitudinal spin transfer is found to be $D_{LL}$ = -0.036 $pm$ 0.048 (stat) $pm$ 0.013(sys) for $Lambda$ hyperons and $D_{LL}$ = 0.032 $pm$ 0.043,(stat) $pm$ 0.013,(sys) for $bar{Lambda}$ anti-hyperons. The dependences on $eta$ and $p_T$ are presented and compared with model evaluations.
We report our measurement on longitudinal spin transfer, D_LL, from high energy polarized protons to $Lambda$ and $bar{Lambda}$ hyperons in proton-proton collisions at $sqrt{s} = 200 GeV$ with the STAR detector at RHIC. The current measurements cover
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