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Register a new userLongitudinal and transverse spin transfer to $Lambda$ and $barLambda$ hyperons in p+p collisions at STAR
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Qing-Hua Xu
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The longitudinal or transverse spin transfer to Lambda and anti-Lambda hyperons in polarized proton-proton collisions is expected to be sensitive to the helicity or transversity distributions of strange and anti-strange quarks of the proton, and to the corresponding polarized fragmentation function. We report the first measurement of the transverse spin transfer to $Lambda$ and $bar Lambda$ along the polarization direction of the fragmenting quark, $D_{TT}$, in transversely polarized proton-proton collisions at 200 GeV with the STAR experiment at RHIC. The data correspond to an integrated luminosity of 18 pb$^{-1}$, and cover a kinematic range of |$eta$|< 1.2 and transverse momentum $p_T$ up to 8 GeV/c. We also report an improved measurement of the longitudinal spin transfer $D_{LL}$ to $Lambda$ and $bar Lambda$ with $p_T$ up to 6 GeV/c, using data with about twelve times larger figure-of-merit than the previously published STAR results. The prospects of hyperon polarization measurements in the forward pseudo-rapidity region (2.5<$eta$<4) in p+p collision in the year of 2021 and beyond will also be discussed, which is based on the STAR forward detector upgrade plan including a forward tracking system and a forward calorimeter system.
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Measurements of the longitudinal spin transfer, $D_{LL}$, and the transverse spin transfer, $D_{TT}$, of the $Lambda(bar{Lambda}$) hyperon in polarized $p$+$p$ collisions are expected to be sensitive to the helicity distribution and transversity distribution of the $s(bar{s})$ quark in proton and the corresponding polarized fragmentation functions. This contribution presents the new preliminary results of the $Lambda(bar{Lambda}$) $D_{LL}$ and $D_{TT}$ using data collected at RHIC-STAR experiment in 2015, with twice larger statistics than previously published results.
Inclusive production of $Lambda$-hyperons was measured with the large acceptance NA61/SHINE spectrometer at the CERN SPS in inelastic p+p interactions at beam momentum of 158~GeVc. Spectra of transverse momentum and transverse mass as well as distributions of rapidity and x$_{_F}$ are presented. The mean multiplicity was estimated to be $0.120,pm0.006;(stat.),pm 0.010;(sys.)$. The results are compared with previous measurements and predictions of the EPOS, UrQMD and FRITIOF models.
The transverse spin transfer from polarized protons to $Lambda$ and $bar{Lambda}$ hyperons is expected to provide sensitivity to the transversity distribution of the nucleon and to the transversely polarized fragmentation functions. We report the first measurement of the transverse spin transfer to $Lambda$ and $bar{Lambda}$ along the polarization direction of the fragmenting quark, $D_mathrm{TT}$, in transversely polarized proton-proton collisions at $sqrt{s}=200,mathrm{GeV}$ with the STAR detector at RHIC. The data correspond to an integrated luminosity of $18,mathrm{pb}^{-1}$ and cover the pseudorapidity range $left|etaright| < 1.2$ and transverse momenta $p_{mathrm{T}}$ up to $8,mathrm{GeV}/c$. The dependence on $p_mathrm{T}$ and $eta$ are presented. The $D_mathrm{TT}$ results are found to be comparable with a model prediction, and are also consistent with zero within uncertainties.
The results on J/psi pT spectra in 200 GeV p+p and Au+Au collisions at STAR with pT in the range of 3-10 GeV/c are presented. Nuclear modification factor of high-pT J/psi is found to be consistent with no suppression in peripheral Au+Au collisions and significantly smaller than unity in central Au+Au collisions. The J/psi elliptic flow is measured to be consistent with no flow at pT < 10 GeV/c in 20-60% Au+Au collisions.
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 proton, 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.
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