Since the first surprising results on the spin structure of the proton by the EMC experiment in the late 1980s, much progress has been made in understanding the origin of the proton spin. However, the sea quark contribution to the proton spin, for example, the helicity distributions of the strange quark (anti-quark), $s(\bar{s})$, is still not well constrained by experimental data. Since the $s(\bar{s})$ is expected to carry a substantial fraction of the spin of the $Λ(\barΛ)$ hyperon, measurements of the longitudinal spin transfer, $D_{LL}$, of the $Λ(\barΛ$) hyperon can thus shed light on the helicity distribution of the $s(\bar{s})$ and the longitudinally polarized fragmentation functions. In these proceedings, we will present the status of the $Λ(\barΛ$) $D_{LL}$ analysis using data collected at RHIC-STAR in 2015, for the pseudo-rapidity $|η| < 1.2$ and transverse momenta up to $8.0$ GeV$/c$. The $D_{LL}$ as a function of the longitudinal momentum fraction of the $Λ(\barΛ)$ hyperon in the jet is also investigated. This data set is about twice as large as the 2009 data used for the previously published $D_{LL}$ results.
Measurements of the longitudinal spin transfer, $D_{LL}$, and the transverse spin transfer, $D_{TT}$, of the $Λ(\barΛ$) 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 $Λ(\barΛ$) $D_{LL}$ and $D_{TT}$ using data collected at RHIC-STAR experiment in 2015, with twice larger statistics than previously published results.
The transverse spin transfer, $D_{TT}$, of $Λ$ and $\overlineΛ$ hyperons in $p$+$p$ collisions is expected to be sensitive to the $s$ and $\bar{s}$ quark transversity distributions in the proton and to the transversely polarized fragmentation functions. The STAR experiment has published the first measurement of the transverse spin transfer of $Λ$ and $\overlineΛ$ hyperons in transversely polarized $p$+$p$ collisions at $\sqrt{s}$ = 200 GeV within pseudo-rapidity $|η| < 1.2$ and for the transverse momenta up to 8 GeV/$c$ based on the data taken in 2012. In 2015, a data sample of $p$+$p$ collisi…
We calculate the inclusive production of a polarized $Λ$ or $\barΛ$ hyperon from the single longitudinally polarized proton and proton ($pp$) collision at RHIC. By comparing the data reported by the STAR Collaboration, we find that this process is sensitive to the polarization of strange and antistrange quarks of the proton in the experimental range. By introducing asymmetric coefficients with the minimization of $χ^2$, we further identify the asymmetry of the polarized strange-antistrange quarks in the proton sea and find that the first moment is $Δs \approx -0.025\pm 0.019$ for strange quark…
Using the self-analyzing decay of the $Λ$, the longitudinal spin transfer $D_{LL'}$ to the hyperon from a polarized electron beam scattering off an unpolarized proton target can be determined. For $Λ$s produced in the current fragmentation region, this quantity is proportional to the helicity dependent fragmentation function $G_1^Λ$ and can provide insight into the spin structure of the $Λ$. Currently, limited experimental data on $D_{LL'}$ cannot discriminate between different models of $Λ$ spin structure. This contribution reports on the status of the ongoing analysis of the longitudinal spi…
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 $Λ$ and $\bar Λ$ 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…
We make a systematic study of $Λ$ hyperon polarizations in unpolarized lepton induced semi-inclusive reactions such as $e^-N\to e^-ΛX$ and $e^+e^-\toΛh X$. We present the general form of cross sections in terms of structure functions obtained from a general kinematic analysis. This already shows that the produced hyperons can be polarized in three orthogonal directions, i.e., the longitudinal direction along the hyperon momentum, the normal direction of the production plane, and the transverse direction in the production plane. We present the parton model results at the leading twist and leadi…
We study the production of polarized $Λ$ hyperon in semi-inclusive deep inelastic scattering off an unpolarized target. We include the cases in which the $Λ$ hyperon is longitudinally polarized or transversely polarized, and in which the lepton beam is unpolarized or longitudinally polarized. Within the framework of the transverse momentum dependent factorization, we take into account the complete decomposition of the parton correlator for fragmentation up to twist-3. We present the cross section of the process to order $1/Q$. The expressions of the polarized structure functions, which may giv…
The double longitudinal-spin asymmetry, $A_{LL}$, of the $J/ψ$ production in polarized proton-proton collisions is presented in this paper at QCD next-to-leading order. It is found that the obtained values of $A_{LL}$ are in general consistent with the PHENIX measurements. Various sets of the long-distance matrix elements (LDMEs) are employed in our calculation to study the possible theoretical uncertainties. It is found that, for $p_t<5\gev$, all these LDMEs lead to almost the same results, which are within the tolerance of the experimental data uncertainties.
The global polarization of the $Λ$ and $\overlineΛ$ hyperons is measured for Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 and 5.02 TeV recorded with the ALICE at the LHC. The results are reported differentially as a function of collision centrality and hyperon's transverse momentum ($p_{\rm{T}}$) for the range of centrality 5-50%, $0.5 < p_{\rm{T}} <5$ GeV/$c$, and rapidity $|y|<0.5$. The hyperon global polarization averaged for Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 and 5.02 TeV is found to be consistent with zero, $\langle P_{\rm{H}}\rangle$ (%) $\approx$ - 0.01 $\pm$ 0.05 (stat.…
Polarized proton-proton collisions at the Relativistic Heavy Ion Collider (RHIC) provide unique opportunities to study the spin structure of the nucleon. We will highlight recent results on the nucleon spin structure from the STAR and PHENIX experiments at RHIC: (1) A sizable gluon polarization in the proton is measured with longitudinal double spin asymmetries of jet and hadron production; (2) Longitudinal single spin asymmetries in W boson production improve constraints on the sea quark polarization. The new spin asymmetry results for W boson confirmed the SU(2) flavor asymmetry of the light…
We evaluate centrality dependence of hyperon, $Λ, Ξ, Ω$ and $K$ meson yields from Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV using rate equation and compare with experimental observations. An increase in the yield per participating nucleon is observed with centrality. Higher rate of multistrange productions compared to single-strange are also observed in case of central collisions. Using rate equation or momentum integrated Boltzmann equation we discuss the yield microscopically which are then normalised with thermal pions to get the yield ratio,($H_s+\bar{H_s}$)/($π^++π^-$) at various centra…
We investigate the spin-dependent (naive) T-odd fragmentation function $D^\perp_{1T}$, which can provide an explanation on the transverse polarization of the $Λ^0$ hyperon produced in an unpolarized process. We calculate $D^\perp_{1T}$ for light flavors in the spectator diquark model, with a Gaussian form factor at the hyperon-quark-diquark vertex. We include in the calculation both the scalar diquark and axial-vector diquark spectators. We determine the values of the model parameters by fitting the unpolarized fragmentation function $D^Λ_1$ to the DSV parametrization for $D^Λ_1$. In addition,…
The production of $W^{\pm}$ bosons in longitudinally polarized $\vec{p}+\vec{p}$ collisions at RHIC provides a new means of studying the spin-flavor asymmetries of the proton sea quark distributions. Details of the $W^{\pm}$ event selection in the $e^{\pm}$ decay channel at mid-rapidity are presented, along with preliminary results for the production cross section and parity-violating single-spin asymmetry, $A_L$, from the STAR Collaboration's 2009 data at $\sqrt{s}=500$ GeV.
The STAR Collaboration is performing a wide range of measurements to determine the gluon helicity distribution in the proton. Gluon-gluon and quark-gluon scattering dominate jet production in proton-proton collisions at RHIC, so the longitudinal double-spin asymmetry, $A_{LL}$, for jet production places significant constraints on the gluon polarization in the proton. In recent years STAR has recorded large longitudinally polarized $pp$ data sets at both $\sqrt{s} = 200$ GeV and $510$ GeV. The 2009 STAR inclusive jet $A_{LL}$ measurements at $\sqrt{s} = 200$ GeV show the first experimental evid…
We perform a study of $W$-boson production in polarized proton-proton collisions through next-to-next-to-leading order (NNLO) in perturbative QCD. This calculation is required to extend the extraction of polarized parton distribution functions to NNLO accuracy. We present differential distributions at $\sqrt{s}=510$ GeV, relevant for comparison to measurements from the Relativistic Heavy Ion Collider (RHIC). The NNLO QCD corrections significantly reduce the scale dependence of the cross section. We compare the longitudinal single-spin asymmetries as a function of lepton pseudorapidity to RHIC …
We report the measurements of global spin polarization of hyperons ($P_Λ$) from FAIR, RHIC and LHC energies. The $P_Λ$ continue to follow an increasing trend at $\sqrt{s_{\mathrm NN}}$ < 7.7 GeV indicating that enormous vorticity prevail even in hadronic dominant region. New measurements of local spin polarization ($P_{z,2}$) from isobar collisions follow the same pattern observed in previous RHIC and LHC energies. An observable motivated by predicted baryonic Spin Hall Effect, the net local polarization ($P_{z,2}^{\mathrm{net}}$), shows negative value in Au+Au collisions at $\sqrt{s_{\mathrm …
Initial simulations investigating using the RHIC-EIC proton beam as the drive beam in a plasma wakefield acceleration experiment are presented. The proton beam enters the plasma and undergoes self-modulation, forming a series of microbunches. These microbunches resonantly drive electron density perturbations within the plasma, exciting a longitudinal electric field with accelerating gradients in excess of $\mathrm{GVm^{-1}}$. Injecting electrons into the resulting wakefield offers an efficient method for accelerating electron bunches for use in the proposed EIC collider.
With the kinetic freeze-out nucleons and antinucleons obtained from the quark combination model, we study the production of light nuclei and antinuclei in the (anti-)nucleon coalescence mechanism in relativistic heavy ion collisions. We derive analytic formulas of the momentum distributions of different light nuclei and apply them to compute transverse momentum ($p_T$) spectra of (anti-)deuterons ($d$, $\bar d$) and (anti-)tritons ($t$, $\bar t$) in Au-Au collisions at $\sqrt{s_{NN}}=$7.7, 11.5, 19.6, 27, 39, 54.4 GeV. We find that the experimental data available for these $p_T$ spectra can be…
The RHIC Cold QCD program has produced a remarkable breadth of physics results and experimental techniques in the exploration of the fundamental structure of strongly interacting matter over the years. In this document, we present highlights of longitudinal and transverse spin physics to date and the 25 years of innovation in accelerator science from the RHIC Spin program. These measurements and techniques will be essential to fully realize the scientific missions of the Electron-Ion Collider (EIC) by providing a comprehensive set of measurements in hadronic collisions and laying the foundatio…
