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Institute
We report the first multi-differential measurements of strange hadrons of K−, ϕ and Ξ− yields as well as the ratios of ϕ/K− and ϕ/Ξ− in Au+Au collisions at sNN−−−√=3GeV with the STAR experiment fixed target configuration at RHIC. The ϕ mesons and Ξ− hyperons are measured through hadronic decay channels, ϕ→K+K− and Ξ−→Λπ−. Collision centrality and rapidity dependence of the transverse spectra for these strange hadrons are presented. The 4π yields and ratios are compared to thermal model and hadronic transport model predictions. At the collision energy, thermal model with grand canonical ensemble (GCE) under-predicts the ϕ/K− ratio while the result of canonical ensemble (CE) calculations reproduce well the ratios of ϕ/K−, with the correlation length rc∼2.7\,fm, and ϕ/Ξ−, rc∼4.2\,fm, for the 0-10\% central collisions. Hadronic transport models including high mass resonance decays could also describe the ratios. While thermal calculations with GCE work well for strangeness production in high energy collisions, the change to CE at 3GeV implies a rather different medium property at high baryon density.
We report the first multi-differential measurements of strange hadrons of K−, ϕ and Ξ− yields as well as the ratios of ϕ/K− and ϕ/Ξ− in Au+Au collisions at sNN−−−√=3GeV with the STAR experiment fixed target configuration at RHIC. The ϕ mesons and Ξ− hyperons are measured through hadronic decay channels, ϕ→K+K− and Ξ−→Λπ−. Collision centrality and rapidity dependence of the transverse momentum spectra for these strange hadrons are presented. The 4π yields and ratios are compared to thermal model and hadronic transport model predictions. At this collision energy, thermal model with grand canonical ensemble (GCE) under-predicts the ϕ/K− ratio while the result of canonical ensemble (CE) calculations reproduce well the ratios of ϕ/K−, with the correlation length rc∼2.7\,fm, and ϕ/Ξ−, rc∼4.2\,fm, for the 0-10\% central collisions. Hadronic transport models including high mass resonance decays could also describe the ratios. While thermal calculations with GCE work well for strangeness production in high energy collisions, the change to CE at 3GeV implies a rather different medium property at high baryon density.
The STAR Collaboration reports measurements of back-to-back azimuthal correlations of di-π0s produced at forward pseudorapidities (2.6<η<4.0) in p+p, p+Al, and p+Au collisions at a center-of-mass energy of 200 GeV. We observe a clear suppression of the correlated yields of back-to-back π0 pairs in p+Al and p+Au collisions compared to the p+p data. The observed suppression of back-to-back pairs as a function of event activity and transverse momentum suggests nonlinear gluon dynamics arising at high parton densities. The larger suppression found in p+Au relative to p+Al collisions exhibits a dependence of the saturation scale, Q2s, on the mass number, A. The suppression in high-activity p+Au collisions is consistent with theoretical predictions including gluon saturation effects.
We report measurements of the longitudinal double-spin asymmetry, ALL, for inclusive jet and dijet production in polarized proton-proton collisions at midrapidity and center-of-mass energy s√ = 510 GeV, using the high luminosity data sample collected by the STAR experiment in 2013. These measurements complement and improve the precision of previous STAR measurements at the same center-of-mass energy that probe the polarized gluon distribution function at partonic momentum fraction 0.015 ≲x≲ 0.25. The dijet asymmetries are separated into four jet-pair topologies, which provide further constraints on the x dependence of the polarized gluon distribution function. These measurements are in agreement with previous STAR measurements and with predictions from current next-to-leading order global analyses. They provide more precise data at low dijet invariant mass that will better constraint the shape of the polarized gluon distribution function of the proton.
Measurement of cold nuclear matter effects for inclusive J/ψ in p+Au collisions at √sNN = 200 GeV
(2021)
Measurement by the STAR experiment at RHIC of the cold nuclear matter (CNM) effects experienced by inclusive J/ψ at mid-rapidity in p+Au collisions at sNN−−−√ = 200 GeV is presented. Such effects are quantified utilizing the nuclear modification factor, RpAu, obtained by taking a ratio of J/ψ yield in p+Au collisions to that in p+p collisions scaled by the number of binary nucleon-nucleon collisions. The differential J/ψ yield in both p+p and p+Au collisions is measured through the dimuon decay channel, taking advantage of the trigger capability provided by the Muon Telescope Detector in the RHIC 2015 run. Consequently, the J/ψ RpAu is derived within the transverse momentum (pT) range of 0 to 10 GeV/c. A suppression of approximately 30% is observed for pT<2 GeV/c, while J/ψ RpAu becomes compatible with unity for pT greater than 3 GeV/c, indicating the J/ψ yield is minimally affected by the CNM effects at high pT. Comparison to a similar measurement from 0-20% central Au+Au collisions reveals that the observed strong J/ψ suppression above 3 Gev/c is mostly due to the hot medium effects, providing strong evidence for the formation of the quark-gluon plasma in these collisions. Several model calculations show qualitative agreement with the measured J/ψ RpAu, while their agreement with the J/ψ yield in p+p and p+Au collisions is worse.
We study ηc production at center-of-mass energies s√ from 4.18 to 4.60 GeV in e+e− annihilation data collected with the BESIII detector operating at the BEPCII storage ring, corresponding to 7.3 fb−1 of integrated luminosity. We measure the cross sections of the three different exclusive reactions e+e−→ηcπ+π−π0, e+e−→ηcπ+π−, and e+e−→ηcπ0γ. We find significant ηc production in e+e−→ηcπ+π−π0 at s√ of 4.23 GeV and 4.26 GeV and observe a significant energy-dependent Born cross section that we measure to be consistent with the production via the intermediate Y(4260) resonance. In addition, we perform a search for a charmonium-like Zc state close to the DD¯ threshold that decays to ηcπ, involving ground state charmonium, and observe no signal. Corresponding upper limits on the cross section of ηc and Zc production are provided, where the yields are not found to be significant.
By analyzing 4.48×108 ψ(3686) events collected with the BESIII detector, we observe the decays χcJ→nK0SΛ¯+c.c. (J=0, 1, 2) for the first time, via the radiative transition ψ(3686)→γχcJ. The branching fractions are determined to be (6.67±0.26stat±0.41syst)×10−4, (1.71±0.12stat±0.12syst)×10−4, and (3.66±0.17stat±0.23syst)×10−4 for J=0, 1, and 2, respectively.
The cross sections of the process e+e−→K0SK0L are measured at fifteen center-of-mass energies s√ from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results are found to be consistent with those obtained by BaBar. A resonant structure around 2.2 GeV is observed, with a mass and width of 2273.7±5.7±19.3 MeV/c2 and 86±44±51 MeV, respectively, where the first uncertainties are statistical and the second ones are systematic. The product of its radiative width (Γe+e−) with its branching fraction to K0SK0L (BrK0SK0L) is 0.9±0.6±0.7 eV.
Based on 14.7 fb−1 of e+e− annihilation data collected with the BESIII detector at the BEPCII collider at 17 different center-of-mass energies between 3.7730 GeV and 4.5995 GeV, Born cross sections of the two processes e+e−→pp¯η and e+e−→pp¯ω are measured for the first time. No indication of resonant production through a vector state V is observed, and upper limits on the Born cross sections of e+e−→V→pp¯η and e+e−→V→pp¯ω at the 90% confidence level are calculated for a large parameter space in resonance masses and widths. For the current world average parameters of the ψ(4230) of m=4.2187 GeV/c2 and Γ=44 MeV, we find upper limits on resonant production of the pp¯η and pp¯ω final states of 7.5 pb and 10.4 pb at the 90% CL, respectively.