1,722,257 research outputs found
Coherent diffractive photoproduction of {\ensuremath{\rho}}^{0} mesons on gold nuclei at 200 GeV/nucleon-pair at the Relativistic Heavy Ion Collider
No full textThe STAR Collaboration reports on the photoproduction of π+π− pairs in gold-gold collisions at a center-of-mass energy of 200 GeV/nucleon-pair. These pion pairs are produced when a nearly real photon emitted by one ion scatters from the other ion
Charge-dependent pair correlations relative to a third particle in + Au and + Au collisions at RHIC
No full textQuark interactions with topological gluon configurations can induce chirality imbalance and local parity violation in quantum chromodynamics. This can lead to electric charge separation along the strong magnetic field in relativistic heavy-ion collisions - the chiral magnetic effect (CME). We report measurements by the STAR collaboration of a CME-sensitive observable in +Au and +Au collisions at 200 GeV, where the CME is not expected, using charge-dependent pair correlations relative to a third particle. We observe strong charge-dependent correlations similar to those measured in heavy-ion collisions. This bears important implications for the interpretation of the heavy-ion data
Methods for a blind analysis of isobar data collected by the STAR collaboration
No full textIn 2018, the STAR collaboration collected data from {44}^{96}Ru+_{44}^{96}Ru and {40}^{96}Zr+_{40}^{96}Zr at sqrt{s_{NN}}=200 GeV to search for the presence of the chiral magnetic effect in collisions of nuclei. The isobar collision species alternated frequently between {44}^{96}Ru+_{44}^{96}Ru and {40}^{96}Zr+_{40}^{96}Zr. In order to conduct blind analyses of studies related to the chiral magnetic effect in these isobar data, STAR developed a three-step blind analysis procedure. Analysts are initially provided a "reference sample" of data, comprised of a mix of events from the two species, the order of which respects time-dependent changes in run conditions. After tuning analysis codes and performing time-dependent quality assurance on the reference sample, analysts are provided a species-blind sample suitable for calculating efficiencies and corrections for individual approx30-minute data-taking runs. For this sample, species-specific information is disguised, but individual output files contain data from a single isobar species. Only run-by-run corrections and code alteration subsequent to these corrections are allowed at this stage. Following these modifications, the "frozen" code is passed over the fully un-blind data, completing the blind analysis. As a check of the feasibility of the blind analysis procedure, analysts completed a "mock data challenge," analyzing data from Au+Au collisions at sqrt{s_{NN}}=27 GeV, collected in 2018. The Au+Au data were prepared in the same manner intended for the isobar blind data. The details of the blind analysis procedure and results from the mock data challenge are presented
Evidence for Nonlinear Gluon Effects in QCD and Their Mass Number Dependence at STAR
No full textThe STAR Collaboration reports measurements of back-to-back azimuthal correlations of di-0s produced at forward pseudorapidities (2.6 \u3c \u3c 4.0) in +, +Al, and +Au collisions at a center-of-mass energy of 200 GeV. We observe a clear suppression of the correlated yields of back-to-back 0 pairs in +Al and +Au collisions compared to the + data. The observed suppression of back-to-back pairs as a function of transverse momentum suggests nonlinear gluon dynamics arising at high parton densities. The larger suppression found in +Au relative to +Al collisions exhibits a dependence of the saturation scale 2/ on the mass number . A linear scaling of the suppression with 1/3 is observed with a slope of −0.09 ±0.01
Rapidity correlations in the RHIC Beam Energy Scan Data
No full textA pair-normalized two-particle covariance versus the rapidity of the two particles, called R2, was originally studied in ISR and FNAL data in the 1970's. This variable has recently seen renewed interest for the study of the dynamics of heavy-ion collisions in the longitudinal direction. These rapidity correlations can be decomposed into a basis set of Legendre polynomials with prefactors (amn), which can be considered the rapidity analog of the decomposition of azimuthal anisotropies into a set of cosine functions with prefactors vn. The (amn) values have been suggested to be sensitive to the number of particle emitting sources, baryon stopping, viscosities, and critical behavior. The rapidity correlations have been measured by the STAR collaboration as a function of the beam energy for 0–5% central Au+Au collisions with beam energies ranging from 7.7 to 200 GeV. The experimental results and comparisons to the UrQMD model are presented
Longitudinal double-spin asymmetries for {\ensuremath{\pi}}^{0}\mathrm{s} in the forward direction for 510 GeV polarized collisions
No full textThe STAR Collaboration reports measurements of the longitudinal double-spin asymmetry, ALL, for neutral pions produced at forward directions in polarized proton-proton collisions, at a center-of-mass energy of 510 GeV. Results are given for transverse momenta in the range 2<pT<10 GeV/c within two regions of pseudorapidity that span 2.65<η<3.9. These results are sensitive to the polarized gluon parton distribution function, Δg(x), down to the region of Bjorken x∼10−3. The asymmetries observed are less than ±5×10−3 in magnitude and will help constrain the contribution to the spin of the proton from polarized gluons at low x, when combined with other measurements as part of a global analysis
Measurement of the _{\mathrm{\ensuremath{\Lambda}}}^{3}\mathrm{H} lifetime in Au+Au collisions at the BNL Relativistic Heavy Ion Collider
No full textAn improved measurement of the 3ΛH lifetime is presented. In this paper, the mesonic decay modes 3ΛH→3He + π− and 3ΛH→d+p+π− are used to reconstruct the 3ΛH from Au+Au collision data collected by the STAR collaboration at Relativistic Heavy Ion Collider (RHIC). A minimum χ2 estimation is used to determine the lifetime of τ=142+24−21(stat.)±29(syst.) ps. This lifetime is about 50% shorter than the lifetime τ=263±2 ps of a free Λ, indicating strong hyperon-nucleon interaction in the hypernucleus system. The branching ratios of the mesonic decay channels are also determined to satisfy B.R.(3He+π−)/(B.R.(3He+π−)+B.R.(d+p+π−))=0.32±0.05(stat.)±0.08(syst.). Our ratio result favors the assignment J(3ΛH)=12 over J(3ΛH)=32. These measurements will help to constrain models of hyperon-baryon interactions
Evidence for Nonlinear Gluon Effects in QCD and Their Mass Number Dependence at STAR
No full textThe 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 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. A linear scaling of the suppression with A1/3 is observed with a slope of −0.09±0.01
Three-Pion Hanbury Brown–Twiss Correlations in Relativistic Heavy-Ion Collisions from the STAR Experiment
Full text linkData from the first physics run at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory, Au+Au collisions at √sNN=130 GeV, have been analyzed by the STAR Collaboration using three-pion correlations with charged pions to study whether pions are emitted independently at freeze-out. We have made a high-statistics measurement of the three-pion correlation function and calculated the normalized three-particle correlator to obtain a quantitative measurement of the degree of chaoticity of the pion source. It is found that the degree of chaoticity seems to increase with increasing particle multiplicity
Measurement of the mass difference and the binding energy of the hypertriton and antihypertriton
No full textThe STAR collaboration reports a measurement of the mass difference and binding energy of the hypertriton and its antiparticle. This work constrains the hyperon–nucleon interaction and allows us to test the CPT theorem in a nucleus with strangeness
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