18 research outputs found
Proton-Λ correlations in central Au+Au collisions at √s\u3csub\u3eNN\u3c/sub\u3e = 200 GeV
We report on p−Λ,p− ¯Λ¯ ,¯p¯−Λ, and ¯p¯− ¯Λ¯ correlation functions constructed in central Au-Au collisions at √sNN=200 GeV by the STAR experiment at RHIC. The proton and lambda source size is inferred from the p−Λ and p− ¯Λ¯; correlation functions. It is found to be smaller than the pion source size also measured by the STAR experiment at smaller transverse masses, in agreement with a scenario of a strong universal collective flow. The ¯p¯− Λ and p− ¯Λ¯ correlation functions, which are measured for the first time, exhibit a large anticorrelation. Annihilation channels and/or a negative real part of the spin-averaged scattering length must be included in the final-state interactions calculation to reproduce the measured correlation function
Transverse-momentum correlations on from mean- fluctuations in Au-Au collisions at 200 GeV
We present first measurements of the pseudorapidity and azimuth
bin-size dependence of event-wise mean transverse momentum
fluctuations for Au-Au collisions at GeV. We invert that
dependence to obtain autocorrelations on differences
interpreted to represent velocity/temperature
distributions on (). The general form of the autocorrelations
suggests that the basic correlation mechanism is parton fragmentation. The
autocorrelations vary strongly with collision centrality, which suggests that
fragmentation is strongly modified by a dissipative medium in the more central
Au-Au collisions relative to peripheral or p-p collisions. \\Comment: 7 pages, 3 figure
Identified hadron spectra at large transverse momentum in p+p and d+Au collisions at √sNN = 200 GeV
We present the transverse momentum (pT) spectra for identified charged pions, protons and anti-protons from p+p and d+Au collisions at . The spectra are measured around midrapidity (|y|/c with particle identification from the ionization energy loss and its relativistic rise in the time projection chamber and time-of-flight in STAR. The charged pion and proton + anti-proton spectra at high pT in p+p and d+Au collisions are in good agreement with a phenomenological model (EPOS) and with next-to-leading order perturbative quantum chromodynamic (NLO pQCD) calculations with a specific fragmentation scheme and factorization scale. We found that all proton, anti-proton and charged pion spectra in p+p collisions follow xT-scaling for the momentum range where particle production is dominated by hard processes (pT≳2 GeV/c). The nuclear modification factor around midrapidity is found to be greater than unity for charged pions and to be even larger for protons at 2T/c
Energy dependence of charged pion, proton and anti-proton transverse momentum spectra for Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV
We study the energy dependence of the transverse momentum (pT) spectra for
charged pions, protons and anti-protons for Au+Au collisions at \sqrt{s_NN} =
62.4 and 200 GeV. Data are presented at mid-rapidity (|y| < 0.5) for 0.2 < pT <
12 GeV/c. In the intermediate pT region (2 < pT < 6 GeV/c), the nuclear
modification factor is higher at 62.4 GeV than at 200 GeV, while at higher pT
(pT >7 GeV/c) the modification is similar for both energies. The p/pi+ and
pbar/pi- ratios for central collisions at \sqrt{s_NN} = 62.4 GeV peak at pT ~ 2
GeV/c. In the pT range where recombination is expected to dominate, the p/pi+
ratios at 62.4 GeV are larger than at 200 GeV, while the pbar/pi- ratios are
smaller. For pT > 2 GeV/c, the pbar/pi- ratios at the two beam energies are
independent of pT and centrality indicating that the dependence of the pbar/pi-
ratio on pT does not change between 62.4 and 200 GeV. These findings challenge
various models incorporating jet quenching and/or constituent quark
coalescence.Comment: 19 pages and 6 figure
Transverse-momentum p\u3csub\u3et\u3c/sub\u3e correlations on (η,ϕ) from mean-p\u3csub\u3et\u3c/sub\u3e fluctuations in Au–Au collisions at √s\u3csub\u3eNN\u3c/sub\u3e = 200 GeV
We present first measurements of the pseudorapidity and azimuth (η, ϕ) binsize dependence of event-wise mean transverse-momentum ⟨pt⟩ fluctuations for Au–Au collisions at √sNN = 200 GeV. We invert that dependence to obtain pt autocorrelations on differences (η∆, ϕ∆) interpreted to represent velocity/temperature distributions on (η, ϕ). The general form of the autocorrelations suggests that the basic correlation mechanism is parton fragmentation. The autocorrelations vary rapidly with collision centrality, which suggests that fragmentation is strongly modified by a dissipative medium in the more central Au–Au collisions relative to peripheral or p–p collisions
Forward Neutral Pion Production in p + p and d + Au Collisions at √ sNN = 200 GeV
Measurements of the production of forward π0 mesons from p+p and d+Au collisions at √sNN=200 GeV are reported. The p+p yield generally agrees with next-to-leading order perturbative QCD calculations. The d+Au yield per binary collision is suppressed as η increases, decreasing to ∼30% of the p+p yield at ⟨η⟩=4.00, well below shadowing expectations. Exploratory measurements of azimuthal correlations of the forward π0 with charged hadrons at η≈0 show a recoil peak in p+p that is suppressed in d+Au at low pion energy. These observations are qualitatively consistent with a saturation picture of the low-x gluon structure of heavy nuclei
Hadronization geometry from net-charge angular correlations on momentum subspace () in Au-Au collisions at GeV
We present the first measurements of charge-dependent correlations on angular
difference variables (pseudorapidity) and
(azimuth) for primary charged hadrons with transverse momentum GeV/ and from Au-Au collisions at GeV. We observe correlation structures not predicted by theory but
consistent with evolution of hadron emission geometry with increasing
centrality from one-dimensional fragmentation of color strings along the beam
direction to an at least two-dimensional hadronization geometry along the beam
and azimuth directions of a hadron-opaque bulk medium.Comment: 8 pages, 4 figure
Cosmoglobe DR1 results. II. Constraints on isotropic cosmic birefringence from reprocessed WMAP and Planck LFI data
International audienceCosmic birefringence is a parity-violating effect that might have rotated the plane of linearly polarized light of the cosmic microwave background (CMB) by an angle since its emission. This has recently been measured to be non-zero at a statistical significance of in the official Planck PR4 and 9-year WMAP data. In this work, we constrain using the reprocessed BeyondPlanck LFI and Cosmoglobe DR1 WMAP polarization maps. These novel maps have both lower systematic residuals and a more complete error description than the corresponding official products. Foreground correlations could bias measurements of , and while thermal dust emission has been argued to be statistically non-zero, no evidence for synchrotron power has been reported. Unlike the dust-dominated Planck HFI maps, the majority of the LFI and WMAP polarization maps are instead dominated by synchrotron emission. Simultaneously constraining and the polarization miscalibration angle, , of each channel, we find a best-fit value of with LFI and WMAP data only. When including the Planck HFI PR4 maps, but fitting separately for dust-dominated, , and synchrotron-dominated channels, , we find . This differs from zero with a statistical significance of , and the main contribution to this value comes from the LFI 70 GHz channel. While the statistical significances of these results are low on their own, the measurement derived from the LFI and WMAP synchrotron-dominated maps agrees with the previously reported HFI-dominated constraints, despite the very different astrophysical and instrumental systematics involved in all these experiments
Cosmoglobe DR1 results. II. Constraints on isotropic cosmic birefringence from reprocessed WMAP and Planck LFI data
International audienceCosmic birefringence is a parity-violating effect that might have rotated the plane of linearly polarized light of the cosmic microwave background (CMB) by an angle since its emission. This has recently been measured to be non-zero at a statistical significance of in the official Planck PR4 and 9-year WMAP data. In this work, we constrain using the reprocessed BeyondPlanck LFI and Cosmoglobe DR1 WMAP polarization maps. These novel maps have both lower systematic residuals and a more complete error description than the corresponding official products. Foreground correlations could bias measurements of , and while thermal dust emission has been argued to be statistically non-zero, no evidence for synchrotron power has been reported. Unlike the dust-dominated Planck HFI maps, the majority of the LFI and WMAP polarization maps are instead dominated by synchrotron emission. Simultaneously constraining and the polarization miscalibration angle, , of each channel, we find a best-fit value of with LFI and WMAP data only. When including the Planck HFI PR4 maps, but fitting separately for dust-dominated, , and synchrotron-dominated channels, , we find . This differs from zero with a statistical significance of , and the main contribution to this value comes from the LFI 70 GHz channel. While the statistical significances of these results are low on their own, the measurement derived from the LFI and WMAP synchrotron-dominated maps agrees with the previously reported HFI-dominated constraints, despite the very different astrophysical and instrumental systematics involved in all these experiments
Cosmoglobe DR1 results. II. Constraints on isotropic cosmic birefringence from reprocessed WMAP and Planck LFI data
International audienceCosmic birefringence is a parity-violating effect that might have rotated the plane of linearly polarized light of the cosmic microwave background (CMB) by an angle since its emission. This has recently been measured to be non-zero at a statistical significance of in the official Planck PR4 and 9-year WMAP data. In this work, we constrain using the reprocessed BeyondPlanck LFI and Cosmoglobe DR1 WMAP polarization maps. These novel maps have both lower systematic residuals and a more complete error description than the corresponding official products. Foreground correlations could bias measurements of , and while thermal dust emission has been argued to be statistically non-zero, no evidence for synchrotron power has been reported. Unlike the dust-dominated Planck HFI maps, the majority of the LFI and WMAP polarization maps are instead dominated by synchrotron emission. Simultaneously constraining and the polarization miscalibration angle, , of each channel, we find a best-fit value of with LFI and WMAP data only. When including the Planck HFI PR4 maps, but fitting separately for dust-dominated, , and synchrotron-dominated channels, , we find . This differs from zero with a statistical significance of , and the main contribution to this value comes from the LFI 70 GHz channel. While the statistical significances of these results are low on their own, the measurement derived from the LFI and WMAP synchrotron-dominated maps agrees with the previously reported HFI-dominated constraints, despite the very different astrophysical and instrumental systematics involved in all these experiments