We present results for the ratios of mean (MB), variance (σB2), skewness (SB) and kurtosis (κB) of net baryon-number fluctuations obtained in lattice QCD calculations with physical values of light ...and strange quark masses. Using next-to-leading order Taylor expansions in baryon chemical potential we find that qualitative features of these ratios closely resemble the corresponding experimentally measured cumulant ratios of net proton-number fluctuations for beam energies down to sNN≥19.6 GeV. We show that the difference in cumulant ratios for the mean net baryon-number, MB/σB2=χ1B(T,μB)/χ2B(T,μB), and the normalized skewness, SBσB=χ3B(T,μB)/χ2B(T,μB), naturally arises in QCD thermodynamics. Moreover, we establish a close relation between skewness and kurtosis ratios, SBσB3/MB=χ3B(T,μB)/χ1B(T,μB) and κBσB2=χ4B(T,μB)/χ2B(T,μB), valid at small values of the baryon chemical potential.
We report on the first lattice calculation of the QCD phase transition using chiral fermions with physical quark masses. This calculation uses 2+1 quark flavors, spatial volumes between (4 fm)(3) and ...(11 fm)(3) and temperatures between 139 and 196 MeV. Each temperature is calculated at a single lattice spacing corresponding to a temporal Euclidean extent of N(t) = 8. The disconnected chiral susceptibility, χ(disc) shows a pronounced peak whose position and height depend sensitively on the quark mass. We find no metastability near the peak and a peak height which does not change when a 5 fm spatial extent is increased to 10 fm. Each result is strong evidence that the QCD "phase transition" is not first order but a continuous crossover for m(π) = 135 MeV. The peak location determines a pseudocritical temperature T(c) = 155(1)(8) MeV, in agreement with earlier staggered fermion results. However, the peak height is 50% greater than that suggested by previous staggered results. Chiral SU(2)(L) × SU(2)(R) symmetry is fully restored above 164 MeV, but anomalous U(1)(A) symmetry breaking is nonzero above T(c) and vanishes as T is increased to 196 MeV.
Using combined data from the Relativistic Heavy Ion and Large Hadron Colliders, we constrain the shear and bulk viscosities of quark-gluon plasma (QGP) at temperatures of ∼ 150 – 350 MeV . We use ...Bayesian inference to translate experimental and theoretical uncertainties into probabilistic constraints for the viscosities. With Bayesian model averaging we propagate an estimate of the model uncertainty generated by the transition from hydrodynamics to hadron transport in the plasma's final evolution stage, providing the most reliable phenomenological constraints to date on the QGP viscosities.
Equation of state in ( 2 + 1 )-flavor QCD Bazavov, A.; Bhattacharya, Tanmoy; DeTar, C. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
11/2014, Letnik:
90, Številka:
9
Journal Article
Recenzirano
Odprti dostop
We present results for the equation of state in (2 + 1)-flavor QCD using the highly improved staggered quark action and lattices with temporal extent N sub(tau) = 6, 8, 10, and 12. We show that these ...data can be reliably extrapolated to the continuum limit and obtain a number of thermodynamic quantities and the speed of sound in the temperature range 130-400 MeV. We compare our results with previous calculations and provide an analytic parameterization of the pressure, from which other thermodynamic quantities can be calculated, for use in phenomenology. We show that the energy density in the crossover region, 145 MeV < or = T < or = 163 MeV, defined by the chiral transition, is varepsilonc = (0.18-0.5) GeV /fm super(3), i.e., (1.2-3.1) varepsilon sub(nuclear). At high temperatures, we compare our results with resummed and dimensionally reduced perturbation theory calculations. As a byproduct of our analyses, we obtain the values of the scale parameters r sub(0) from the static quark potential and w sub(0) from the gradient flow.
The detection of special nuclear materials (SNM) in commercial cargoes is a major objective in the field of nuclear security. In this work we investigate the use of two-neutron time-correlations from ...photo-fission using the Prompt Neutrons from Photofission (PNPF) detectors in Passport Systems Inc.’s (PSI) Shielded Nuclear Alarm Resolution (SNAR) platform for the purpose of detecting ∼5 kg quantities of fissionable materials in seconds. The goal of this effort was to extend the secondary scan mode of this system to differentiate fissile materials, such as highly enriched uranium, from fissionable materials, such as low enriched and depleted uranium (LEU and DU). Experiments were performed using a variety of material samples, and data were analyzed using the variance-over-mean technique referred to as Y2F or Feynman-α. Results were compared to computational models to improve our ability to predict system performance for distinguishing fissile materials. Simulations were then combined with empirical formulas to generate receiver operating characteristics (ROC) curves for a variety of shielding scenarios. We show that a 10 second screening with a 200 μA 9 MeV X-ray beam is sufficient to differentiate kilogram quantities of HEU from DU in various shielding scenarios in a standard cargo container.
PHENIX beam energy scan results Soltz, R.A.
Nuclear physics. A,
November 2014, 2014-11-00, 2014-11-01, Letnik:
931, Številka:
C
Journal Article
Recenzirano
Odprti dostop
We present results from the PHENIX Experiment for Au+Au collisions with sNN=7.9,19.6,27,39,62, and 200 GeV. Measurements of the charged particle multiplicity at central rapidity scale linearly with ...the number of participant quarks for sNN=62 GeV and above; for sNN=27 GeV and below the multiplicity scales with the number of participant nucleons. For the HBT radii we perform a linear interpolation for radii from PHENIX, STAR, and ALICE to a mT=0.26 GeV and calculate ratios and differences in quadrature at this value of the transverse mass. We observe a non-monotonic behavior near sNN=19 GeV in the form of a peak in Ro2−Rs2 and a dip in (Rs−2R¯)/Rl.
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