Nuclear Theory·nucl-th

Monday·August 31, 2015

9 papers—3 primary·6 cross-listed

01
[Submitted on 27 Aug 2015]
Towards a Deeper Understanding of How Experiments Constrain the Underlying Physics of Heavy-Ion Collisions
Evan Sangaline🇺🇸 · Scott Pratt🇺🇸
Recent work has provided the means to rigorously determine properties of super-hadronic matter from experimental data through the application of broad scale modeling of high-energy nuclear collisions within a Bayesian framework. These studies have provided unprecedented statistical inferences about the physics underlying nuclear collisions by virtue of simultaneously considering a wide range of model parameters and experimental observables. Notably, this approach has been used to constrain both the QCD equation of state and the shear viscosity above the quark-hadron transition. Although the inferences themselves have a clear meaning, the complex nature of the relationships between model parameters and observables have remained relatively obscure. We present here a novel extension of the standard Bayesian Markov Chain Monte Carlo approach that allows for the quantitative determination of how inferences of model parameters are driven by experimental measurements and their uncertainties. This technique is then applied in the context of heavy ion collisions in order to explore previous results in greater depth. The resulting relationships are useful for identifying model weaknesses, prioritizing future experimental measurements, and most importantly: developing an intuition for the role that different observables play in constraining our understanding of the underlying physics.
Comments:
14 pages, 5 figures (Figure 4 replaced in new version with correct figure)
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1508.07017 [pdf]
PRC(2016)·80 citations
02
[Submitted on 27 Aug 2015]
Production of Charge in Heavy Ion Collisions
Scott Pratt🇺🇸 · William Patrick McCormack🇺🇸 · Claudia Ratti🇺🇸
By analyzing preliminary experimental measurements of charge-balance functions from the STAR Collaboration at the Relativistic-Heavy-Ion Collider (RHIC), it is found that pictures where balancing charges are produced in a single surge, and therefore separated by a single length scale, are inconsistent with data. In contrast, a model that assumes two surges, one associated with the formation of a thermalized quark-gluon plasma and a second associated with hadronization, provides a far superior reproduction of the data. A statistical analysis of the model comparison finds that the two-surge model best reproduces the data if the charge production from the first surge is similar to expectations for equilibrated matter taken from lattice gauge theory. The charges created in the first surge appear to separate by approximately one unit of spatial rapidity before emission, while charges from the second wave appear to have separated by approximately a half unit or less.
Comments:
17 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1508.07031 [pdf]
PRC(2015)·32 citations
03
[Submitted on 28 Aug 2015]
Reducible chiral four-body interactions in nuclear matter
N. Kaiser · R. Milkus
The method of unitary transformations generates five classes of leading-order reducible chiral four-nucleon interactions which involve pion-exchanges and a spin-spin contact-term. Their first-order contributions to the energy per particle of isospin-symmetric nuclear matter and pure neutron matter are evaluated in detail. For most of the closed four-loop diagrams the occurring integrals over four Fermi-spheres can be reduced to easily manageable one- or two-parameter integrals. One observes substantial cancelations among the different contributions arising from 2-ring and 1-ring diagrams. Altogether, the net attraction generated by the chiral four-nucleon interaction does not exceed values of $- 1.3$ \,MeV for densities $ρ < 2 ρ_{0}$ .
Comments:
13 pages, 6 figures, submitted to European Physical Journal A
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1508.07323 [pdf]
EPJA(2016)·22 citations
04
[Submitted on 27 Aug 2015] (cross-list from hep-ph)
Electromagnetic Heavy Lepton Pair Production in Relativistic Heavy-Ion Collisions
M. Y. Sengul🇹🇷 · M. C. Guclu🇹🇷 · O. Mercan🇹🇷 · N. G. Karakus🇹🇷
We calculate the cross sections of electromagnetic productions of muon and tauon pair productions from the ultra-relativistic heavy ion collisions. Since the Compton wavelengths of muon and tauon are comparable to the radius of the colliding ions, nuclear form factors play important roles for calculating the cross sections. Recent measurement [1] indicates that the neutrons are differently distributed from the protons therefore this affects the cross section of the heavy lepton pair production. In order to see the effects of the neutron distributions in the nucleus, we used analytical expression of the Fourier transforms of the Wood-Saxon distribution. Cross section calculations show that Wood-Saxon distribution function is more sensitive to the parameter R compare to the parameter a.
Comments:
14 pages, 33 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1508.07051 [pdf]
EPJC(2016)·18 citations
05
[Submitted on 28 Aug 2015] (cross-list from hep-lat)
Lattice study on QCD-like theory with exact center symmetry
Takumi Iritani🇯🇵 · Etsuko Itou🇯🇵 · Tatsuhiro Misumi🇯🇵
We investigate QCD-like theory with exact center symmetry, with emphasis on the finite-temperature phase transition concerning center and chiral symmetries. On the lattice, we formulate center symmetric $S U (3)$ gauge theory with three fundamental Wilson quarks by twisting quark boundary conditions in a compact direction ( $Z_{3}$ -QCD model). We calculate the expectation value of Polyakov loop and the chiral condensate as a function of temperature on 16^3 x 4 and 20^3 x 4 lattices along the line of constant physics realizing $m_{P S} / m_{V} = 0.70$ . We find out the first-order center phase transition, where the hysteresis of the magnitude of Polyakov loop exists depending on thermalization processes. We show that chiral condensate decreases around the critical temperature in a similar way to that of the standard three-flavor QCD, as it has the hysteresis in the same range as that of Polyakov loop. We also show that the flavor symmetry breaking due to the twisted boundary condition gets qualitatively manifest in the high-temperature phase. These results are consistent with the predictions based on the chiral effective model in the literature. Our approach could provide novel insights to the nonperturbative connection between the center and chiral properties.
Comments:
25 pages, 6 figures, to apper in JHEP
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1508.07132 [pdf]
JHEP(2015)·38 citations
06
[Submitted on 28 Aug 2015] (cross-list from hep-ph)
The light scalar mesons as tetraquarks
Gernot Eichmann🇩🇪 · Christian S. Fischer🇩🇪 · Walter Heupel🇩🇪
We present a numerical solution of the four-quark Bethe-Salpeter equation for ground-state scalar tetraquarks with J^PC = 0^++. We find that the four-body equation dynamically generates pseudoscalar-meson poles in the Bethe-Salpeter amplitude. The resulting tetraquarks are genuine four-quark states that are dominated by pseudoscalar meson-meson correlations. Diquark-antidiquark contributions are subleading because of their larger mass scale. In the light quark sector, the sensitivity of the tetraquark wave function to the pion poles leads to an isoscalar tetraquark mass M_sigma ~ 350 MeV which is comparable to that of the sigma/f0(500). The masses of its multiplet partners kappa and a0/f0 follow a similar pattern. This provides support for a tetraquark interpretation of the light scalar meson nonet in terms of 'meson molecules'.
Comments:
7 pages, 4 figures; version accepted by PLB
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1508.07178 [pdf]
PLB(2016)·90 citations
07
[Submitted on 28 Aug 2015] (cross-list from hep-ph)
Thermalization, evolution and LHC observables in an integrated hydrokinetic model of A+A collisions
V.Yu. Naboka🇺🇦 · Iu.A. Karpenko🇺🇦 · Yu.M. Sinyukov🇺🇦
A further development of the evolutionary picture of A+A collisions, which we call the integrated HydroKinetic Model (iHKM), is proposed. The model comprises a generator of the initial state GLISSANDO, pre-thermal dynamics of A+A collisions leading to thermalization, subsequent relativistic viscous hydrodynamic expansion of quark-gluon and hadron medium (vHLLE), its particlization, and finally hadronic cascade ultrarelativistic QMD. We calculate mid-rapidity charged-particle multiplicities, pion, kaon, and antiproton spectra, charged-particle elliptic flows, and pion interferometry radii for Pb+Pb collisions at the energies available at the CERN Large Hadron Collider, $s = 2.76$ TeV, at different centralities. We find that the best description of the experimental data is reached when the initial states are attributed to the very small initial time 0.1 fm/c, the pre-thermal stage (thermalization process) lasts at least until 1 fm/c, and the shear viscosity at the hydrodynamic stage of the matter evolution has its minimal value, $η / s = \frac{1}{4 π}$ . At the same time it is observed that the various momentum anisotropies of the initial states, different initial and relaxation times, as well as even a treatment of the pre-thermal stage within just viscous or ideal hydrodynamic approach, leads sometimes to worse but nevertheless similar results, if the normalization of maximal initial energy density in most central events is adjusted to reproduce the final hadron multiplicity in each scenario. This can explain a good enough data description in numerous variants of hybrid models without a prethermal stage when the initial energy densities are defined up to a common factor.
Comments:
22 pages, 11 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1508.07204 [pdf]
PRC(2016)·28 citations
08
[Submitted on 27 Aug 2015] (cross-list from physics.plasm-ph)
Direct and secondary nuclear excitation with x-ray free-electron lasers
Jonas Gunst · Yuanbin Wu · Naveen Kumar · Christoph H. Keitel · Adriana Pálffy
The direct and secondary nuclear excitation produced by an x-ray free electron laser when interacting with a solid-state nuclear target is investigated theoretically. When driven at the resonance energy, the x-ray free electron laser can produce direct photoexcitation. However, the dominant process in that interaction is the photoelectric effect producing a cold and very dense plasma in which also secondary processes such as nuclear excitation by electron capture may occur. We develop a realistic theoretical model to quantify the temporal dynamics of the plasma and the magnitude of the secondary excitation therein. Numerical results show that depending on the nuclear transition energy and the temperature and charge states reached in the plasma, secondary nuclear excitation by electron capture may dominate the direct photoexcitation by several orders of magnitude, as it is the case for the 4.8 keV transition from the isomeric state of $^{93}$ Mo, or it can be negligible, as it is the case for the 14.4 keV Mössbauer transition in $^{57} Fe$ . These findings are most relevant for future nuclear quantum optics experiments at x-ray free electron laser facilities.
Comments:
17 pages, 7 figures; minor corrections made; accepted by Physics of Plasmas
Subjects:
Plasma Physics (physics.plasm-ph); Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph)
arXiv:
1508.07264 [pdf]
Phys.Plasmas(2015)·15 citations
09
[Submitted on 28 Aug 2015] (cross-list from hep-ph)
New physics effects on neutrinoless double beta decay from right-handed current
Shao-Feng Ge🇩🇪 · Manfred Lindner🇩🇪 · Sudhanwa Patra🇩🇪
We study the impact of new physics contributions to neutrinoless double beta decay arising from right-handed current in comparison with the standard mechanism. If the light neutrinos obtain their masses from Type-II seesaw within left-right symmetric model, where the Type-I contribution is suppressed to negligible extent, the right-handed PMNS matrix is the same as its left-handed counterpart, making it highly predictable and can be tested at next-generation experiments. It is very attractive, especially with recent cosmological constraint favoring the normal hierarchy under which the neutrinoless double beta decay is too small to be observed unless new physics appears as indicated by the recent diboson excess observed at ATLAS. The relative contributions from left- and right-handed currents can be reconstructed with the ratio between lifetimes of two different isotopes as well as the ratio of nuclear matrix elements. In this way, the theoretical uncertainties in the calculation of nuclear matrix elements can be essentially avoided. We also discuss the interplay of neutrinoless double beta decay measurements with cosmology, beta decay, and neutrino oscillation.
Comments:
10 pages, 5 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1508.07286 [pdf]
JHEP(2015)·51 citations

Affiliations

first authorsco-authorsvia INSPIRE