Nuclear Theory·nucl-th

Friday·March 1, 2019

13 papers—6 primary·7 cross-listed

07
Chiral imbalance in hadron matter : its manifestation in photon polarization asymmetries
A.A.Andrianov🇷🇺 · V.A.Andrianov🇷🇺 · D.Espriu🇪🇸 · A.V.Iakubovich🇷🇺 · A.E.Putilova🇷🇺
The possibility of the formation of a local parity breaking (LPB) in a quark-hadron medium is examined as a result of chiral symmetry violation, i.e, the appearance of difference between the average densities of right- and left-handed quarks in the fireball after heavy-ion collisions (HIC). Using the effective meson Lagrangian motivated by QCD extended to the chiral medium the properties of light scalar and pseudoscalar mesons are analyzed. It is establish that exotic decays of scalar mesons arise due to mixing of $π$ and $a_{0}$ vacuum states in the presence of chiral imbalance. The pion electromagnetic formfactor obtains a parity-odd supplement which generates a photon polarization asymmetry in pion polarizability. We conjecture that the above-mentioned properties of LPB can be revealed in experiments on LHC, RHIC, FAIR and NICA accelerators.
↳ hep-phnucl-thPhys.Part.Nucl.Lett.(2019)·3 citations
08
Finite-temperature extension for cold neutron star equations of state
Carolyn A. Raithel · Feryal Ozel · Dimitrios Psaltis
Observations of isolated neutron stars place constraints on the equation of state (EOS) of cold, neutron-rich matter, while nuclear physics experiments probe the EOS of hot, symmetric matter. Many dynamical phenomena, such as core-collapse supernovae, the formation and cooling of proto-neutron stars, and neutron star mergers, lie between these two regimes and depend on the EOS at finite temperatures for matter with varying proton fractions. In this paper, we introduce a new framework to accurately calculate the thermal pressure of neutron-proton-electron matter at arbitrary density, temperature, and proton fraction. This framework can be expressed using a set of five physically-motivated parameters that span a narrow range of values for realistic EOS and are able to capture the leading-order effects of degenerate matter on the thermal pressure. We base two of these parameters on a new approximation of the Dirac effective mass, with which we reproduce the thermal pressure to within <~30% for a variety of realistic EOS at densities of interest. Three additional parameters, based on the behavior of the symmetry energy near the nuclear saturation density, allow for the extrapolation of any cold EOS in beta-equilibrium to arbitrary proton fractions. Our model thus allows a user to extend any cold nucleonic EOS, including piecewise-polytropes, to arbitrary temperature and proton fraction, for use in calculations and numerical simulations of astrophysical phenomena. We find that our formalism is able to reproduce realistic finite-temperature EOS with errors of <~20% and offers a 1-3 orders-of-magnitude improvement over existing ideal-fluid models.
↳ astro-ph.HEnucl-thApJ(2019)·88 citations
09
Nature of the $Y (4260)$ : A light-quark perspective
Yun-Hua Chen🇨🇳 · Ling-Yun Dai🇨🇳 · Feng-Kun Guo🇨🇳 · Bastian Kubis🇩🇪
The $Y (4260)$ has been one of the most puzzling pieces among the so-called $X Y Z$ states. In this paper, we try to gain insights into the structure of the $Y (4260)$ from the light-quark perspective. We study the dipion invariant mass spectrum of the $e^{+} e^{-} \to Y (4260) \to J / ψ π^{+} π^{-}$ process and the ratio of the cross sections $σ (e^{+} e^{-} \to J / ψ K^{+} K^{-}) / σ (e^{+} e^{-} \to J / ψ π^{+} π^{-})$ . In particular, we consider the effects of different light-quark SU(3) eigenstates inside the $Y (4260)$ . The strong pion-pion final-state interactions as well as the $K K ˉ$ coupled channel in the $S$ -wave are taken into account in a model-independent way using dispersion theory. We find that the SU(3) octet state plays a significant role in these transitions, implying that the $Y (4260)$ contains a large light-quark component. Our findings suggest that the $Y (4260)$ is neither a hybrid nor a conventional charmonium state, and they are consistent with the $Y (4260)$ having a sizeable $D ˉ D_{1}$ component which, however, is not completely dominant.
↳ hep-phhep-exnucl-thPRD(2019)·44 citations
10
Generalized Crossover in Interacting Fermions within the Low-Energy Expansion
Hiroyuki Tajima
We generalize the Bardeen-Cooper-Schrieffer-Bose-Einstein-condensation (BCS-BEC) crossover of two-component fermions, which is realized by tuning the $s$ -wave scattering length $a$ between the fermions, to the case of an arbitrary effective range $r_{e}$ . By using the Nozières-Schmitt-Rink (NSR) approach, we show another crossover by changing $r_{e}$ and present several similarities and differences between these two crossovers. Furthermore, the region ( $r_{e} > a /2$ ) where the effective range expansion breaks down and the Hamiltonian becomes non-Hermitian is found, being consistent with the Wigner's causality bound. Our results are universal for low-density interacting fermions with low-energy constants $a$ and $r_{e}$ and are directly relevant to ultracold Fermi atomic gases as well as dilute neutron matter.
↳ cond-mat.quant-gasnucl-thJ.Phys.Soc.Jap.(2019)·6 citations
11
Determination of the quark-gluon string parameters from the data on pp, pA and AA collisions at wide energy range using Bayesian Gaussian Process Optimization
Vladimir Kovalenko (Saint Petersburg State University)🇷🇺
Bayesian Gaussian Process Optimization can be considered as a method of the determination of the model parameters, based on the experimental data. In the range of soft QCD physics, the processes of hadron and nuclear interactions require using phenomenological models containing many parameters. In order to minimize the computation time, the model predictions can be parameterized using Gaussian Process regression, and then provide the input to the Bayesian Optimization. In this paper, the Bayesian Gaussian Process Optimization has been applied to the Monte Carlo model with string fusion. The parameters of the model are determined using experimental data on multiplicity and cross section of pp, pA and AA collisions at wide energy range. The results provide important constraints on the transverse radius of the quark-gluon string ( $r_{s t r}$ ) and the mean multiplicity per rapidity from one string ( $μ_{0}$ ).
↳ physics.data-anhep-phnucl-thPoS(2019)·1 citation
12
Shape staggering of mid-shell mercury isotopes from in-source laser spectroscopy compared with Density Functional Theory and Monte Carlo Shell Model calculations
S. Sels🇧🇪 · T. Day Goodacre🇬🇧 · B. A. Marsh🇨🇭 · A. Pastore🇬🇧 · W. Ryssens🇫🇷 · Y. Tsunoda🇯🇵 · N. Althubiti🇬🇧 · B. Andel🇸🇰 · A. N. Andreyev🇬🇧 · D. Atanasov🇩🇪 · A. E. Barzakh🇷🇺 · M. Bender🇫🇷 and 36 other authors
Neutron-deficient $^{177 - 185}$ Hg isotopes were studied using in-source laser resonance-ionization spectroscopy at the CERN-ISOLDE radioactive ion-beam facility, in an experiment combining different detection methods tailored to the studied isotopes. These include either alpha-decay tagging or Multi-reflection Time-of-Flight gating to identify the isotopes of interest. The endpoint of the odd-even nuclear shape staggering in mercury was observed directly by measuring for the first time the isotope shifts and hyperfine structures of $^{177 - 180}$ Hg. Changes in the mean-square charge radii for all mentioned isotopes, magnetic dipole and electric quadrupole moments of the odd-A isotopes and arguments in favor of $I = 7/2$ spin assignment for $^{177, 179}$ Hg were deduced. Experimental results are compared with Density Functional Theory (DFT) and Monte-Carlo Shell Model (MCSM) calculations. DFT calculations with several Skyrme parameterizations predict a large jump in the charge radius around the neutron $N = 104$ mid shell, with an odd-even staggering pattern related to the coexistence of nearly-degenerate oblate and prolate minima. This near-degeneracy is highly sensitive to many aspects of the effective interaction, a fact that renders perfect agreement with experiment out of reach for current functionals. Despite this inherent diffculty, the SLy5s1 and a modified UNEDF1^{SO} parameterization predict a qualitatively correct staggering that is off by two neutron numbers. MCSM calculations of states with the experimental spins and parities show good agreement for both electromagnetic moments and the observed charge radii. A clear mechanism for the origin of shape staggering within this context is identified: a substantial change in occupancy of the proton $π h_{9/2}$ and neutron $ν i_{13/2}$ orbitals.
↳ nucl-exnucl-thPRC(2019)·65 citations
13
Novel Method for Precisely Measuring the $X (3872)$ Mass
Feng-Kun Guo🇨🇳
The $X (3872)$ is the first and the most interesting one amongst the abundant $X Y Z$ states. Its mass coincides exactly with the $D^{0} D ˉ^{* 0}$ threshold with an uncertainty of 180 keV. Precise knowledge of its mass is crucial to understand the $X (3872)$ . However, whether it is above or below the $D^{0} D ˉ^{* 0}$ threshold is still unknown. We propose a completely new method to measure the $X (3872)$ mass precisely by measuring the $X (3872) γ$ line shape between 4010 and 4020 MeV, which is strongly sensitive to the $X (3872)$ mass relative to the $D^{0} D ˉ^{* 0}$ threshold due to a triangle singularity. This method can be applied to experiments which produce copious $D^{* 0} D ˉ^{* 0}$ pairs, such as electron-positron, proton-antiproton and other experiments, and may lead to much more precise knowledge about the $X (3872)$ mass.
↳ hep-phhep-exnucl-exnucl-thPRL(2019)·77 citations

Affiliations

first authorsco-authorsvia INSPIRE

Chiral imbalance in hadron matter : its manifestation in photon polarization asymmetries

Finite-temperature extension for cold neutron star equations of state

Nature of the Y(4260): A light-quark perspective

Generalized Crossover in Interacting Fermions within the Low-Energy Expansion

Determination of the quark-gluon string parameters from the data on pp, pA and AA collisions at wide energy range using Bayesian Gaussian Process Optimization

Shape staggering of mid-shell mercury isotopes from in-source laser spectroscopy compared with Density Functional Theory and Monte Carlo Shell Model calculations

Novel Method for Precisely Measuring the X(3872) Mass

Affiliations

Nature of the $Y (4260)$ : A light-quark perspective

Novel Method for Precisely Measuring the $X (3872)$ Mass