Nuclear Theory·nucl-th

Wednesday·January 23, 2019

23 papers—10 primary·13 cross-listed

01
Heavy-Flavor Theory at "Hard and Electromagnetic Probes 2018"
Ralf Rapp🇺🇸
An overview is given of the theoretical developments on heavy quarks and quarkonia in heavy-ion collisions as reported at the "Hard and EM Probes 2018" conference. Specifically, we address progress in the understanding of heavy-flavor diffusion and its hadronization, quarkonium transport and the extraction of quarkonium melting temperatures, energy loss of heavy quarks at high momentum, and their rescattering in small colliding systems.
nucl-thhep-phnucl-exPoS(2019)·3 citations
02
Role of pair-vibrational correlations in forming the odd-even mass difference
K. Neergård · I. Bentley
In the random-phase-approximation-amended (RPA-amended) Nilsson-Strutinskij method of calculating nuclear binding energies, the conventional shell correction terms derived from the independent-nucleon model and the Bardeen-Cooper-Schrieffer pairing theory are supplemented by a term which accounts for the pair-vibrational correlation energy. This term is derived by means of the RPA from a pairing Hamiltonian which includes a neutron-proton pairing interaction. The method was used previously in studies of the pattern of binding energies of nuclei with approximately equal numbers $N$ and $Z$ of neutrons and protons and even mass number $A = N + Z$ . Here it is applied to odd- $A$ nuclei. Three sets of such nuclei are considered: (i) The sequence of nuclei with $Z = N - 1$ and $25 \leq A \leq 99$ . (ii) The odd- $A$ isotopes of In, Sn, and Sb with $46 \leq N \leq 92$ . (iii) The odd- $A$ isotopes of Sr, Y, Zr, Nb, and Mo with $60 \leq N \leq 64$ . The RPA correction is found to contribute significantly to the calculated odd-even mass differences, particularly in the light nuclei. In the upper $s d$ shell this correction accounts for almost the entire odd-even mass difference for odd $Z$ and about half of it for odd $N$ . The size and sign of the RPA contribution varies, which is explained qualitatively in terms of a closed expression for a smooth RPA counter term.
nucl-thPRC(2019)·5 citations
03
Consistency Examinations of Calculations of Nuclear Matrix Elements of Double- $β$ Decay by QRPA
J. Terasaki🇨🇿
The neutrinoless double- $β$ decay is a hypothetical rare nuclear decay, which can be used for determining the neutrino-mass scale. The scheme to use this decay for determining the neutrino-mass scale is one of few limited methods possible to determine that. Nuclear matrix element of this decay is an important input to this method, and this matrix element cannot be determined by experiment. I examine the validity of the transition density used for calculating the nuclear matrix element by comparing the experimental data and my calculated result of the charge-change strength functions of $^{48}$ Ca and $^{48}$ Ti. The nuclear wave functions are obtained by the quasiparticle random-phase approximation. A new idea is proposed on the transition operator for this strength function, and the data of those nuclei are reproduced well consistently. Reduced half-life of a few nuclei to the neutrinoless double- $β$ decay are shown.
nucl-thhep-exnucl-exNucl.Theor.(2018)·0 citations
04
Determination of Strength of Isoscalar Pairing Interaction by a Mathematical Identity in QRPA
J. Terasaki🇨🇿
I propose a new method to determine the strength of the isoscalar proton-neutron pairing interaction by a mathematical identity derived in the quasiparticle random-phase approximation. This method is applied for a few nuclei possibly having the neutrinoless double- $β$ decay. Reduced half-life, the theoretical quantity necessary for determining the effective neutrino mass, is calculated for $^{48}$ Ca.
nucl-thnucl-ex0 citations
05
Paramagnetic squeezing of a uniformly expanding quark-gluon plasma in and out of equilibrium
N. Sadooghi🇮🇷 · S.M.A. Tabatabaee🇮🇷
The plasma of quarks and gluons created in ultrarelativistic heavy-ion collisions turns out to be paramagnetic. In the presence of a background magnetic field, this paramagnetism thus leads to a pressure anisotropy, similar to anisotropies appearing in a viscous fluid. In the present paper, we use this analogy, and develop a framework similar to anisotropic hydrodynamics, to take the pressure anisotropy caused, in particular, by the nonvanishing magnetization of a plasma of quarks and gluons into account. We consider the first two moments of the classical Boltzmann equation in the presence of an electromagnetic source in the relaxation-time approximation, and derive a set of coupled differential equations for the anisotropy parameter $ξ_{0}$ and the effective temperature $λ_{0}$ of an ideal fluid with nonvanishing magnetization. We also extend this method to a dissipative fluid with finite magnetization in the presence of a strong and dynamical magnetic field. We present a systematic method leading to the one-particle distribution function of this magnetized dissipative medium in a first-order derivative expansion, and arrive at analytical expressions for the shear and bulk viscosities in terms of the anisotropy parameter $ξ$ and effective temperature $λ$ . We then solve the corresponding differential equations for $(ξ_{0}, λ_{0})$ and $(ξ, λ)$ numerically, and determine, in this way, the proper time and temperature dependence of the energy density, directional pressures, speed of sound, and the magnetic susceptibility of a longitudinally expanding magnetized quark-gluon plasma in and out of equilibrium.
nucl-thcond-mat.str-elhep-lathep-phPRD(2019)·8 citations
06
Symmetry restoration in mean-field approaches
J.A. Sheikh🇮🇳 · J. Dobaczewski🇬🇧 · P. Ring🇩🇪 · L. M. Robledo🇪🇸 · C. Yannouleas🇺🇸
The mean-field approximation based on effective interactions or density functionals plays a pivotal role in the description of finite quantum many-body systems that are too large to be treated by ab initio methods. Some examples are strongly interacting medium and heavy mass atomic nuclei and mesoscopic condensed matter systems. In this approach, the linear Schrodinger equation for the exact many-body wave function is mapped onto a non-linear density-dependent one-body potential problem. This approximation, not only provides computationally very simple solutions even for systems with many particles, but due to the non-linearity, it also allows for obtaining solutions that break essential symmetries of the system, often connected with phase transitions. In this way, additional correlations are subsumed in the system. However, the mean-field approach suffers from the drawback that the corresponding wave functions do not have sharp quantum numbers and, therefore, many results cannot be compared directly with experimental data. In this article, we discuss general group-theory techniques to restore the broken symmetries, and provide detailed expressions on the restoration of translational, rotational, spin, isospin, parity and gauge symmetries, where the latter corresponds to the restoration of the particle number. In order to avoid the numerical complexity of exact projection techniques, various approximation methods available in the literature are examined. Applications of the projection methods are presented for simple nuclear models, realistic calculations in relatively small configuration spaces, nuclear energy density functional theory, as well as in other mesoscopic systems. Further, unresolved problems in the application of the symmetry restoration methods to the energy density functional theories are highlighted in the present work.
nucl-thcond-mat.othernucl-exJ.Phys.G(2021)·144 citations
07
Centrality dependence of the direct photon multiplicity in heavy ion collisions
Charles Gale🇨🇦 · Sangyong Jeon🇨🇦 · Scott McDonald🇨🇦 · Jean-François Paquet🇺🇸 · Chun Shen🇺🇸
Measurements indicate that the centrality dependence of the direct photon multiplicity scales approximately with the number of binary nucleon collisions. Importantly, these same measurements suggest that this scaling does not depend on the cutoff used to define the photon multiplicity. In this work we provide a theoretical perspective on these observations. We emphasize the importance of stronger experimental constraints, in particular for the cutoff independence of the centrality scaling. We highlight the importance of revisiting theoretical studies of jet-medium photons and of medium-modified prompt photons to clarify their contribution to the direct photon multiplicity, as well as the magnitude and direction of their momentum anisotropy.
nucl-thPoS(2019)·3 citations
08
Parton energy loss in the reformulated weakly-coupled kinetic approach
Tianyu Dai🇺🇸 · Steffen A. Bass🇺🇸 · Jean-François Paquet🇺🇸 · Derek Teaney🇺🇸
Interactions between hard partons and the quark-gluon plasma range from frequent soft interactions to rare hard scatterings. The larger number of soft interactions makes possible an effective stochastic description of parton-plasma interactions in terms of drag and diffusion transport coefficients. In this work, we present a numerical implementation that builds upon this systematic division between soft and hard parton-plasma interactions. We study the dependence of the single parton distribution on the cutoff between soft and hard parton-plasma interactions, both for small and phenomenological values of the strong coupling constant.
nucl-thhep-phPoS(2019)·1 citation
09
Nuclear coalescence from correlation functions
Kfir Blum🇮🇱 · Masahiro Takimoto🇮🇱
We derive a simple formula relating the cross section for light cluster production (defined via a coalescence factor) to the two-proton correlation function measured in heavy-ion collisions. The formula generalises earlier coalescence-correlation relations found by Scheibl & Heinz and by Mrowczynski for Gaussian source models. It motivates joint experimental analyses of Hanbury Brown-Twiss (HBT) and cluster yield measurements in existing and future data sets.
nucl-thhep-phnucl-exPRC(2019)·71 citations
10
Resonance states 0+ of the Boron isotope B8 from the Jost-matrix analysis of experimental data
S.A. Rakityansky · S.N. Ershov · T.J. Tshipi
The available R-matrix parametrization of experimental data on the excitation functions for the elastic and inelastic p-Be7 scattering at the collision energies up to 3.4 MeV is used to generate the corresponding partial-wave cross sections in the states with J^pi=0+. Thus obtained data are considered as experimental partial cross sections and are fitted using the semi-analytic two-channel Jost matrix with proper analytic structure and some adjustable parameters. Then the spectral points are sought as zeros of the Jost matrix determinant (which correspond to the S-matrix poles) at complex energies. The correct analytic structure makes it possible to calculate the fitted Jost matrix on any sheet of the Riemann surface whose topology involves not only the square-root but also the logarithmic branching caused by the Coulomb interaction. In this way, two overlapping 0+ resonances at the excitation energies ~1.79 MeV and ~1.96 MeV have been found.
nucl-thIJMPE(2019)·5 citations

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