Nuclear Theory·nucl-th

Friday·March 25, 2022

10 papers—9 primary·1 cross-listed

01
Impact of event activity variable on the ratio of observables in isobar collisions
Jiangyong Jia🇺🇸 · Gang Wang🇺🇸 · Chunjian Zhang🇺🇸
The STAR isobar data of $^{96}$ Ru+ $^{96}$ Ru and $^{96}$ Zr+ $^{96}$ Zr collisions at $s_{NN} = 200$ GeV show that ratios of observables ( $R_{O}$ ) such as the multiplicity distribution, $p (N_{ch})$ , and the harmonic flow, $v_{n}$ , deviate from unity, when presented as a function of centrality, $c$ . These deviations have been attributed to the differences in the shape and radial profiles between $^{96}$ Ru and $^{96}$ Zr nuclei. In addition, the ratios $R_{O} (x)$ depend on the choice of the event activity variable $x$ , which could be either $N_{ch}$ or centrality. We estimate the difference $Δ R$ between these two choices, based on the published $p (N_{ch})$ , as well as those from a multiphase transport (AMPT) model with varied nuclear structure parameters: nuclear radius ( $R_{0}$ ), surface diffuseness ( $a_{0}$ ), quadrupole deformation ( $β_{2}$ ), and octupole deformation ( $β_{3}$ ). In contrary to $R_{v_{n}} (c)$ , $R_{v_{n}} (N_{ch})$ is nearly independent of the analysis approaches, suggesting that nonflow effects are better controlled by $N_{ch}$ than $c$ . The ratios of observables sensitive to the chiral magnetic effect (CME) are also much closer to unity for $x = N_{ch}$ than $x = c$ , indicating that the ratios calculated at the same $N_{ch}$ provide a better baseline for the non-CME background. According to the AMPT results, the dominant parameter for $Δ R$ is $a_{0}$ , while $R_{0}$ and $β_{n}$ are only important in central collisions. The published $p (N_{ch})$ is also used to estimate $Δ R_{⟨ p_{T} ⟩}$ for mean transverse momentum, which is non-negligible compared with $R_{⟨ p_{T} ⟩} - 1$ .
nucl-thhep-phnucl-exPLB(2022)·11 citations
02
Investigating Effects of Relativistic Kinematics, Dimensionality, Interactions, and Short-Range Correlations on the Ratio of Quartic over Quadratic Nuclear Symmetry Energies
Bao-Jun Cai · Bao-An Li
While ample evidence for the so-called empirical parabolic law of the Equation of State (EOS) of isospin asymmetric nuclear matter (ANM) has been obtained in many studies within both non-relativistic and relativistic nuclear many-body theories using various interactions, it has been unclear if there is any fundamental physics reason for the small quartic symmetry energy compared to the quadratic one even as the ANM approaches pure neutron matter. Within both relativistic and non-relativistic Free Fermi Gas (FFG) models in coordinate spaces of arbitrary dimension $d$ with and without considering Short-Range Correlations (SRC) as well as non-linear Relativistic Mean Field (RMF) models, we study effects of relativistic kinematics, dimensionality, interactions and SRC on the ratio $Ψ (ρ)$ of quartic over quadratic symmetry energies in ANM EOSs. We found that the ratio $Ψ (ρ)$ in the FFG model depends strongly on the dimension $d$ . While it is very small already in the normal 3D space, it could be even smaller in spaces with reduced dimensions for sub-systems of particles in heavy-ion reactions and/or whole neutron stars due to constraints, collectivities and/or symmetries. We also found that the ratio $Ψ (ρ)$ could theoretically become very large only at the ultra-relativistic limit far above the density reachable in neutron stars. On the other hand, nuclear interaction directly and/or indirectly through SRC-induced high-momentum nucleons affect significantly the density dependence of $Ψ (ρ)$ compared to the relativistic FFG model prediction. The SRC affects significantly not only the kinetic energy of symmetric nuclear matter but also the ratio $Ψ (ρ)$ while the relativistic corrections are found negligible. The results may help better understand the EOS of dense neutron-rich matter.
nucl-thastro-ph.HEnucl-exPRC(2022)·13 citations
03
A possible trial beyond the conventional random phase approximation for the su(2)-Lipkin model including the case of non-closed shell system
Y. Tsue (Kochi Univ., Japan) · C. Providencia (Univ. de Coimbra, Portugal) · J. da Providencia (Univ. de Coimbra, Portugal) · M. Yamamura (Kansai Univ., Japan)
Concerning the su(2)-Lipkin model, the calculation of the excitation energy to the 1st excited-state gives rise to the following fact: The two results based on the exact treatment and the conventional random phase approximation (RPA) are in unexpected disagreement. In order to remove this discrepancy, the conventional RPA is renewed. With the aim of this renewal, the terms, which cannot be dealt with in the conventional one, are estimated. The basic framework of this new form is not reorganized from that of the conventional one. In addition, the su(2)-Lipkin model itself is also modified so as to be applicable to the case with non-closed shell system. To this modification, one more su(2)-algebra, which has been already proposed by the present authors, is applied. Through the use of this algebra, the su(2)-Lipkin model is applicable to the case with any total fermion number permitted in the model.
nucl-thIJMPE(2022)·0 citations
04
Extended triaxial projected shell model approach for odd-neutron nuclei
S. Jehangir · Nazira Nazir · G. H. Bhat · J. A. Sheikh · N. Rather · S. Chakraborty · R. Palit
In an effort to elucidate the rich band structures observed in odd-neutron systems, triaxial projected shell model approach is extended to include three-quasineutron and five-quasiparticle configurations. This extension makes it possible to investigate the high-spin states up to and including the second band crossing. Detailed investigation has been performed for odd-mass Xe isotopes with the extended basis, and it is shown that character of the band crossing along the yrast line changes with shell filling of the 1h11/2 orbital. Further, it is observed that the three-quasiparticle state that crosses the ground-state configuration, leading to the normal band crossing phenomenon along the yrast line, first crosses the {\gamma} band based on the ground-state configuration at an earlier spin value. This crossing feature explains the occurrence of the signature inversion observed in the {\gamma} bands for some of the studied isotopes.
nucl-thPRC(2022)·14 citations
05
Deuteron VVCS and nuclear structure effects in muonic deuterium at N3LO in pionless EFT
Vadim Lensky🇩🇪 · Franziska Hagelstein🇩🇪 · Astrid Hiller Blin🇩🇪 · Vladimir Pascalutsa🇩🇪
We present our studies of the forward unpolarised doubly-virtual Compton scattering (VVCS) off the deuteron and the closely related two-photon-exchange ( $2 γ$ -exchange) corrections to the Lamb shift of muonic deuterium. The deuteron VVCS amplitude is calculated in the framework of pionless effective field theory, up to next-to-next-to-next-to-leading order (N3LO) for the longitudinal and next-to-leading order (NLO) for the transverse amplitude. The charge elastic form factor of the deuteron, obtained from the residue of the longitudinal VVCS amplitude, is used to extract the value of the single unknown two-nucleon one-photon contact coupling that enters the longitudinal amplitude at N3LO. The obtained deuteron VVCS amplitude serves as a high-precision model-independent input to examine the $2 γ$ -exchange corrections. Substantial differences with the recent dispersive evaluations are identified, namely, the elastic contribution appears to be larger by several standard deviations, thus ameliorating the current discrepancy between theory and experiment on the size of $2 γ$ -exchange effects. A correlation between the values of the deuteron charge and Friar radii is found that can be used to judge on the quality of a parametrisation of the deuteron charge elastic form factor. The discrepancy between the theory and the empirical result for the $2 γ$ -exchange correction in muonic deuterium appears to be completely eliminated. To further confirm this, we revisit the hydrogen-deuterium isotope shift in the same framework. Our work provides an alternative self-consistent and high-precision evaluation of the $2 γ$ -exchange correction in (muonic) deuterium.
nucl-thhep-phnucl-exPoS(2024)·1 citation
06
Two-neutrino double- $β$ decay in the mapped interacting boson model
Kosuke Nomura🇭🇷
A calculation of two-neutrino double- $β$ ( $2 ν β β$ ) decay matrix elements within the interacting boson model (IBM) that is based on the nuclear density functional theory is presented. The constrained self-consistent mean-field (SCMF) calculation using a universal energy density functional (EDF) and a pairing interaction provides potential energy surfaces with triaxial quadrupole degrees of freedom for even-even nuclei corresponding to the initial and final states of the $2 ν β β$ decays of interest. The SCMF energy surface is then mapped onto the bosonic one, and this procedure determines the IBM Hamiltonian for the even-even nuclei. The same SCMF calculation provides the essential ingredients of the interacting boson fermion-fermion model (IBFFM) for the intermediate odd-odd nuclei and the Gamow-Teller and Fermi transition operators. The EDF-based IBM and IBFFM provide a simultaneous description of excitation spectra and electromagnetic transition rates for each nucleus, and single- $β$ and $β β$ decay properties. The calculated $2 ν β β$ -decay nuclear matrix elements are compared with experiment and with those from earlier theoretical calculations.
nucl-thnucl-exPRC(2022)·22 citations
07
Theory of Halo Nuclei
H.-W. Hammer
Halo nuclei are characterized by a few weakly bound halo nucleons and a more tightly bound core. This separation of scales can be exploited in a few-body description of halo nuclei, since the detailed structure of the core is not resolved by the halo nucleons. We present an introduction to the effective (field) theory for low-energy properties of halo nuclei. The focus is on halos with S-wave interactions for which universal properties are most pronounced. The special role of the unitary limit is illustrated using the example of multineutron systems and the Efimov effect as a universal binding mechanism for halo nuclei. Connections to ultracold atoms and hadron physics are highlighted and extensions to higher partial waves, Coulomb forces and nuclear reactions are briefly touched upon.
nucl-th10 citations
08
Coriolis mixing of the K=1 and K=0 mixed symmetry states in the well deformed even-even nuclei
N. Yu. Shirikova · A. V. Sushkov · R. V. Jolos
The Coriolis matrix elements responsible for mixing of the $1^{+} K = 1$ and $1^{+} K = 0$ states are calculated in the framework of the Quasiparticle Phonon Model for several Gd and Dy isotopes. In many considered cases these matrix elements are equal to several tens of keV and are comparable with energy distances between the mixed levels. The results obtained indicates that Gd isotopes could be more suitable for finding deviations from Alaga rules in M1 transitions from $1^{+}$ state to the states of the ground band.
nucl-thEPJA(2022)·0 citations
09
Direct Photons in Hydrodynamic Modeling of Relativistic Nuclear Collisions
Akihiko Monnai🇯🇵
We review direct photons in the phenomenology of nuclear collisions at relativistic energies. Direct photons carry information about the space-time evolution of nuclear collisions because the QCD medium is transparent against colorless particles. After a status summary of theoretical and experimental studies, transverse momentum spectra and azimuthal momentum anisotropies of direct photons are studied in the context of the hydrodynamic modeling of relativistic nuclear collisions with emphasis on pre-equilibrium photons. It is implied that pre-equilibrium photons can be as important as thermal and prompt photons for comprehensive understanding of direct photon production.
nucl-thhep-phnucl-exInt.J.Mod.Phys.A(2022)·16 citations

Affiliations

first authorsco-authorsvia INSPIRE