Nuclear Theory·nucl-th

Tuesday·December 1, 2020

17 papers—10 primary·7 cross-listed

01
$η$ mesons in hot and dense asymmetric nuclear matter
Rajesh Kumar🇮🇳 · Arvind Kumar🇮🇳
We study the $η N$ interactions in the hot and dense isospin asymmetric nuclear matter using two different approaches. In the first approach, the in-medium mass and optical potential of $η$ -meson have been calculated in the chiral SU(3) model, considering the effect of explicit symmetry breaking term and range terms in the $η N$ interaction Lagrangian density. In the second scenario, the conjunction of chiral perturbation theory and chiral SU(3) model is employed. In this case, the next-to-leading order $η N$ interactions are evaluated from the chiral perturbation theory (ChPT), and the in-medium contribution of scalar densities are taken as input from chiral SU(3) model. We observe a larger negative mass-shift in the ChPT+chiral model approach compared to the chiral SU(3) model alone as a function of nuclear density. Moreover, the increase in the asymmetry and temperature cause a decrease in the magnitude of mass-shift. We have also studied the impact of $η N$ scattering length $a^{η N}$ on the $η$ meson mass $m_{η}^{*}$ and observed that the $m_{η}^{*}$ decrease more for increasing the value of scattering length.
nucl-thhep-phPRC(2020)·8 citations
02
Hadron-Quark phase transition in the context of GW190814
I. A. Rather🇮🇳 · A. A. Usmani🇮🇳 · S. K. Patra🇮🇳
The properties of the neutron stars are calculated for the hadronic matter within the density-dependent relativistic mean-field model (DD-RMF). The phase transition to the quark matter is studied and the hybrid star matter properties are systematically calculated using the Vector-Enhanced Bag model (vBag). The maximum mass of neutron star with DD-LZ1 and DD-RMF parameter sets is found to be around 2.55 $M_{⊙}$ for pure hadronic phase and around 2 $M_{⊙}$ for hadron-quark mixed phase using both Gibbs and Maxwell construction. The tidal deformability for the hybrid EoS at 1.4 $M_{⊙}$ , $Λ_{1.4}$ , remains unchanged from the pure hadronic EoS with Maxwell construction, but decreases with the increasing neutron star mass for Gibbs construction. While the pure hadron matter EoS satisfies the mass constraint from recently observed GW190814 data, implying a stiff neutron star EoS, the hadron-quark phase transition satisfies the constraints from the recent observations GW170817. Therefore, we cannot exclude the possibility of the secondary object in GW190814 as a neutron star with a phase transition to the quark matter that satisfies the 2 $M_{⊙}$ maximum mass limit.
nucl-thJ.Phys.G(2021)·26 citations
03
Fusion reaction of a weakly-bound nucleus with a deformed target
Ki-Seok Choi · K. S. Kim · Myung-Ki Cheoun · W. Y. So · K. Hagino
We discuss the role of deformation of the target nucleus in the fusion reaction of the $^{15}$ C + $^{232}$ Th system at energies around the Coulomb barrier, for which $^{15}$ C is a well-known one-neutron halo nucleus. To this end, we construct the potential between $^{15}$ C and $^{232}$ Th with the double folding procedure, assuming that the projectile nucleus is composed of the core nucleus, $^{14}$ C, and a valance neutron. By taking into account the halo nature of the projectile nucleus as well as the deformation of the target nucleus, we simultaneously reproduce the fusion cross sections for the $^{14}$ C + $^{232}$ Th and the $^{15}$ C + $^{232}$ Th systems. Our calculation indicates that the net effect of the breakup and the transfer channels is small for this system.
nucl-thnucl-exPRC(2021)·6 citations
04
Proton superconductivity in pasta phases in neutron star crusts
Zhao-Wen Zhang · C. J. Pethick
In the so-called pasta phases predicted to occur in neutron star crusts, protons are able to move easily over large distances because the nuclear matter regions are extended in space. Consequently, electrical currents can be carried by protons, an effect not possible in conventional crystalline matter with isolated nuclei. With emphasis on the so-called lasagna phase, which has sheet-like nuclei, we describe the magnetic properties of the pasta phases allowing for proton superconductivity. We predict that these phases will be Type II superconductors and we calculate the energy per unit length of a flux line, which is shown to be strongly anisotropic. If, as seems likely, the pasta structure is imperfect, flux lines will be pinned and matter will behave as a good electrical conductor and flux decay times will be long. We describe some possible astrophysical manifestations of our results.
nucl-thPRC(2021)·12 citations
05
Probing the nature of the conjectured low-spin wobbling bands in atomic nuclei
S. Guo🇨🇳 · X. H. Zhou🇨🇳 · C. M. Petrache🇫🇷 · E. A. Lawrie🇿🇦 · S. Mthembu🇿🇦 · Y. D. Fang🇨🇳 · H. Y. Wu🇨🇳 · H. L. Wang🇨🇳 · H. Y. Meng🇨🇳 · G. S. Li🇨🇳 · Y. H. Qiang🇨🇳 · J. G. Wang🇨🇳 and 19 other authors
Precession is a unique motion in which the orientation of the rotational axis of a rotating body is not fixed but moving, and it generally exists in the Universe from giant stars through tiny atomic nuclei. In principle, the precession of an atomic nuclide can be approximately described as wobbling motion, arising from the coupling of a rotation and a harmonic vibration. Recently, a number of wobbling bands were reported at low spin, which violate the wobbling approximation that can be valid only at high spin. Here we explore the nature of the reported low-spin wobbling bands. Via a new experiment, we demonstrate that one such band in $^{187}$ Au is generated by dominant single-particle excitation rather than by the excitation of a wobbling phonon. We point out that the imperfect research paradigm used previously would lead to unreliable identification of low-spin wobbling bands. Consequently, new experimental approaches should be developed to distinguish among the different excitation mechanisms that can give rise to the observed low-spin bands in odd-even nuclei.
nucl-thnucl-exPLB(2022)·19 citations
06
Constraints on Nuclear Saturation Properties from Terrestrial Experiments and Astrophysical Observations of Neutron Stars
Soonchul Choi · Tsuyoshi Miyatsu · Myung-Ki Cheoun · Koichi Saito
Taking into account the terrestrial experiments and the recent astrophysical observations of neutron stars and gravitational-wave signals, we impose restrictions on the equation of state (EoS) for isospin-asymmetric nuclear matter. Using the relativistic mean-field model with SU(3) flavor symmetry, we investigate the impacts of effective nucleon mass, nuclear incompressibility, and slope parameter of nuclear symmetry energy on the nuclear and neutron-star properties. It is found that the astrophysical information of massive neutron stars and tidal deformabilities as well as the nuclear experimental data plays an important role to restrict the EoS for neutron stars. Especially, the softness of the nuclear EoS due to the existence of hyperons in the core gives stringent constraints on those physical quantities. Furthermore, it is possible to put limits on the curvature parameter of nuclear symmetry energy by means of the nuclear and astrophysical calculations.
nucl-thastro-ph.HEApJ(2021)·27 citations
07
Alpha-induced inelastic scattering and alpha-transfer reactions in $^{12}$ C and $^{16}$ O within the Algebraic Cluster Model
J. Casal · L. Fortunato · E. G. Lanza · A. Vitturi
The molecular algebraic model based on three and four alpha clusters is used to describe the inelastic scattering of alpha particles populating low-lying states in $^{12}$ C and $^{16}$ O. Optical potentials and inelastic formfactors are obtained by folding densities and transition densities obtained within the molecular model. One-step and multi-step processes can be included in the reaction mechanism calculation. In spite of the simplicity of the approach the molecular model with rotations and vibrations provides a reliable description of reactions where $α$ -cluster degrees of freedom are involved and good results are obtained for the excitation of several low-lying states. Within the same model we briefly discuss the expected selection rules for the $α$ -transfer reactions from $^{12}$ C and $^{16}$ O.
nucl-thnucl-exEPJA(2021)·13 citations
08
Present Status of Nuclear Shell-Model Calculations of Neutrinoless Double-Beta Decay Matrix Elements
L. Coraggio🇮🇹 · N. Itaco🇮🇹 · G. De Gregorio🇮🇹 · A. Gargano🇮🇹 · R. Mancino🇮🇹 · S. Pastore🇺🇸
Neutrinoless double beta decay searches are currently among the major foci of experimental physics. The observation of such a decay will have important implications in our understanding of the intrinsic nature of neutrinos and shed light on the limitations of the Standard Model. The rate of this process depends on both the unknown neutrino effective mass and the nuclear matrix element associated with the given neutrinoless double-beta decay transition. The latter can only be provided by theoretical calculations, hence the need of accurate theoretical predictions of the nuclear matrix element for the success of the experimental programs. This need drives the theoretical nuclear physics community to provide the most reliable calculations of the nuclear matrix elements. Among the various computational models adopted to solve the many-body nuclear problem, the shell model is widely considered as the basic framework of the microscopic description of the nucleus. Here, we review the most recent and advanced shell-model calculations of the nuclear matrix elements considering the light-neutrino-exchange channel for nuclei of experimental interest. We report the sensitivity of the theoretical calculations with respect to variations in the model spaces and the shell-model nuclear Hamiltonians.
nucl-thhep-exnucl-exUniverse(2020)·15 citations
09
Production of Heavy Elements During the Explosion of a Low-Mass Neutron Star in a Close Binary
I.V. Panov · A.V. Yudin
The nucleosynthesis of heavy elements in the scenario for the evolution of a close binary of neutron stars differing greatly in mass is considered. In contrast to the scenario for the merger of two neutron stars of comparable masses considered repeatedly in the literature, the evolution of such a binary at the final stage consists in a rapid mass transfer to the more massive star and an explosive disruption of the low-mass component. We provide the details of the explosion and calculate the abundances of the heavy elements produced in this process for various initial conditions.
nucl-thastro-ph.HEastro-ph.SRAstron.Lett.(2020)·16 citations
10
Neutron tunneling: A new mechanism to power explosive phenomena in neutron stars, magnetars, and neutron star mergers
Carlos A. Bertulani · Ronaldo V. Lobato
Neutron tunneling between neutron-rich nuclei in inhomogeneous dense matter encountered in neutron star crusts can release enormous energy on a short-timescale to power explosive phenomena in neutron stars. In this work we clarify aspects of this process that can occur in the outer regions of neutron stars when oscillations or cataclysmic events increase the ambient density. We use a time-dependent Hartree-Fock-Bogoliubov formalism to determine the rate of neutron diffusion and find that large amounts of energy can be released rapidly. The role of nuclear binding, the two-body interaction and pairing, on the neutron diffusion times is investigated. We consider a one-dimensional quantum diffusion model and extend our analysis to study the impact of diffusion in three-dimensions. We find that these novel neutron transfer reactions can generate energy at the amount of $≃ 1 0^{40} - 1 0^{44}$ ergs under suitable conditions.
nucl-thastro-ph.HEastro-ph.SRApJ(2021)·1 citation
11
Form Factors of the Nucleon Axial Current
Chen Chen🇩🇪 · Christian S. Fischer🇩🇪 · Craig D. Roberts🇨🇳 · Jorge Segovia🇪🇸
A symmetry-preserving Poincaré-covariant quark+diquark Faddeev equation treatment of the nucleon is used to deliver parameter-free predictions for the nucleon's axial and induced pseudoscalar form factors, $G_{A}$ and $G_{P}$ , respectively. The result for $G_{A}$ can reliably be represented by a dipole form factor characterised by an axial charge $g_{A} = G_{A} (0) = 1.25 (3)$ and a mass-scale $M_{A} = 1.23 (3) m_{N}$ , where $m_{N}$ is the nucleon mass; and regarding $G_{P}$ , the induced pseudoscalar charge $g_{p}^{*} = 8.80 (23)$ , the ratio $g_{p}^{*} / g_{A} = 7.04 (22)$ , and the pion pole dominance Ansatz is found to provide a reliable estimate of the directly computed result. The ratio of flavour-separated quark axial charges is also calculated: $g_{A}^{d} / g_{A}^{u} = - 0.16 (2)$ . This value expresses a marked suppression of the size of the $d$ -quark component relative to that found in nonrelativistic quark models and owes to the presence of strong diquark correlations in the nucleon Faddeev wave function -- both scalar and axial-vector, with the scalar diquark being dominant. The predicted form for $G_{A}$ should provide a sound foundation for analyses of the neutrino-nucleus and antineutrino-nucleus cross-sections that are relevant to modern accelerator neutrino experiments.
↳ hep-phhep-exhep-latnucl-ex+1PLB(2021)·32 citations
12
Charged-particle multiplicity dependence of charm-baryon-to-meson ratio in high-energy proton-proton collisions
Yu Chen🇨🇳 · Min He🇨🇳
We propose that the charged-particle multiplicity dependence of the charm-baryon-to-meson ratio observed in high-energy $pp$ collisions can be explained by canonical treatment of quantum charges in the statistical hadronization model (SHM). Taking the full particle listings of PDG complemented by additional charm-baryon states from relativistic quark model predictions, we evaluate the canonical partition function and the charm-hadron chemical factors that measure the canonical suppression arising from the requirement of strict conservation of quantum charges. We demonstrate that, while charm number conservation induces common suppression on the production of both charm-baryons and -mesons, baryon (strangeness) number conservation causes further suppression on charm-baryons (charm-strange mesons) relative to nonstrange charm-mesons, thereby resulting in a decreasing $Λ_{c} / D^{0}$ ( $D_{s} / D^{0}$ ) ratio toward smaller multiplicity events. The charm-hadron thermal densities thus computed are then used as pertinent weights to perform charm-quark fragmentation simulations yielding $p_{T}$ -dependent $Λ_{c} / D^{0}$ and $D_{s} / D^{0}$ ratios at varying multiplicities in fair agreement with ALICE measurements.
↳ hep-phhep-exnucl-exnucl-thPLB(2021)·25 citations
13
Explaining the Many Threshold Structures in the Heavy-Quark Hadron Spectrum
Xiang-Kun Dong🇨🇳 · Feng-Kun Guo🇨🇳 · Bing-Song Zou🇨🇳
Tremendous progress has been made experimentally in the hadron spectrum containing heavy quarks in the last two decades. It is surprising that many resonant structures are around thresholds of a pair of heavy hadrons. There should be a threshold cusp at any $S$ -wave threshold. By constructing a nonrelativistic effective field theory with open channels, we discuss the generalities of threshold behavior, and offer an explanation of the abundance of near-threshold peaks in the heavy quarkonium regime. We show that the threshold cusp can show up as a peak only for channels with attractive interaction, and the width of the cusp is inversely proportional to the reduced mass relevant for the threshold. We argue that there should be threshold structures at any threshold of a pair of heavy-quark and heavy-antiquark hadrons, which have attractive interaction at threshold, in the invariant mass distribution of a heavy quarkonium and light hadrons that couple to that open-flavor hadron pair. The structure becomes more pronounced if there is a near-threshold pole. Predictions of the possible pairs are also given for the ground state heavy hadrons. Precisely measuring the threshold structures will play an important role in revealing the heavy-hadron interactions, and thus understanding the puzzling hidden-charm and hidden-bottom structures.
↳ hep-phhep-exhep-latnucl-thPRL(2021)·165 citations
14
Decay: A Monte Carlo library for the decay of a particle with ROOT compatibility
R.A. Kycia🇨🇿 · P. Lebiedowicz🇵🇱 · A. Szczurek🇵🇱
Recently, there is a need for a general-purpose event generator of decays of an elementary particle or a hadron to a state of higher multiplicity ( $N > 2$ ) that is simple to use and universal. We present the structure of such a library to produce generators that generate kinematics of decay processes and can be used to integrate any matrix element squared over phase space of this decay. Some test examples are presented, and results are compared with results known from the literature. As one of examples we consider the Standard Model Higgs boson decay into four leptons. The generators discussed here are compatible with the ROOT interface.
↳ hep-phcs.CEhep-thnucl-thCommun.Comput.Phys.(2021)·2 citations
15
Spin polarization dynamics in the Gubser-expanding background
Rajeev Singh🇵🇱 · Gabriel Sophys🇵🇱 · Radoslaw Ryblewski🇵🇱
Evolution of spin polarization in the Gubser-expanding conformal perfect-fluid hydrodynamic background is studied. The analysis of the conformal transformation properties of the conservation laws is extended to the case of the angular momentum conservation. The explicit forms of equations of motion for spin components are derived and analysed, and some special solutions are found.
↳ hep-phnucl-thPRD(2021)·80 citations
16
Progress in the Glauber model at collider energies
David d'Enterria🇨🇭 · Constantin Loizides🇺🇸
We review the theoretical and experimental progress in the Glauber model of multiple nucleon and/or parton scatterings, after the last 10--15 years of operation with proton and nuclear beams at the CERN Large Hadron Collider (LHC) and with various light and heavy colliding ions at the BNL Relativistic Heavy Ion Collider (RHIC). The main developments and the state-of-the-art of the field are summarized. These encompass measurements of the inclusive inelastic proton and nuclear cross sections, advances in the description of the proton and nuclear density profiles and their fluctuations, inclusion of subnucleonic degrees of freedom, experimental procedures and issues related to the determination of the collision centrality, validation of the binary scaling prescription for hard scattering cross sections, and constraints on transport properties of quark-gluon matter from varying initial-state conditions in relativistic hydrodynamics calculations. These advances confirm the validity and usefulness of the Glauber formalism for quantitative studies of QCD matter produced in high-energy collisions of systems, from protons to uranium nuclei, of vastly different size.
↳ hep-phhep-exnucl-exnucl-thAnn.Rev.Nucl.Part.Sci.(2021)·138 citations
17
Lattice Nucleon Isovector Unpolarized Parton Distribution in the Physical-Continuum Limit
Huey-Wen Lin🇺🇸 · Jiunn-Wei Chen🇹🇼 · Rui Zhang🇺🇸
We present the first lattice-QCD calculation of the nucleon isovector unpolarized parton distribution functions (PDFs) at the physical-continuum limit using Large-Momentum Effective Theory (LaMET). The lattice results are calculated using ensembles with multiple sea pion masses with the lightest one around 135~MeV, 3 lattice spacings $a \in [0.06, 0.12]$ ~fm, and multiple volumes with $M_{π} L$ ranging 3.3 to 5.5. We perform a simultaneous chiral-continuum extrapolation to obtain RI/MOM renormalized nucleon matrix elements with various Wilson-link displacements in the continuum limit at physical pion mass. Then, we apply one-loop perturbative matching to the quasi-PDFs to obtain the lightcone PDFs. We find the lattice-spacing dependence to be much larger than the dependence on pion mass and lattice volume for these LaMET matrix elements. Our physical-continuum limit unpolarized isovector nucleon PDFs are found to be consistent with global-PDF results.
↳ hep-lathep-phnucl-th44 citations

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