Nuclear Theory·nucl-th

Wednesday·January 5, 2022

6 papers—4 primary·2 cross-listed

01
Symmetry breaking of Gamow-Teller and magnetic-dipole transitions and its restoration in calcium isotopes
Tomohiro Oishi · Ante Ravlic · Nils Paar
Nuclear magnetic-dipole (M1) and Gamow-Teller (GT) transitions provide insight into the spin-isospin properties of atomic nuclei. By considering them as unified spin-isospin transitions, the M1/GT transition strengths and excitation energies are subject to isospin symmetry. The excitation properties associated to the M1/GT symmetry need to be clarified within consistent theoretical approach. In this work, the relationship between the M1 and GT transitions in Ca isotopes is investigated in a unified framework based on the relativistic energy-density functional (REDF) with point-coupling interactions, using the relativistic quasi-particle random-phase approximation (RQRPA). It is shown that the isovector-pseudovector (IV-PV) residual interaction affects both transitions, and the symmetry of M1 and giant-GT transitions is disrupted by this interaction in closed-shell nuclei. In open-shell Ca isotopes, the proton-neutron pairing in the residual RQRPA interaction also plays a role in GT transitions. Due to the interplay between these interactions, the M1/GT symmetry can be restored especially in the $^{42}$ Ca nucleus, i.e., the giant-GT strength can become comparable to that of the M1 mode in terms of the unified spin-isospin transitions by adjusting the PN-pairing strength to reproduce the experimental low-lying GT-excitation energies. The mirror symmetry of both M1 and GT transitions is also demonstrated for open-shell mirror partners, $^{42}$ Ca and $^{42}$ Ti. Further improvements are required to achieve simultaneous reproduction of M1 and GT-transition energies in the REDF framework.
nucl-thnucl-exPRC(2022)·4 citations
02
The single-particle space-momentum angle distribution effect on two-pion HBT correlation with the Coulomb interaction
Hang Yang🇨🇳 · Qichun Feng🇨🇳 · Jingbo Zhang🇨🇳
We calculate the HBT radius Rs for {\pi}+ particles with the Coulomb interaction by using the string melting version of a multiphase transport(AMPT) model. We study the relationship between the single-particle space-momentum angle and the particle sources and discuss HBT radii without single-particle space-momentum correlation. Additionally, we study the Coulomb interaction effect on the numerical connection between the single-particle space-momentum angle distribution and the transverse momentum dependence of Rs.
nucl-thhep-phCPC(2022)·0 citations
03
Higher-order isospin-symmetry breaking corrections to nuclear matrix elements of superallowed $0^{+} \to 0^{+}$ Fermi $β$ decay of $T = 1$ nuclei
Latsamy Xayavong🇱🇦 · Nadezda Smirnova🇫🇷
We study the shell-model formalism to include the isospin-symmetry-breaking correction ( $δ_{C}$ ) to nuclear matrix element of superallowed $0^{+} \to 0^{+}$ Fermi $β$ decays of $T = 1$ nuclei. Based on a perturbation expansion in a small quantity, such as the deviation of the overlap integral between proton and neutron radial wave functions from unity or of the transition density from its isospin-symmetry value, we derive that $δ_{C}$ can be obtained as a sum of six terms, including two leading order (LO) terms, two next-to-leading order (NLO) terms, one next-to-next-to-leading order (NNLO) term and one next-to-next-to-next-to-leading order (NNNLO) term. The first two terms have been considered in a series of shell-model calculations of Towner and Hardy as well as in the recent calculation of the present authors, while the remaining four terms are usually neglected. A numerical calculation has been carried out for 13 transitions in the $p$ , $s d$ and the lower part of $p f$ shells. Our results indicate that the magnitude of the sum of all higher order terms is of the order of $1 0^{- 3}$ %. This number is well below typical theoretical errors quantified within the shell model with Woods-Saxon radial wave functions.
nucl-th0 citations
04
Effects of neutron-skin thickness on direct hard photon emission from reactions induced by the neutron-rich projectile $^{50}$ Ca
S. S. Wang · Y. G. Ma · D. Q. Fang · X. G. Cao
Direct hard photon emissions from incoherent proton-neutron bremsstrahlung in collisions of the neutron-rich projectile $^{50}$ Ca with $^{12}$ C and $^{40}$ Ca targets are simulated in the framework of the isospin-dependent quantum molecular dynamics (IQMD) model. By adjusting the diffuseness parameter of neutron density in the droplet model to obtain different neutron skin thicknesses for $^{50}$ Ca, the effects of neutron skin thickness on direct hard photon emission are investigated via several probes. The results show that more direct hard photons are produced with increasing neutron skin thickness in peripheral collisions. Meanwhile, we find that the multiplicity yield ratio $R_{c p} (σ_{γ})$ between central collisions and peripheral collisions as well as the rapidity dependence of multiplicity for direct hard photons are sensitive to neutron skin thickness. The results indicate that direct hard photon emission can be taken as an experimental observable to extract information on neutron skin thickness.
nucl-thnucl-exPRC(2022)·8 citations
05
Emergence of pion parton distributions
Z.-F. Cui🇨🇳 · M. Ding🇩🇪 · J. M. Morgado🇪🇸 · K. Raya🇪🇸 · D. Binosi🇮🇹 · L. Chang🇨🇳 · F. De Soto🇪🇸 · C. D. Roberts🇨🇳 · J. Rodríguez-Quintero🇪🇸 · S. M. Schmidt🇩🇪
Supposing only that there is an effective charge which defines an evolution scheme for parton distribution functions (DFs) that is all-orders exact, strict lower and upper bounds on all Mellin moments of the valence-quark DFs of pion-like systems are derived. Exploiting contemporary results from numerical simulations of lattice-regularised quantum chromodynamics (QCD) that are consistent with these bounds, parameter-free predictions for pion valence, glue, and sea DFs are obtained. The form of the valence-quark DF at large values of the light-front momentum fraction is consistent with predictions derived using the QCD-prescribed behaviour of the pion wave function.
↳ hep-phhep-exhep-latnucl-ex+1PRD(2022)·51 citations
06
Lattice simulations of the QCD chiral transition at real $μ_{B}$
Attila Pasztor🇭🇺 · Szabolcs Borsanyi🇩🇪 · Zoltan Fodor🇭🇺 · Matteo Giordano🇭🇺 · Sandor D. Katz🇭🇺 · Daniel Nogradi🇭🇺 · Chik Him Wong🇩🇪
Most lattice studies of hot and dense QCD matter rely on extrapolation from zero or imaginary chemical potentials. The ill-posedness of numerical analytic continuation puts severe limitations on the reliability of such methods. We studied the QCD chiral transition at finite real baryon density with the more direct sign reweighting approach. We simulate up to a baryochemical potential-temperature ratio of $μ_{B} / T = 2.7$ , covering the RHIC Beam Energy Scan range, and penetrating the region where methods based on analytic continuation are unpredictive.This opens up a new window to study QCD matter at finite $μ_{B}$ from first principles.
↳ hep-lathep-phnucl-thSciPost Phys.Proc.(2022)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Symmetry breaking of Gamow-Teller and magnetic-dipole transitions and its restoration in calcium isotopes

The single-particle space-momentum angle distribution effect on two-pion HBT correlation with the Coulomb interaction

Higher-order isospin-symmetry breaking corrections to nuclear matrix elements of superallowed 0+→0+ Fermi β decay of T=1 nuclei

Effects of neutron-skin thickness on direct hard photon emission from reactions induced by the neutron-rich projectile 50Ca

Emergence of pion parton distributions

Lattice simulations of the QCD chiral transition at real μB​

Affiliations

Higher-order isospin-symmetry breaking corrections to nuclear matrix elements of superallowed $0^{+} \to 0^{+}$ Fermi $β$ decay of $T = 1$ nuclei

Effects of neutron-skin thickness on direct hard photon emission from reactions induced by the neutron-rich projectile $^{50}$ Ca

Lattice simulations of the QCD chiral transition at real $μ_{B}$