Nuclear Theory·nucl-th

Friday·April 13, 2018

14 papers—12 primary·2 cross-listed

01
Improved description of the $2 ν β β$ -decay and a possibility to determine the effective axial-vector coupling constant
Fedor Šimkovic🇸🇰 · Rastislav Dvornický🇸🇰 · Dušan Štefánik🇸🇰 · Amand Faessler🇩🇪
An improved formalism of the two-neutrino double-beta decay ( $2 ν β β$ -decay) rate is presented, which takes into account the dependence of energy denominators on lepton energies via the Taylor expansion. Till now, only the leading term in this expansion has been considered. The revised $2 ν β β$ -decay rate and differential characteristics depend on additional phase-space factors weighted by the ratios of $2 ν β β$ -decay nuclear matrix elements with different powers of the energy denominator. For nuclei of experimental interest all phase-space factors are calculated by using exact Dirac wave functions with finite nuclear size and electron screening. For isotopes with measured $2 ν β β$ -decay half-life the involved nuclear matrix elements are determined within the quasiparticle random phase approximation with partial isospin restoration. The importance of correction terms to the $2 ν β β$ -decay rate due to Taylor expansion is established and the modification of shape of single and summed electron energy distributions is discussed. It is found that the improved calculation of the $2 ν β β$ -decay predicts slightly suppressed $2 ν β β$ -decay background to the neutrinoless double-beta decay signal. Further, a novel approach to determine the value of effective weak-coupling constant in nuclear medium $g_{A}^{eff}$ is proposed.
nucl-thPRC(2018)·83 citations
02
Effects of in-medium nucleon-nucleon cross section on collective flow and nuclear stopping in heavy-ion collisions in the Fermi-energy domain
Pengcheng Li🇨🇳 · Yongjia Wang🇨🇳 · Qingfeng Li🇨🇳 · Chenchen Guo🇨🇳 · Hongfei Zhang🇨🇳
With the newly updated version of the ultrarelativistic quantum molecular dynamics (UrQMD) model, a systematic investigation of the effects of in-medium nucleon-nucleon ( $N N$ ) elastic cross section on the collective flow and the stopping observables in $^{197} Au +^{197} Au$ collisions at beam energies from 40 to 150 MeV/nucleon is performed. Simulations with the medium correction factor $F = σ_{N N}^{in-medium} / σ_{N N}^{free} = 0.2, 0.3, 0.5$ , and the one obtained with the FU3FP1 parametrization which depends on both the density and the momentum are compared to the FOPI and INDRA experimental data. It is found that, to best fit the experimental data of the slope of the directed flow and the elliptic flow at mid-rapidity as well as the nuclear stopping, the correction factor $F$ =0.2 and 0.5 are required for reactions at beam energies of 40 and 150 MeV/nucleon, respectively. While calculations with the FU3FP1 parametrization can simultaneously reproduce these experimental data reasonably well. And, the observed increasing nuclear stopping with increasing beam energy in experimental data can also be reproduced by using the FU3FP1 parametrization, while the calculated stopping power in Au+Au collisions with beam energies from 40 to 150 MeV $/$ nucleon almost keeps constant when take $F$ equal to a fixed value.
nucl-thnucl-exPRC(2018)·37 citations
03
Determination of the nuclear incompressibility from the rapidity-dependent elliptic flow in heavy-ion collisions at beam energies 0.4\emph{A} - 1.0\emph{A} GeV
Yongjia Wang🇨🇳 · Chenchen Guo🇨🇳 · Qingfeng Li🇨🇳 · Arnaud Le Fevre🇩🇪 · Yvonne Leifels🇩🇪 · Wolfgang Trautmann🇩🇪
Heavy-ion-collision measurements in combination with transport model simulations serve as important tools for extracting the nuclear incompressibility. However, uncertainties in transport models (or model dependence) partly affect the reliability of the extracted result. In the present work, by using the recently measured data of rapidity-dependent flows, we constrain the incompressibility of nuclear matter and analyse the impact of model uncertainties on the obtained value. The method is based on the newly updated version of the ultrarelativistic quantum molecular dynamics (UrQMD) model in which the Skyrme potential energy-density functional is introduced. Three different Skyrme interactions which give different incompressibilities varying from $K_{0}$ =201 to 271 MeV are adopted. The incompressibility is deduced from the comparison of the UrQMD model simulations and the FOPI data for rapidity-dependent elliptic flow in Au+Au collisions at beam energies 0.4\emph{A} - 1.0\emph{A} GeV. The elliptic flow $v_{2}$ as a function of rapidity $y_{0}$ can be well described by a quadratic fit $v_{2} = v_{20} + v_{22} \cdot y_{0}^{2}$ . It is found that the quantity $v_{2 n}$ defined by $v_{2 n} = ∣ v_{20} ∣ + ∣ v_{22} ∣$ is quite sensitive to the incompressibility $K_{0}$ and the in-medium nucleon-nucleon cross section, but not sensitive to the slope parameter $L$ of the nuclear symmetry energy. With the FU3FP4 parametrization of the in-medium nucleon-nucleon cross section, an averaged $K_{0} = 220 \pm 40$ ~MeV is extracted from the $v_{2 n}$ of free protons and deuterons. However, remaining systematic uncertainties, partly related to the choice of in-medium nucleon-nucleon cross sections, are of the same magnitude ( $\pm 40$ ~MeV). Overall, the rapidity dependent elliptic flow supports a soft symmetric-matter equation-of-state.
nucl-thnucl-exPLB(2018)·67 citations
04
The effect of Lorentz-like force on collective flows of K $^{+}$ in Au+Au collisions at 1.5 GeV/nucleon}{The effect of Lorentz-like force on collective flows of $K^{+}$ in Au+Au collisions at 1.5 GeV/nucleon
Yushan Du🇨🇳 · Yongjia Wang🇨🇳 · Qingfeng Li🇨🇳 · Ling Liu🇨🇳
Producing kaon mesons in heavy-ion collisions at beam energies below their threshold energy is an important way to investigate the properties of dense nuclear matter. In this study, based on the newly updated version of the ultrarelativistic quantum molecular dynamics model, we introduce the kaon-nucleon (KN) potential, including both the scalar and vector (also dubbed Lorentz-like) aspects. We revisit the influence of the KN potential on the collective flow of K $^{+}$ mesons produced in Au+Au collisions at $E_{l ab}$ = 1.5 GeV/nucleon and find that the contribution of the newly included Lorentz-like force is very important, particulary for describing the directed flow of K $^{+}$ . Finally, the corresponding KaoS data of both directed and elliptic flows can be simultaneously reproduced well.
nucl-thnucl-exSCPMA(2018)·16 citations
05
Collective flows of pions in Au+Au collisions at energies 1.0 and 1.5 GeV/nucleon
Yangyang Liu🇨🇳 · Yongjia Wang🇨🇳 · Qingfeng Li🇨🇳 · Ling Liu🇨🇳
Based on the newly updated version of the ultrarelativistic quantum molecular dynamics (UrQMD) model, the pion potentials obtained from the in-medium dispersion relation of the $Δ$ -hole model and from the modified phenomenological approach are further introduced. Both the rapidity $y_{0}$ and transverse-velocity $u_{t 0}$ dependence of directed $v_{1}$ and elliptic $v_{2}$ flows of $π^{+}$ and $π^{-}$ charged mesons produced from Au+Au collisions at two beam energies of 1.0 GeV/nucleon and 1.5 GeV/nucleon and within a large centrality region of $0 < b_{0} < 0.55$ are scanned. Calculations with pion potentials as well as without considering the pion potential are compared to the newly experimental data released by the FOPI collaboration at GSI. It is found that the directed flow is more sensitive to the pion potential than the elliptic one, and the attractive pion potential from the phen.B mode of the phenomenological approach is too strong to describe the flow data and can be safely ruled out. The relatively weak pion potential from the $Δ$ -hole model can supply a good description for the FOPI data of both flows as functions of both centrality and rapidity. A two-peak/valley structure occurs in the transverse-velocity dependent directed flow but the elliptic flow drops monotonously with increasing $u_{t 0}$ . Finally, both $v_{1}$ and $v_{2}$ flows with large $u_{t 0}$ from semi-central heavy ion collisions can be taken as sensitive probes for the pion potential.
nucl-thnucl-exPRC(2018)·20 citations
06
LOCV calculation of the equation of state and properties of rapidly rotating neutron stars
A.H. Farajian · M. Bigdeli · S. Belbasi
In this paper, we have investigated the structural properties of rotating neutron stars using the numerical RNS code and the equation of states which have been calculated within the lowest order constrained variational approach. In order to calculate the equation of state of nuclear matter, we have used UV $_{14}$ $+$ TNI and AV $_{18}$ potentials. Here, we have computed the maximum mass of the neutron star and the corresponding equatorial radius at different angular velocity. We have also computed the structural properties of Keplerian rotating neutron star for maximum mass configuration, $M_{K}$ , $R_{K}$ , $f_{K}$ and $j_{ma x}$ .
nucl-thCPC(2018)·0 citations
07
Screening and anti-screening of the pairing interaction in low-density neutron matter
S. Ramanan🇮🇳 · M. Urban🇫🇷
We study pairing in low-density neutron matter including the screening interaction due to the exchange of particle-hole and RPA excitations. As bare force we employ the effective low-momentum interaction $V_{l o w k}$ , while the Fermi-liquid parameters are taken from a phenomenological energy density functional (SLy4) which correctly reproduces the equation of state of neutron matter. At low density, we find screening, i.e., pairing is reduced, while at higher densities, we find anti-screening, i.e., pairing is enhanced. This enhancement is mostly due to the strongly attractive Landau parameter $f_{0}$ . We discuss in detail the critical temperature $T_{c}$ in the limit of low densities and show that the suppression of $T_{c}$ predicted by Gor'kov and Melik-Barkhudarov can only be reproduced if the cutoff of the $V_{l o w k}$ interaction is scaled with the Fermi momentum. We also discuss the effect of non-condensed pairs on the density dependence of $T_{c}$ in the framework of the Nozières-Schmitt-Rink theory.
nucl-thastro-ph.HEcond-mat.quant-gasPRC(2018)·16 citations
08
Constraints on the nuclear symmetry energy and its density slope from the {\alpha} decay process
W. M. Seif · A. S. Hashem
We study the impact of the nuclear symmetry energy and its density dependence on the {\alpha}-decay process. Within the frame work of the performed cluster model and the energy density formalism, we use different parameterizations of the Skyrme energy density functionals that yield different equations of state EOSs. Each EOS is characterized by a particular symmetry-energy coefficient (asym) and a corresponding density-slope parameters L. The stepwise trends of the neutron (proton) skin thickness of the involved nuclei with both asym and L do not clarify the obtained oscillating behaviors of the {\alpha}-decay half-life T{\alpha} with them. We find that the change of the skin thickness after {\alpha}-decay satisfactory explains these behaviors. The presented results provide constrains on asym centered around an optimum value asym= 32 MeV, and on L between 41 and 57 MeV. These values of asym and L, which indicate larger reduction of the proton-skin thickness and less increase in the neutron-skin thickness after an {\alpha}-decay, yield minimum calculated half-life with the same extracted value of the {\alpha}-preformation factor inside the parent nucleus.
nucl-thCPC(2018)·16 citations
09
Nuclear chiral doublet bands data tables
Binwu Xiong · Yuanyuan Wang
Since the prediction of nuclear chirality in 1997, tremendous progresses both theoretically and experimentally have been achieved. Experimentally, 59 chiral doublet bands in 47 chiral nuclei (including 8 nuclei with multiple chiral doublets) have been reported in $A \sim 80, 100, 130$ ,~and~190 mass regions. The spins, parities, energies, ratios of the magnetic dipole transition strengths to the electric quadrupole transition strengths, and related references for these nuclei are compiled and listed in Table 1. For these nuclei with the magnetic dipole transition strengths and the electric quadrupole transition strengths measured, the corresponding results are given in Table 2. A brief discussion is provided after the presentation of energy $E$ , energy difference $Δ E$ , energy staggering parameter $S (I)$ , rotational frequency $ω$ , kinematic moment of inertia $J^{(1)}$ , dynamic moment of inertia $J^{(2)}$ , and ratio of the magnetic dipole transition strength to the electric quadrupole transition strength $B (M 1) / B (E 2)$ versus spin $I$ in each mass region.
nucl-thnucl-exAtom.Data Nucl.Data Tabl.(2019)·97 citations
10
Giant Dipole Resonance Parameters of Ground-State Photoabsorption: Experimental Values with Uncertainties
V. A. Plujko · O. M. Gorbachenko · R. Capote · P. Dimitriou
Updated values and corresponding uncertainties of Isovector Giant Dipole Resonance (GDR) parameters which are obtained by the least-squares fitting of theoretical photoabsorption cross sections to experimental data are presented. The theoretical photoabsorption cross sections are taken as a sum of the components corresponding to the excitation of the GDR and quasideuteron photodisintegration. The current compilation is an extension and improvement of the earlier compilations of Lorentzian parameters for ground-state photoneutron and photoabsorption cross sections and covers experimental data made available up to June 2017.
nucl-thnucl-exAtom.Data Nucl.Data Tabl.(2018)·55 citations
11
Large proton cumulants from the superposition of ordinary multiplicity distributions
Adam Bzdak🇵🇱 · Volker Koch🇺🇸 · Dmytro Oliinychenko🇺🇸 · Jan Steinheimer🇩🇪
We construct a multiplicity distribution characterized by large factorial cumulants (integrated correlation functions) from a simple combination of two ordinary multiplicity distributions characterized by small factorial cumulants. We find that such a model, which could be interpreted as representing two event classes, reproduces the preliminary data for the proton cumulants measured by the STAR collaboration at $7.7$ GeV very well. This model then predicts very large values for the fifth and sixth order factorial cumulants, which can be tested in experiment.
nucl-thhep-exhep-phnucl-exPRC(2018)·32 citations
12
Branching ratios for deexcitation processes of daughter nuclei following invisible dinucleon decays in $^{16}$ O
K. Hagino🇯🇵 · M. Nirkko🇬🇧
Various theories beyond the standard model of particle physics predict the existence of baryon number violating processes resulting in nucleon decay. When occurring within an atomic nucleus, such a decay will be followed by secondary decays of the daughter nucleus unless its ground state is directly populated. In this paper, we estimate branching ratios for processes associated with dinucleon decays of the $^{16}$ O nucleus. To this end, we use a simple shell model for the ground state of $^{16}$ O. For decays from the 1 $s_{1/2}$ configuration, which result in highly excited states in the daughter nucleus, we employ a statistical model with the Hauser-Feshbach theory. Our analysis indicates that the branching ratio for gamma-ray emission in the energy range between 5 and 9 MeV, which is relevant to low-threshold water Cherenkov experiments such as SNO+, is 4.53%, 35.7%, and 20.2% for the $nn$ , $pp$ , and $p n$ decays in $^{16}$ O, respectively. In particular, emission of 6.09 MeV and 7.01 MeV gamma-rays from $^{14}$ C, and 6.45 MeV and 7.03 MeV gamma-rays from $^{14}$ N, have branching ratios as large as 10.9%, 20.1%, 7.73% and 8.90%, respectively.
nucl-thhep-exhep-phnucl-exJ.Phys.G(2018)·4 citations

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first authorsco-authorsvia INSPIRE