Nuclear Theory·nucl-th

Tuesday·February 23, 2016

20 papers—15 primary·5 cross-listed

01
Revised analysis of $^{40}$ Ca+ $^{96}$ Zr fusion reactions
H. Esbensen · G. Montagnoli · A. M. Stefanini
Fusion data for $^{40}$ Ca+ $^{96}$ Zr are analyzed by coupled-channels calculations that are based on a standard Woods-Saxon potential and include couplings to multiphonon excitations and transfer channels. The couplings to multiphonon excitations are the same as used in a previous work. The transfer couplings are calibrated to reproduce the measured neutron transfer data. This type of calculation gives a poor fit to the fusion data. However, by multiplying the transfer couplings with a $2$ one obtains an excellent fit. The scaling of the transfer strengths is supposed to simulate the combined effect of neutron and proton transfer, and the calculated one- and two-nucleon transfer cross sections are indeed in reasonable agreement with the measured cross sections.
nucl-thPRC(2016)·20 citations
02
Understanding the negative binomial multiplicity fluctuations in relativistic heavy ion collisions
Hao-jie Xu🇨🇳
By deriving a general expression for multiplicity distribution (a conditional probability distribution) in statistical model, we demonstrate the mismatches between experimental measurements and previous theoretical calculations on multiplicity fluctuations. From the corrected formula, we develop an improved baseline measure for multiplicity distribution under Poisson approximation in statistical model to replace the traditional Poisson expectations. We find that the ratio of the mean multiplicity to the corresponding reference multiplicity are crucial to systemically explaining the measured scale variances of total charge distributions in different experiments, as well as understanding the centrality resolution effect observed in experiment. The improved statistical expectations, albeit simple, work well in describing the negative binomial multiplicity distribution measured in experiments, e.g. the cumulants (cumulant products) of total (net) electric charge distributions.
nucl-thhep-phnucl-ex6 citations
03
First-forbidden transitions and stellar $β$ -decay rates of Zn and Ge isotopes
Jameel-Un Nabi · Necla Cakmak · Sabin Stoica · Zafar Iftikhar
First-forbidden (FF) charge-changing transitions become relatively important for nuclei as their proton number increases. This is because the strength of allowed Gamow-Teller (GT) transitions decreases with increasing Z. The FF transitions play an important role in reducing the half-lives as against those calculated from taking the GT transitions alone into account. In this paper we calculate allowed GT as well as $0^{+} \to 0^{-}$ and $0^{+} \to 2^{-}$ transitions for neutron-rich Zn and Ge isotopes. Two different pn-QRPA models were used with a schematic separable interaction to calculate GT and FF transitions. Half-lives calculated after inclusion of FF transitions were in excellent agreement with the experimental data. Our calculations were also compared to previous QRPA calculations and were found to be in better agreement with measured data. Stellar $β$ -decay rates were calculated for these nuclei including allowed GT and unique FF transitions for astrophysical applications. $^{86, 88}$ Ge has a sizeable contribution to the total stellar rate from unique FF transitions.
nucl-thPhys.Scripta(2015)·8 citations
04
First-forbidden $β$ -decay rates, energy rates of $β$ -delayed neutrons and probability of $β$ -delayed neutron emissions for neutron-rich nickel isotopes
Jameel-Un Nabi · Necla Cakmak · Zafar Iftikhar
First-forbidden (FF) transitions can play an important role in decreasing the calculated half-lives specially in environments where allowed Gamow-Teller (GT) transitions are unfavored. Of special mention is the case of neutron-rich nuclei where, due to phase-space amplification, FF transitions are much favored. We calculate the allowed GT transitions in various pn-QRPA models for even-even neutron-rich isotopes of nickel. Here we also study the effect of deformation on the calculated GT strengths. The FF transitions for even-even neutron-rich isotopes of nickel are calculated assuming the nuclei to be spherical. Later we take into account deformation of nuclei and calculate GT + unique FF transitions, stellar $β$ -decay rates, energy rate of $β$ -delayed neutrons and probability of $β$ -delayed neutron emissions. The calculated half-lives are in excellent agreement with measured ones and might contribute in speeding-up of the $r$ -matter flow.
nucl-thEPJA(2016)·17 citations
05
Gamow-Teller strength distributions and neutrino energy loss rates due to chromium isotopes in stellar matter
Jameel-Un Nabi · Ramoona Shehzadi · Muhammad Fayaz
Gamow-Teller transitions in isotopes of chromium play a consequential role in the presupernova evolution of massive stars. $β$ -decay and electron capture rates on chromium isotopes significantly affect the time rate of change of lepton fraction ( $Y_{e} ˙$ ). Fine-tuning of this parameter is one of the key for simulating a successful supernova explosion. The (anti)neutrinos produced as a result of electron capture and $β$ -decay are transparent to stellar matter during presupernova phases. They carry away energy and this result in cooling the stellar core. In this paper we present the calculations of Gamow-Teller strength distributions and (anti)neutrino energy loss rates due to weak interactions on chromium isotopes of astrophysical importance. We compare our results with measured data and previous calculations wherever available.
nucl-thAstrophys.Space Sci.(2016)·3 citations
06
Gamow-Teller (GT $\pm$ ) strength distributions of $^{56} N i$ for ground and excited states
Jameel-Un Nabi · Muneeb-Ur Rahman · Muhammad Sajjad
Gamow-Teller (GT) transitions play an important and consequential role in many astrophysical phenomena. These include, but are not limited to, electron and positron capture rates which determine the fate of massive stars and play an intricate role in the dynamics of core collapse. These $G T_{\pm}$ transitions rates are the significant inputs in the description of supernova explosions. $G T_{\pm}$ strength function values are sensitive to the $^{56} N i$ core excitation in the middle \textit{pf}-shell region and to the size of the model space as well. We used the pn-QRPA theory for extracting the GT strength for ground and excited states of $^{56} N i$ . We then used these GT strength distributions to calculate the electron \textit{and} positron capture rates which show differences with the earlier calculations. One curious finding of this paper is our enhanced electron capture rates on $^{56} N i$ at presupernova temperatures. These differences need to be taken into account for the modeling of the early stages of Type II supernova evolution.
nucl-thActa Phys.Polon.B(2008)·3 citations
07
Effects of finite size and symmetry energy on the phase transition of stellar matter at subnuclear densities
S. S. Bao🇨🇳 · H. Shen🇨🇳
We study the liquid-gas phase transition of stellar matter with the inclusion of the finite-size effect from surface and Coulomb energies. The equilibrium conditions for two coexisting phases are determined by minimizing the total free energy including the surface and Coulomb contributions, which are different from the Gibbs conditions used in the bulk calculations. The finite-size effect can significantly reduce the region of the liquid-gas mixed phase. The influence of the symmetry energy on the liquid-gas phase transition is investigated with the inclusion of finite-size effects. It is found that the slope of the symmetry energy plays an important role in determining the boundary and properties of the mixed phase.
nucl-thPRC(2016)·14 citations
08
Coulomb breakup of 22C in a four-body model
E. C. Pinilla · P. Descouvemont
Breakup cross sections are determined for the Borromean nucleus 22C by using a four-body eikonal model, including Coulomb corrections. Bound and continuum states are constructed within a 20C + n + n three-body model in hyperspherical coordinates. We compute continuum states with the correct asymptotic behavior through the R-matrix method. For the n+ n potential, we use the Minnesota interaction. As there is no precise experimental information on 21C, we define different parameter sets for the 20C + n potentials. These parameter sets provide different scattering lengths, and resonance energies of an expected 3/2+ excited state. Then we analyze the 22C ground-state energy and rms radius, as well as E1 strength distributions and breakup cross sections. The E1 strength distribution presents an enhancement at low energies. Its amplitude is associated with the low binding energy, rather than with a three-body resonance. We show that the shape of the cross section at low energies is sensitive to the ground-state properties. In addition, we suggest the existence of a low-energy 2+ resonance, which should be observable in breakup experiments.
nucl-thPRC(2016)·15 citations
09
Light-Front Dynamics and the 3He Spectral Function
Emanuele Pace🇮🇹 · Alessio Del Dotto🇮🇹 · Leonid Kaptari🇷🇺 · Matteo Rinaldi🇮🇹 · Giovanni Salme'🇮🇹 · Sergio Scopetta🇮🇹
Two topics are presented. The first one is a novel approach for a Poincare' covariant description of nuclear dynamics based on light-front Hamiltonian dynamics. The key quantity is the light-front spectral function, where both normalization and momentum sum rule can be satisfied at the same time. Preliminary results are discussed for an initial analysis of the role of relativity in the EMC effect in 3He. A second issue, very challenging, is considered in a non-relativistic framework, namely a distorted spin-dependent spectral function for 3He in order to take care of the final state interaction between the observed pion and the remnant in semi-inclusive deep inelastic electron scattering off polarized 3He. The generalization of the analysis within the light-front dynamics is outlined.
nucl-thFew Body Syst.(2016)·10 citations
10
Constraints on $s - s ˉ$ asymmetry of the proton in chiral effective theory
X.G. Wang🇦🇺 · Chueng-Ryong Ji🇺🇸 · W. Melnitchouk🇺🇸 · Y. Salamu🇨🇳 · A.W. Thomas🇦🇺 · P. Wang🇨🇳
We compute the $s - s ˉ$ asymmetry in the proton in chiral effective theory, using phenomenological constraints based upon existing data. Unlike previous meson cloud model calculations, which accounted for kaon loop contributions with on-shell intermediate states alone, this work includes off-shell terms and contact interactions, which impact the shape of the $s - s ˉ$ difference. We identify a valence-like component of $s (x)$ which is balanced by a $δ$ -function contribution to $s ˉ (x)$ at $x = 0$ , so that the integrals of $s$ and $s ˉ$ over the experimentally accessible region $x > 0$ are not equal. Using a regularization procedure that preserves chiral symmetry and Lorentz invariance, we find that existing data limit the integrated value of the second moment of the asymmetry to the range $- 0.07 \times 1 0^{- 3} \leq ⟨ x (s - s ˉ)⟩ \leq 1.12 \times 1 0^{- 3}$ at a scale of $Q^{2} = 1$ GeV $^{2}$ . This is too small to account for the NuTeV anomaly and of the wrong sign to enhance it.
nucl-thhep-lathep-phPLB(2016)·27 citations
11
Particle-Hole Symmetry in Generalized Seniority, Microscopic Interacting Boson (Fermion) Model, Nucleon-Pair Approximation, and Others
L. Y. Jia
The particle-hole symmetry (equivalence) of the full shell-model Hilbert space is straightforward and routinely used in practical calculations. In this work we show that this symmetry is preserved in the subspace truncated at a certain generalized seniority, and give the explicit transformation between the states in the two types (particle and hole) of representations. Based on the results, we study the particle-hole symmetry in popular theories that could be regarded as further truncations on top of the generalized seniority, including the microscopic interacting boson (fermion) model, the nucleon-pair approximation, and others.
nucl-thPRC(2016)·7 citations
12
Excited hadrons and the analytical structure of bound-state interaction kernels
Bruno El-Bennich🇧🇷 · Gastão Krein🇧🇷 · Eduardo Rojas🇨🇴 · Fernando E. Serna🇧🇷
We highlight Hermiticity issues in bound-state equations whose kernels are subject to a highly asymmetric mass and momentum distribution and whose eigenvalue spectrum becomes complex for radially excited states. We trace back the presence of imaginary components in the eigenvalues and wave functions to truncation artifacts and suggest how they can be eliminated in the case of charmed mesons. The solutions of the gap equation in the complex plane, which play a crucial role in the analytic structure of the Bethe-Salpeter kernel, are discussed for several interaction models and qualitatively and quantitatively compared to analytic continuations by means of complex-conjugate pole models fitted to real solutions.
nucl-thhep-lathep-phnucl-exFew Body Syst.(2016)·37 citations
13
Modification of the Nuclear Landscape in the Inverse Problem Framework using the Generalized Bethe-Weizsäcker Mass Formula
S.Cht. Mavrodiev · M.A. Deliyergiyev
The dependence on the structure functions and Z, N numbers of the nuclear binding energy is investigated within the inverse problem(IP) approach. This approach allows us to infer the underlying model parameters from experimental observation, rather than to predict the observations from the model parameters. The IP was formulated for the numerical generalization of the semi-empirical mass formula of BW. It was solved in step by step way based on the AME2012 nuclear database. The established parametrization describes the measured nuclear masses of 2564 isotopes with a maximum deviation less than 2.6 MeV, starting from the number of protons and number of neutrons equal to 1. The set of parameters ${a_{i}}$ , $i = 1, \dots, N_{param}$ of our fit represent the solution of an overdetermined system of nonlinear equations, which represent equalities between the binding energy $E_{B, j}^{Expt} (A, Z)$ and its model $E_{B, j}^{Th} (A, Z, {a_{i}})$ , where $j$ is the index of the given isotope. The solution of the overdetermined system of nonlinear equations has been obtained with the help of the Aleksandrov's auto-regularization method of Gauss-Newton(GN) type for ill-posed problems. The efficiency of the above methods was checked by comparing relevant results with the results obtained independently. The explicit form of unknown functions was discovered in a step-by-step way using the modified least $χ^{2}$ procedure, that realized in the algorithms which were developed by Aleksandrov to solve nonlinear systems of equations via the GN method, lets us to choose between two functions with same $χ^{2}$ the better one. In the obtained generalized model the corrections to the binding energy depend on nine proton (2, 8, 14, 20, 28, 50, 82, 108, 124) and ten neutron (2, 8, 14, 20, 28, 50, 82, 124, 152, 202) magic numbers as well on the asymptotic boundaries of their influence.
nucl-thIJMPE(2018)·12 citations
14
Time Reversal Invariance Violating and Parity Conserving effects in Proton Deuteron Scattering
Young-Ho Song🇰🇷 · Rimantas Lazauskas🇫🇷 · Vladimir Gudkov🇺🇸
Time reversal invariance violating parity conserving (TVPC) effects are calculated for elastic proton deuteron scattering with proton energies up to $2$ MeV. Distorted Wave Born Approximation is employed to estimate TVPC matrix elements, based on hadronic wave functions, obtained by solving three-body Faddeev-Merkuriev equations in configuration space with realistic potentials.
nucl-thhep-phPRC(2016)·2 citations
15
Investigation of Nuclear Phase Transition by Solvababe supersymmetric algebraic model and its application in Ru-Rh and Zn-Cu Isotopes
M. A. Jafarizadeh · M.Ghapanvari · N.Fouladi · Z.Ranjbar · A.Sadighzadeh
Solvable supersymmetric algebraic model for descriptions of the spherical to gama unstable shape- phase transition in even and odd mass nuclei is proposed. This model is based on dual algebraic structure and Richardson - Gaudin method, where the duality relations between the unitary and quasispin algebraic structures for the boson and fermion systems are extended to mixed boson- fermion system. The structure of two type of nuclear supersymmetry schemes, based on the U(6/2) and U(6/4) supergroups, is discussed. We investigate the change in level structure induced by the phase transition by doing a quantal analysis. By using the generalized quasispin algebra, it is shown that the nuclear supersymmetry concept can be also used for transitional regions in addition to dynamical symmetry limits. Experimental evidence for the U(5)-O(6) transition in Ru-Rh and Zn- Cu supermultiplets is presented. The low-states energy spectra and B(E2)values for these nuclei have been calculated and compared with the experimental data.
nucl-th1 citation

Affiliations

first authorsco-authorsvia INSPIRE