Nuclear Theory·nucl-th

Tuesday·October 3, 2017

25 papers—15 primary·10 cross-listed

01
Nuclear deformation in the laboratory frame
C.N. Gilbreth · Y. Alhassid · G.F. Bertsch
We develop a formalism for calculating the distribution of the axial quadrupole operator in the laboratory frame within the rotationally invariant framework of the configuration-interaction shell model. The calculation is carried out using a finite-temperature auxiliary-field quantum Monte Carlo method. We apply this formalism to isotope chains of even-mass samarium and neodymium nuclei, and show that the quadrupole distribution provides a model-independent signature of nuclear deformation. Two technical advances are described that greatly facilitate the calculations. The first is to exploit the rotational invariance of the underlying Hamiltonian to reduce the statistical fluctuations in the Monte Carlo calculations. The second is to determine quadruple invariants from the distribution of the axial quadrupole operator. This allows us to extract effective values of the intrinsic quadrupole shape parameters without invoking an intrinsic frame or a mean-field approximation.
nucl-thcond-mat.mes-hallPRC(2018)·15 citations
02
Revealing Fine Structure in the Antineutrino Spectra From a Nuclear Reactor
A. A. Sonzogni🇺🇸 · M. Nino🇺🇸 · E. A. McCutchan🇺🇸
We calculate the Inverse Beta Decay (IBD) antineutrino spectrum generated by nuclear reactors using the summation method to understand deviations from the smooth Huber-Mueller model due to the decay of individual fission products, showing that plotting the ratio of two adjacent spectra points can effectively reveal these deviations. We obtained that for binning energies of 0.1 MeV or lower, abrupt changes in the spectra due to the jagged nature of the individual antineutrino spectra could be observed for highly precise experiments. Surprisingly, our calculations also reveal a peak-like feature in the adjacent points ratio plot at 4.5 MeV even with a 0.25 MeV binning interval, which we find is present in the IBD Daya Bay spectrum published in 2016. We show that this 4.5 MeV feature is caused by the contributions of just four fission products, 95Y, 98,101N and 102Tc. This would be the first evidence of the decay of a few fission products in the IBD antineutrino spectrum from a nuclear reactor.
nucl-thhep-exhep-phnucl-exPRC(2018)·40 citations
03
Correlated Prompt Fission Data in Transport Simulations
P. Talou · R. Vogt · J. Randrup · M.E. Rising · S.A. Pozzi · J. Verbeke · M.T. Andrews · S.D. Clarke · P. Jaffke · M. Jandel · T. Kawano · M.J. Marcath and 6 other authors
Detailed information on the fission process can be inferred from the observation, modeling and theoretical understanding of prompt fission neutron and $γ$ -ray~observables. Beyond simple average quantities, the study of distributions and correlations in prompt data, e.g., multiplicity-dependent neutron and \gray~spectra, angular distributions of the emitted particles, $n$ - $n$ , $n$ - $γ$ , and $γ$ - $γ$ ~correlations, can place stringent constraints on fission models and parameters that would otherwise be free to be tuned separately to represent individual fission observables. The FREYA~and CGMF~codes have been developed to follow the sequential emissions of prompt neutrons and $γ$ -rays~from the initial excited fission fragments produced right after scission. Both codes implement Monte Carlo techniques to sample initial fission fragment configurations in mass, charge and kinetic energy and sample probabilities of neutron and $γ$ ~emission at each stage of the decay. This approach naturally leads to using simple but powerful statistical techniques to infer distributions and correlations among many observables and model parameters. The comparison of model calculations with experimental data provides a rich arena for testing various nuclear physics models such as those related to the nuclear structure and level densities of neutron-rich nuclei, the $γ$ -ray~strength functions of dipole and quadrupole transitions, the mechanism for dividing the excitation energy between the two nascent fragments near scission, and the mechanisms behind the production of angular momentum in the fragments, etc. Beyond the obvious interest from a fundamental physics point of view, such studies are also important for addressing data needs in various nuclear applications. (See text for full abstract.)
nucl-thnucl-exEPJA(2018)·46 citations
04
Alternative methods to measure global polarization of $Λ$ hyperons
Irfan Siddique🇨🇳 · Zuo-tang Liang🇨🇳 · Michael Annan Lisa🇺🇸 · Qun Wang🇨🇳 · Zhang-bu Xu🇨🇳
We propose alternative methods to measure the global polarization of $Λ$ hyperons. These methods involve event averages of proton's and $Λ$ 's momenta in the lab frame. We carry out simulations using these methods and show that all of them work equivalently well in obtaining the global polarization of $Λ$ hyperons.
nucl-thCPC(2019)·5 citations
05
Peeling off neutron skins from neutron-rich nuclei: Constraints on the symmetry energy from neutron-removal cross sections
T. Aumann · C.A. Bertulani · F. Schindler · S. Typel
An experimentally constrained equation of state of neutron-rich matter is fundamental for the physics of nuclei and the astrophysics of neutron stars, mergers, core-collapse supernova explosions and the synthesis of heavy elements. To this end, we investigate the potential of constraining the density dependence of the symmetry energy close to saturation density through measurements of neutron-removal cross sections in high-energy nuclear collisions of a few hundreds MeV/nucleon to GeV/nucleon. We show that the sensitivity of the total neutron-removal cross section is high enough so that the required accuracy can be reached experimentally with the recent developments of new detection techniques. We quantify two crucial points to minimize the model dependence of the approach and to reach the required accuracy: the contribution to the cross section from inelastic scattering has to be measured separately in order to allow a direct comparison of experimental cross sections to theoretical cross sections based on density functional theory and eikonal theory. The accuracy of the reaction model should be investigated and quantified by the energy and target dependence of various nucleon-removal cross sections. Our calculations explore the dependence of neutron-removal cross sections on the neutron skin of medium-heavy neutron-rich nuclei, and we demonstrate that the slope parameter L of the symmetry energy could be constrained down to +/-10 MeV by such a measurement with a 2% accuracy of the measured and calculated cross sections.
nucl-thnucl-exPRL(2017)·58 citations
06
Partial restoration of spin-isospin SU(4) Symmetry and the One-QRPA method in Double Beta Decay
V. dos S. Ferreira🇧🇷 · F. Krmpotić🇦🇷 · C.A. Barbero🇦🇷 · A. R. Samana🇧🇷
The one-QRPA method is used to describe simultaneously both double decay beta modes, giving special attention to the partial restoration of spin-isospin SU(4) symmetry. To implement this restoration and to fix the model parameters, we resort to the energetics of Gamow-Teller resonances and to the minima of the single $β^{+}$ -decay strengths. This makes the theory predictive regarding the $β β_{2 ν}$ -decay, producing the $2 ν$ moments in $^{48}$ Ca, $^{76}$ Ge, $^{82}$ Se, $^{96}$ Zr, $^{100}$ Mo, $^{128, 130}$ Te, and $^{150}$ Nd, that are of the same order of magnitude as the experimental ones; however, the agreement with $β β_{2 ν}$ data is only modest. To include contributions coming from induced nuclear weak currents, we extend the $β β_{0 ν}$ -decay formalism employed previously in C. Barbero et. al, Nuc. Phys. A628, 170 (1998). The numerical results for the $β β_{0 ν}$ moments in the above mentioned nuclei are similar to those obtained in other theoretical studies although smaller on averag by $\sim 40%$ . We attribute this difference basically to the one-QRPA-method, employed here for the first time, instead of the currently used two-QRPA-method. The difference is partially due to the way of carrying out the restoration of the spin-isospin symmetry. It is hard to say which is the best way to make the restoration, since the $β β_{0 ν}$ moments are not experimentally measurable. The numerical uncertainties in the $β β$ moments, related with i) their strong dependence on the residual interaction in the p-p channel when evaluated within the QRPA, and ii) lack of proper knowledge of single-particle energies, have been quantified. It is concluded that the partial restoration of the SU (4) symmetry is crucial in the description of the $β β$ -decays, regardless of the nuclear model used.
nucl-thPRC(2017)·9 citations
07
Charmonium Coherent Photoproduction and Hadroproduction with Effects of Quark Gluon Plasma
Wei Shi · Wangmei Zha🇨🇳 · Baoyi Chen
We study the charmonium coherent photoproduction and hadroproduction consistently with modifications from both cold and hot nuclear matters. The strong electromagnetic fields from fast moving nucleus interact with the other target nucleus, producing abundant charmonium in the extremely low transverse momentum region $p_{T} < 0.1$ GeV/c. This results in significative enhancement of $J / ψ$ nuclear modification factor in semi-central and peripheral collisions. In the middle $p_{T}$ region such as $p_{T} < 3 \sim 5$ GeV/c, $J / ψ$ final yield is dominated by the combination process of single charm and anti-charm quarks moving in the deconfined matter, $c + c ˉ \to J / ψ + g$ . In the higher $p_{T}$ region, $J / ψ$ production are mainly from parton initial hard scatterings at the beginning of nucleus-nucleus collisions and decay of B hadrons. We include all of these production mechanisms and explain the experimental data well in different colliding centralities and transverse momentum regions.
nucl-thnucl-exPLB(2018)·41 citations
08
Two neutrino double- $β$ decay of $94 \leq A \leq 150$ nuclei for the 0 $^{+} \to$ 2 $^{+}$ transition
Yash Kaur Singh · R. Chandra · P.K. Raina · P.K. Rath
Within the PHFB approach, the $0^{+} \to 2^{+}$ transition of two neutrino double- $β$ decay of $^{94, 96}$ Zr, $^{100}$ Mo, $^{104}$ Ru, $^{110}$ Pd, $^{128, 130}$ Te and $^{150}$ Nd isotopes is studied employing wave functions generated with four different parametrizations of the pairing plus multipole type of two-nucleon interaction and the summation method. In comparison to the $0^{+} \to 0^{+}$ transition, the nuclear transition matrix elements $M_{2 ν} (2^{+})$ are quite sensitive to the deformation of the yrast 2 $^{+}$ state. Consideration of the available theoretical and experimental results suggest that the observation of the 02 $^{+}$ transition of $2 ν β^{-} β^{-}$ decay may be possible in $^{96}$ Zr, $^{100}$ Mo, $^{130}$ Te and $^{150}$ Nd isotopes. The effect of deformation on the $M_{2 ν} (2^{+})$ is also studied.
nucl-thEPJA(2017)·5 citations
09
Cluster formation in pre-compound nuclei in the time-dependent framework
Bastian Schuetrumpf · Witold Nazarewicz
Background: Applications of nuclear time-dependent density functional theory (TDDFT) are often capable of providing quantitative description of heavy ion reactions. However, the structure of pre-compound states produced in heavy ion reactions are difficult to assess theoretically in TDDFT as the s.p. density alone is a weak indicator of shell structure and cluster states. Purpose: We employ the time-dependent nucleon localization function (NLF) to reveal structure of pre-compound states in nuclear reactions involving light and medium-mass ions. We primarily focus on spin saturated systems with N = Z. Furthermore, we study reactions with oxygen and carbon ions, for which experimental evidence for {\alpha} clustering in pre-compound states exists. Method: We utilize the symmetry-free TDDFT approach and compute the NLFs to describe $^{16}$ O + $^{16}$ O, $^{40}$ Ca + $^{16}$ O, $^{40}$ Ca + $^{40}$ Ca, and $^{16, 18}$ O + $^{12}$ C collisions at energies above the Coulomb barrier. Results: We show that NLFs reveal a variety of time-dependent modes involving cluster structures. For instance, the $^{16}$ O + $^{16}$ O collision results in a vibrational mode of a quasi-molecular \alpha- $^{12}$ C- $^{12}$ C-\alpha{} state. For heavier ions, a variety of cluster configurations are predicted. For the collision of $^{16, 18}$ O + $^{12}$ C, we showed that the pre-compound system has a tendency to form {\alpha} clusters. This result supports the experimental findings that the presence of cluster structures in the projectile and target nuclei gives rise to strong entrance channel effects and enhanced {\alpha} emission. Conclusion: The time-dependent NLF is a good indicator of clusters structures in complex pre-compound states formed in heavy-ion fusion reactions. The localization reveals the presence of collective vibrations involving cluster structures, which dominate the initial dynamics of the fusing system.
nucl-thPRC(2017)·42 citations
10
Hyperspherical harmonics expansion on Lagrange meshes for bosonic systems in one dimension
N.K. Timofeyuk · D. Baye
A one-dimensional system of bosons interacting with contact and single-Gaussian forces is studied with an expansion in hyperspherical harmonics. The hyperradial potentials are calculated using the link between the hyperspherical harmonics and the single-particle harmonic-oscillator basis while the coupled hyperradial equations are solved with the Lagrange-mesh method. Extensions of this method are proposed to achieve good convergence with small numbers of mesh points for any truncation of hypermomentum. The convergence with hypermomentum strongly depends on the range of the two-body forces: it is very good for large ranges but deteriorates as the range decreases, being the worst for the contact interaction. In all cases, the lowest-order energy is within 4.5 $%$ of the exact solution and shows the correct cubic asymptotic behaviour at large boson numbers. Details of the convergence studies are presented for 3, 5, 20 and 100 bosons. A special treatment for three bosons was found to be necessary. For single-Gaussian interactions, the convergence rate improves with increasing boson number, similar to what happens in the case of three-dimensional systems of bosons.
nucl-thFew Body Syst.(2017)·7 citations
11
Beth-Uhlenbeck approach for repulsive interactions between baryons in a hadron gas
Volodymyr Vovchenko🇩🇪 · Anton Motornenko🇩🇪 · Mark I. Gorenstein🇺🇦 · Horst Stoecker🇩🇪
The quantum mechanical Beth-Uhlenbeck (BU) approach for repulsive hard-core interactions between baryons is applied to the thermodynamics of a hadron gas. The second virial coefficient $a_{2}$ -- the "excluded volume" parameter -- calculated within the BU approach is found to be temperature dependent, and it differs dramatically from the classical excluded volume (EV) model result. At temperatures $T = 100 - 200$ MeV, the widely used classical EV model underestimates the EV parameter for nucleons at a given value of the nucleon hard-core radius by large factors of 3-4. Previous studies, which employed the hard-core radii of hadrons as an input into the classical EV model, have to be re-evaluated using the appropriately rescaled EV parameters. The BU approach is used to model the repulsive baryonic interactions in the hadron resonance gas (HRG) model. Lattice data for the second and fourth order net baryon susceptibilities are described fairly well when the temperature dependent BU baryonic excluded volume parameter corresponds to nucleon hard-core radii of $r_{c} = 0.25 - 0.3$ fm. Role of the attractive baryonic interactions is also considered. It is argued that HRG model with a constant baryon-baryon EV parameter $v_{N N} ≃ 1$ fm $^{3}$ provides a simple yet efficient description of baryon-baryon interaction in the crossover temperature region.
nucl-thhep-phPRC(2018)·34 citations
12
Optical Potentials Derived from Nucleon-Nucleon Chiral Potentials at N4LO
M. Vorabbi🇨🇦 · P. Finelli🇮🇹 · C. Giusti🇮🇹
Background: Elastic scattering is probably the main event in the interactions of nucleons with nuclei. Even if this process has been extensively studied in the last years, a consistent description, i.e., starting from microscopic two- and many-body forces connected by the same symmetries and principles, is still under development. Purpose: In a previous paper we derived a theoretical optical potential from NN chiral potentials at fourth order (N3LO). In the present work we use NN chiral potentials at fifth order (N4LO), with the purpose to check the convergence and to assess the theoretical errors associated with the truncation of the chiral expansion in the construction of an optical potential. Methods: The optical potential is derived as the first-order term within the spectator expansion of the nonrelativistic multiple scattering theory and adopting the impulse approximation and the optimum factorization approximation. Results: The pp and np Wolfenstein amplitudes and the cross section, analyzing power, and spin rotation of elastic proton scattering from 16O, 12C, and 40Ca nuclei are presented at an incident proton energy of 200 MeV. The results obtained with different versions of chiral potentials at N4LO are compared. Conclusions: Our results indicate that convergence has been reached at N4LO. The agreement with the experimental data is comparable with the agreement obtained in our previous work. We confirm that building an optical potential within chiral perturbation theory is a promising approach for describing elastic proton-nucleus scattering.
nucl-thPRC(2017)·22 citations
13
Constant temperature description of the nuclear level densities
Mihai Horoi · Jayani Dissanayake
The spin and parity dependent nuclear level densities (NLD) are calculated for medium-heavy nuclei using shell model techniques. The NLD are used to calculate cross sections and reaction rates of interest for nuclear astrophysics and nuclear energy applications. We investigate a new approach of describing the shell model NLD via a constant temperature parametrization. This approach provides new information about the effects of symmetries on the temperature of the low-lying nuclear states, and it is shown to be more versatile for applications.
nucl-thAIP Conf.Proc.(2017)·2 citations
14
Neutron width statistics in a realistic resonance-reaction model
P. Fanto · G. F. Bertsch · Y. Alhassid
A recent experiment on s-wave neutron scattering from $^{192, 194, 196}$ Pt found that the reduced neutron width distributions deviate significantly from the expected Porter-Thomas distribution (PTD), and several explanations have been proposed within the statistical model of compound nucleus reactions. Here, we study the statistics of reduced neutron widths in the reaction $n +^{194}$ Pt within a model that combines the standard statistical model with a realistic treatment of the neutron channel. We find that, if the correct secular energy dependence of the average neutron widths is used, then the reduced neutron width distribution is in excellent agreement with the PTD for a reasonable range of the neutron-nucleus coupling strength and depth of the neutron channel potential. Within our parameter range, there can be a near-threshold bound or virtual state of the neutron channel potential that modifies the energy dependence of the average width from the $E$ dependence, commonly assumed in experimental analysis, in agreement with the proposal of H. A. Weidenmüller [1]. In these cases, the reduced neutron width distributions extracted using the $E$ dependence are significantly broader than the PTD. We identify a relatively narrow range of parameters where this effect is significant.
nucl-thcond-mat.mes-hallPRC(2018)·15 citations
15
A data-driven analysis for the temperature and momentum dependence of the heavy quark diffusion coefficient in relativistic heavy-ion collisions
Yingru Xu🇺🇸 · Marlene Nahrgang🇺🇸 · Shanshan Cao🇺🇸 · Jonah E. Bernhard🇫🇷 · Steffen A. Bass🇺🇸
By applying a Bayesian model-to-data analysis, we estimate the temperature and momentum dependence of the heavy quark diffusion coefficient in an improved Langevin framework. The posterior range of the diffusion coefficient is obtained by performing a Markov chain Monte Carlo random walk and calibrating on the experimental data of $D$ -meson $R_{AA}$ and $v_{2}$ in three different collision systems at RHIC and the LHC: AuAu collisions at 200 GeV, PbPb collisions at 2.76 and 5.02 TeV. The spatial diffusion coefficient is found to be consistent with lattice QCD calculations and comparable with other models' estimation. We demonstrate the capability of our improved Langevin model to simultaneously describe the $R_{AA}$ and $v_{2}$ at both RHIC and the LHC energies, as well as the higher order flow coefficient such as $D$ -meson $v_{3}$ . We show that by applying a Bayesian analysis, we are able to quantitatively and systematically study the heavy flavor dynamics in heavy-ion collisions.
nucl-thPRC(2018)·166 citations

Affiliations

first authorsco-authorsvia INSPIRE