Nuclear Theory·nucl-th

Tuesday·September 17, 2019

17 papers—14 primary·3 cross-listed

01
Quasielastic lepton scattering and back-to-back nucleons in the short-time approximation
Saori Pastore🇺🇸 · Joseph Carlson🇺🇸 · Stefano Gandolfi🇺🇸 · Rocco Schiavilla🇺🇸 · Robert B. Wiringa🇺🇸
Understanding quasielastic electron- and neutrino-scattering from nuclei has taken on new urgency with current and planned neutrino oscillation experiments, and with electron scattering experiments measuring specific final states, such as those involving nucleon pairs in ``back-to-back'' configurations. Accurate many-body methods are available for calculating the response of light ( $A \leq 12$ ) nuclei to electromagnetic and weak probes, but they are computationally intensive and only applicable to the inclusive response. In the present work we introduce a novel approach, based on realistic models of nuclear interactions and currents, to evaluate the short-time (high-energy) inclusive and exclusive response of nuclei. The approach accounts reliably for crucial two-nucleon dynamics, including correlations and currents, and provides information on back-to-back nucleons observed in electron and neutrino scattering experiments. We demonstrate that in the quasielastic regime and at moderate momentum transfers both initial- and final-state correlations, and two-nucleon currents are important for a quantitatively successful description of the inclusive response and final state nucleons. Finally, the approach can be extended to include relativistic---kinematical and dynamical---effects, at least approximately in the two-nucleon sector, and to describe the response in the resonance-excitation region.
nucl-thPRC(2020)·50 citations
02
Benchmark neutrinoless double-beta decay matrix elements in a light nucleus
R.A.M. Basili🇺🇸 · J.M. Yao🇺🇸 · J. Engel🇺🇸 · H. Hergert🇺🇸 · M. Lockner🇺🇸 · P. Maris🇺🇸 · J.P. Vary🇺🇸
We compute nuclear matrix elements of neutrinoless double-beta decay mediated by light Majorana-neutrino exchange in the A = 6 system. The goal is to benchmark two many-body approaches, the No-Core Shell Model and the Multi-Reference In-Medium Similarity Renormalization Group. We use the SRG-evolved chiral N3LO-EM500 potential for the nuclear interaction, and make the approximation that isospin is conserved. We compare the results of the two approaches as a function of the cutoff on the many-body basis space. Although differences are seen in the predicted nuclear radii, the ground-state energies and neutrinoless double-beta decay matrix elements produced by the two approaches show significant agreement. We discuss the implications for calculations in heavier nuclei.
nucl-thPRC(2020)·26 citations
03
Symmetry energy of super-dense neutron-rich matter from integrating barotropic pressures in neutron stars and heavy-ion reactions
Bao-An Li🇺🇸 · Wen-Jie Xie🇺🇸
Within the minimum model of neutron stars (NS) consisting of neutrons, protons and electrons, a new approach is proposed for inferring the symmetry energy of super-dense neutron-rich nucleonic matter above twice the saturation density $ρ_{0}$ of nuclear matter directly from integrating iteratively barotropic pressures in both neutron stars and heavy-ion reactions. Simultaneously, the proton fraction of NSs at $β$ equilibrium is extracted as a function of baryon density from the same procedure. An application of this approach using the NS pressure from GW170817 and the pressure in cold symmetric nuclear matter (SNM) extracted earlier by analyzing nuclear collective flow data in relativistic heavy-ion collisions provides a useful constraining band for the symmetry energy above $2 ρ_{0}$ .
nucl-thastro-ph.HEastro-ph.SRnucl-exPLB(2020)·7 citations
04
Influence of electromagnetic fields in proton-nucleus collisions at relativistic energy
Lucia Oliva🇩🇪 · Pierre Moreau🇩🇪 · Vadim Voronyuk🇷🇺 · Elena Bratkovskaya🇩🇪
We study proton-gold collisions at RHIC energy $s_{N N} = 200$ GeV within the Parton-Hadron-String Dynamics (PHSD) off-shell transport approach, investigating the influence of the intense electromagnetic fields generated in these small systems. We show the space-time evolution of the magnetic and electric components, emphasizing the huge values of the latter one, in particular the electric field $E_{x}$ along the impact parameter direction whose magnitude is comparable to the magnetic field $B_{y}$ perpendicular to the reaction plane. We find a fair agreement of the charged particle pseudorapidity density of the high-multiplicity events with respect to the experimental result of the PHENIX Collaboration. Focusing on the most central collision, we show rapidity distributions and spectra as well as the flow coefficients $v_{1}$ and $v_{2}$ and we discuss the impact of the electromagnetic fields on identified particle observables. We compute the directed flow $v_{1}$ of $π^{+}$ , $π^{-}$ , $K^{+}$ , $K^{-}$ for collisions at fixed impact parameter and predict that an electromagnetically-induced splitting in the $v_{1}$ of positively and negatively charged particles is generated in the Au-going side of p+Au reaction mainly driven by the huge $E_{x}$ component. We find that this effect is stronger for the strange mesons and increases for increasing impact parameter. Furthermore, we highlight the amount of directed flow generated in the deconfined phase, finding that it constitutes the main contribution in the central rapidity region, especially for kaons. Thus, we support the idea that the directed flow is a promising probe for the electromagnetic fields generated in relativistic nuclear collisions and show that in proton-induced reactions the electric component along the impact parameter axis is the primary origin of a charge-odd $v_{1}$ of pions and kaons.
nucl-thPRC(2020)·27 citations
05
Effects of $P_{tot}$ gates and velocity gates on light-particle momentum correlation in intermediate-energy heavy-ion collisions
Ting-Ting Wang🇨🇳 · Yu-Gang Ma🇨🇳 · Zheng-Qiao Zhang🇨🇳
Momentum correlation functions at small relative momenta are calculated for light particles $(n, p, d, t)$ emitted from $^{197}$ Au + $^{197}$ Au collisions at different impact parameters and beam energies within the framework of the isospin-dependent quantum molecular dynamics model complemented by the $L e d ni c k y ˊ$ and $L y u b os hi t z$ analytical method. We first make sure our model is able to reproduce the FOPI data of proton-proton momentum correlation in a wide energy range from 0.4 $A$ GeV to 1.5 $A$ GeV. Then we explore more physics insights through the emission times and momentum correlations among different light particles. The specific emphasize is the effects of total pair momentum among different light particles, impact parameters and in-medium nucleon-nucleon cross section. Both two-deuteron and two-triton correlation functions are anti-correlation due to the final state interaction, and they are affected by in-medium nucleon-nucleon cross section for the higher total momentum of the particle pairs, but not for the lower ones. In addition, impact parameter and in-medium nucleon-nucleon cross section dependences of the emission source radii are extracted by fitting the momentum correlation functions. The results indicate that momentum correlation functions gating with total pair momentum is stronger for the smaller in-medium nucleon-nucleon cross section factor $(η)$ or impact parameter $(b)$ . Non-identical particle correlations ( $n p, p d, pt,$ and $d t$ ) are also investigated by the velocity-gated correlation functions which can give information of the particles' emission sequence, and the result indicates that heavier ones $(d e u t er o n / t r i t o n)$ are, one the average, emitted earlier than protons, in the small relative momentum region.
nucl-thnucl-exPRC(2019)·15 citations
06
Energy staggering parameters in nuclear magnetic rotational bands
Wu-Ji Sun · Jian Li
The systematics of energy staggering for the magnetic rotational bands with $M 1$ and $E 2$ transition properties strictly consistent with the features of good candidates of magnetic rotational bands in the $A \sim 80$ , 110, 130 and 190 mass regions are presented. The regularities exhibited by these bands concerning the staggering parameter which increases with increasing spin are in agreement with the semiclassical description of shears mechanism. In addition, the abnormal behaviours in the backbend regions or close to band termination have also been discussed. Taking the magnetic dipole bands with same configuration in three $N = 58$ isotones, i.e., $^{103}$ Rh, $^{105}$ Ag, and~ $^{107}$ In, as examples, the transition from chiral rotation to magnetic rotation with the proton number approaching $Z = 50$ is presented. Moreover, the self-consistent tilted axis cranking and principle axis cranking relativistic mean-field theories are applied to investigate the rotational mechanism in dipole band of $^{105}$ Ag.
nucl-thCPC(2019)·4 citations
07
Shell Model Symmetries-Honoring Franco Iachello
Levering Wolfe🇺🇸 · Larry Zamick🇺🇸
We discuss L=0 vs L=2 couplings, symmetries of the pairing interaction for neutrons and protons, and the J_{max} interaction. We show that certain schematic interactions yield exponentially decreasing transition strengths.We compare shell model calculations of B(E2)'s and quadrupole moments in the p-f shell with collective model results.
nucl-thnucl-exquant-phAIP Conf.Proc.(2019)·0 citations
08
Microscopic quantum ideal triaxial rotor model and related self-consistent cranking model: slow-wobbling rotation in Ne-20
Parviz Gulshani
A microscopic quantum ideal rotor-model intrinsic Hamiltonian for triaxial rotation is derived from the nuclear Schrodinger equation by applying a rotation operator to a deformed nuclear ground state. This Hamiltonian is obtained only when a rigid-flow prescription is used for the three rotation angles in the rotation operator. Using Hartree-Fock variational and second quantization methods, the rotor Hamiltonian is transformed into that of a self-consistent triaxial cranking model (MSCRM-3) with a self-consistent angular-velocity vector, plus residual terms associated with the square of the angular momentum operator and with a two-body interaction. The approximations underlying the conventional cranking model are revealed. For a self-consistent deformed harmonic oscillator potential, the MSCRM-3 Schrodinger equation is transformed into that of a uniaxial cranking model plus local potential-energy cross terms using a rotation of the co-ordinate system. It is shown that uniform rotation is not generally possible. However, for a slow-wobbling rotation, an approximate uniform rotation becomes possible. In this limiting wobbly motion, the potential-energy cross terms are negligibly small, and the uni-axial cranking-model equation is solved analytically using a generalization of the isotropic-velocity-distribution condition of Bohr-Mottelson and Ripka-Blaizot-Kassis. The ground-state rotational-band excitation energy and quadrupole moment are calculated and compared with the measured data in Ne-20 . The results explain the mysterious decrease in the excitation-energy level spacing with increasing angular momentum. The impact of the residual of the square of the angular momentum and a separable quadrupole-quadrupole two-body interaction is studied in the Tamm-Dancoff approximation.
nucl-th0 citations
09
Particle-vibration coupling for giant resonances beyond the diagonal approximation
Shihang Shen · Gianluca Colò · Xavier Roca-Maza
A self-consistent particle-vibration coupling (PVC) model without diagonal approximation is presented. The diagonal approximation, that neglects completely the interaction between the doorway states, has been removed by taking into account the interaction between the two particle-holes inside the doorway states. As applications, isoscalar giant monopole, dipole, and quadrupole resonances in 16O are investigated based on the use of Skyrme functionals. The diagonal approximation is found to clearly impact the strength distribution of the giant quadrupole resonance, and the description of the experimental data is improved without this approximation. The impact of the diagonal approximation is analyzed in detail, especially its effect on the eigenenergies and the induced coupling between neutron and proton particle-hole configurations. The latter is a direct and physically sound effect of the improvement on our formalism. The importance of using self-consistently the full effective interaction in the PVC vertex, and the effect of its renormalization via the subtraction method, are also discussed. For completeness, we also analyze the dependence of our results on the Skyrme parametrization.
nucl-thPRC(2020)·14 citations
10
Nuclear shape coexistence from the perspective of an algebraic many-nucleon version of the Bohr-Mottelson unified model
David J. Rowe
A fully quantal algebraic version of the Bohr-Mottelson unified model is presented with the important property that its quantisation is defined by its irreducible unitary representations which span the many-nucleon Hilbert space of every nucleus. The model is uniquely defined by the requirement that its Lie algebra of observables includes the nuclear quadrupole moments and kinetic energy. It then follows that there can be no non-zero isoscalar E2 transitions between any states belonging to its different irreducible representations and, as a result, the states of the model are uniquely defined with the property that observed transitions between rotational states of nuclei are to be expressed in terms of mixtures of the model irreps. The algebraic version of the unified model parallels the Bohr-Mottelson model in most respects, including the possibility of including the effects of Coriolis and centrifugal forces as subsequent perturbations. However, it corrects its treatment of angular momentum quantisation and no longer uses an over-complete set of coordinates. These changes have significant implications for the dynamics of nuclear rotations which are hidden when its moments of inertia are considered as inertial masses in the standard expression of rotational kinetic energies. Thus, the developments put a new perspective on the phenomenon of shape coexistence.
nucl-thPRC(2020)·11 citations
11
Improvement of heavy flavor productions in a multi-phase transport model updated with modern nPDFs
L. Zheng🇨🇳 · C. Zhang🇨🇳 · S.S. Shi🇨🇳 · Z.W. Lin🇨🇳
Recently we have updated a multi-phase transport (AMPT) model with modern parton distribution functions of nuclei (nPDFs). Here we study open charm production in the updated AMPT model and compare to the experimental data from $pp$ and $AA$ collisions over a wide range of collision energies. Besides the update of nPDFs, we have removed the transverse momentum cutoff on initial heavy quark productions and also included the resultant heavy flavor cross section into the total minijet cross section in the initial condition as described by the HIJING model. We show that the AMPT model with these updates provides a much better description of the yields and transverse momentum spectra of various open charm hadrons in comparison with the experimental data. This lays the foundation for further heavy flavor studies within the transport model approach.
nucl-thhep-phnucl-exPRC(2020)·21 citations
12
The delimiting/frontier lines of the constituents of matter
Diógenes Galetti · Salomon S. Mizrahi
Looking at the \emph{chart of nuclides} displayed at the URL of the International Atomic Energy Agency (IAEA) \cite{IAEA} -- that contains all the known nuclides, the natural and those produced artificially in labs -- one verifies the existence of two, not quite regular, \emph{delimiting lines} between which dwell all the nuclides constituting matter. These lines are established by the highly unstable radionuclides located the most far away from those in the central locus, the\emph{valley of stability}. Here, making use of the "old" semi-empirical mass formula for stable nuclides together with the energy-time uncertainty relation of quantum mechanics, by a simple calculation we show that the obtained \emph{frontier lines}, for proton and neutron excesses, present an appreciable agreement with the delimiting lines. For the sake of presenting a somewhat comprehensive panorama of the matter in our Universe and their relation with the frontier lines, we narrate, in brief, what is currently known about the astrophysical nucleogenesis processes.
nucl-thRev.Bras.Ens.Fis.(2019)·0 citations
13
Three-body description of $^{12}$ C: From the hyperspherical formulation to the algebraic cluster model and its application to $α +^{12}$ C inelastic scattering
J. Casal · L. Fortunato · A. Vitturi · E. G. Lanza
Form factors for $α +^{12}$ C inelastic scattering are obtained within two theoretical ( $α + α + α$ ) approaches: The hyperspherical framework for three identical bosons, and the algebraic cluster model assuming the $D_{3 h}$ symmetry of an equilateral triangle subject to rotations and vibrations. Results show a good agreement, with form factors involving the Hoyle state having a slightly larger extension within the hyperspherical approach. Coupled-channel calculations using these form factors are ongoing.
nucl-thEPJ Web Conf.(2019)·0 citations
14
$S$ -factor and scattering-parameter extractions from $^{3} He +^{4} He \to^{7} Be + γ$
Xilin Zhang · Kenneth M. Nollett · D. R. Phillips
Previous studies of the reaction $^{3} He +^{4} He \to^{7} Be + γ$ have focused on providing the best central value and error bar for the $S$ factor at solar energies. Measurements of this capture reaction, the $^{3} He$ - $^{4} He$ scattering phase shifts, as well as properties of $^{7} Be$ , have been used to constrain employed theoretical models. Here we show that much more information than was previously appreciated can be extracted from angle-integrated capture data alone. We use the next-to-leading-order (NLO) amplitude in an effective field theory (EFT) for the reaction to perform the extrapolation. At this order the EFT describes the reaction using an s-wave scattering length and effective range, the asymptotic properties of the final bound states, and short-distance contributions to the $E 1$ capture amplitude. We extract the multi-dimensional posterior of all these parameters via a Bayesian analysis. We find that properties of the $^{7} Be$ ground and excited states are well constrained. The total $S$ factor $S (0) = 0.57 8_{- 0.016}^{+ 0.015}$ keV~b, while the branching ratio for excited- to ground-state capture at zero energy, $B r (0) = 0.40 6_{- 0.011}^{+ 0.013}$ , both at 68\% degree of belief. This $S (0)$ is broadly consistent with other recent evaluations, including the previously recommended value $S (0) = 0.56 \pm 0.03$ eV b, but has a smaller error bar. We also find significant constraints on the scattering parameters, and we obtain constraints on the $S (E)$ 's angular dependence. The path forward seems to lie with better measurements of the scattering phase shift and $S (E)$ 's angular dependence, together with better understanding of the asymptotic normalization coefficients of the $^{7}$ Be bound states' wave functions. Data on these could further reduce $S (0)$ 's uncertainty.
nucl-thastro-ph.SRnucl-exJ.Phys.G(2020)·39 citations

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