Nuclear Theory·nucl-th

Tuesday·November 10, 2015

13 papers—6 primary·7 cross-listed

01
Nuclear isospin asymmetry in $α$ decays of heavy nuclei
Eunkyoung Shin · Yeunhwan Lim · Chang Ho Hyun · Yongseok Oh
The effects of nuclear isospin asymmetry on $α$ decay lifetimes of heavy nuclei are investigated within various phenomenological models of nuclear potential for the $α$ particle. We consider the widely used simple square well potential and Woods-Saxon potential, and modify them by including an isospin asymmetry term. We then suggest a model for the potential of the $α$ particle motivated by a microscopic phenomenological approach of the Skyrme force model, which naturally introduce the isospin dependent form of the nuclear potential for the $α$ particle. The empirical $α$ decay lifetime formula of Viola and Seaborg is also modified to include isospin asymmetry effects. The obtained $α$ decay half-lives are in good agreement with the experimental data and we find that including the nuclear isospin effects somehow improves the theoretical results for $α$ decay half-lives. The implications of these results are discussed and the predictions on the $α$ decay lifetimes of superheavy elements are also presented.
nucl-thnucl-exPRC(2016)·45 citations
02
Observables and initial conditions for rotating and expanding fireballs with spheroidal symmetry
T. Csorgo🇭🇺 · M.I. Nagy🇭🇺 · I. F. Barna🇭🇺
Utilizing a recently found class of exact, analytic rotating solutions of non-relativistic fireball hydrodynamics, we calculate analytically the single-particle spectra, the elliptic flows and two-particle Bose-Einstein correlation functions for rotating and expanding fireballs with spheroidal symmetry. We demonstrate, that rotation generates final state momentum anisotropies even for a spatially symmetric, spherical initial geometry of the fireball. The mass dependence of the effective temperatures, as well as the HBT radius parameters and the elliptic flow are shown to be sensitive not only to radial flow effects but also to the magnitude of the initial angular momentum.
nucl-thhep-exhep-phnucl-exPRC(2016)·12 citations
03
Correlations between the fragmentation modes and light charged particles emission in heavy ion collisions
Yingxun Zhang · Chengshuang Zhou · Jixian Chen · Ning Wang · Kai Zhao · Zhuxia Li
The correlations between the shape of rapidity distribution of the yield of light charged particles and the fragmentation modes in semi-peripheral collisions for $^{70}$ Zn+ $^{70}$ Zn, $^{64}$ Zn+ $^{64}$ Zn and $^{64}$ Ni+ $^{64}$ Ni at the beam energy of 35MeV/nucleon are investigated based on ImQMD05 code. Our studies show there is an interplay between the binary, ternary and multi-fragmentation break-up modes. The binary and ternary break-up modes more prefer to emit light charged particles at middle rapidity and give larger values of $R_{y i e l d}^{mi d}$ compared with the multi-fragmentation break-up mode does. The reduced rapidity distribution for the normalized yields of p, d, t, $^{3}$ He, $^{4}$ He and $^{6}$ He and the corresponding values of $R_{y i e l d}^{mi d}$ can be used to estimate the probability of multi-fragmentation break-up modes. By comparing to experimental data, our results illustrate that $\geq$ 40\% of the collisions events belong to the multi-fragmentation break-up mode for the reactions we studied.
nucl-thSCPMA(2015)·8 citations
04
Production of hypertritons in heavy ion collisions around the threshold of strangeness production
Christoph Hartnack🇫🇷 · Arnaud Le Fèvre🇩🇪 · Yvonne Leifels🇩🇪 · Jörg Aichelin🇫🇷
We use the Isospin Quantum Molecular Dynamics approach supplemented with a phase space coalescence to study the properties of the production of hypertritons. We see strong influences of the hyperon rescattering on the yields. The hypertritons show up to be quite aligned to the properties of nuclear matter underlining the necessity of rescattering to transport the hyperons to the spectator matter.
nucl-th4 citations
05
Ground and excited states of doubly open-shell nuclei from ab initio valence-space Hamiltonians
S. R. Stroberg🇨🇦 · H. Hergert🇺🇸 · J. D. Holt🇨🇦 · S. K. Bogner🇺🇸 · A. Schwenk🇩🇪
We present ab initio predictions for ground and excited states of doubly open-shell fluorine and neon isotopes based on chiral two- and three-nucleon interactions. We use the in-medium similarity renormalization group, in both flow-equation and Magnus formulations, to derive mass-dependent sd valence-space Hamiltonians. The experimental ground-state energies are reproduced through neutron number N=14, beyond which a new targeted normal-ordering procedure improves agreement with data and large-scale multi-reference calculations. For spectroscopy, we focus on neutron-rich 23-26F and 24-26Ne isotopes near N=14,16 magic numbers. In all cases we find an agreement with experiment competitive with established phenomenology. Moreover, yrast states are well described in 20Ne and 24Mg, providing an ab initio description of deformation in the medium-mass region.
nucl-thnucl-exPRC(2016)·145 citations
06
Approximate restoration of translational and rotational symmetries within the Lipkin method
Y. Gao · J. Dobaczewski · P. Toivanen
Background: Nuclear self-consistent mean-field approaches are rooted in the density functional theory and, through the spontaneous symmetry breaking mechanism, allow for including important correlations, while keeping the simplicity of the approach. Because real ground states should have all symmetries of the nuclear Hamiltonian, these methods require subsequent symmetry restoration. Purpose: We implement and study Lipkin method of approximate variation after projection applied to the restoration of the translational or rotational symmetries. Methods: We use Lipkin operators up to quadratic terms in momenta or angular momenta with self-consistently determined values of the Peierls-Yoccoz translational masses or moments of inertia, respectively. Calculations based on Skyrme energy-density functional are performed for heavy, deformed, and paired nuclei. Results: In deformed nuclei, the Peierls-Yoccoz translational masses along three different principal-axes directions of the intrinsic system can be different, which illustrates different widths of the total-momentum distributions. Numerically, the differences are only of the order of a few per cent. For the rotational-symmetry restoration, the Lipkin method compares favorably with the exact angular-momentum projection, which requires much larger computational effort. Conclusions: The Lipkin method of translational and rotational symmetry restoration is a practical low-cost method of determining the corresponding correlation energies. It allows for a simultaneous restoration of several symmetries and can be relatively easily implemented in the standard self-consistent mean-field calculations, including those required for the parameter adjustments.
nucl-th1 citation
07
Instanton-dyon Ensemble with two Dynamical Quarks: the Chiral Symmetry Breaking
Rasmus Larsen🇺🇸 · Edward Shuryak🇺🇸
This is the second paper of the series aimed at understanding the ensemble of instanton-dyons, now with two flavors of light dynamical quarks. The partition function is appended by the fermionic factor, $(d e tT)^{N_{f}}$ and Dirac eigenvalue spectra at small values are derived from the numerical simulation of 64 and 128 dyons. Those spectra show clear chiral symmetry breaking pattern at high dyon density.
↳ hep-phhep-latnucl-thPRD(2016)·43 citations
08
Nuclear Parity Violation from Lattice QCD
Thorsten Kurth · Evan Berkowitz · Enrico Rinaldi · Pavlos Vranas · Amy Nicholson · Mark Strother · Andre Walker-Loud
The electroweak interaction at the level of quarks and gluons are well understood from precision measurements in high energy collider experiments. Relating these fundamental parameters to Hadronic Parity Violation in nuclei however remains an outstanding theoretical challenge. One of the most interesting observables in this respect is the parity violating hadronic neutral current: it is hard to measure in collider experiments and is thus the least constrained observable of the Standard Model. Precision measurements of parity violating transitions in nuclei can help to improve these constraints. In these systems however, the weak interaction is masked by effects of the seven orders of magnitude stronger non-perturbative strong interaction. Therefore, in order to relate experimental measurements of the parity violating pion-nucleon couplings to the fundamental Lagrangian of the SM, these non-perturbative effects have to be well understood. In this paper, we are going to present a Lattice QCD approach for computing the $Δ I = 2$ parity violating matrix element in proton proton scattering. This process does not involve disconnected diagrams in the isospin symmetric limit and is thus a perfect testbed for studying the feasibility of the more involved calculation of the parity violating pion-nucleon coupling.
↳ hep-lathep-phnucl-thPoS(2016)·14 citations
09
Two-nucleon scattering in multiple partial waves
Amy Nicholson🇺🇸 · Evan Berkowitz🇺🇸 · Enrico Rinaldi🇺🇸 · Pavlos Vranas🇺🇸 · Thorsten Kurth🇺🇸 · Balint Joo🇺🇸 · Mark Strother🇺🇸 · Andre Walker-Loud🇺🇸
We determine scattering phase shifts for S,P,D, and F partial wave channels in two-nucleon systems using lattice QCD methods. We use a generalization of Luscher's finite volume method to determine infinite volume phase shifts from a set of finite volume ground- and excited-state energy levels on two volumes, V=(3.4 fm)^3 and V=(4.5 fm)^3. The calculations are performed in the SU(3)-flavor limit, corresponding to a pion mass of approximately 800 MeV. From the energy dependence of the phase shifts we are able to extract scattering parameters corresponding to an effective range expansion.
↳ hep-latnucl-thPoS(2016)·7 citations
10
Low energy scattering phase shifts for meson-baryon systems
William Detmold🇺🇸 · Amy Nicholson🇺🇸
In this work, we calculate meson-baryon scattering phase shifts in four channels using lattice QCD methods. From a set of calculations at four volumes, corresponding to spatial sizes of 2, 2.5, 3, and 4 fm, and a pion mass of m_pi ~ 390 MeV, we determine the scattering lengths and effective ranges for these systems at the corresponding quark masses. We also perform the calculation at a lighter quark mass, m_pi ~ 230 MeV, on the largest volume. Using these determinations, along with those in previous work, we perform a chiral extrapolation of the scattering lengths to the physical point after correcting for the effective range contributions using the multi-volume calculations performed at m_pi ~ 390 MeV.
↳ hep-latnucl-thPRD(2016)·31 citations
11
Proximity of $f_{0} (1500)$ and $f_{0} (1710)$ to the scalar glueball
Amir H. Fariborz🇺🇸 · Azizollah Azizi🇮🇷 · Abdorreza Asrar🇮🇷
Within a nonlinear chiral Lagrangian framework, the underlying mixings among quark-antiquark, four-quark and glue components of $f_{0} (1500)$ and $f_{0} (1710)$ are studied in a global picture that includes all isosinglet scalar mesons below 2 GeV. The quark components are introduced in the Lagrangian in terms of two separate nonets (a quark-antiquark nonet and a four-quark nonet) which can mix with each other and with a scalar glueball. The free parameters of the Lagrangian are studied by a simultaneous fit to more than 20 experimental data and constraints on the mass spectrum, decay widths, and decay ratios of the isosinglet scalars below 2 GeV. Moreover, constraints on the mass spectrum and decay widths of isodoublet and isovector scalars below 2 GeV as well as pion-pion scattering amplitude are also taken into account. The insights gained in this global picture, due to the complexities of the mixings as well as the experimental uncertainties, are mainly qualitative but are relatively robust, and reveal that the lowest scalar glueball hides between $f_{0} (1500)$ and $f_{0} (1710)$ , resulting in a considerable mixing with various quark components of these two states. The overall current experimental and theoretical uncertainties do not allow to pin down the exact glue components of isosinglet states, nevertheless it is shown that the $f_{0} (1500)$ and $f_{0} (1710)$ have the highest glue component. While this global study does not allow precision predictions for each individual state, it provides useful "family" correlations among the isosinglet states that are found insightful in probing the substructure of all scalars, in general, and the isosinglets, in particular. The overall estimate of the scalar glueball mass is found to be $1.58 \pm 0.18$ GeV.
↳ hep-phhep-exhep-latnucl-thPRD(2015)·15 citations
12
Presupernova neutrinos: realistic emissivities from stellar evolution
Kelly M. Patton🇺🇸 · Cecilia Lunardini🇺🇸 · Robert J. Farmer🇺🇸
We present a new calculation of neutrino emissivities and energy spectra from a massive star going through the advanced stages of nuclear burning (presupernova) in the months before becoming a supernova. The contributions from beta decay and electron capture, pair annihilation, plasmon decay, and the photoneutrino process are modeled in detail, using updated tabulated nuclear rates. We also use realistic conditions of temperature, density, electron fraction and nuclear isotopic composition of the star from the state of the art stellar evolution code MESA. Results are presented for a set of progenitor stars with mass between 15 $M_{⊙}$ and 30 $M_{⊙}$ . It is found that beta processes contribute substantially to the neutrino emissivity above realistic detection thresholds of few MeV, at selected positions and times in the evolution of the star.
↳ astro-ph.SRnucl-thApJ(2017)·51 citations
13
Sensitivity to oscillation with a sterile fourth generation neutrino from ultra-low threshold neutrino-nucleus coherent scattering
Bhaskar Dutta · Yu Gao · Andrew Kubik · Rupak Mahapatra · Nader Mirabolfathi · Louis E. Strigari · Joel W. Walker
We discuss prospects for probing short-range sterile neutrino oscillation using neutrino-nucleus coherent scattering with ultra-low energy ( $\sim 10$ eV - 100 eV) recoil threshold cryogenic Ge detectors. The analysis is performed in the context of a specific and contemporary reactor-based experimental proposal, developed in cooperation with the Nuclear Science Center at Texas A\&M University, and references developing technology based upon economical and scalable detector arrays. The baseline of the experiment is substantially shorter than existing measurements, as near as about 2 meters from the reactor core, and is moreover variable, extending continuously up to a range of about 10 meters. This proximity and variety combine to provide extraordinary sensitivity to a wide spectrum of oscillation scales, while facilitating the tidy cancellation of leading systematic uncertainties in the reactor source and environment. With 100~eV sensitivity, for exposures on the order of 200 kg $\cdot$ y, we project an estimated sensitivity to first/fourth neutrino oscillation with a mass gap $Δ m^{2} \sim 1 eV^{2}$ at an amplitude $sin^{2} 2 θ \sim 1 0^{- 1}$ , or $Δ m^{2} \sim 0.2 eV^{2}$ at unit amplitude. Larger exposures, around 5,000 kg $\cdot$ y, together with 10 eV sensitivity are capable of probing more than an additional order of magnitude in amplitude.
↳ hep-phhep-exnucl-exnucl-thPRD(2016)·71 citations

Affiliations

first authorsco-authorsvia INSPIRE