Nuclear Theory·nucl-th

Friday·July 29, 2016

9 papers—7 primary·2 cross-listed

01
[Submitted on 28 Jul 2016]
Single-particle and collective motion in unbound deformed $^{39} Mg$
K. Fossez · J. Rotureau · N. Michel · Quan Liu · W. Nazarewicz
Background: Deformed neutron-rich magnesium isotopes constitute a fascinating territory where the interplay between collective rotation and single-particle motion is strongly affected by the neutron continuum. The unbound $f p$ -shell nucleus $^{39} Mg$ is an ideal candidate to study this interplay. Purpose: In this work, we predict the properties of low-lying resonant states of $^{39} Mg$ , using a suite of realistic theoretical approaches rooted in the open quantum system framework. Method: To describe the spectrum and decay modes of $^{39} Mg$ we use the conventional Shell Model, Gamow Shell Model, Resonating Group Method, Density Matrix Renormalization Group method, and the non-adiabatic Particle-Plus-Rotor model formulated in the Berggren basis. Results: The unbound ground state of $^{39} Mg$ is predicted to be either a $J^{π} = 7/2^{-}$ state or a $3/2^{-}$ state. A narrow $J^{π} = 7/2^{-}$ ground-state candidate exhibits a resonant structure reminiscent of that of its one-neutron halo neighbor $^{37} Mg$ , which is dominated by the $f_{7/2}$ partial wave at short distances and a $p_{3/2}$ component at large distances. A $J^{π} = 3/2^{-}$ ground-state candidate is favored by the large deformation of the system. It can be associated with the $1/2^{-} [321]$ Nilsson orbital dominated by the $ℓ = 1$ wave; hence its predicted width is large. The excited $J^{π} = 1/2^{-}$ and $5/ 2^{-}$ states are expected to be broad resonances, while the $J^{π} = 9/2^{-}$ and $11/2^{-}$ members of the ground-state rotational band are predicted to have very small neutron decay widths. Conclusion: We demonstrate that the subtle interplay between deformation, shell structure, and continuum coupling can result in a variety of excitations in an unbound nucleus just outside the neutron drip line.
Comments:
9 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1607.08436 [pdf]
PRC(2016)·31 citations
02
[Submitted on 28 Jul 2016]
Emission of neutron-proton and proton-proton pairs in neutrino scattering
I. Ruiz Simo🇪🇸 · J.E. Amaro🇪🇸 · M.B. Barbaro🇮🇹 · A. De Pace🇮🇹 · J.A. Caballero🇪🇸 · G.D. Megias🇪🇸 · T.W. Donnelly🇺🇸
We use a recently developed model of relativistic meson-exchange currents to compute the neutron-proton and proton-proton yields in $(ν_{μ}, μ^{-})$ scattering from $^{12}$ C in the 2p-2h channel. We compute the response functions and cross sections with the relativistic Fermi gas model for different kinematics from intermediate to high momentum transfers. We find a large contribution of neutron-proton configurations in the initial state, as compared to proton-proton pairs. In the case of charge-changing neutrino scattering the 2p-2h cross section of proton-proton emission ({\it i.e.,} np in the initial state) is much larger than for neutron-proton emission ({\it i.e.,} two neutrons in the initial state) by a $(ω, q)$ -dependent factor. The different emission probabilities of distinct species of nucleon pairs are produced in our model only by meson-exchange currents, mainly by the $Δ$ isobar current. We also analyze other effects including exchange contributions and the effect of the axial and vector currents.
Comments:
9 pages and 8 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1607.08451 [pdf]
PLB(2016)·45 citations
03
[Submitted on 28 Jul 2016]
Fusion-fission probabilities, cross sections and structure notes of super-heavy nuclei
Michał Kowal · Tomasz Cap · Piotr Jachimowicz · Janusz Skalski · Krystyna Siwek-Wilczyńska · Janusz Wilczyński
Fusion - fission probabilities in the synthesis of heaviest elements are discussed in the context of the latest experimental reports. Cross sections for superheavy nuclei are evaluated using "Fusion by Diffusion" (FBD) model. Predictive power of this approach is shown for experimentally known Lv, Og isotopes and predictions given for Z=119,120. Ground state and saddle point properties as: masses, shell corrections, pairing energies and deformations necessary for cross section estimations are calculated systematically within the multidimensional microscopic - macroscopic method based on the deformed Woods-Saxon single particle potential. In the frame of FBD approach predictions for production of elements heavier than Z = 118 are not too optimistic. For this reason, and because of high instability of superheavy nuclei, we comment on some structure effects, connected with the K-isomerism phenomenon which could lead to a significant increase in the stability of these systems.
Comments:
Lecture given during Nobel symposium; "Chemistry and Physics of Heavy and Superheavy Elements" - May 29 - June 3, 2016, at Bäckaskog Castle
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1607.08462 [pdf]
EPJ Web Conf.(2016)·2 citations
04
[Submitted on 28 Jul 2016]
Large-scale deformed quasiparticle random-phase approximation calculations of the $γ$ -ray strength function using the Gogny force
M. Martini🇫🇷 · S. Péru🇫🇷 · S. Hilaire🇫🇷 · S. Goriely🇧🇪 · F. Lechaftois🇫🇷
Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we present large-scale calculations of the $E 1$ $γ$ -ray strength function obtained in the framework of the axially-symmetric deformed QRPA based on the finite-range Gogny force. This approach is applied to even-even nuclei, the strength function for odd nuclei being derived by interpolation. The convergence with respect to the adopted number of harmonic oscillator shells and the cut-off energy introduced in the 2-quasiparticle (2- $q p$ ) excitation space is analyzed. The calculations performed with two different Gogny interactions, namely D1S and D1M, are compared. A systematic energy shift of the $E 1$ strength is found for D1M relative to D1S, leading to a lower energy centroid and a smaller energy-weighted sum rule for D1M. When comparing with experimental photoabsorption data, the Gogny-QRPA predictions are found to overestimate the giant dipole energy by typically $\sim$ 2 MeV. Despite the microscopic nature of our self-consistent Hartree-Fock-Bogoliubov plus QRPA calculation, some phenomenological corrections need to be included to take into account the effects beyond the standard 2- $q p$ QRPA excitations and the coupling between the single-particle and low-lying collective phonon degrees of freedom. For this purpose, three prescriptions of folding procedure are considered and adjusted to reproduce experimental photoabsorption data at best. All of them are shown to lead to rather similar predictions of the $E 1$ strength, both at low energies and for exotic neutron-rich nuclei. Predictions of $γ$ -ray strength functions and Maxwellian-averaged neutron capture rates for the whole Sn isotopic chain are also discussed and compared with previous theoretical calculations.
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Experiment (nucl-ex)
arXiv:
1607.08483 [pdf]
PRC(2016)·103 citations
05
[Submitted on 27 Jul 2016]
Exact versus Taylor-expanded energy density in the study of the neutron star crust-core transition
T. R. Routray · X. Viñas · D. N. Basu · S. P. Pattnaik · M. Centelles · L. Robledo · B. Behera
The importance of the fourth and higher order terms in the Taylor series expansion of the energy of the isospin asymmetric nuclear matter in the study of the neutron star crust-core phase transition is investigated using the finite range simple effective interaction. Analytic expressions for the evaluation of the second and fourth order derivative terms in the Taylor series expansion for any general finite range interaction of Yukawa, exponential or Gaussian form have been obtained. The effect of the nuclear matter incompressibility, symmetry energy and slope parameters on the predictions for the crust-core transition density is examined. The crustal moment of inertia is calculated and the prediction for the radius of the Vela pulsar is analyzed using different equations of state.
Comments:
35 pages including 4 Tables & 12 figures; The article has been accepted for publication in J.Phys. G
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1607.08531 [pdf]
J.Phys.G(2016)·26 citations
06
[Submitted on 28 Jul 2016]
Charged-current neutrino-nucleus reactions within the SuSAv2-MEC approach
G.D. Megias🇪🇸 · J.E. Amaro🇪🇸 · M.B. Barbaro🇮🇹 · J.A. Caballero🇪🇸 · T.W. Donnelly🇺🇸 · I. Ruiz Simo🇪🇸
We present a detailed study of charged-current (CC) neutrino-nucleus reactions in a fully relativis- tic framework and comparisons with recent experiments spanning an energy range from hundreds of MeV up to 100 GeV within the SuperScaling Approach, which is based on the analysis of electron- nucleus scattering data and has been recently improved with the inclusion of Relativistic Mean Field theory effects. We also evaluate and discuss the impact of two-particle two-hole meson-exchange currents (2p-2h MEC) on neutrino-nucleus interactions through the analysis of two-particle two-hole axial and vector contributions to weak response functions in a fully relativistic Fermi gas. The results show a fairly good agreement with experimental data over the whole range of neutrino energies.
Comments:
23 pages, 17 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1607.08565 [pdf]
PRD(2016)·159 citations
07
[Submitted on 28 Jul 2016]
Three-nucleon bound states and the Wigner-SU(4) limit
Jared Vanasse🇺🇸 · Daniel R. Phillips🇺🇸
We examine the extent to which the properties of three-nucleon bound states are well-reproduced in the limit that nuclear forces satisfy Wigner's SU(4) (spin-isospin) symmetry. To do this we compute the charge radii up to next-to-leading order (NLO) in an effective field theory (EFT) that is an expansion in powers of $R / a$ , with $R$ the range of the nuclear force and $a$ the nucleon-nucleon ( $N N$ ) scattering lengths. In the Wigner-SU(4) limit, the triton and Helium-3 point charge radii are equal. At NLO in the range expansion both are $1.66$ fm. Adding the first-order corrections due to the breaking of Wigner symmetry in the $N N$ scattering lengths gives a $^{3} H$ point charge radius of $1.58$ fm, which is remarkably close to the experimental number, $1.5978 \pm 0.040$ fm (Angeli and Marinova in At Data Nucl Data Tables 99:69-95, 2013). For the $^{3} He$ point charge radius we find $1.70$ fm, about 4% away from the experimental value of $1.77527 \pm 0.0054$ fm (Angeli and Marinova 2013). We also examine the Faddeev components that enter the tri-nucleon wave function and find that an expansion of them in powers of the symmetry-breaking parameter converges rapidly. Wigner's SU(4) symmetry is thus a useful starting point for understanding tri-nucleon bound-state properties.
Comments:
v1: 22 pages, 6 figures, v2: 23 pages 6 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1607.08585 [pdf]
Few Body Syst.(2017)·34 citations
08
[Submitted on 27 Jul 2016] (cross-list from hep-ph)
IC at IC: IceCube can constrain the intrinsic charm of the proton
Ranjan Laha🇺🇸 · Stanley J. Brodsky🇺🇸
The discovery of extraterrestrial neutrinos in the $\sim$ 30 TeV -- PeV energy range by IceCube provides new constraints on high energy astrophysics. An important background to the signal are the prompt neutrinos which originate from the decay of charm hadrons produced by high energy cosmic-ray particles interacting in the Earth's atmosphere. It is conventional to use the calculations of charm hadroproduction using gluon splitting $g \to c c ˉ$ alone. However, QCD predicts an additional "intrinsic" component of the heavy quark distribution which arises from diagrams where heavy quarks are multiply connected to the proton's valence quarks. We estimate the prompt neutrino spectrum due to intrinsic charm. We find that the atmospheric prompt neutrino flux from intrinsic charm is comparable to those calculated using QCD computations not including intrinsic charm, once we normalize the intrinsic charm differential cross sections to the ISR and the LEBC-MPS collaboration data. In future, IceCube will constrain the intrinsic charm content of the proton and will contribute to one of the major questions in high energy physics phenomenology.
Comments:
v3: 13 pages, 4 figures. Added more details about the calculation. Conclusions unchanged. Accepted in PRD
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1607.08240 [pdf]
PRD(2017)·54 citations
09
[Submitted on 28 Jul 2016] (cross-list from nucl-ex)
Kinematic sensitivity to the Fierz term of $β$ -decay differential spectra
Martin Gonzalez-Alonso🇫🇷 · Oscar Naviliat-Cuncic🇺🇸
The current most stringent constraints on exotic scalar or tensor couplings in neutron and nuclear $β$ decay, involving left-handed neutrinos, are obtained from the Fierz interference term. The sensitivity to this term in a correlation coefficient is usually driven by an energy-averaged kinematic factor that increases monotonically toward smaller values of the $β$ endpoint energies. We first point out here that this property does not hold for certain differential observables that are directly sensitive to the Fierz term, such as the $β$ or the recoil energy spectrum. This observation is relevant for the selection of sensitive transitions in searches for exotic couplings through spectrum shape measurements. We then point out previous errors in the exploitation of measurements of the $β - ν$ angular correlation coefficient and discuss their impact on the extraction of constraints on exotic couplings.
Comments:
7 pages, 5 figures
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1607.08347 [pdf]
PRC(2016)·44 citations

Affiliations

first authorsco-authorsvia INSPIRE