Nuclear Theory·nucl-th

Tuesday·July 25, 2017

18 papers—11 primary·7 cross-listed

01
[Submitted on 21 Jul 2017]
Modeling alignment enhancement for solid polarized targets
Dustin Keller🇺🇸
A model of dynamic orientation using optimized radiofrequency (RF) irradiation produced perpendicular to the holding field is developed for the spin-1 system required for tensor-polarized fixed-target experiments. The derivation applies to RF produced close to the Larmor frequency of the nucleus and requires the electron spin-resonance linewidth to be much smaller than the nuclear magnetic resonance frequency. The rate equations are solved numerically to study a semi-saturated steady-state resulting from the two sources of irradiation: microwave from the DNP process and the additional RF used to manipulate the tensor polarization. The steady-state condition and continuous-wave NMR lineshape are found that optimize the spin-1 alignment in the polycrystalline materials used as solid polarized targets in charged-beam nuclear and particle physics experiments.
Comments:
13 pages, 12 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1707.07065 [pdf]
EPJA(2017)·8 citations
02
[Submitted on 22 Jul 2017]
Emergence of low-energy monopole strength in the neutron-rich calcium isotopes
J. Piekarewicz
The isoscalar monopole response of neutron-rich nuclei is sensitive to both the incompressibility coefficient of symmetric nuclear matter and the density dependence of the symmetry energy. The main goal of this paper is to explore the emergence, evolution, and origin of low energy monopole strength along the even-even calcium isotopes: from 40Ca to 60Ca. The distribution of isoscalar monopole strength is computed in a relativistic random phase approximation (RPA) using three effective interactions that have been calibrated to the properties of finite nuclei and neutron stars. A non-spectral approach is adopted that allows for an exact treatment of the continuum without any reliance on discretization. For the stable calcium isotopes, no evidence of low-energy monopole strength is observed, even as the 1f7/2 neutron orbital is being filled and the neutron-skin thickness progressively grows. Further, in contrast to experimental findings, a mild softening of the monopole response with increasing mass number is predicted. Beyond 48Ca, a significant amount of low-energy monopole strength emerges as soon as the weak-binding neutron orbitals (2p and 1f5/2) become populated. The emergence and evolution of low-energy strength is identified with transitions from these weakly-bound states into the continuum. Moreover, given that models with a soft symmetry energy tend to reach the neutron-drip line earlier than their stiffer counterparts, we identify an inverse correlation between the neutron-skin thickness and the inverse energy weighted sum.
Comments:
14 pages, 8 figures, and 5 tables
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1707.07185 [pdf]
PRC(2017)·7 citations
03
[Submitted on 22 Jul 2017]
Estimates and power counting in uniform matter with softened interactions
A. Dyhdalo🇺🇸 · S.K. Bogner🇺🇸 · R.J. Furnstahl🇺🇸
Modern softened nucleon-nucleon interactions are well-suited for perturbative many-body calculations, but a many-body power counting scheme is lacking. Estimates of diagrammatic contributions at finite density are important ingredients in such a scheme. Here we show how to make quantitative estimates of the particle-particle and hole-hole channel in uniform nuclear matter for soft interactions. We also use estimates to assess the role of normal-ordered three-body forces for a pure contact interaction.
Comments:
36 pages, 12 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1707.07199 [pdf]
PRC(2017)·6 citations
04
[Submitted on 23 Jul 2017]
Investigating different $Λ$ and $Λ ˉ$ polarizations in relativistic heavy-ion collisions
Zhang-Zhu Han🇨🇳 · Jun Xu🇨🇳
Based on the chiral kinetic equations of motion, spin polarizations of various quarks, due to the magnetic field induced by spectator protons as well as the quark-antiquark vector interaction, are studied within a partonic transport approach. Although the magnetic field in QGP enhances the splitting of the spin polarizations of partons compared to the results under the magnetic field in vacuum, the spin polarizations of $s$ and $s ˉ$ quarks are also sensitive to the quark-antiquark vector interaction, challenging that the different $Λ$ and $Λ ˉ$ spin polarization is a good measure of the magnetic field in relativistic heavy-ion collisions. It is also found that there is no way to obtain the large splitting of the spin polarization between $Λ$ and $Λ ˉ$ at $s_{N N} = 7.7$ GeV with partonic dynamics.
Comments:
6 pages, 4 figures, a few typos corrected
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex)
arXiv:
1707.07262 [pdf]
PLB(2018)·33 citations
05
[Submitted on 23 Jul 2017]
$^{1} S_{0}$ pairing in neutron matter
H.-H. Fan · E. Krotscheck · J.W. Clark
We report calculations of the superfluid pairing gap in neutron matter for the $^{1} S_{0}$ components of the Reid soft-core $V_{6}$ and the Argonne $V_{4}^{'}$ two-nucleon interactions. Ground-state calculations have been carried out using the central part of the operator-basis representation of these interactions to determine optimal Jastrow-Feenberg correlations and corresponding effective pairing interactions within the correlated-basis formalism (CBF), the required matrix elements in the correlated basis being evaluated by Fermi hypernetted-chain techniques. Different implementations of the Fermi-Hypernetted Chain Euler-Lagrange method (FHNC-EL) agree at the percent level up to nuclear matter saturation density. For the assumed interactions, which are realistic within the low density range involved in $^{1} S_{0}$ neutron pairing, we did not find a dimerization instability arising from divergence of the in-medium scattering length, as was reported recently for simple square-well and Lennard-Jones potential models (Phys. Rev. A {\bf 92}, 023640 (2015)).
Comments:
25 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas)
arXiv:
1707.07268 [pdf]
J.Low Temp.Phys.(2017)·14 citations
06
[Submitted on 23 Jul 2017]
Effects of hadronic mean-field potentials on Hanbury-Brown-Twiss correlations in relativistic heavy-ion collisions
Chun-Jian Zhang🇨🇳 · Jun Xu🇨🇳
With the parameters fitted by the particle multiplicity, the energy density at chemical freeze-out, and the charged particle elliptic flow, we have studied the effects of the hadronic mean-field potentials on the Hanbury-Brown and Twiss (HBT) correlation in relativistic heavy-ion collisions based on a multiphase transport model. The hadronic mean-field potentials are found to delay the emission time of the system and lead to large HBT radii extracted from the correlation function. Effects on the energy dependence of $R_{o}^{2} - R_{s}^{2}$ and $R_{o} / R_{s}$ as well as the eccentricity of the emission source are discussed. The HBT correlations can also be useful in understanding the mean-field potentials of protons, kaons, and antiprotons as well as baryon-antibaryon annihilations.
Comments:
9 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex)
arXiv:
1707.07272 [pdf]
PRC(2017)·9 citations
07
[Submitted on 23 Jul 2017]
Random-interaction study on linear systematics of $I^{π} = 11/ 2^{-}$ electromagnetic moments in Cd isotope chain
Z. Z. Qin · Y. Lei
In the random-interaction ensembles, electromagnetic moments of Cd $I^{π} = 11/ 2^{-}$ isomers predominately present linear systematics as changing the neutron number, which has been reported in realistic nuclear system. Quadrupole-like and $δ$ -like $p n$ interaction are responsible for such linear systematics of quadrupole and magnetic moments, respectively.
Comments:
5 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1707.07311 [pdf]
0 citations
08
[Submitted on 23 Jul 2017]
Correlations within the Non-Equilibrium Green's Function Method
M. H. Mahzoon (Michigan State U) · P. Danielewicz (Michigan State U) · A. Rios (U Surrey)
Non-equilibrium Green's Function (NGF) method is a powerful tool for studying the evolution of quantum many-body systems. Different types of correlations can be systematically incorporated within the formalism. The time evolution of the single-particle Green's functions is described in terms of the Kadanoff-Baym equations. The current work initially focuses on introducing the correlations within infinite nuclear matter in one dimension and then in a finite system in the NGF approach. Starting from the harmonic oscillator Hamiltonian, by switching on adiabatically the mean-field and correlations simultaneously, a correlated state with ground-state characteristics is arrived at within the NGF method. Furthermore the use of cooling to for improving the adiabatic switching is explored.
Comments:
Contribution to Proc. 5th Conference on Nuclei and Mesoscopic Physics, E Lansing, 6-10 March 2017; 9 pages, 8 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex); Computational Physics (physics.comp-ph)
arXiv:
1707.07355 [pdf]
AIP Conf.Proc.(2017)·1 citation
09
[Submitted on 24 Jul 2017]
Octupole deformation in the nuclear chart based on the 3D Skyrme Hartree-Fock plus BCS model
Shuichiro Ebata · Takashi Nakatsukasa
We have performed a systematic study of the ground state for even-even 1,002 nuclei in which 28 octupole-deformed nuclei are found. The interplay between the spatial deformation and the pairing correlation, plays important roles in nuclear structure. Our model is based on the Skyrme Hartree-Fock plus BCS model represented in the three-dimensional Cartesian coordinate space which can describe any kind of nuclear shape. The quadrupole and octupole deformed nuclei appear in the mass region with characteristic neutron and proton numbers which are consistent with previous studies. In our results, there appear only pear shape ( $β_{30}$ ) in the octupole deformed nuclei. We investigate the potential energy surfaces as functions of the octupole deformations ( $β_{3 m}, m = 0, 1, 2, 3$ ), which tells us that. $^{220}$ Rn has also local minima in the $β_{31}$ and $β_{32}$ potential energy surfaces.
Comments:
7 pages, 4 figures, Focus issue on Nuclear Shapes and Symmetries: From Experiment to Theory
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1707.07416 [pdf]
Phys.Scripta(2017)·56 citations
10
[Submitted on 24 Jul 2017]
Shell model results for $T = 1$ and $T = 0$ bands in $^{66}$ As
Praveen C. Srivastava · R. Sahu · V.K.B. Kota
Results of a comprehensive shell model (SM) analyses, within the full $f_{5/2} p g_{9/2}$ model space, of the recently available experimental data [P. Ruotsalainen et al., Phy. Rec. C {88}, 024320 (2013)] with four $T = 0$ bands and one $T = 1$ band in the odd-odd $N = Z$ nucleus $^{66}$ As are presented. The calculations are performed using jj44b effective interaction developed recently by B.A. Brown and A.F. Lisetskiy for this model space. For the lowest two $T = 0$ bands and the $T = 1$ band, the results are in reasonable agreement with experimental data and deformed shell model is used to identify their intrinsic structure. For the $T = 1$ band, structural change at $8^{+}$ is predicted. For the third $9^{+}$ band with $T = 0$ , the shell model $B (E 2)$ values and quadrupole moments (in addition to energies) are consistent with the interpretation in terms of aligned isoscalar $n p$ pair in $g_{9/2}$ orbit coupled to the $^{64}$ Ge ground band. Similarly, the $9^{+}$ level of band 4 and a close lying $5^{+}$ level are found to be isomeric states in the analysis. Finally, energies of the band 5 members calculated using shell model with both positive and negative parity show that the observed levels are most likely negative parity levels. The SM results with jj44b are also compared with the results obtained using JUN45 interaction.
Comments:
9 pages, 7 figures and 3 tables: Accepted for Publication in Journal of Physics G: Nuclear and Particle Physics
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1707.07527 [pdf]
J.Phys.G(2017)·6 citations
11
[Submitted on 21 Jul 2017]
Transverse Momentum Distribution and Elliptic Flow of Charged Hadrons in $U$ + $U$ collisions at $s_{N N} = 193$ GeV using HYDJET++
Arpit Singh🇮🇳 · P. K. Srivastava🇮🇳 · O. S. K. Chaturvedi🇮🇳 · S. Ahmad🇮🇳 · B. K. Singh🇮🇳
Recent experimental observations of the charged hadron properties in $U + U$ collisions at $193$ GeV contradict many of the theoretical models of particle production including two-component Monte Carlo Glauber model. The experimental results show a small correlation between the charged hadron properties and the initial geometrical configurations (e.g. body-body, tip-tip etc.) of $U + U$ collisions. In this article, we have modified the Monte Carlo HYDJET++ model to study the charged hadron production in $U + U$ collisions at $193$ GeV center-of-mass energy in tip-tip and body-body initial configurations. We have modified the hard as well as soft production processes to make this model suitable for $U + U$ collisions. We have calculated the pseudorapidity distribution, transverse momentum distribution and elliptic flow distribution of charged hadrons with different control parameters in various geometrical configurations possible for $U + U$ collision. We find that HYDJET++ model supports a small correlation between the various properties of charged hadrons and the initial geometrical configurations of $U + U$ collision. Further, the results obtained in modified HYDJET++ model regarding $d n_{c h} / d η$ and elliptic flow ( $v_{2}$ ) suitably matches with the experimental data of $U + U$ collisions in minimum bias configuration.
Comments:
29 pages, 25 figures. Accepted for Publication in EPJC
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1707.07552 [pdf]
EPJC(2018)·15 citations
12
[Submitted on 19 Jul 2017] (cross-list from hep-th)
Rigorous constraints on the matrix elements of the energy-momentum tensor
Peter Lowdon🇺🇸 · Kelly Yu-Ju Chiu🇺🇸 · Stanley J. Brodsky🇺🇸
The structure of the matrix elements of the energy-momentum tensor play an important role in determining the properties of the form factors $A (q^{2})$ , $B (q^{2})$ and $C (q^{2})$ which appear in the Lorentz covariant decomposition of the matrix elements. In this paper we apply a rigorous frame-independent distributional-matching approach to the matrix elements of the Poincaré generators in order to derive constraints on these form factors as $q \to 0$ . In contrast to the literature, we explicitly demonstrate that the vanishing of the anomalous gravitomagnetic moment $B (0)$ and the condition $A (0) = 1$ are independent of one another, and that these constraints are not related to the specific properties or conservation of the individual Poincaré generators themselves, but are in fact a consequence of the physical on-shell requirement of the states in the matrix elements and the manner in which these states transform under Poincaré transformations.
Comments:
11 pages; v2: additional comments added, matches published version
Subjects:
High Energy Physics — Theory (hep-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1707.06313 [pdf]
PLB(2017)·44 citations
13
[Submitted on 21 Jul 2017] (cross-list from hep-ph)
Different Realizations of Cooper-Frye Sampling with Conservation Laws
C. Schwarz🇩🇪 · D. Oliinychenko🇩🇪 · L.-G. Pang🇩🇪 · S. Ryu🇩🇪 · H. Petersen🇩🇪
Approaches based on viscous hydrodynamics for the hot and dense stage and hadronic transport for the final dilute rescattering stage are successfully applied to the dynamic description of heavy ion reactions at high beam energies. One crucial step in such hybrid approaches is the so called particlization, the transition between the hydrodynamic description to microscopic degrees of freedom. For this purpose, individual particles are sampled on the Cooper-Frye hypersurface. In this work, 4 different realizations of sampling algorithms are compared, where three of them incorporate global conservation laws of quantum numbers in each event. The algorithms are compared within two types of scenarios: simple "box" hypersurface consisting of only one static cell and a typical particlization hypersurface for Au+Au collisions at $s_{NN} = 200$ GeV. For all algorithms the mean multiplicities (or particle spectra) remain unaffected by global conservation laws in the case of large volumes. In contrast, the fluctuations of the particle numbers are affected considerably. The fluctuations of the newly developed SPREW algorithm based on exponential weights and the recently suggested SER algorithm based on ensemble rejection are smaller than without conservation laws and agree with the expectation from the canonical ensemble. The previously applied mode sampling algorithm produces dramatically larger fluctuations, than it is expected in the corresponding microcanonical ensemble, and therefore should be avoided in fluctuation studies. This study might be of interest for investigations of particle fluctuations and correlations, e.g. the suggested signatures for a phase transition or a critical endpoint, in hybrid approaches that are affected by global conservation laws.
Comments:
11 pages, 8 figures, version accepted to publication in Journal of Physics G
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1707.07026 [pdf]
J.Phys.G(2018)·17 citations
14
[Submitted on 22 Jul 2017] (cross-list from hep-ph)
Holographic estimate of the meson cloud contribution to nucleon axial form factor
G. Ramalho🇧🇷
We use light-front Holography to estimate the valence quark and the meson cloud contributions to the nucleon axial form factor. The free couplings of the holographic model are determined by the empirical data and by the information extracted from lattice QCD. The holographic model provides a good description of the empirical data when we consider a meson cloud mixture of about 30\% in the physical nucleon state. The estimate of the valence quark contribution to the nucleon axial form factor compares well with the lattice QCD data for small pion masses. Our estimate of the meson cloud contribution to the nucleon axial form factor has a slower falloff with the square momentum transfer compared to typical estimates from quark models with meson cloud dressing.
Comments:
14 pages, 5 figures. Published version. Extension of the first version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1707.07206 [pdf]
PRD(2018)·12 citations
15
[Submitted on 23 Jul 2017] (cross-list from hep-ph)
$ψ (2 S)$ versus $J / ψ$ suppression in proton-nucleus collisions from factorization violating soft color exchanges
Yan-Qing Ma🇨🇳 · Raju Venugopalan🇺🇸 · Kazuhiro Watanabe🇨🇳 · Hong-Fei Zhang🇨🇳
We argue that the large suppression of the $ψ (2 S)$ inclusive cross-section relative to the $J / ψ$ inclusive cross-section in proton-nucleus (p+A) collisions can be attributed to factorization breaking effects in the formation of quarkonium. These factorization breaking effects arise from soft color exchanges between charm-anticharm pairs undergoing hadronization and comoving partons that are long-lived on time scales of quarkonium formation. We compute the short distance pair production of heavy quarks in the Color Glass Condensate (CGC) effective field theory and employ an improved Color Evaporation model (ICEM) to describe their hadronization into quarkonium at large distances. The combined CGC+ICEM model provides a quantitative description of $J / ψ$ and $ψ (2 S)$ data in proton-proton (p+p) collisions from both RHIC and the LHC. Factorization breaking effects in hadronization, due to additional parton comovers in the nucleus, are introduced heuristically by imposing a cutoff $Λ$ , representing the momentum kick from soft color exchanges, in the ICEM model. Such soft exchanges have no perceptible effect on $J / ψ$ suppression in p+A collisions. In contrast, the interplay of the physics of these soft exchanges at large distances, with the physics of semi-hard rescattering at short distances, causes a significant additional suppression of $ψ (2 S)$ yields relative to that of the $J / ψ$ . A good fit of all RHIC and LHC $J / ψ$ and $ψ (2 S)$ data, for transverse momenta $P_{⊥} \leq 5$ GeV in p+p and p+A collisions, is obtained for $Λ \sim 10$ MeV.
Comments:
16 pages, 12 figures. v2: version accepted for publication in PRC
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1707.07266 [pdf]
PRC(2018)·58 citations
16
[Submitted on 23 Jul 2017] (cross-list from hep-ph)
Sudakov suppression of jets in QCD media
Yacine Mehtar-Tani🇺🇸 · Konrad Tywoniuk🇨🇭
We compute modifications to the jet spectrum in the presence of a dense medium. We show that in the large- $N_{c}$ approximation and at leading logarithmic accuracy the jet nuclear modification factor factorizes into a quenching factor associated to the total jet color charge and a Sudakov suppression factor which accounts for the energy loss of jet substructure fluctuations. This factor, called the jet collimator, implements the fact that subjets, that are not resolved by the medium, lose energy coherently as a single color charge, whereas resolved large angle fluctuations suffer more quenching. For comparison, we show that neglecting color coherence results in a stronger suppression of the jet nuclear modification factor.
Comments:
5 pages, 1 figure
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1707.07361 [pdf]
PRD(2018)·82 citations
17
[Submitted on 24 Jul 2017] (cross-list from hep-ph)
Resonances in positron scattering on a supercritical nucleus and spontaneous production of $e^{+} e^{-}$ pairs
S.I. Godunov🇷🇺 · B. Machet🇫🇷 · M.I. Vysotsky🇷🇺
We re-examine the physics of supercritical nuclei, specially focusing on the scattering phase $δ_{ϰ}$ and its dependence on the energy $ε$ of the diving electronic level, for which we give both exact and approximate formulas. The Coulomb potential $Z α / r$ is rounded to the constant $Z α / R$ for $r < R$ . We confirm the resonant behavior of $δ_{ϰ}$ that we investigate in details. In addition to solving the Dirac equation for an electron, we solve it for a positron, in the field of the same nucleus. This clarifies the interpretation of the resonances. Our results are compared with claims made in previous works.
Comments:
18 pages, 3 figures, 1 table
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1707.07497 [pdf]
EPJC(2017)·24 citations
18
[Submitted on 24 Jul 2017] (cross-list from hep-ph)
Excited Hadrons and Quark-Hadron Duality
E. Ruiz Arriola🇪🇸 · P. Masjuan🇪🇸 · W. Broniowski🇵🇱
We review how Quark-Hadron Duality (QHD) for (u,d) flavors at high energies and in the scaling regime suggests a radial and angular behaviour of mesonic and baryonic resonance masses of the Regge form $M_{n J}^{2} = μ^{2} n + β^{2} J + M_{0}^{2}$ . The radial mass dependence is asymptotically consistent with a common two-body dynamics for mesons and baryons in terms of the quark-antiquark ( $q q ˉ)$ and quark-diquark ( $q D$ ) degrees of freedom, respectively. This formula is validated phenomenologically within an uncertainty determined by half the width of the resonances, $Δ M_{n J}^{2} \sim Γ_{n J} M_{n J}$ . With this error prescription we find from the non-strange PDG hadrons different radial slopes $μ_{q ˉ q}^{2} = 1.34 (4) GeV^{2}$ and $μ_{q D}^{2} = 0.75 (3) GeV^{2}$ , but similar angular slopes $β_{q ˉ q}^{2} \sim β_{q D}^{2} \sim 1.15 GeV^{2}$ .
Comments:
6 pages, 4 figures, Acta Physica Polonica B style, talk by E. Ruiz Arriola at workshop "Excited QCD 2017", Sintra, Portugal, May 7-13, 2017
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1707.07508 [pdf]
Acta Phys.Polon.Supp.(2017)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE