Nuclear Theory·nucl-th

Wednesday·June 6, 2018

12 papers—8 primary·4 cross-listed

01
Proton tensor charges from a Poincaré-covariant Faddeev equation
Qing-Wu Wang🇨🇳 · Si-Xue Qin🇨🇳 · Craig D. Roberts🇺🇸 · Sebastian M. Schmidt🇩🇪
The proton's tensor charges are calculated at leading order in a symmetry-preserving truncation of all matter-sector equations relevant to the associated bound-state and scattering problems. In particular, the nucleon three-body bound-state equation is solved without using a diquark approximation of the two-body scattering kernel. The computed charges are similar to those obtained in contemporary simulations of lattice-regularised quantum chromodynamics, an outcome which increases the tension between theory and phenomenology. Curiously, the theoretical calculations produce a value of the scale-invariant ratio $(- δ_{T} d / δ_{T} u)$ which matches that obtained in simple quark models, even though the individual charges are themselves different. The proton's tensor charges can be used to constrain extensions of the Standard Model using empirical limits on nucleon electric dipole moments.
nucl-thhep-lathep-phPRD(2018)·54 citations
02
Estimation of the freeze-out parameters reachable in the AFTER@LHC project
Viktor Begun🇵🇱 · Daniel Kikoła🇵🇱 · Volodymyr Vovchenko🇩🇪 · Daniel Wielanek🇵🇱
Estimation of the freeze-out parameters as the function of rapidity in Pb+Pb collisions at $s_{N N} = 72$ GeV in the AFTER@LHC project is performed. The conventional hadron resonance gas model is used for the analysis of the events generated by the UrQMD model. The results indicate that one may obtain at least $2.5$ times increase of baryon chemical potential $μ_{B}$ in the forward rapidity range as compared to the mid-rapidity. The $μ_{B}$ values in the rapidity range of $0 < y < 4.5$ for AFTER@LHC are comparable to that covered by the RHIC Beam Energy Scan program. Thus, a rapidity scan in the AFTER@LHC project provides a complementary approach to study the QCD phase diagram.
nucl-thhep-exhep-phnucl-exPRC(2018)·17 citations
03
Beam Spin Asymmetry in Electroproduction of Pseudoscalar or Scalar Meson Production off the Scalar Target
Chueng-Ryong Ji🇺🇸 · Ho-Meoyng Choi🇰🇷 · Andrew Lundeen🇺🇸 · Bernard L. G. Bakker🇳🇱
We discuss the electroproduction of pseudoscalar ( $0^{-+}$ ) or scalar ( $0^{++}$ ) meson production off the scalar target. The most general formulation of the differential cross section for the $0^{-+}$ or $0^{++}$ meson production process involves only one or two hadronic form factors, respectively, on a scalar target. The Rosenbluth-type separation of the differential cross section provides the explicit relation between the hadronic form factors and the different parts of the differential cross section in a completely model-independent manner. The absence of the beam spin asymmetry for the pseudoscalar meson production provides a benchmark for the experimental data analysis. The measurement of the beam spin asymmetry for the scalar meson production may also provide a unique opportunity not only to explore the imaginary part of the hadronic amplitude in the general formulation but also to examine the significance of the chiral-odd generalized parton distribution (GPD) contribution in the leading-twist GPD formulation.
nucl-thhep-phPRD(2019)·4 citations
04
Coupling charge-exchange vibrations to nucleons in a relativistic framework: effect on Gamow-Teller transitions and beta-decay half-lives
Caroline Robin · Elena Litvinova
The nuclear response theory for isospin-transfer modes in the relativistic particle-vibration coupling framework is extended to include coupling of single nucleons to isospin-flip (charge-exchange) phonons, in addition to the usual neutral vibrations. This new coupling introduces dynamical pion and rho-meson exchange, beyond the Hartree-Fock approximation, up to infinite order. We investigate the impact of this new mechanism on the Gamow-Teller response of a few doubly-magic neutron-rich nuclei, namely $^{48}$ Ca, $^{78}$ Ni, $^{132}$ Sn and $^{208}$ Pb. It is found that the coupling to isospin-flip vibrations can have a non negligible impact on the strength distribution and quenching of the giant resonance, globally improving the agreement with the experimental data. The corresponding beta-decay half-lives of $^{78}$ Ni and $^{132}$ Sn are also calculated, and found to be decreased by a factor $\sim 2$ by the inclusion of the new phonons.
nucl-thnucl-exPRC(2018)·38 citations
05
The Effect of Multiplicity Cut on Particle Ratios at 7 TeV Proton-Proton Collisions
Ehab Abbas🇪🇬
The final state hadronic composition of proton-proton collisions at 7 TeV as a function of charged particle multiplicity density is studied. The thermal model is adjusted to match the experimental conditions in order to understand the effect of the experimental cuts on rapidity and multiplicity. This study indicates that the measured hadronic composition under a simultaneous cut on rapidity and multiplicity does not coincide with the fireball hadronic composition. Excluding proton to pion ratio, the adjusted model can explain the measured particle ratios. Therefore, the observed strangeness enhancement as a function of charged particle multiplicity density could be an effect of the experimental cuts.
nucl-thhep-ph0 citations
06
Realistic shell-model calculations for p-shell nuclei including contributions of a chiral three-body force
T. Fukui · L. De Angelis · Y. Z. Ma · L. Coraggio · A. Gargano · N. Itaco · F. R. Xu
In this paper we present an evolution of our derivation of the shell-model effective Hamiltonian, namely introducing effects of three-body contributions. More precisely, we consider a three-body potential at next-to-next-to-leading order in chiral perturbation theory, and the induced three-body forces that arise from many-body correlations among valence nucleons. The first one is included, in the derivation of the effective Hamiltonian for one- and two-valence nucleon-systems, at first order in the many-body perturbation theory. Namely, we include only the three-body interaction between one or two valence nucleons and those belonging to the core. For nuclei with more than two valence particles, both induced - turned on by the two-body potential - and genuine three-body forces come into play. Since it is difficult to perform shell-model calculations with three-body forces, these contributions are estimated for the ground-state energy only. In order to establish the reliability of our approximations, we focus attention on nuclei belonging to the p shell, aiming to benchmark our calculations against those performed with the ab initio no-core shell-model. The obtained results are satisfactory, and pave the way to the application of our approach to nuclear systems with heavier masses.
nucl-thPRC(2018)·50 citations
07
QCD sum rules for the $Δ$ isobar in neutron matter
Jesuel Marques L.🇧🇷 · Su Houng Lee🇰🇷 · Aaron Park🇰🇷 · R. D. Matheus🇧🇷 · Kie Sang Jeong🇰🇷
We study the properties of the $Δ$ isobar in the symmetric and asymmetric nuclear matter using the QCD sum rules approach based on the energy dispersion relation. Allowing for different continuum thresholds for the polarization tensors with different dimensions, we find stable masses for the $Δ$ in both the vacuum and the medium. Compared to the nucleon case, we find that the vector repulsion is smaller for the $Δ$ while the scalar attraction is similar (75 MeV vector repulsion and 150 MeV scalar attraction in the symmetric matter). The smaller vector repulsion can be understood using the Pauli principle and a constituent quark model. Also the isospin dependence of the quasiparticle energy, which mainly comes from the vector self energy, is quite weak. We also allow for an explicit $π - N$ continuum contribution to the polarization function, but find its effect to be minimal. Phenomenological consequences of our results are discussed.
nucl-thhep-phPRC(2018)·7 citations
08
Semiclassical calculations of complete and incomplete fusion in collisions of weakly bound nuclei
G.D. Kolinger · L.F. Canto · R. Donangelo · S.R. Souza
We use an improved version of the semiclassical method described in Refs. [1,2,3] to evaluate fusion cross sections in collisions of weakly bound nuclei. This version takes into account the static effects of the low breakup threshold, uses better bin states in the discretization of the continuum and avoids the excitation of closed channels. The population of these channels is a consequence of the violation of energy conservation, which is inherent in the semiclassical method. The method is employed to evaluate complete fusion and total fusion cross section in collisions of the weakly bound 6,7Li projectiles with 159Tb and 197Au targets, for which data is available. The overall agreement between theory and experiment is fairly good.
nucl-thnucl-exPRC(2018)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE