Nuclear Theory·nucl-th

Monday·January 12, 2015

8 papers—2 primary·6 cross-listed

01
Electromagnetic and neutral-weak response functions of 4He and 12C
A. Lovato🇺🇸 · S. Gandolfi🇺🇸 · J. Carlson🇺🇸 · Steven C. Pieper🇺🇸 · R. Schiavilla🇺🇸
Ab initio calculations of the quasi-elastic electromagnetic and neutral-weak response functions of 4He and 12C are carried out for the first time. They are based on a realistic approach to nuclear dynamics, in which the strong interactions are described by two- and three-nucleon potentials and the electroweak interactions with external fields include one- and two-body terms. The Green's function Monte Carlo method is used to calculate directly the Laplace transforms of the response functions, and maximum-entropy techniques are employed to invert the resulting imaginary-time correlation functions with associated statistical errors. The theoretical results, confirmed by experiment in the electromagnetic case, show that two-body currents generate excess transverse strength from threshold to the quasi-elastic to the dip region and beyond. These findings challenge the conventional picture of quasi-elastic inclusive scattering as being largely dominated by single-nucleon knockout processes.
nucl-thhep-exhep-phPRC(2015)·91 citations
02
Problems with meson spectroscopy involving perturbative loop corrections
K. P. Khemchandani🇧🇷 · Eef Van Beveren🇵🇹 · George Rupp🇵🇹
In this talk we review the limitations of including meson loops as perturbative corrections in a solvable quark model. We first discuss meson-meson scattering within a formalism which treats confined quark pairs and mesons on an equal footing. The interaction between the mesons proceeds through $s$ -channel meson-exchange diagrams. Next, we develop a perturbative expansion of the model, and show that the resonance poles found in such a treatment, even by accounting for contributions up to fourth order, do not coincide with those obtained with the full model. We conclude that the resonance predictions based on perturbative approximations in quark models are not reliable, especially in those cases where the coupling to the scattering channels is large.
nucl-thhep-phActa Phys.Polon.Supp.(2015)·0 citations
03
Quasi-power law ensembles
Grzegorz Wilk🇵🇱 · Zbigniew Włodarczyk🇵🇱
Quasi-power law ensembles are discussed from the perspective of nonextensive Tsallis distributions characterized by a nonextensive parameter $q$ . A number of possible sources of such distributions are presented in more detail. It is further demonstrated that data suggest that nonextensive parameters deduced from Tsallis distributions functions $f (p_{T})$ , $q_{1}$ , and from multiplicity distributions (connected with Tsallis entropy), $q_{2}$ , are not identical and that they are connected via $q_{1} + q_{2} = 2$ . It is also shown that Tsallis distributions can be obtained directly from Shannon information entropy, provided some special constraints are imposed. They are connected with the type of dynamical processes under consideration (additive or multiplicative). Finally, it is shown how a Tsallis distribution can accommodate the log-oscillating behavior apparently seen in some multiparticle data.
↳ cond-mat.stat-mechhep-phnucl-thActa Phys.Polon.B(2015)·31 citations
04
Neutrino-driven supernova of a low-mass iron-core progenitor boosted by three-dimensional turbulent convection
Tobias Melson (1,2) · Hans-Thomas Janka (1) · Andreas Marek (3) ((1) MPI Astrophysics, Garching, (2) Physik Dept., TUM, Garching, (3) RZG Garching)
We present the first successful simulation of a neutrino-driven supernova explosion in three dimensions (3D), using the Prometheus-Vertex code with an axis-free Yin-Yang grid and a sophisticated treatment of three-flavor, energy-dependent neutrino transport. The progenitor is a nonrotating, zero-metallicity 9.6 Msun star with an iron core. While in spherical symmetry outward shock acceleration sets in later than 300 ms after bounce, a successful explosion starts at ~130 ms postbounce in two dimensions (2D). The 3D model explodes at about the same time but with faster shock expansion than in 2D and a more quickly increasing and roughly 10 percent higher explosion energy of >10^50 erg. The more favorable explosion conditions in 3D are explained by lower temperatures and thus reduced neutrino emission in the cooling layer below the gain radius. This moves the gain radius inward and leads to a bigger mass in the gain layer, whose larger recombination energy boosts the explosion energy in 3D. These differences are caused by less coherent, less massive, and less rapid convective downdrafts associated with postshock convection in 3D. The less violent impact of these accretion downflows in the cooling layer produces less shock heating and therefore diminishes energy losses by neutrino emission. We thus have, for the first time, identified a reduced mass accretion rate, lower infall velocities, and a smaller surface filling factor of convective downdrafts as consequences of 3D postshock turbulence that facilitate neutrino-driven explosions and strengthen them compared to the 2D case.
↳ astro-ph.SRastro-ph.HEnucl-thApJL(2015)·239 citations
05
Neutrino-nucleus interactions and the short-range structure of nuclei
F. Cavanna🇺🇸 · O. Palamara🇺🇸 · R. Schiavilla🇺🇸 · M. Soderberg🇺🇸 · R.B. Wiringa🇺🇸
Improvements in theoretical modeling of Short Range structures and phenomena, and comparisons with data, will require sustained collaboration between nuclear theorists and neutrino experimentalists. The extensive history of studying this area of nuclear physics in electron- and hadron-scattering experiments, coupled with the transformative capabilities of LArTPCs to identify neutrinos, will provide a ripe opportunity for new discoveries that will further our understanding of the nucleus.
↳ nucl-exnucl-th7 citations
06
The nature of $Z_{b}$ states from a combined analysis of $Υ (5 S) \to h_{b} (m P) π^{+} π^{-}$ and $Υ (5 S) \to B^{(*)} B ˉ^{(*)} π$
Wen-Sheng Huo🇨🇳 · Guo-Ying Chen🇨🇳
With a combined analysis of data on $Υ (5 S) \to h_{b} (1 P, 2 P) π^{+} π^{-}$ and $Υ (5 S) \to B^{(*)} B ˉ^{(*)} π$ in an effective field theory approach, we determine resonance parameters of $Z_{b}$ states in two scenarios. In one scenario we assume that $Z_{b}$ states are pure molecular states, while in the other one we assume that $Z_{b}$ states contain compact components. We find that the present data favor that there should be some compact components inside $Z_{b}^{(')}$ associated with the molecular components. By fitting the invariant mass spectra of $Υ (5 S) \to h_{b} (1 P, 2 P) π^{+} π^{-}$ and $Υ (5 S) \to B^{(*)} B ˉ^{*} π$ , we determine that the probability of finding the compact components in $Z_{b}$ states may be as large as about $40%$ .
↳ hep-phhep-exnucl-thEPJC(2016)·20 citations
07
Direct observation of quark-hadron duality in the free neutron F_2 structure function
I. Niculescu🇺🇸 · G. Niculescu🇺🇸 · W. Melnitchouk🇺🇸 · J. Arrington🇺🇸 · M.E. Christy🇺🇸 · R. Ent🇺🇸 · K.A. Griffioen🇺🇸 · N. Kalantarians🇺🇸 · C.E. Keppel🇺🇸 · S. Kuhn🇺🇸 · S. Tkachenko🇺🇸 · J. Zhang🇺🇸
Using data from the recent BONuS experiment at Jefferson Lab, which utilized a novel spectator tagging technique to extract the inclusive electron-free neutron scattering cross section, we obtain the first direct observation of quark-hadron duality in the neutron F_2 structure function. The data are used to reconstruct the lowest few (N=2, 4 and 6) moments of F_2 in the three prominent nucleon resonance regions, as well as the moments integrated over the entire resonance region. Comparison with moments computed from global parametrizations of parton distribution functions suggest that quark--hadron duality holds locally for the neutron in the second and third resonance regions down to Q^2 ~ 1 GeV^2, with violations possibly up to 20% observed in the first resonance region.
↳ hep-exhep-phnucl-thPRC(2015)·17 citations
08
The Resonance Scattering Phenomenon of Fast Negatively Charged Particles in a Single Crystal
Gennady V. Kovalev
The energy spectrum of the extended attractive potential of a crystallographic row for negatively charged particles has quasi-bound states. It follows that a negatively charged particle with small transversal momentum component ( $p_{⊥} R << 1$ ) may undergo resonance scattering. Thus the resonance scattering phenomenon can be observed in a single crystal, when fast electrons move with a small glancing angle ( $θ_{0} << 1/ pR$ ) to a crystallographic axis. The calculated results for the electrons and angular widths of resonance peaks are consistent with experimental data.
↳ cond-mat.mes-hallnucl-thNuclear Instruments and Methods, 1980, Vo…·0 citations

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