Nuclear Theory·nucl-th

Tuesday·October 6, 2015

20 papers—8 primary·12 cross-listed

01
A consistent four-body CDCC model of low-energy reactions: Application to 9Be + 208Pb
M. S. Hussein · P. Descouvemont · L. F. Canto
We investigate the $^{9}$ Be + $^{208}$ Pb elastic scattering, breakup and fusion at energies around the Coulomb barrier. The three processes are described simultaneously, with identical conditions of calculations. The $^{9}$ Be nucleus is defined in an $α + α$ + n three-body model, using the hyperspherical coordinate method. We first analyze spectroscopic properties of $^{9}$ Be, and show that the model provides a fairly good description of the low-lying states. The scattering with $^{208}$ Pb is then studied with the Continuum Discretized Coupled Channel (CDCC) method, where the $α + α$ + n continuum is approximated by a discrete number of pseudostates. Optical potentials for the $α$ + $^{208}$ Pb and n+ $^{208}$ Pb systems are taken from the literature. We present elastic-scattering and fusion cross sections at different energies.
nucl-thnucl-exEPJ Web Conf.(2016)·1 citation
02
Astrophysical S-factor for $^{6}$ Li $(p, γ)$ $^{7}$ Be in the coupled-channel Gamow shell model
G.X. Dong🇫🇷 · K. Fossez🇺🇸 · N. Michel🇫🇷 · M. Płoszajczak🇫🇷
We have applied the Gamow shell model (GSM) in the coupled-channel representation to study the astrophysical $S$ -factor for the proton radiative capture reaction of $^{6}$ Li. Reaction channels are built by coupling the proton wave function expanded in different partial waves with the GSM wave functions of the ground state ( $1^{+}$ ) and the excited states ( $3_{1}^{+}$ , $0_{1}^{+}$ and $2_{1}^{+}$ ) of $^{6}$ Li. All relevant $E 1$ , $M 1$ , and $E 2$ transitions from the initial continuum states in $^{7}$ Be to the final bound states ( $3/2_{1}^{-}$ and $1/2_{1}^{-}$ ) states are included. It is found that the calculated total astrophysical $S$ factor for this reaction agrees well with the experimental data.
nucl-thEPJ Web Conf.(2016)·0 citations
03
Systematic investigations of deep sub-barrier fusion reactions using an adiabatic approach
Takatoshi Ichikawa
To describe fusion hindrance observed in fusion reactions at extremely low incident energies, I propose a novel extension of the standard CC model by introducing a damping factor that describes a smooth transition from sudden to adiabatic processes. I demonstrate the performance of this model by systematically investigating various deep sub-barrier fusion reactions. I extend the standard CC model by introducing a damping factor into the coupling matrix elements in the standard CC model. I adopt the Yukawa-plus-exponential (YPE) model as a basic heavy ion-ion potential, which is advantageous for a unified description of the one- and two-body potentials. For the purpose of these systematic investigations, I approximate the one-body potential with a third-order polynomial function based on the YPE model. Calculated fusion cross sections for the medium-heavy mass systems of $^{64}$ Ni + $^{64}$ Ni, $^{58}$ Ni + $^{58}$ Ni, and $^{58}$ Ni + $^{54}$ Fe, the medium-light mass systems of $^{40}$ Ca + $^{40}$ Ca, $^{48}$ Ca + $^{48}$ Ca, and $^{24}$ Mg + $^{30}$ Si, and the mass-asymmetric systems of $^{48}$ Ca + $^{96}$ Zr and $^{16}$ O + $^{208}$ Pb are consistent with the experimental data. The astrophysical S factor and logarithmic derivative representations of these are also in good agreement with the experimental data. Since the results calculated with the damping factor are in excellent agreement with the experimental data in all systems, I conclude that the smooth transition from the sudden to adiabatic processes occurs and that a coordinate-dependent coupling strength is responsible for the fusion hindrance. In all systems, the potential energies at the touching point $V_{Touch}$ strongly correlate with the incident threshold energies for which the fusion hindrance starts to emerge, except for the medium-light mass systems.
nucl-thnucl-exPRC(2015)·52 citations
04
Bound on the variation in the fine structure constant implied by Oklo data
Leila Hamdan🇰🇼 · Edward D. Davis🇰🇼
Dynamical models of dark energy can imply that the fine structure constant $α$ varies over cosmological time scales. Data on shifts in resonance energies $E_{r}$ from the Oklo natural fission reactor have been used to place restrictive bounds on the change in $α$ over the last 1.8 billion years. We review the uncertainties in these analyses, focussing on corrections to the standard estimate of $k_{α} = α d E_{r} / d α$ due to Damour and Dyson. Guided, in part, by the best practice for assessing systematic errors in theoretical estimates spelt out by Dobaczewski et al. [in J. Phys. G: Nucl. Part. Phys. 41, 074001 (2014)], we compute these corrections in a variety of models tuned to reproduce existing nuclear data. Although the net correction is uncertain to within a factor of 2 or 3, it constitutes at most no more than 25% of the Damour-Dyson estimate of $k_{α}$ . Making similar allowances for the uncertainties in the modeling of the operation of the Oklo reactors, we conclude that the relative change in $α$ since the Oklo reactors were last active (redshift $z ≃ 0.14$ ) is less than $\sim 10$ parts per billion. To illustrate the utility of this bound at low- $z$ , we consider its implications for the string theory-inspired runaway dilaton model of Damour, Piazza and Veneziano.
nucl-thastro-ph.CO1 citation
05
Impact of phonon coupling on the radiative nuclear reaction characteristics
Oleg Achakovskiy · Alexander Avdeenkov · Sergei Kamerdzhiev
The pygmy dipole resonance and photon strength functions (PSF) in stable and unstable Ni and Sn isotopes are calculated within the microscopic self-consistent version of the extended theory of finite fermi systems in the quasiparticle time blocking approximation. The approach includes phonon coupling (PC) effects in addition to the standard QRPA approach. The Skyrme force SLy4 is used. A pygmy dipole resonance in 72Ni is predicted at the mean energy of 12.4 MeV exhausting 25.7% of the total energy-weighted sum rule. With our microscopic E1 PSFs in the EMPIRE 3.1 code, the following radiative nuclear reaction characteristics have been calculated for several stable and unstable even-even Sn and Ni isotopes: 1) neutron capture cross sections, 2) corresponding neutron capture gamma-spectra, 3) average radiative widths of neutron resonances. Here, three variants of the microscopic nuclear level density models have been used and a comparison with the phenomenological generalized superfluid model (GSM) has been performed. In all the considered properties, including the recent experimental data for PSF in Sn isotopes, the PC contributions turned out to be significant, as compared with the QRPA one, and necessary to explain the available experimental data. The phenomenological GSM NLD model used in EMPIRE3.1 gives, on the whole, the worse results than the microscopic HFB plus combinatorial NLD model.
nucl-thnucl-exEPJ Web Conf.(2016)·2 citations
06
An effective method to accurately calculate the phase space factors for $β^{-} β^{-}$ decay
Andrei Neacsu🇺🇸 · Mihai Horoi🇺🇸
Accurate calculations of the electron phase space factors are necessary for reliable predictions of double-beta decay rates, and for the analysis of the associated electron angular and energy distributions. We present an effective method to calculate these phase space factors that takes into account the distorted Coulomb field of the daughter nucleus, yet allows one to easily calculate the phase space factors with good accuracy relative to the most exact methods available in the recent literature.
nucl-thhep-phAdv.High Energy Phys.(2016)·29 citations
07
Skyrme RPA for spherical and axially symmetric nuclei
Anton Repko · Jan Kvasil · V.O. Nesterenko · P.-G. Reinhard
Random Phase Approximation (RPA) is the basic method for calculation of excited states of nuclei over the Hartree-Fock ground state, suitable also for energy density functionals (EDF or DFT). We developed a convenient formalism for expressing densities and currents in a form of reduced matrix elements, which allows fast calculation of spectra for spherical nuclei. All terms of Skyrme functional were taken into account, so it is possible to calculate electric, magnetic and vortical/toroidal/compression transitions and strength functions of any multipolarity. Time-odd (spin) terms in Skyrme functional become important for magnetic M1 and isovector toroidal E1 transitions. It was also found that transition currents in pygmy region (low-lying part of E1 resonance) exhibit isoscalar toroidal flow, so the previously assumed picture of neutron-skin vibration is not the only mechanism present in pygmy transitions. RPA calculations with heavy axially-symmetric nuclei now become feasible on ordinary PC. Detailed formulae for axial Skyrme RPA are given. Some numerical results are shown in comparison with the approximate approach of separable RPA, previously developed in our group for fast calculation of strength functions.
nucl-thProceedings of the ISTROS 2015 Internatio…·23 citations
08
Initial conditions from the shadowed Glauber model
Sandeep Chatterjee🇮🇳 · Sushant K. Singh🇮🇳 · Snigdha Ghosh🇮🇳 · Md Hasanujjaman🇮🇳 · Jane Alam🇮🇳 · Sourav Sarkar🇮🇳
The two component Monte-Carlo Glauber model predicts a knee-like structure in the centrality dependence of elliptic flow $v_{2}$ in Uranium+Uranium collisions at $s_{N N} = 193$ GeV. It also produces a strong anti-correlation between $v_{2}$ and $d N_{c h} / d y$ in the case of top ZDC events. However, none of these features have been observed in data. We address these discrepancies by including the effect of nucleon shadowing to the two component Monte-Carlo Glauber model. Apart from addressing successfully the above issues, we find that the nucleon shadow suppresses the event by event fluctuation of various quantities, e.g. $ε_{2}$ which is in accordance with expectation from the dynamical models of initial condition based on gluon saturation physics.
nucl-thhep-phnucl-exPLB(2016)·26 citations
09
From controversy to precision on the sigma meson: a review on the status of the non-ordinary $f_{0} (500)$ resonance
J.R. Pelaez (universidad Complutense de Madrid)🇪🇸
The existence and properties of the sigma meson have been controversial for almost six decades, despite playing a central role in the spontaneous chiral symmetry of QCD or in the nucleon-nucleon attraction. This controversy has also been fed by the strong indications that it is not an ordinary quark-antiquark meson. Here we review both the recent and old experimental data and the model independent dispersive formalisms which have provided precise determinations of its mass and width, finally settling the controversy and leading to its new name: $f_{0} (500)$ . We then provide a rather conservative average of the most recent and advanced dispersive determinations of its pole position $s_{σ} = 44 9_{- 16}^{+ 22} - i (275 \pm 12)$ . In addition, after comprehensive introductions, we will review within the modern perspective of effective theories and dispersion theory, its relation to chiral symmetry, unitarization techniques, its quark mass dependence, popular models, as well as the recent strong evidence, obtained from the QCD $1/ N_{c}$ expansion or Regge theory, for its non ordinary nature in terms of quarks and gluons.
↳ hep-phnucl-thPhys.Rept.(2016)·499 citations
10
Direct and indirect constraints on CP-violating Higgs-quark and Higgs-gluon interactions
Y.-T. Chien🇺🇸 · V. Cirigliano🇺🇸 · W. Dekens🇳🇱 · J. de Vries🇩🇪 · E. Mereghetti🇺🇸
We investigate direct and indirect constraints on the complete set of anomalous CP-violating Higgs couplings to quarks and gluons originating from dimension-6 operators, by studying their signatures at the LHC and in electric dipole moments (EDMs). We show that existing uncertainties in hadronic and nuclear matrix elements have a significant impact on the interpretation of EDM experiments, and we quantify the improvements needed to fully exploit the power of EDM searches. Currently, the best bounds on the anomalous CP-violating Higgs interactions come from a combination of EDM measurements and the data from LHC Run 1. We argue that Higgs production cross section and branching ratios measurements at the LHC Run 2 will not improve the constraints significantly. On the other hand, the bounds on the couplings scale roughly linearly with EDM limits, so that future theoretical and experimental EDM developments can have a major impact in pinning down interactions of the Higgs.
↳ hep-phhep-latnucl-exnucl-thJHEP(2016)·122 citations
11
Modifications of Nucleons in Nuclei
Sebastian E. Kuhn🇺🇸
I summarize recent results and discuss upcoming and planned experiments that attempt to elucidate how the structure of nucleons might be modified by nuclear binding.
↳ nucl-exnucl-th1 citation
12
Uncovering the Matter-Neutrino Resonance
D. Vaananen🇺🇸 · G. C. McLaughlin🇺🇸
Matter Neutrino Resonances (MNRs) can drastically modify neutrino flavor evolution in astrophysical environments and may significantly impact nucleosynthesis. Here we further investigate the underlying physics of MNR type flavor transitions. We provide generalized resonance conditions and make analytical predictions for the behavior of the system. We discuss the adiabatic evolution of these transitions, considering both Symmetric and Standard scenarios. Symmetric MNR transitions differ from Standard MNR transitions in that both neutrinos and antineutrinos can completely transform to other flavors simultaneously. We provide an example of the simplest system in which such transitions can occur with a neutrino and an antineutrino having a single energy and emission angle. We further apply linearized stability analysis to predict the location of self-induced nutation type (or bipolar) oscillations due to neutrino-neutrino interactions in the regions where MNR is ineffective. In all cases, we compare our analytical predictions to numerical calculations.
↳ hep-phastro-ph.HEnucl-thPRD(2016)·35 citations
13
3D Structure and Nuclear Targets
R. Dupré🇫🇷 · S. Scopetta🇮🇹
Recent experimental and theoretical ideas are laying the ground for a new era in the knowledge of the parton structure of nuclei. We report on two promising directions beyond inclusive deep inelastic scattering experiments, aimed at, among other goals, unveiling the three dimensional structure of the bound nucleon. The 3D structure in coordinate space can be accessed through deep exclusive processes, whose non-perturbative content is parametrized in terms of generalized parton distributions. In this way the distribution of partons in the transverse plane will be obtained, providing a pictorial view of the realization of the European Muon Collaboration effect. In particular, we show how, through the generalized parton distribution framework, non nucleonic degrees of freedom in nuclei can be unveiled. Analogously, the momentum space 3D structure can be accessed by studying transverse momentum dependent parton distributions in semi-inclusive deep inelastic scattering processes. The status of measurements is also summarized, in particular novel coincidence measurements at high luminosity facilities, such as Jefferson Laboratory. Finally the prospects for the next years at future facilities, such as the 12~GeV Jefferson Laboratory and the Electron Ion Collider, are presented.
↳ nucl-exhep-exhep-phnucl-thEPJA(2016)·35 citations
14
The nature of near-threshold XYZ states
Martin Cleven🇨🇳 · Feng-Kun Guo🇩🇪 · Christoph Hanhart🇩🇪 · Qian Wang🇩🇪 · Qiang Zhao🇨🇳
We demonstrate that the recently observed $X$ , $Y$ , $Z$ states cannot be purely from kinematic effect. Especially the narrow near-threshold structures in elastic channels call for nearby poles of the $S$ -matrix which are qualified as states. We propose a way to distinguish cusp effects from genuine states and demonstrate that (not all of) the recently observed $X$ , $Y$ , $Z$ states cannot be purely from kinematic effects. Especially, we show that the narrow near-threshold structures in elastic channels call for nearby poles of the $S$ -matrix, since the normal kinematic cusp effect cannot produce that narrow structures in the elastic channels in contrast to genuine $S$ -matrix poles. In addition, it is also discussed how spectra can be used to distinguish different scenarios proposed for the structure of those poles, such as hadro-quarkonia, tetraquarks and hadronic molecules. The basic tool employed is heavy quark spin symmetry.
↳ hep-phhep-exnucl-exnucl-thJPS Conf.Proc.(2016)·6 citations
15
Deduction of $M (S i g ma p i)$ for $L amb d a (1405)$ with mixed $T_{S i g ma p i l e f t a r r o w K^{-} p} an d T_{S i g ma p i l e f t a r r o w S i g ma p i}$ from Hemingway's data
Maryam Hassanvand🇯🇵 · Yoshinori Akaishi🇯🇵 · Toshimitsu Yamazaki🇯🇵
We formulated the $L amb d a (1405)$ (abbreviated as $L amb d a^{*}$ ) $r i g h t a r r o w (S i g ma p i)^{0}$ invariant-mass spectra produced in the $K^{-} + p r i g h t a r r o w S i g m a^{+} (1660) + p i^{-}$ , followed by $S i g m a^{+} (1660) r i g h t a r r o w L amb d a (1405) + p i^{+} r i g h t a r r o w S i g ma p i + p i^{+}$ , processes at $p (K^{-}) = 4.2$ GeV/ $c$ , in which both the incident channel for a quasi-bound $K^{-} p$ state and its decay process to $(S i g ma p i)^{0}$ were taken into account realistically. We calculated $M (S i g ma p i)$ spectral shapes using mixed transition matrices, $T_{21} = T_{S i g ma p i l e f t a r r o w K^{-} p}$ and $T_{22} = T_{S i g ma p i l e f t a r r o w S i g ma p i}$ , for various theoretical models involving $L amb d a^{*}$ . The asymmetric spectra were compared to old experimental data of Hemingway, and it was found that the mixing of the two channels, written as $(1 - f), T_{21} + f, T_{22}$ , gave a better result than considering the individual channels, yielding $f = 0.37 6_{- 0.019}^{+ 0.021}$ , $M (L amb d a^{*}) = 1406. 6_{- 3.3}^{+ 3.4}$ MeV/ $c^{2}$ and $G amma = 70 p m 2$ MeV, nearly consistent with the 2014 PDG values.
↳ hep-phnucl-thPRC(2015)·1 citation
16
Instructive discussion of an effective block algorithm for baryon-baryon correlators
Hidekatsu Nemura🇯🇵
We describe an approach for the efficient calculation of a large number of four-point correlation functions for various baryon-baryon (BB) channels, which are the primary quantities for studying the nuclear and hyperonic nuclear forces from lattice quantum chromodynamics. Using the four-point correlation function of a proton- $Λ$ system as a specific example, we discuss how an effective block algorithm significantly reduces the number of iterations. The effective block algorithm is applied to calculate 52 channels of the four-point correlation functions from nucleon $-$ nucleon to $Ξ - Ξ$ , in order to study the complete set of isospin symmetric BB interactions. The elapsed times measured for hybrid parallel computation on BlueGene/Q demonstrate that the performance of the present algorithm is reasonable for various combinations of the number of OpenMP threads and the number of MPI nodes. The numerical results are compared with the results obtained using the unified contraction algorithm for all computed sites of the 52 four-point correlators.
↳ hep-latnucl-thComput.Phys.Commun.(2016)·12 citations
17
Photoproduction of the Scalar Meson $f_{0} (500)$
Je-Hee Lee🇰🇷 · Hui-Young Ryu🇰🇷 · Byung-Geel Yu🇰🇷 · Hyun-Chul Kim🇰🇷
In the present talk, we report a recent investigation on photoproduction of the $γ N \to f_{0} (500) N$ within a framework of the effective Lagrangian. We include the nucleon resonances with pin $1/2$ in the $s$ channel. The coupling constants have been etermined by assuming that the decay process $N^{*} \to (π π)_{I = 0, J = 0} N$ can be regarded as $N^{*} \to f_{0} (500) N$ . We discuss the numerical results for the total cross sections and possible extension of the present work.
↳ hep-phhep-exnucl-exnucl-thJPS Conf.Proc.(2016)·0 citations
18
Spectrum of heavy baryons in the quark model
Tetsuya Yoshida🇯🇵 · Emiko Hiyama🇯🇵 · Atsushi Hosaka🇯🇵 · Makoto Oka🇯🇵 · Katsunori Sadato🇯🇵
Single- and double- heavy baryons are studied in the constituent quark model. The model Hamiltonian is chosen as a standard one with two exceptions : (1) The color-Coulomb term depend on quark masses, and (2) an antisymmetric $L S$ force is introduced. Model parameters are fixed by the strange baryon spectra, $Λ$ and $Σ$ baryons. The masses of the observed charmed and bottomed baryons are, then, fairly well reproduced. Our focus is on the low-lying negative-parity states, in which the heavy baryons show specific excitation modes reflecting the mass differences of heavy and light quarks. By changing quark masses from the SU(3) limit to the strange quark mass, further to the charm and bottom quark masses, we demonstrate that the spectra change from the SU(3) symmetry patterns to the heavy quark symmetry ones.
↳ hep-phnucl-thPRD(2015)·283 citations
19
Entropy production in chemically non-equilibrium quark-gluon plasma created in central Pb+Pb collisions at LHC energies
V. Vovchenko🇩🇪 · M.I. Gorenstein🇩🇪 · L.M. Satarov🇩🇪 · I.N. Mishustin🇩🇪 · L.P. Csernai🇳🇴 · I. Kisel🇩🇪 · H. Stoecker🇩🇪
We study the possibility that partonic matter produced at early stage of ultrarelativistic heavy-ion collisions is out of chemical equilibrium. It is assumed that initially this matter is mostly composed of gluons, but quarks and antiquarks are produced at later times. The dynamical evolution of partonic system is described by the Bjorken-like ideal hydrodynamics with a time dependent quark fugacity. The results of this model are compared with those obtained by assuming the complete chemical equilibrium of partons already at the initial stage. It is shown that in a chemically non-equilibrium scenario the entropy gradually increases, and about 25% of the total final entropy is generated during the hydrodynamic evolution of deconfined matter. We argue that the (anti)quark suppression included in this approach may be responsible for reduced (anti)baryon to meson ratios observed in heavy-ion collisions at LHC energies.
↳ hep-phnucl-thPRC(2016)·15 citations
20
The Proton Radius from Electron Scattering Data
Douglas W. Higinbotham · Al Amin Kabir · Vincent Lin · David Meekins · Blaine Norum · Brad Sawatzky
[Background] The proton charge radius extracted from recent muonic hydrogen Lamb shift measurements is significantly smaller than that extracted from atomic hydrogen and electron scattering measurements. [Purpose] In an attempt to understand the discrepancy, we review high-precision electron scattering results from Mainz, Jefferson Lab, Saskatoon and Stanford. [Method] We make use of stepwise regression techniques using the $F$ -test as well as the Akaike information criterion to systematically determine the predictive variables to use for a given set and range of electron scattering data as well as to provide multivariate error estimates. [Results] Starting with the precision, low four-momentum transfer ( $Q^{2}$ ) data from Mainz (1980) and Saskatoon (1974), we find that a stepwise regression of the Maclaurin series using the $F$ -test as well as the Akaike information criterion justify using a linear extrapolation which yields a value for the proton radius that is consistent with the result obtained from muonic hydrogen measurements. Applying the same Maclaurin series and statistical criteria to the 2014 Rosenbluth results on $G_{E}$ from Mainz, we again find that the stepwise regression tends to favor a radius consistent with the muonic hydrogen radius but produces results that are extremely sensitive to the range of data included in the fit. Making use of the high- $Q^{2}$ data on $G_{E}$ to select functions which extrapolate to high $Q^{2}$ , we find that a Padé ( $N = M = 1$ ) statistical model works remarkably well, as does a dipole function with a 0.84 fm radius, $G_{E} (Q^{2}) = (1 + Q^{2} /0.66 GeV^{2})^{- 2}$ . [Conclusions] From this statistical analysis, we conclude that the electron scattering result and the muonic hydrogen result are consistent. It is the atomic hydrogen results that are the outliers.
↳ nucl-exmath-phmath.MPnucl-thPRC(2016)·94 citations

Affiliations

first authorsco-authorsvia INSPIRE