Nuclear Theory·nucl-th

Tuesday·November 8, 2016

12 papers—7 primary·5 cross-listed

01
[Submitted on 4 Nov 2016]
Uncertainty Quantification for Optical Model Parameters
A.E. Lovell · F.M. Nunes · J. Sarich · S.M. Wild
Although uncertainty quantification has been making its way into nuclear theory, these methods have yet to be explored in the context of reaction theory. For example, it is well known that different parameterizations of the optical potential can result in different cross sections, but these differences have not been systematically studied and quantified. The purpose of this work is to investigate the uncertainties in nuclear reactions that result from fitting a given model to elastic-scattering data, as well as to study how these uncertainties propagate to the inelastic and transfer channels. We use statistical methods to determine a best fit and create corresponding 95\% confidence bands. A simple model of the process is fit to elastic-scattering data and used to predict either inelastic or transfer cross sections. In this initial work, we assume that our model is correct, and the only uncertainties come from the variation of the fit parameters. We study a number of reactions involving neutron and deuteron projectiles with energies in the range of 5-25 MeV/u, on targets with mass $A$ =12-208. We investigate the correlations between the parameters in the fit. The case of deuterons on $^{12}$ C is discussed in detail: the elastic-scattering fit and the prediction of $^{12}$ C(d,p) $^{13}$ C transfer angular distributions, using both uncorrelated and correlated $χ^{2}$ minimization functions. The general features for all cases are compiled in a systematic manner to identify trends. Our work shows that, in many cases, the correlated $χ^{2}$ functions (in comparison to the uncorrelated $χ^{2}$ functions) provide a more natural parameterization of the process. These correlated functions do, however, produce broader confidence bands. Further optimization may require improvement in the models themselves and/or more information included in the fit.
Comments:
11 pages, 7 figures, accepted to Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1611.01526 [pdf]
PRC(2017)·38 citations
02
[Submitted on 6 Nov 2016]
Stellar electron capture rates on neutron-rich nuclei and their impact on core-collapse
Ad. R. Raduta🇷🇴 · F. Gulminelli🇫🇷 · M. Oertel🇫🇷
During the late stages of gravitational core-collapse of massive stars, extreme isospin asymmetries are reached within the core. Due to the lack of microscopic calculations of electron capture (EC) rates for all relevant nuclei, in general simple analytic parameterizations are employed. We study here several extensions of these parameterizations, allowing for a temperature, electron density and isospin dependence as well as for odd-even effects. The latter extra degrees of freedom considerably improve the agreement with large scale microscopic rate calculations. We find, in particular, that the isospin dependence leads to a significant reduction of the global EC rates during core collapse with respect to fiducial results, where rates optimized on calculations of stable $f p$ -shell nuclei are used. Our results indicate that systematic microscopic calculations and experimental measurements in the $N \approx 50$ neutron rich region are desirable for realistic simulations of the core-collapse.
Comments:
14 pages, 8 figures, accepted for publication in Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1611.01744 [pdf]
PRC(2017)·27 citations
03
[Submitted on 6 Nov 2016]
Nuclear symmetry energy and the role of three-body forces
S. Goudarzi · H. R. Moshfegh · P. Haensel
Density dependence of nuclear symmetry energy as well as its partial wave decomposition is studied within the framework of lowest-order constrained variational (LOCV) method using AV18 two-body interaction supplemented by UIX three-body force. The main focus of the present work is to introduce a revised version of three-body force which is based on an isospin-dependent parametrization of coefficients in the UIX force, in order to overcome the inability to produce correct saturation-point parameters} in the framework of LOCV method. We find that employing the new model of {\ph three-body force} in the LOCV formalism leads to successfully reproducing the semi-empirical parameters of cold nuclear matter, including} $E_{sy m} (ρ_{0})$ , $L$ , and $K_{sy m}$ . All our models of three-body force combined with AV18 two-body force give maximum neutron star mass higher than $2 M_{⊙}$ . The fraction of protons in the nucleon cores of neutron stars strongly depends on the three-body force parametrization.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1611.01768 [pdf]
NPA(2018)·23 citations
04
[Submitted on 7 Nov 2016]
Symmetry Energy III: Isovector Skins
Pawel Danielewicz (NSCL MSU) · Pardeep Singh (DCRUST) · Jenny Lee (U Hong Kong)
Isoscalar density is a sum of neutron and proton densities and isovector is a normalized difference. Here, we report on the experimental evidence for the displacement of the isovector and isoscalar surfaces in nuclei, by $\sim$ $0.9 fm$ from each other. We analyze data on quasielastic (QE) charge exchange (p,n) reactions, concurrently with proton and neutron elastic scattering data for the same target nuclei, following the concepts of the isoscalar and isovector potentials combined into Lane optical potential. The elastic data largely probe the geometry of the isoscalar potential and the (p,n) data largely probe a relation between the geometries of the isovector and isoscalar potentials. The targets include $^{48}$ Ca, $^{90}$ Zr, $^{120}$ Sn and $^{208}$ Pb and projectile incident energy values span the range of (10-50) $MeV$ . In our fit to elastic and QE charge-exchange data, we allow the values of isoscalar and isovector radii, diffusivities and overall potential normalizations to float away from those in the popular Koning and Delaroche parametrization. We find that the best-fit isovector radii are consistently larger than isoscalar and the best-fit isovector surfaces are steeper. Upon identifying the displacement of the potential surfaces with the displacement of the surfaces for the densities in the Skyrme-Hartree-Fock calculations, and by supplementing the results with those from analysing excitation energies to isobaric analog states in the past, we arrive at the slope and value of the symmetry energy at normal density of $70 < L < 101 MeV$ and $33.5 < a_{a}^{V} < 36.4 MeV$ , respectively.
Comments:
58 pages, 21 figures, 3 tables; version accepted for Nuclear Physics A
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1611.01871 [pdf]
NPA(2017)·90 citations
05
[Submitted on 7 Nov 2016]
Nuclear structure calculations in $^{20}$ Ne with No-Core Configuration-Interaction model
Maciej Konieczka · Wojciech Satuła
Negative parity states in $^{20}$ Ne and Gamow-Teller strength distribution for the ground-state beta-decay of $^{20}$ Na are calculated for the very first time using recently developed No-Core Configuration-Interaction model. The approach is based on multi-reference density functional theory involving isospin and angular-momentum projections. Advantages and shortcomings of the method are briefly discussed.
Comments:
Contributed talk presented at the Zakopane Conference on Nuclear Physics, Zakopane, Poland, August 28 - September 4, 2016
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1611.01979 [pdf]
Acta Phys.Polon.B(2017)·1 citation
06
[Submitted on 7 Nov 2016]
Theoretical photo-disintegration of $^{16}$ O
M. Katsuma
The photodisintegration of $^{16}$ O is predicted to be dominated by $E$ 2 excitation in the vicinity of the $α$ -particle threshold. The reaction rates of $^{12}$ C( $α$ , $γ$ ) $^{16}$ O are expected to be determined from this reaction.
Comments:
3 pages, 2 figures, Proceedings of Nuclei in the Cosmos (NIC-XIV). 19-24 June 2016, Niigata, Japan
Subjects:
Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Experiment (nucl-ex)
arXiv:
1611.02057 [pdf]
JPS Conf.Proc.(2017)·2 citations
07
[Submitted on 4 Nov 2016]
Effect of the final state interaction of $η^{'} N$ on the $η^{'}$ photoproduction off nucleon
Shuntaro Sakai🇯🇵 · Atsushi Hosaka🇯🇵 · Hideko Nagahiro🇯🇵
We investigate the $η^{'}$ photoproduction off the nucleon with a particular interest in the effect of the final-state interaction (FSI) of the $η^{'}$ meson and nucleon $(η^{'} N)$ based on three-flavor linear sigma model. We find an enhancement in the cross section of the $η^{'}$ photoproduction near the $η^{'} N$ -threshold energy owing to the $η^{'} N$ FSI. With the $η^{'}$ meson at forward angles, the energy dependence near the $η^{'} N$ threshold is well reproduced with the $η^{'} N$ FSI. The cross section at backward angles can also be a good probe to investigate the strength of the $η^{'} N$ interaction.
Comments:
19 pages, 11 figures. Introduction is revised, and some considerations are added
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1611.02156 [pdf]
PRC(2017)·3 citations
08
[Submitted on 4 Nov 2016] (cross-list from hep-ph)
Nonlocal wave turbulence in non-Abelian plasmas
Yacine Mehtar-Tani🇺🇸
We investigate driven wave turbulence in non-Abelian plasmas, in the framework of kinetic theory where both elastic and inelastic processes are considered in the small angle approximation. The gluon spectrum, that forms in the presence of a steady source, is shown to be controlled by nonlocal interactions in momentum space, in contrast to the universal Kolmogorov-Zakharov spectra. Assuming strongly nonlocal interactions, we show that inelastic processes are dominant in the IR and cause a thermal bath to form below the forcing scale, as a result of a detailed balance between radiation and absorption of soft gluons by the hard ones. Above the forcing scale, the inelastic collision term reduces to an inhomogeneous diffusion-like equation yielding a spectrum that spreads to the UV as $t^{1/2}$ , similarly to elastic processes. Due to nonlocal interactions the non-universal turbulent spectrum is not steady and flattens when time goes on toward the thermal distribution. This analysis is complemented by numerical simulations, where we observe that in the explored time interval the spectral exponent of the nonlocal turbulent cascade is close to $- 2$ in agreement with simulations of classical Yang-Mills equations.
Comments:
77 pages, 19 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); nlin.CD (nlin.CD); Nuclear Theory (nucl-th)
arXiv:
1611.01527 [pdf]
NPA(2017)·4 citations
09
[Submitted on 6 Nov 2016] (cross-list from nucl-ex)
Jets and high- $p_{T}$ probes measured in the STAR experiment
Nihar Ranjan Sahoo (for the STAR collaboration)🇺🇸
Hard probes created through large momentum transfers are used to study the properties of QCD matter created in heavy-ion collisions, by comparing the measurements to those in p+p collisions. Jets, and the "quenching" or suppression of jets in the medium created in heavy-ion collisions, are studied through various different observables. We present the most recent measurements from $s_{N N}$ = 200 GeV Au+Au collisions, with p+p collisions as the reference, by the STAR Collaboration. The observables are semi-inclusive charged jets and di-jet transverse momentum imbalance. Additionally, correlation measurements of direct photon-hadron and neutral pion-hadron are presented and discussed.
Comments:
5 pages, 4 figures, ICHEP 2016, Chicago, USA
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1611.01728 [pdf]
PoS(2016)·0 citations
10
[Submitted on 7 Nov 2016] (cross-list from cond-mat.quant-gas)
In-medium bound-state formation and inhomogeneous condensation in Fermi gases in a hard-wall box
Dietrich Roscher · Jens Braun
The formation of bosonic bound states underlies the formation of a superfluid ground state in the many-body phase diagram of ultracold Fermi gases. We study bound-state formation in a spin- and mass-imbalanced ultracold Fermi gas confined in a box with hard-wall boundary conditions. Because of the presence of finite Fermi spheres, the center-of-mass momentum of the potentially formed bound states can be finite, depending on the parameters controlling mass and spin imbalance as well as the coupling strength. We exploit this observation to estimate the potential location of inhomogeneous phases in the many-body phase diagram as a function of spin- and mass imbalance as well as the box size. Our results suggest that a hard-wall box does not alter substantially the many-body phase diagram calculated in the thermodynamic limit. Therefore, such a box may serve as an ideal trap potential to bring experiment and theory closely together and facilitate the search for exotic inhomogeneous ground states.
Comments:
12 pages, 4 figures
Subjects:
Quantum Gases (cond-mat.quant-gas); Superconductivity (cond-mat.supr-con); Nuclear Theory (nucl-th)
arXiv:
1611.02081 [pdf]
J.Phys.B(2017)·3 citations
11
[Submitted on 7 Nov 2016] (cross-list from hep-ph)
The fourth dimension of the nucleon structure: spacetime analysis of the timelike electromagnetic proton form factors
Andrea Bianconi🇮🇹 · Egle Tomasi-Gustafsson🇫🇷
As well known, spacelike proton form factors expressed in the Breit frame may be interpreted as the Fourier transform of static space distributions of electric charge and current. In particular, the electric form factor is simply the Fourier transform of the charge distribution $F (q) = \int e^{i q \cdot r} ρ (r) d^{3} r$ . We don't have an intuitive interpretation of the same level of simplicity for the proton timelike form factor appearing in the reactions $e^{+} e^{-} \leftrightarrow p ˉ p$ . However, one may suggest that in the center of mass (CM) frame, where $q_{μ} x^{μ} = q t$ , a timelike electric form factor is the Fourier transform $F (q) = \int e^{i q t} R (t) d t$ of a function $R (t)$ expressing how the electric properties of the forming (or annihilating) proton-antiproton pair evolve in time. Here we analyze in depth this idea, show that the functions $ρ (r)$ and $R (t)$ can be formally written as the time and space integrals of a unique correlation function depending on both time and space coordinates.
Comments:
8 figures, 15 pages
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1611.02149 [pdf]
PRC(2017)·9 citations
12
[Submitted on 7 Nov 2016] (cross-list from hep-ph)
Applications of KP Nuclear Parton Distributions
Sergey Kulagin🇷🇺 · Roberto Petti🇺🇸
We review the nuclear parton distribution functions computed on the basis of our microscopic model taking into account a number of nuclear effects including Fermi motion and nuclear binding, nuclear meson-exchange currents, off-shell corrections to bound nucleon distributions and nuclear shadowing. We discuss applications to a number of different processes including lepton-nucleus deep inelastic scattering, proton-nucleus Drell-Yan lepton pair production at Fermilab, as well as $W^{\pm}$ and $Z^{0}$ boson production in proton-lead collisions at the LHC.
Comments:
6 pages, 3 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1611.02245 [pdf]
PoS(2016)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE