Nuclear Theory·nucl-th

Friday·November 13, 2015

16 papers—9 primary·7 cross-listed

01
[Submitted on 11 Nov 2015]
Shell model predictions for $^{124}$ Sn double-beta decay
Mihai Horoi🇺🇸 · Andrei Neacsu🇺🇸
Neutrinoless double-beta ( $0 ν β β$ ) decay is a promising beyond Standard Model process. Two-neutrino double-beta ( $2 ν β β$ ) decay is an associated process that is allowed by the Standard Model, and it was observed in about 10 isotopes, including decays to the excited states of the daughter. $^{124}$ Sn was the first isotope whose double-beta decay modes were investigated experimentally, and despite few other recent efforts, no signal has been seen so far. Shell model calculations were able to make reliable predictions for $2 ν β β$ decay half-lives. Here we use shell model calculations to predict the $2 ν β β$ decay half-life of $^{124}$ Sn. Our results are quite different from the existing quasiparticle random-phase approximation (QRPA) results, and we envision that they will be useful for guiding future experiments. We also present shell model nuclear matrix elements for two potentially competing mechanisms to the $0 ν β β$ decay of $^{124}$ Sn.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.03711 [pdf]
PRC(2016)·154 citations
02
[Submitted on 12 Nov 2015]
A simplified BBGKY hierarchy for correlated fermionic systems from a Stochastic Mean-Field approach
Denis Lacroix🇫🇷 · Yusuke Tanimura🇫🇷 · Sakir Ayik🇺🇸 · Bulent Yilmaz🇹🇷
The stochastic mean-field (SMF) approach allows to treat correlations beyond mean-field using a set of independent mean-field trajectories with appropriate choice of fluctuating initial conditions. We show here, that this approach is equivalent to a simplified version of the Bogolyubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy between one-, two-, ..., N-body degrees of freedom. In this simplified version, one-body degrees of freedom are coupled to fluctuations to all orders while retaining only specific terms of the general BBGKY hierarchy. The use of the simplified BBGKY is illustrated with the Lipkin-Meshkov-Glick (LMG) model. We show that a truncated version of this hierarchy can be useful, as an alternative to the SMF, especially in the weak coupling regime to get physical insight in the effect beyond mean-field. In particular, it leads to approximate analytical expressions for the quantum fluctuations both in the weak and strong coupling regime. In the strong coupling regime, it can only be used for short time evolution. In that case, it gives information on the evolution time-scale close to a saddle point associated to a quantum phase-transition. For long time evolution and strong coupling, we observed that the simplified BBGKY hierarchy cannot be truncated and only the full SMF with initial sampling leads to reasonable results.
Comments:
10 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
arXiv:
1511.03815 [pdf]
EPJA(2016)·18 citations
03
[Submitted on 12 Nov 2015]
Probing surface distributions of $α$ clusters in $^{20}$ Ne via $α$ -transfer reaction
Tokuro Fukui · Yasutaka Taniguchi · Tadahiro Suhara · Yoshiko Kanada-En'yo · Kazuyuki Ogata
Direct evidence of the $α$ -cluster manifestation in bound states has not been obtained yet, although a number of experimental studies were carried out to extract the information of the clustering. In particular in conventional analyses of $α$ -transfer reactions, there exist a few significant problems on reaction models, which are insufficient to qualitatively discuss the cluster structure. We aim to verify the development of the $α$ -cluster structure from observables. As the first application, we plan to extract the spatial information of the cluster structure of the $^{20}$ Ne nucleus in its ground state through the cross section of the $α$ -transfer reaction $^{16}$ O( $^{6}$ Li,~ $d$ ) $^{20}$ Ne. For the analysis of the transfer reaction, we work with the coupled-channel Born approximation (CCBA) approach, in which the breakup effect of $^{6}$ Li is explicitly taken into account by means of the continuum-discretized coupled-channel method based on the three-body $α + d +^{16}$ O model. The two methods are adopted to calculate the overlap function between $^{20}$ Ne and $α +^{16}$ O; one is the microscopic cluster model (MCM) with the generator coordinate method, and the other is the phenomenological two-body potential model (PM). We show that the CCBA calculation with the MCM wave function gives a significant improvement of the theoretical result on the angular distribution of the transfer cross section, which is consistent with the experimental data. Employing the PM, it is discussed which region of the cluster wave function is probed on the transfer cross section. It is found that the surface region of the cluster wave function is sensitive to the cross section. The present work is situated as the first step in obtaining important information to systematically investigate the cluster structure.
Comments:
9 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1511.03862 [pdf]
PRC(2016)·19 citations
04
[Submitted on 12 Nov 2015]
Unified description of structure and reactions: implementing the Nuclear Field Theory program
Ricardo A. Broglia🇮🇹 · Pier Francesco Bortignon🇮🇹 · Francisco Barranco🇪🇸 · Enrico Vigezzi🇮🇹 · Andrea Idini🇫🇮 · Gregory Potel🇺🇸
The modern theory of the atomic nucleus results from the merging of the liquid drop (Niels Bohr and Fritz Kalckar) and of the shell model (Marie Goeppert Meyer and Axel Jensen), which contributed the concepts of collective excitations and of independent-particle motion respectively. The unification of these apparently contradictory views in terms of the particle-vibration (rotation) coupling (Aage Bohr and Ben Mottelson) has allowed for an ever increasingly complete, accurate and detailed description of the nuclear structure, Nuclear Field Theory (NFT, developed by the Copenhagen-Buenos Aires collaboration) providing a powerful quantal embodiment. In keeping with the fact that reactions are not only at the basis of quantum mechanics (statistical interpretation, Max Born) , but also the specific tools to probe the atomic nucleus, NFT is being extended to deal with processes which involve the continuum in an intrinsic fashion, so as to be able to treat them on an equal footing with those associated with discrete states (nuclear structure). As a result, spectroscopic studies of transfer to continuum states could eventually use at profit the NFT rules, extended to take care of recoil effects. In the present contribution we review the implementation of the NFT program of structure and reactions, setting special emphasis on open problems and outstanding predictions.
Comments:
submitted to Physica Scripta to the Focus Issue on Nuclear Structure: Celebrating the 1975 Nobel Prize
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.03874 [pdf]
Phys.Scripta(2016)·25 citations
05
[Submitted on 12 Nov 2015]
Shell model description of Gamow-Teller strengths in $p f$ -shell nuclei
Vikas Kumar · P.C. Srivastava
A systematic shell model description of the experimental Gamow-Teller transition strength distributions in $^{42}$ Ti, $^{46}$ Cr, $^{50}$ Fe and $^{54}$ Ni is presented. These transitions have been recently measured via $β$ decay of these $T_{z}$ =-1 nuclei, produced in fragmentation reactions at GSI and also with ( $^{3}$ {He}, $t$ ) charge-exchange (CE) reactions corresponding to $T_{z} = + 1$ to $T_{z} = 0$ carried out at RCNP-Osaka.The calculations are performed in the $p f$ model space, using the GXPF1a and KB3G effective interactions. Qualitative agreement is obtained for the individual transitions, while the calculated summed transition strengths closely reproduce the observed ones.
Comments:
8 pages, 5 figures; Accepted for publication in The European Physical Journal A : Hadrons and Nuclei
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1511.03887 [pdf]
EPJA(2016)·22 citations
06
[Submitted on 12 Nov 2015]
Linear and cubic response to the initial eccentricity in heavy-ion collisions
Jacquelyn Noronha-Hostler🇺🇸 · Li Yan🇫🇷 · Fernando G. Gardim🇧🇷 · Jean-Yves Ollitrault🇫🇷
We study the relation between elliptic flow, $v_{2}$ and the initial eccentricity, $ε_{2}$ , in heavy-ion collisions, using hydrodynamic simulations. Significant deviations from linear eccentricity scaling are seen in more peripheral collisions. We identify the mechanism responsible for these deviations as a cubic response, which we argue is a generic property of the hydrodynamic response to the initial density profile. The cubic response increases elliptic flow fluctuations, thereby improving agreement of initial condition models with experimental data.
Comments:
7 pages. v2: bugs corrected in Figs.1,2,4,5, text unchanged
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1511.03896 [pdf]
PRC(2016)·143 citations
07
[Submitted on 12 Nov 2015]
Gluon contribution to open heavy-meson production in heavy-ion collisions
Shanshan Cao🇺🇸 · Guang-You Qin🇨🇳 · Xin-Nian Wang🇺🇸
A sizable contribution to heavy quark production in high-energy hadronic and nuclear collisions comes from heavy quark-antiquark pair production from gluon splitting during the parton shower evolution. We investigate the effect of gluon-medium interaction on open heavy flavor spectra in ultra-relativistic heavy-ion collisions. The interaction of hard gluons and heavy quarks with the hot QCD medium is simulated by utilizing a Langevin transport model that simultaneously incorporates contributions from collisional and radiative processes. It is found that while the gluon splitting channel has quite an important contribution to the single $D$ meson production cross section, its influence on the final heavy meson nuclear modification turns out to be quite modest because the average lifetime of hard gluons is short before splitting into heavy quark-antiquark pairs during the evolution and propagation of the parton shower.
Comments:
5 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1511.04009 [pdf]
PRC(2016)·9 citations
08
[Submitted on 12 Nov 2015]
Separable Potentials for (d,p) Reaction Calculations
Ch. Elster · L. Hlophe · V. Eremenko · F.M. Nunes · I.J. Thompson · G. Arbanas · J.E. Escher
An important ingredient for applications of nuclear physics to e.g. astrophysics or nuclear energy are the cross sections for reactions of neutrons with rare isotopes. Since direct measurements are often not possible, indirect methods like $(d, p)$ reactions must be used instead. Those $(d, p)$ reactions may be viewed as effective three-body reactions and described with Faddeev techniques. An additional challenge posed by $(d, p)$ reactions involving heavier nuclei is the treatment of the Coulomb force. To avoid numerical complications in dealing with the screening of the Coulomb force, recently a new approach using the Coulomb distorted basis in momentum space was suggested. In order to implement this suggestion, one needs to derive a separable representation of neutron- and proton-nucleus optical potentials and compute their matrix elements in this basis.
Comments:
submitted to proceedings of the 21st International School on Nuclear Physics, Neutron Physics and Applications and International Symposium on Exotic Nuclei (ISEN-2015), September 9-11, 2015, Varna, Bulgaria. arXiv admin note: text overlap with arXiv:1410.1227
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.04038 [pdf]
J.Phys.Conf.Ser.(2016)·0 citations
09
[Submitted on 12 Nov 2015]
Electromagnetic form factors of one neutron halos with spin 1/2+ ground state
Lakma Fernando (North Carolina Central U.) · Akshay Vaghani (Mississippi State U.) · Gautam Rupak (Mississippi State U.)
The electromagnetic form factors for single neutron halo nuclei Be-11, C-15 and C-19 are calculated. The calculations are performed in halo effective field theory (EFT) where the halo nuclei are approximated as made of a single neutron and a core. The form factors depend on the single neutron separation energy, the s-wave neutron-core scattering effective range and a two-body current. The EFT expressions are presented to leading order for C-15 and next-to-leading order for Be-11 and C-19.
Comments:
19 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.04054 [pdf]
13 citations

Affiliations

first authorsco-authorsvia INSPIRE