Nuclear Theory·nucl-th

Friday·November 13, 2015

16 papers—9 primary·7 cross-listed

01
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.
nucl-thPRC(2016)·154 citations
02
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.
nucl-thcond-mat.str-elquant-phEPJA(2016)·18 citations
03
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.
nucl-thnucl-exPRC(2016)·19 citations
04
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.
nucl-thPhys.Scripta(2016)·25 citations
05
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.
nucl-thnucl-exEPJA(2016)·22 citations
06
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.
nucl-thhep-phnucl-exPRC(2016)·143 citations
07
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.
nucl-thhep-phPRC(2016)·9 citations
08
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.
nucl-thJ.Phys.Conf.Ser.(2016)·0 citations
09
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.
nucl-th13 citations
10
Will protons become gray at 13 TeV and 100 TeV?
I.M. Dremin🇷🇺
It is shown that the regime of pp-interactions at 7 TeV is a critical one. The LHC data about elastic pp-scattering at 7 and 8 TeV are used to get some information about both elastic and inelastic profiles of pp-collisions. They are discussed in the context of two phenomenological models which pretend to describe the high energy pp-data with high accuracy. Some predictions following from these models for LHC energy 13 TeV and for energy 95 TeV of the newly proposed collider are discussed. It is claimed that the center of the inelastic interaction region will become less dark with increase of energy albeit very slowly.
↳ hep-phhep-exnucl-exnucl-thBull.Lebedev Phys.Inst.(2017)·9 citations
11
Study of entropy production in Yang-Mills theory with use of Husimi function
Hidekazu Tsukiji🇯🇵 · Hideaki Iida🇯🇵 · Teiji Kunihiro🇯🇵 · Akira Ohnishi🇯🇵 · Toru T. Takahashi🇯🇵
Understanding the thermalization process in a pure quantum system is a challenge in theoretical physics. In this work, we explore possible thermalization mechanism in Yang-Mills(YM) theory by using a positive semi-definite quantum distribution function called a Husimi function which is given by a coarse graining of the Wigner function within the minimum uncertainty. Then entropy is defined in terms of the Husimi function, which is called the Husimi-Wehrl(HW) entropy. We propose two numerical methods to calculate the HW entropy. We find that it is feasible to apply the semi-classical approximation with the use of classical YM equation. It should be noted that the semi-classical approximation is valid in the systems of physical interest including the early stage of heavy-ion collisions. Using a product ansatz for the Husimi function, which is confirmed to reproduce the HW entropy within 20% error (overestimate) for a few-body quantum system, we succeed in a numerical evaluation of HW entropy of YM fields and show that it surely has a finite value and increases in time.
↳ hep-phnucl-thquant-phPoS(2016)·0 citations
12
Heavy-ion double charge exchange reactions: a tool towards 0v\b{eta}\b{eta} nuclear matrix elements
F. Cappuzzello🇮🇹 · M. Cavallaro🇮🇹 · C. Agodi🇮🇹 · M. Bond`ı🇮🇹 · D. Carbone🇮🇹 · A. Cunsolo🇮🇹 · A. Foti🇮🇹
The knowledge of the nuclear matrix elements for the neutrinoless double beta decay is fundamental for neutrino physics. In this paper, an innovative technique to extract information on the nuclear matrix elements by measuring the cross section of a double charge exchange nuclear reaction is proposed. The basic point is that the initial and final state wave functions in the two processes are the same and the transition operators are similar. The double charge exchange cross sections can be factorized in a nuclear structure term containing the matrix elements and a nuclear reaction factor. First pioneering experimental results for the 40Ca(18O,18Ne)40Ar reaction at 270 MeV incident energy show that such cross section factorization reasonably holds for the crucial 0+ --> 0+ transition to 40Args, at least at very forward angles.
↳ nucl-exnucl-thEPJA(2015)·152 citations
13
QCD running in neutrinoless double beta decay: Short-range mechanisms
M. González🇨🇱 · M. Hirsch🇪🇸 · S.G. Kovalenko🇨🇱
The decay rate of neutrinoless double beta ( $0 ν β β$ ) decay contains terms from heavy particle exchange, which lead to dimension-9 (d=9) six fermion operators at low energies. Limits on the coefficients of these operators have been derived previously neglecting the running of the operators between the high-scale, where they are generated, and the energy scale of double beta decay, where they are measured. Here we calculate the leading order QCD corrections to all possible d=9 operators contributing to the $0 ν β β$ amplitude and use RGE running to calculate 1-loop improved limits. Numerically, QCD running changes limits by factors of the order of or larger than typical uncertainties in nuclear matrix element calculations. For some specific cases, operator mixing in the running changes limits even by up to two orders of magnitude. Our results can be straightforwardly combined with new experimental limits or improved nuclear matrix element calculations to re-derive updated limits on all short-range contributions to $0 ν β β$ decay.
↳ hep-phhep-exnucl-exnucl-thPRD(2016)·41 citations
14
On the nature of an emergent symmetry in QCD
Thomas D. Cohen🇺🇸
Remarkable symmetry properties appear to arise in lattice calculations of correlation functions in which the lowest-lying eigenmodes of the Dirac operator in quark propagators are removed by hand. The Banks-Casher relation ties the chiral condensate to the density of low lying modes; thus, it is plausible that removal of such modes could lead to a regime where spontaneous chiral symmetry breaking does not occur. Surprising, a pattern of identical correlation functions was observed that is larger than can be explained by a restoration of chiral symmetry. This suggests that a larger symmetry---one that is not present in the QCD lagrangian---emerges when these modes are removed. Previously it was argued that this emergent symmetry was SU(4). However, when the low-lying modes are removed, the correlation functions of sources in the SU(4) 15-plet of spin-1 mesons appear to coincide with the correlation function of the SU(4) singlet. A natural explanation for this is an emergent symmetry larger than SU(4). In this work, it is shown that there exists no continuous symmetry whose generators in the field theory are spatial integrals of local operators that can account for the full pattern of identical correlation functions unless the apparent coincidence of the singlet channel with the 15-plet is accidental.
↳ hep-lathep-phhep-thnucl-thPRD(2016)·13 citations
15
q-Gamow States as continuous linear functionals on analytical test functions
A. Plastino · M. C. Rocca
We define here q-Gamow states corresponding to Tsallis' q-statistics. We compute for them their norm, mean energy value an the q-analogue of the Breit-Wigner distribution (a q-Breit-Wigner).
↳ math.CAcond-mat.stat-mechnucl-thquant-phNPA(2016)·6 citations
16
Chiral Magnetic and Vortical Effects in High-Energy Nuclear Collisions --- A Status Report
D. E. Kharzeev🇺🇸 · J. Liao🇺🇸 · S. A. Voloshin🇺🇸 · G. Wang🇺🇸
The interplay of quantum anomalies with magnetic field and vorticity results in a variety of novel non-dissipative transport phenomena in systems with chiral fermions, including the quark-gluon plasma. Among them is the Chiral Magnetic Effect (CME) -- the generation of electric current along an external magnetic field induced by chirality imbalance. Because the chirality imbalance is related to the global topology of gauge fields, the CME current is topologically protected and hence non-dissipative even in the presence of strong interactions. As a result, the CME and related quantum phenomena affect the hydrodynamical and transport behavior of strongly coupled quark-gluon plasma, and can be studied in relativistic heavy ion collisions where strong magnetic fields are created by the colliding ions. Evidence for the CME and related phenomena has been reported by the STAR Collaboration at Relativistic Heavy Ion Collider at BNL, and by the ALICE Collaboration at the Large Hadron Collider at CERN. The goal of the present review is to provide an elementary introduction into the physics of anomalous chiral effects, to describe the current status of experimental studies in heavy ion physics, and to outline the future work, both in experiment and theory, needed to eliminate the existing uncertainties in the interpretation of the data.
↳ hep-phcond-mat.str-elhep-thnucl-ex+1PPNP(2016)·837 citations

Affiliations

first authorsco-authorsvia INSPIRE