Nuclear Theory·nucl-th

Wednesday·May 17, 2017

10 papers—7 primary·3 cross-listed

01
[Submitted on 15 May 2017]
Pairing and deformation effects in nuclear excitation spectra
A. Repko · J. Kvasil · V.O. Nesterenko · P.-G. Reinhard
We investigate effects of pairing and of quadrupole deformation on two sorts of nuclear excitations, $γ$ -vibrational $K^{π} = 2^{+}$ states and dipole resonances (isovector dipole, pygmy, compression, toroidal). The analysis is performed within the quasiparticle random-phase approximation (QRPA) based on the Skyrme energy functional using the Skyrme parametrization SLy6. Particular attention is paid to i) the role of the particle-particle (pp) channel in the residual interaction of QRPA, ii) comparison of volume pairing (VP) and surface pairing (SP), iii) peculiarities of deformation splitting in the various resonances. We find that the impact of the pp-channel on the considered excitations is negligible. This conclusion applies also to any other excitation except for the $K^{π} = 0^{+}$ states. Furthermore, the difference between VP and SP is found small (with exception of peak height in the toroidal mode). In the low-energy isovector dipole (pygmy) and isoscalar toroidal modes, the branch $K^{π} = 1^{-}$ is shown to dominate over $K^{π} = 0^{-}$ one in the range of excitation energy $E <$ 8--10 MeV. The effect becomes impressive for the toroidal resonance whose low-energy part is concentrated in a high peak of almost pure $K^{π} = 1^{-}$ nature. This peculiarity may be used as a fingerprint of the toroidal mode in future experiments. The interplay between pygmy, toroidal and compression resonances is discussed, the interpretation of the observed isoscalar giant dipole resonance is partly revised.
Comments:
12 pages, 12 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1705.05436 [pdf]
EPJA(2017)·28 citations
02
[Submitted on 16 May 2017]
Ab initio electromagnetic observables with the in-medium similarity renormalization group
N. M. Parzuchowski🇺🇸 · S. R. Stroberg🇨🇦 · P. Navrátil🇨🇦 · H. Hergert🇺🇸 · S. K. Bogner🇺🇸
We present the formalism for consistently transforming transition operators within the in-medium similarity renormalization group framework. We implement the operator transformation in both the equations-of-motion and valence-space variants, and present first results for electromagnetic transitions and moments in medium-mass nuclei using consistently-evolved operators, including the induced two-body parts. These results are compared to experimental values, and--where possible--the results of no-core shell model calculations using the same input chiral interaction. We find good agreement between the equations-of-motion and valence space approaches. Magnetic dipole observables are generally in reasonable agreement with experiment, while the more collective electric quadrupole and octupole observables are significantly underpredicted, often by over an order of magnitude, indicating missing physics at the present level of truncation.
Comments:
19 pages, 13 figures, 3 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1705.05511 [pdf]
PRC(2017)·92 citations
03
[Submitted on 16 May 2017]
Comment on "Three-dimensional study of the six-body bound-state for the case of effective three-body configuration model" [Int. J. Mod. Phys. E 25, 9 (2016) 1650072]
M. R. Hadizadeh · M. Radin · S. Bayegan
The authors argue that the calculated $^{6}$ He binding energies by the solution of the coupled Faddeev-Yakubovsky integral equation in a Three-dimensional scheme reported by E. Ahmadi Pouya and A. A. Rajabi [Int. J. Mod. Phys. E 25, 9 (2016) 1650072] are incorrect. The formalism of the paper has serious mistakes and the numerical results are quite misleading because such a calculation even with small grids for Jacobi momenta and the angle variables leads to a huge memory of 37.8 PB (petabyte) which cannot even be achieved on present supercomputers.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1705.05538 [pdf]
IJMPE(2017)·1 citation
04
[Submitted on 16 May 2017]
Description of odd-mass nuclei within the interacting boson-fermion model based on the Gogny energy density functional
K. Nomura · R. Rodríguez-Guzmán · L. M. Robledo
Spectroscopic properties of odd-mass nuclei are studied within the framework of the interacting boson-fermion model (IBFM) with parameters based on the Hartree-Fock-Bogoliubov (HFB) approximation. The parametrization D1M of the Gogny energy density functional (EDF) has been used at the mean-field level to obtain the deformation energy surfaces for the considered nuclei in terms of the quadrupole deformations ( $β, γ$ ). In addition to the energy surfaces, both single particle energies and occupation probabilities have been used as a microscopic input for building the IBFM Hamiltonian. Only three strength parameters for the particle-boson-core coupling are fitted to experimental spectra. The IBFM Hamiltonian is then used to compute the energy spectra and electromagnetic transition rates for selected odd-mass Eu and Sm nuclei as well as for $^{195}$ Pt and $^{195}$ Au. A reasonable agreement with the available experimental data is obtained for the considered odd-mass nuclei.
Comments:
14 pages, 16 figures, 9 tables
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1705.05539 [pdf]
PRC(2017)·24 citations
05
[Submitted on 16 May 2017]
Production of Charm Quarks in a Parton Cascade Model for Relativistic Heavy Ion Collisions at $s_{NN}$ = 200 GeV
Dinesh K. Srivastava🇮🇳 · Steffen A. Bass🇺🇸 · Rupa Chatterjee🇮🇳
We study the production and dynamics of heavy quarks in the parton cascade model for relativistic heavy ion collisions. The model is motivated by the QCD parton picture and describes the dynamics of an ultra-relativistic heavy-ion collision in terms of cascading partons which undergo scattering and multiplication while propagating. We focus on the dynamics of charm quark production and evolution in p+p and Au+Au collisions for several different interaction scenarios, i.e. collisions only between primary partons without radiation of gluons, multiple collisions without radiation of gluons and multiple collisions with radiation of gluons, allowing us to isolate the contributions of parton rescattering and radiation to charm production. We also discuss results of an eikonal approximation of the collision which provides a valuable comparison with mini-jet calculations and clearly brings out the importance of multiple collisions.
Comments:
17 pages, 18 figures, 2 tables. 1 new figure, more references and discussions added. Accepted for publication in Physical Review C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1705.05542 [pdf]
PRC(2017)·9 citations
06
[Submitted on 16 May 2017]
Magneto-Vortical evolution of QGP in heavy ion collisions
Ashutosh Dash🇮🇳 · Victor Roy🇮🇳 · Bedangadas Mohanty🇮🇳
The interplay of magnetic field and thermal vorticity in a relativistic ideal fluid might generate fluid vorticity during the fluid evolution provided the flow fields and the entropy density of the fluid is inhomogeneous \cite{Mahajan:2010}. Exploiting this fact and assuming large magnetic Reynolds number we study the evolution of generalised magnetic field ( $B^$ ) which is defined as a combination of the usual magnetic field ( $B$ ) and relativistic thermal vorticity ( $ω^{μν}$ ), in a 2(space)+1(time) dimensional isentropic evolution of Quark Gluon Plasma (QGP) with longitudinal boost invariance. The temporal evolution of $B^$ is found to be different than $B$ , and the $B^$ evolution also depends on the position of the fluid along the beam direction (taken along the z axis) with respect to the mid-plane $z = 0$ . Further it is observed that the transverse components ( $B_{x}^$ , $B_{y}^$ ) evolve differently around the mid-plane.
Comments:
8 pages, 2 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1705.05657 [pdf]
J.Phys.G(2019)·11 citations
07
[Submitted on 16 May 2017]
Spectral shapes of forbidden argon beta decays as background component for rare-event searches
J. Kostensalo🇫🇮 · J. Suhonen🇫🇮 · K. Zuber🇩🇪
The spectral shape of the electrons from the two first-forbidden unique beta- decays of Ar-39 and Ar-42 were calculated for the first time to the next-to-leading order. Especially the spectral shape of the Ar-39 decay can be used to characterise this background component for dark matter searches based on argon. Alternatively, due to the low thresholds of these experiments, the spectral shape can be investigated over a wide energy range with high statistics and thus allow a sensitive comparison with the theoretical predictions. This might lead to interesting results for the ratio of the weak vector and axial-vector constants in nuclei.
Comments:
9 pages, 6 figures, submitted
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1705.05726 [pdf]
J.Phys.G(2018)·11 citations
08
[Submitted on 15 May 2017] (cross-list from hep-ph)
The Energy Distribution of Subjets and the Jet Shape
Zhong-Bo Kang🇺🇸 · Felix Ringer🇺🇸 · Wouter J. Waalewijn🇳🇱
We present a framework that describes the energy distribution of subjets of radius $r$ within a jet of radius $R$ . We consider both an inclusive sample of subjets as well as subjets centered around a predetermined axis, from which the jet shape can be obtained. For $r ≪ R$ we factorize the physics at angular scales $r$ and $R$ to resum the logarithms of $r / R$ . For central subjets, we consider both the standard jet axis and the winner-take-all axis, which involve double and single logarithms of $r / R$ , respectively. All relevant one-loop matching coefficients are given, and an inconsistency in some previous results for cone jets is resolved. Our results for the standard jet shape differ from previous calculations at next-to-leading logarithmic order, because we account for the recoil of the standard jet axis due to soft radiation. Numerical results are presented for an inclusive subjet sample for $pp \to jet + X$ at next-to-leading order plus leading logarithmic order.
Comments:
39 pages, 7 figures, v2: journal version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1705.05375 [pdf]
JHEP(2017)·74 citations
09
[Submitted on 15 May 2017] (cross-list from nucl-ex)
The nuclear force imprints revealed on the elastic scattering of protons with $^{10}$ C
A. Kumar🇨🇦 · R. Kanungo🇨🇦 · A. Calci🇨🇦 · P. Navratil🇨🇦 · A. Sanetullaev🇨🇦 · M. Alcorta🇨🇦 · V. Bildstein🇨🇦 · G. Christian🇨🇦 · B. Davids🇨🇦 · J. Dohet-Eraly🇨🇦 · J. Fallis🇨🇦 · A. T. Gallant🇨🇦 and 17 other authors
How does nature hold together protons and neutrons to form the wide variety of complex nuclei in the universe? Describing many-nucleon systems from the fundamental theory of quantum chromodynamics has been the greatest challenge in answering this question. The chiral effective field theory description of the nuclear force now makes this possible but requires certain parameters that are not uniquely determined. Defining the nuclear force needs identification of observables sensitive to the different parametrizations. From a measurement of proton elastic scattering on $^{10}$ C at TRIUMF and ab initio nuclear reaction calculations we show that the shape and magnitude of the measured differential cross section is strongly sensitive to the nuclear force prescription.
Comments:
7 pages, 6 figures
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1705.05409 [pdf]
PRL(2017)·29 citations
10
[Submitted on 15 May 2017] (cross-list from nucl-ex)
Isolating the chiral magnetic effect from backgrounds by pair invariant mass
Jie Zhao🇺🇸 · Hanlin Li🇺🇸 · Fuqiang Wang🇺🇸
Topological gluon configurations in quantum chromodynamics induce quark chirality imbalance in local domains, which can result in the chiral magnetic effect (CME)--an electric charge separation along a strong magnetic field. Experimental searches for the CME in relativistic heavy ion collisions via the charge-dependent azimuthal correlator ( $Δ γ$ ) suffer from large backgrounds arising from particle correlations (e.g. due to resonance decays) coupled with the elliptic anisotropy. We propose differential measurements of the $Δ γ$ as a function of the pair invariant mass ( $m_{inv}$ ), by restricting to high $m_{inv}$ thus relatively background free, and by studying the $m_{inv}$ dependence to separate the possible CME signal from backgrounds. We demonstrate by model studies the feasibility and effectiveness of such measurements for the CME search.
Comments:
16 preprint pages 5 figures. v2: added a test with a broad "instanton/sphaleron" peak, and added clarifying texts; v3: added event-shape engineering (and two new figures) and expanded discussions on the low invariant mass region; v4: repeated cautionary discussions in introduction and conclusion sections, published version
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1705.05410 [pdf]
EPJC(2019)·56 citations

Affiliations

first authorsco-authorsvia INSPIRE