Nuclear Theory·nucl-th

Wednesday·August 5, 2015

9 papers—3 primary·6 cross-listed

01
Identification of Highly Deformed Even-Even Nuclides in the Neutron- and Proton-Rich Regions of the Nuclear Chart from the B(E2) and E2 Predictions in the Generalized Differential Equation Model
R. C. Nayak · S. Pattnaik
We identify here possible occurrence of large deformations in the neutron- and proton-rich regions of the nuclear chart from extensive predictions of the values of the reduced quadrupole transition probability B-E2 for the transition from the ground state to the first 2+ state and the corresponding excitation energy E2 of even-even nuclei in the recently developed Generalized Differential Equation model exclusively meant for these physical quantities. This is made possible from our analysis of the predicted values of these two physical quantities and the corresponding deformation parameters derived from them such as the quadrupole deformation beta-2, the ratio of beta-2 to the Weisskopf single-particle beta-2 and the intrinsic electric quadruplole moment , calculated for a large number of both known as well as hitherto unknown even-even isotopes of Oxygen to Fermium (Z=8 to 100). Our critical analysis of the resulting data convincingly support possible existence of large collectivity for the nuclides 30,32 Ne, 34 Mg, 60 Ti, 42,62,64 Cr, 50,68 Fe, 52,72 Ni, 72,70,96 Kr, 74,76 Sr,78,80,106,108 Zr , 82,84,110,112 Mo, 140 Te,144 Xe, 148 Ba, 122 Ce, 128,156 Nd, 130,132,158,160 Sm and 138,162,164,166 Gd, whose values of beta-2 are found to exceed 0.3 and even 0.4 in some cases. Our findings of large deformations in the exotic neutron-rich regions support the existence of another Island of Inversion in the heavy-mass region possibly caused by breaking of the N=70 sub-shell closure.
nucl-thIJMPE(2015)·2 citations
02
Sextic potential for $γ$ -rigid prolate nuclei
P. Buganu · R. Budaca
The equation of the Bohr-Mottelson Hamiltonian with a sextic oscillator potential is solved for $γ$ -rigid prolate nuclei. The associated shape phase space is reduced to three variables which are exactly separated. The angular equation has the spherical harmonic functions as solutions, while the $β$ equation is brought to the quasi-exactly solvable case of the sextic oscillator potential with a centrifugal barrier. The energies and the corresponding wave functions are given in closed form and depend, up to a scaling factor, on a single parameter. The $0^{+}$ and $2^{+}$ states are exactly determined, having an important role in the assignment of some ambiguous states for the experimental $β$ bands. Due to the special properties of the sextic potential, the model can simulate, by varying the free parameter, a shape phase transition from a harmonic to an anharmonic prolate $β$ -soft rotor crossing through a critical point. Numerical applications are performed for 39 nuclei: $^{98 - 108}$ Ru, $^{100, 102}$ Mo, $^{116 - 130}$ Xe, $^{132, 134}$ Ce, $^{146 - 150}$ Nd, $^{150, 152}$ Sm, $^{152, 154}$ Gd, $^{154, 156}$ Dy, $^{172}$ Os, $^{180 - 196}$ Pt, $^{190}$ Hg and $^{222}$ Ra. The best candidates for the critical point are found to be $^{104}$ Ru and $^{120, 126}$ Xe, followed closely by $^{128}$ Xe, $^{172}$ Os, $^{196}$ Pt and $^{148}$ Nd.
nucl-thJ.Phys.G(2015)·57 citations
03
General classical and quantum-mechanical description of magnetic resonance: An application to electric-dipole-moment experiments
Alexander J. Silenko🇧🇾
A general theoretical description of a magnetic resonance is presented. This description is necessary for a detailed analysis of spin dynamics in electric-dipole-moment experiments in storage rings. General formulas describing a behavior of all components of the polarization vector at the magnetic resonance are obtained for an arbitrary initial polarization. These formulas are exact on condition that the nonresonance rotating field is neglected. The spin dynamics is also calculated at frequencies far from resonance with allowance for both rotating fields. A general quantum-mechanical analysis of the spin evolution at the magnetic resonance is fulfilled and the full agreement between the classical and quantum-mechanical approaches is shown. Quasimagnetic resonances for particles and nuclei moving in noncontinuous perturbing fields of accelerators and storage rings are considered. Distinguishing features of quasimagnetic resonances in storage ring electric-dipole-moment experiments are investigated in detail. The exact formulas for the effect caused by the electric dipole moment are derived. The difference between the resonance effects conditioned by the rf electric-field flipper and the rf Wien filter is found and is calculated for the first time. The existence of this difference is crucial for the establishment of a consent between analytical derivations and computer simulations and for checking spin tracking programs. Main systematical errors are considered.
nucl-thcond-mat.otherhep-phhep-thEPJC(2017)·13 citations
04
Dark Matter Velocity Spectroscopy
Eric G. Speckhard🇺🇸 · Kenny C. Y. Ng🇺🇸 · John F. Beacom🇺🇸 · Ranjan Laha🇺🇸
Dark matter decays or annihilations that produce line-like spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming experiments will reach the required 0.1% level. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.
↳ astro-ph.COastro-ph.HEhep-exhep-ph+1PRL(2016)·44 citations
05
Toward precision mass measurements of neutron-rich nuclei relevant to $r$ -process nucleosynthesis
B. H. Sun🇨🇳 · Yu.A. Litvinov🇨🇳 · I. Tanihata🇨🇳 · Y. H. Zhang🇨🇳
The open question of where, when, and how the heavy elements beyond iron enrich our Universe has triggered a new era in nuclear physics studies.\ Of all the relevant nuclear physics inputs, the mass of very neutron-rich nuclides is a key quantity for revealing the origin of heavy elements beyond iron.\ Although the precise determination of this property is a great challenge, enormous progress has been made in recent decades, and it has contributed significantly to both nuclear structure and astrophysical nucleosynthesis studies.\ In this review, we first survey our present knowledge of the nuclear mass surface, emphasizing the importance of nuclear mass precision in $r$ -process calculations.\ We then discuss recent progress in various methods of nuclear mass measurement with a few selected examples.\ For each method, we focus on recent breakthroughs and discuss possible ways of improving the weighing of $r$ -process nuclides.
↳ nucl-exhep-exnucl-thFront.Phys.(Beijing)(2015)·20 citations
06
Breaking of axial symmetry in excited heavy nuclei as identified in Giant Dipole Resonance data
Eckart Grosse · Arnd R. Junghans · Ralph Massarczyk
A recent theoretical prediction of a breaking of axial symmetry in quasi all heavy nuclei is confronted to a new critical analysis of photon strength functions of nuclei in the valley of stability. For the photon strength in the isovector giant dipole resonance (IVGDR) regime a parameterization of GDR shapes by the sum of three Lorentzians (TLO) is extrapolated to energies below and above the IVGDR. The impact of non-GDR modes adding to the low energy slope of photon strength is discussed including recent data on photon scattering and other radiative processes. These are shown to be concentrated in energy regions where various model calculations predict intermediate collective strength; thus they are obviously separate from the IVGDR tail. The triple Lorentzian (TLO) ansatz for giant dipole resonances is normalized in accordance to the dipole sum rule. The nuclear droplet model with surface dissipation accounts well for positions and widths without local, nuclide specific, parameters. Very few and only global parameters are needed when a breaking of axial symmetry already in the valley of stability is admitted and hence a reliable prediction for electric dipole strength functions also outside of it is expected.
↳ nucl-exastro-ph.SRnucl-thEPJA(2017)·16 citations
07
Goldstone's Theorem on a Light-Like Plane
Silas R. Beane🇺🇸
I review various aspects of chiral symmetry and its spontaneous breaking on null planes, including the interesting manner in which Goldstone's theorem is realized and the constraints that chiral symmetry imposes on the null-plane Hamiltonians. Specializing to QCD with N massless flavors, I show that there is an interesting limit in which the chiral constraints on the null-plane Hamiltonians can be solved to give the spin-flavor algebra SU(2N), recovering a result originally found by Weinberg using different methods.
↳ hep-phhep-thnucl-thFew Body Syst.(2015)·1 citation
08
Predictions for Boson-Jet Observables and Fragmentation Function Ratios from a Hybrid Strong/Weak Coupling Model for Jet Quenching
Jorge Casalderrey-Solana🇪🇸 · Doga Can Gulhan🇺🇸 · José Guilherme Milhano🇨🇭 · Daniel Pablos🇪🇸 · Krishna Rajagopal🇺🇸
We have previously introduced a hybrid strong/weak coupling model for jet quenching in heavy ion collisions that describes the production and fragmentation of jets at weak coupling, using PYTHIA, and describes the rate at which each parton in the jet shower loses energy as it propagates through the strongly coupled plasma, dE/dx, using an expression computed holographically at strong coupling. The model has a single free parameter that we fit to a single experimental measurement. We then confront our model with experimental data on many other jet observables, focusing here on boson-jet observables, finding that it provides a good description of present jet data. Next, we provide the predictions of our hybrid model for many measurements to come, including those for inclusive jet, dijet, photon-jet and Z-jet observables in heavy ion collisions with energy $s = 5.02$ ATeV coming soon at the LHC. As the statistical uncertainties on near-future measurements of photon-jet observables are expected to be much smaller than those in present data, with about an order of magnitude more photon-jet events expected, predictions for these observables are particularly important. We find that most of our pre- and post-dictions do not depend sensitively on the form we choose for the rate of energy loss dE/dx of the partons in the shower. This gives our predictions considerable robustness. To better discriminate between possible forms for the rate of energy loss, though, we must turn to intrajet observables. Here, we focus on ratios of fragmentation functions. We close with a suggestion for a particular ratio, between the fragmentation functions of inclusive and associated jets with the same kinematics in the same collisions, which is particularly sensitive to the x- and E-dependence of dE/dx, and hence may be used to learn which mechanism of parton energy loss best describes the quenching of jets.
↳ hep-phnucl-thJHEP(2016)·125 citations
09
Two-Nucleon Higher Partial-Wave Scattering from Lattice QCD
Evan Berkowitz🇺🇸 · Thorsten Kurth🇺🇸 · Amy Nicholson🇺🇸 · Balint Joo🇺🇸 · Enrico Rinaldi🇺🇸 · Mark Strother🇺🇸 · Pavlos M. Vranas🇺🇸 · Andre Walker-Loud🇺🇸
We present a determination of nucleon-nucleon scattering phase shifts for l >= 0. The S, P, D and F phase shifts for both the spin-triplet and spin-singlet channels are computed with lattice Quantum ChromoDynamics. For l > 0, this is the first lattice QCD calculation using the Luscher finite-volume formalism. This required the design and implementation of novel lattice methods involving displaced sources and momentum-space cubic sinks. To demonstrate the utility of our approach, the calculations were performed in the SU(3)-flavor limit where the light quark masses have been tuned to the physical strange quark mass, corresponding to m_pi = m_K ~ 800 MeV. In this work, we have assumed that only the lowest partial waves contribute to each channel, ignoring the unphysical partial wave mixing that arises within the finite-volume formalism. This assumption is only valid for sufficiently low energies; we present evidence that it holds for our study using two different channels. Two spatial volumes of V ~ (3.5 fm)^3 and V ~ (4.6 fm)^3 were used. The finite-volume spectrum is extracted from the exponential falloff of the correlation functions. Said spectrum is mapped onto the infinite volume phase shifts using the generalization of the Luscher formalism for two-nucleon systems.
↳ hep-lathep-phnucl-thPLB(2017)·135 citations

Affiliations

first authorsco-authorsvia INSPIRE