Nuclear Theory·nucl-th

Thursday·June 30, 2016

8 papers—4 primary·4 cross-listed

01
Tetrahedral shapes of neutron-rich Zr isotopes from multidimensionally-constrained relativistic Hartree-Bogoliubov model
Jie Zhao · Bing-Nan Lu · En-Guang Zhao · Shan-Gui Zhou
We develop a multidimensionally constrained relativistic Hartree-Bogoliubov (MDC-RHB) model in which the pairing correlations are taken into account by making the Bogoliubov transformation. In this model, the nuclear shape is assumed to be invariant under the reversion of $x$ and $y$ axes; i.e., the intrinsic symmetry group is $V_{4}$ and all shape degrees of freedom $β_{λ μ}$ with even $μ$ are included self-consistently. The RHB equation is solved in an axially deformed harmonic oscillator basis. A separable pairing force of finite range is adopted in the MDC-RHB model. The potential energy curves of neutron-rich even-even Zr isotopes are calculated with relativistic functionals DD-PC1 and PC-PK1 and possible tetrahedral shapes in the ground and isomeric states are investigated. The ground state shape of $^{110}$ Zr is predicted to be tetrahedral with both functionals and so is that of $^{112}$ Zr with the functional DD-PC1. The tetrahedral ground states are caused by large energy gaps around $Z = 40$ and $N = 70$ when $β_{32}$ deformation is included. Although the inclusion of the $β_{30}$ deformation can also reduce the energy around $β_{20} = 0$ and lead to minima with pear-like shapes for nuclei around $^{110}$ Zr, these minima are unstable due to their shallowness.
nucl-thnucl-exPRC(2017)·61 citations
02
Closing the equations of motion of anisotropic fluid dynamics by a judicious choice of moment of the Boltzmann equation
Etele Molnár🇩🇪 · Harri Niemi🇩🇪 · Dirk H. Rischke🇩🇪
In Molnár et al. [Phys. Rev. D 93, 114025 (2016)] the equations of anisotropic dissipative fluid dynamics were obtained from the moments of the Boltzmann equation based on an expansion around an arbitrary anisotropic single-particle distribution function. In this paper we make a particular choice for this distribution function and consider the boost-invariant expansion of a fluid in one dimension. In order to close the conservation equations, we need to choose an additional moment of the Boltzmann equation. We discuss the influence of the choice of this moment on the time evolution of fluid-dynamical variables and identify the moment that provides the best match of anisotropic fluid dynamics to the solution of the Boltzmann equation in the relaxation-time approximation.
nucl-thhep-phphysics.flu-dynphysics.plasm-phPRD(2016)·75 citations
03
Triplet Pairing in pure neutron matter
Sarath Srinivas (IIT M)🇮🇳 · S. Ramanan (IIT M)🇮🇳
We study the zero temperature BCS gaps for the triplet channel in pure neutron matter using Similarity Renormalization Group (SRG) evolved interactions. We use the dependence of the results on the SRG resolution scale, as a tool to analyze medium and many-body corrections. In particular, we study the effects of including the three-body interactions at leading order, which appear at N2LO in the Chiral EFT, as well as that of the first-order self-energy corrections on the zero temperature gap. In addition we also extract the transition temperature as a function of densities and verify the BCS scaling of the zero temperature gaps to the transition temperature. We observe that the self-energy effects are very crucial in order to reduce the SRG resolution scale dependence of the results, while the three-body effects at the leading order do not change the two-body resolution scale dependence. On the other hand, the results depend strongly on the three-body cut-off, emphasizing the importance of the missing higher-order three-body effects. We also observe that self-energy effects reduce the overall gap as well as shift the gap closure to lower densities.
nucl-thcond-mat.quant-gasPRC(2016)·31 citations
04
Quantum Phase Transition in the Shape of Zr isotopes
Tomoaki Togashi · Yusuke Tsunoda · Takaharu Otsuka · Noritaka Shimizu
The rapid shape change in Zr isotopes near neutron number $N$ =60 is identified to be caused by type II shell evolution associated with massive proton excitations to its $0 g_{9/2}$ orbit, and is shown to be a quantum phase transition. Monte Carlo shell-model calculations are carried out for Zr isotopes of $N$ =50-70 with many configurations spanned by eight proton orbits and eight neutron orbits. Energy levels and B(E2) values are obtained within a single framework in a good agreement with experiments, depicting various shapes in going from $N$ =50 to 70. Novel coexistence of prolate and triaxial shapes is suggested.
nucl-thnucl-exPRL(2016)·230 citations
05
The LPM effect in sequential bremsstrahlung: dimensional regularization
Peter Arnold🇺🇸 · Han-Chih Chang🇺🇸 · Shahin Iqbal🇵🇰
The splitting processes of bremsstrahlung and pair production in a medium are coherent over large distances in the very high energy limit, which leads to a suppression known as the Landau-Pomeranchuk-Migdal (LPM) effect. Of recent interest is the case when the coherence lengths of two consecutive splitting processes overlap (which is important for understanding corrections to standard treatments of the LPM effect in QCD). In previous papers, we have developed methods for computing such corrections without making soft-gluon approximations. However, our methods require consistent treatment of canceling ultraviolet (UV) divergences associated with coincident emission times, even for processes with tree-level amplitudes. In this paper, we show how to use dimensional regularization to properly handle the UV contributions. We also present a simple diagnostic test that any consistent UV regularization method for this problem needs to pass.
↳ hep-phnucl-thJHEP(2016)·31 citations
06
Studying the P_c(4450) resonance in J/psi photoproduction off protons
A. N. Hiller Blin🇪🇸 · C. Fernández-Ramírez🇲🇽 · A. Jackura🇺🇸 · V. Mathieu🇺🇸 · V. I. Mokeev🇺🇸 · A. Pilloni🇺🇸 · A. P. Szczepaniak🇺🇸
A resonance-like structure, the P_c(4450), has recently been observed in the J/psi p spectrum by the LHCb collaboration. We discuss the feasibility of detecting this structure in J/psi photoproduction in the CLAS12 experiment at JLab. We present a first estimate of the upper limit for the branching ratio of the P_c(4450) to J/psi p. Our estimates, which take into account the experimental resolution effects, predict that it will be possible to observe a sizable cross section close to the J/psi production threshold and shed light on the P_c(4450) resonance in the future photoproduction measurements.
↳ hep-phhep-exnucl-thPRD(2016)·111 citations
07
First Measurement of Collectivity of Coexisting Shapes based on Type II Shell Evolution: The Case of $^{96}$ Zr
C. Kremer · S. Aslanidou · S. Bassauer · M. Hilcker · A. Krugmann · P. von Neumann-Cosel · T. Otsuka · N. Pietralla · V. Yu. Ponomarev · N. Shimizu · M. Singer · G. Steinhilber and 4 other authors
Background: Type II shell evolution has recently been identified as a microscopic cause for nuclear shape coexistence. Purpose: Establish a low-lying rotational band in 96-Zr. Methods: High-resolution inelastic electron scattering and a relative analysis of transition strengths are used. Results: The B(E2; 0_1^+ -> 2_2^+) value is measured and electromagnetic decay strengths of the secdond 2^+ state are deduced. Conclusions: Shape coexistence is established for 96-Zr. Type II shell evolution provides a systematic and quantitative mechanism to understand deformation at low excitation energies.
↳ nucl-exnucl-thPRL(2016)·112 citations
08
Spectroscopy of the neutron-rich hypernucleus $_{Λ}^{7}$ He from electron scattering
T. Gogami🇯🇵 · C. Chen🇺🇸 · D. Kawama🇯🇵 · P. Achenbach🇩🇪 · A. Ahmidouch🇺🇸 · I. Albayrak🇺🇸 · D. Androic🇭🇷 · A. Asaturyan🇦🇲 · R. Asaturyan🇦🇲 · O. Ates🇺🇸 · P. Baturin🇺🇸 · R. Badui🇺🇸 and 74 other authors
The missing mass spectroscopy of the $_{Λ}^{7}$ He hypernucleus was performed, using the $^{7}$ Li $(e, e^{'} K^{+})_{Λ}^{7}$ He reaction at the Thomas Jefferson National Accelerator Facility Hall C. The $Λ$ binding energy of the ground state (1/2 $^{+}$ ) was determined with a smaller error than that of the previous measurement, being $B_{Λ}$ = 5.55 $\pm$ 0.10(stat.) $\pm$ 0.11(sys.) MeV. The experiment also provided new insight into charge symmetry breaking in p-shell hypernuclear systems. Finally, a peak at $B_{Λ}$ = 3.65 $\pm$ 0.20(stat.) $\pm$ 0.11(sys.) MeV was observed and assigned as a mixture of 3/2 $^{+}$ and 5/2 $^{+}$ states, confirming the "gluelike" behavior of $Λ$ , which makes an unstable state in $^{6}$ He stable against neutron emission.
↳ nucl-exnucl-thPRC(2016)·44 citations

Affiliations

first authorsco-authorsvia INSPIRE