Nuclear Theory·nucl-th

Monday·May 30, 2016

8 papers—5 primary·3 cross-listed

01
Electric dipole response of neutron-rich Calcium isotopes in relativistic quasiparticle time blocking approximation
Irina A. Egorova🇺🇸 · Elena Litvinova🇺🇸
New results for electric dipole strength in the chain of even-even Calcium isotopes with the mass numbers A = 40 - 54 are presented. Starting from the covariant Lagrangian of Quantum Hadrodynamics, spectra of collective vibrations (phonons) and phonon-nucleon coupling vertices for $J \leq 6$ and normal parity were computed in a self-consistent relativistic quasiparticle random phase approximation (RQRPA). These vibrations coupled to Bogoliubov two-quasiparticle configurations (2q $\otimes$ phonon) form the model space for the calculations of the dipole response function in the relativistic quasiparticle time blocking approximation (RQTBA). The results for giant dipole resonance in the latter approach are compared to those obtained in RQRPA and to available data. Evolution of the dipole strength with neutron number is investigated for both high-frequency giant dipole resonance (GDR) and low-lying strength. Development of a pygmy resonant structure on the low-energy shoulder of GDR is traced and analyzed in terms of transition densities. A dependence of the pygmy dipole strength on the isospin asymmetry parameter is extracted.
nucl-thPRC(2016)·47 citations
02
Spectroscopic factor strengths using $ab ini t i o$ approaches
P. C. Srivastava · Vikas Kumar
We have calculated the spectroscopic factor strengths for the one-proton and one-neutron pick-up reactions $^{27}$ Al( $d$ , $^{3}$ He) $^{26}$ Mg and $^{27}$ Al( $d$ , $t$ ) $^{26}$ Al within the framework of the shell model. We employed two different $ab ini t i o$ approaches : an in-medium similarity renormalization targeted for a particular nucleus, and the coupled- cluster effective interaction. We also compared our results with recently determined experimental spectroscopic factors.
nucl-thPRC(2016)·13 citations
03
Simultaneous analysis of matter radii, transition probabilities, and excitation energies of Mg isotopes by angular-momentum-projected configuration-mixing calculations
Mitsuhiro Shimada · Shin Watanabe · Shingo Tagami · Takuma Matsumoto · Yoshifumi R. Shimizu · Masanobu Yahiro
We perform simultaneous analysis of (1) matter radii, (2) $B (E 2; 0^{+} \to 2^{+})$ transition probabilities, and (3) excitation energies, $E (2^{+})$ and $E (4^{+})$ , for $^{24 - 40}$ Mg by using the beyond mean-field (BMF) framework with angular-momentum-projected configuration mixing with respect to the axially symmetric $β_{2}$ deformation with infinitesimal cranking. The BMF calculations successfully reproduce all of the data for $r_{m}$ , $B (E 2)$ , and $E (2^{+})$ and $E (4^{+})$ , indicating that it is quite useful for data analysis, particularly for low-lying states. We also discuss the absolute value of the deformation parameter $β_{2}$ deduced from measured values of $B (E 2)$ and $r_{m}$ . This framework makes it possible to investigate the effects of $β_{2}$ deformation, the change in $β_{2}$ due to restoration of rotational symmetry, $β_{2}$ configuration mixing, and the inclusion of time-odd components by infinitesimal cranking. Under the assumption of axial deformation and parity conservation, we clarify which effect is important for each of the three measurements, and propose the kinds of BMF calculations that are practical for each of the three kinds of observables.
nucl-thPRC(2016)·9 citations
04
Induced Hyperon-Nucleon-Nucleon Interactions and the Hyperon Puzzle
Roland Wirth🇩🇪 · Robert Roth🇩🇪
We present the first ab initio calculations for $p$ -shell hypernuclei including hyperon-nucleon-nucleon (YNN) contributions induced by a Similarity Renormalization Group transformation of the initial hyperon-nucleon interaction. The transformation including the YNN terms conserves the spectrum of the Hamiltonian while drastically improving model-space convergence of the Importance-Truncated No-Core Shell Model, allowing a precise extraction of binding and excitation energies. Results using a hyperon-nucleon interaction at leading order in chiral effective field theory for lower- to mid- $p$ -shell hypernuclei show a good reproduction of experimental excitation energies while hyperon binding energies are typically overestimated. The induced YNN contributions are strongly repulsive and we show that they are related to a decoupling of the $Σ$ hyperons from the hypernuclear system, i.e., a suppression of the $Λ$ - $Σ$ conversion terms in the Hamiltonian. This is linked to the so-called hyperon puzzle in neutron-star physics and provides a basic mechanism for the explanation of strong $Λ$ NN three-baryon forces.
nucl-thastro-ph.SRhep-phPRL(2016)·53 citations
05
Relativistic hydrodynamics in heavy-ion collisions: general aspects and recent developments
Amaresh Jaiswal🇩🇪 · Victor Roy🇩🇪
Relativistic hydrodynamics has been quite successful in explaining the collective behaviour of the QCD matter produced in high energy heavy-ion collisions at RHIC and LHC. We briefly review the latest developments in the hydrodynamical modeling of relativistic heavy-ion collisions. Essential ingredients of the model such as the hydrodynamic evolution equations, dissipation, initial conditions, equation of state, and freeze-out process are reviewed. We discuss observable quantities such as particle spectra and anisotropic flow and effect of viscosity on these observables. Recent developments such as event-by-event fluctuations, flow in small systems (proton-proton and proton-nucleus collisions), flow in ultra central collisions, longitudinal fluctuations and correlations and flow in intense magnetic field are also discussed.
nucl-thhep-phAdv.High Energy Phys.(2016)·205 citations
06
Search for the sterile neutrino mixing with the ICAL detector at INO
S. P. Behera🇮🇳 · Anushree Ghosh🇨🇱 · Sandhya Choubey🇮🇳 · V. M. Datar🇮🇳 · D. K. Mishra🇮🇳 · A. K. Mohanty🇮🇳
The study has been carried out on the prospects of probing the sterile neutrino mixing with the magnetized Iron CALorimeter (ICAL) at the India-based Neutrino Observatory (INO), using atmospheric neutrinos as a source. The so-called 3~ $+$ ~1 scenario is considered for active-sterile neutrino mixing and lead to projected exclusion curves in the sterile neutrino mass and mixing angle plane. The analysis is performed using the neutrino event generator NUANCE, modified for ICAL, and folded with the detector resolutions obtained by the INO collaboration from a full GEANT4 based detector simulation. A comparison has been made between the results obtained from the analysis considering only the energy and zenith angle of the muon and combined with the hadron energy due to the neutrino induced event. A small improvement has been observed with the addition of the hadron information to the muon. In the analysis we consider neutrinos coming from all zenith angles and the Earth matter effects are also included. The inclusion of events from all zenith angles improves the sensitivity to sterile neutrino mixing by about 35 $%$ over the result obtained using only down-going events. The improvement mainly stems from the impact of Earth matter effects on active-sterile mixing. The expected precision of ICAL on the active-sterile mixing is explored and allowed confidence level (C.L.) contours presented. At the assumed true value of $1 0^{\circ}$ for the sterile mixing angles and marginalization over $Δ m_{41}^{2}$ and the sterile mixing angles, the upper bound at 90\% C.L. (from 2 parameter plots) is around $2 0^{\circ}$ for $θ_{14}$ and $θ_{34}$ , and about $1 2^{\circ}$ for $θ_{24}$ .
↳ hep-phhep-exnucl-thEPJC(2017)·17 citations
07
Light-by-light scattering in ultraperipheral heavy-ion collisions at the LHC
Antoni Szczurek🇵🇱 · Mariola Klusek-Gawenda🇵🇱 · Piotr Lebiedowicz🇵🇱
We present cross sections for diphoton production in (semi)exclusive $P b P b$ collisions, relevant for the LHC. The calculation is based on equivalent photon approximation in the impact parameter space. The cross sections for elementary elastic scattering $γ γ \to γ γ$ subprocess are calculated including two mechanisms: box diagrams with leptons and quarks in the loops and a mechanism based on vector-meson dominance (VDM-Regge) model with virtual intermediate vector-like excitations of the photons. We get measureable cross sections in $P b P b$ collisions. We present many interesting differential distributions which could be measured by the ALICE, CMS or ATLAS Collaborations at the LHC. We study whether a separation of box and VDM-Regge contributions is possible. We find that the cross section for elastic $γ γ$ scattering could be measured in the heavy-ion collisions for subprocess energies smaller than $W_{γ γ} \approx 15 - 20$ ~GeV.
↳ hep-phnucl-thActa Phys.Polon.Supp.(2016)·0 citations
08
SU(2) higher-order effective quark interactions from polarization
Fábio L. Braghin🇧🇷
Higher order quark effective interactions are found for SU(2) flavor by departing from a non local quark-quark interaction. By integrating out a component of the quark field, the determinant is expanded in chirally symmetric and symmetry breaking effective interactions up to the fifh order in the quark bilinears. The resulting coupling constants are resolved in the leading order of the longwavelength limit and exact numerical ratios between several of these coupling constants are obtained in the large quark mass limit. In this level, chiral invariant interactions only show up in even powers of the quark bilinears, i.e. $O (ψ ˉ ψ)^{2 n}$ ( $n = 1, 2, 3, ..$ ), whereas (explicit) chiral symmetry breaking terms emerge as $O (ψ ˉ ψ)^{n}$ being always proportional to some power of the Lagrangian quark mass.
↳ hep-phhep-thnucl-thPLB(2016)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE