Nuclear Theory·nucl-th

Tuesday·May 12, 2015

13 papers—4 primary·9 cross-listed

01
Nuclear energy release from fragmentation
Cheng Li · S. R. Souza · M. B. Tsang · Feng-Shou Zhang
Nuclear energy released by splitting Uranium and Thorium isotopes into two, three, four, up to eight fragments with nearly equal size are studied. We found that the energy released come from equally splitting the $^{235, 238}$ U and $^{230, 232}$ Th nuclei into to three fragments is largest. The statistical multifragmentation model is employed to calculate the probability of different breakup channels for the excited nuclei. Weighing the the probability distributions of fragments multiplicity at different excitation energies for the $^{238}$ U nucleus, we found that an excitation energy between 1.2 and 2 MeV/u is optimal for the $^{235}$ U, $^{238}$ U, $^{230}$ Th and $^{232}$ Th nuclei to release nuclear energy of about 0.7-0.75 MeV/u.
nucl-thNPA(2016)·1 citation
02
The virtual-state character of the {9}^Be 1/2^+ state in the {9}^Be({\gamma},n){8}^Be reaction
Myagmarjav Odsuren · Yuma Kikuchi · Takayuki Myo · Masayuki Aikawa · Kiyoshi Kato
We study the character of the first excited 1/2^{+} state of {9}^Be, which is observed as a low-lying sharp peak in the cross section of 9^Be({\gamma},n)2{\alpha} just above the {8}^Be+n threshold. Using the {\alpha}+{\alpha}+n three-body model, we describe the ground and excited unbound states of {9}^Be above the {\alpha}+{\alpha}+n threshold. Applying the complex scaling method to the three-body model, we find no 1/2^{+} resonant solutions, while the low-lying peak in the photodisintegration cross section is reproduced in the present calculation. It is found that the low-lying peak is dominantly explained by the 8^Be+n component. Furthermore, using the analytical continuation of the coupling constant of the three-body interaction for the {\alpha}+{\alpha}+n system, we discuss the virtual-state character of the 1/2^{+} state.
nucl-thPRC(2015)·29 citations
03
Few-body calculations of $η$ -nuclear quasibound states
N. Barnea🇮🇱 · E. Friedman🇮🇱 · A. Gal🇮🇱
We report on precise hyperspherical-basis calculations of $η N N$ and $η N N N$ quasibound states, using energy dependent $η N$ interaction potentials derived from coupled-channel models of the $S_{11}$ $N^{*} (1535)$ nucleon resonance. The $η N$ attraction generated in these models is too weak to generate a two-body bound state. No $η N N$ bound-state solution was found in our calculations in models where Re $a_{η N} ≲ 1$ fm, with $a_{η N}$ the $η N$ scattering length, covering thereby the majority of $N^{*} (1535)$ resonance models. A near-threshold $η N N N$ bound-state solution, with $η$ separation energy of less than 1 MeV and width of about 15 MeV, was obtained in the 2005 Green-Wycech model where Re $a_{η N} \approx 1$ fm. The role of handling self consistently the subthreshold $η N$ interaction is carefully studied.
nucl-thhep-phnucl-exPLB(2015)·33 citations
04
Regularity and chaos in 0+ states of the interacting boson model using quantum measures
S. Karampagia · Dennis Bonatsos · R. F. Casten
Statistical measures of chaos have long been used in the study of chaotic dynamics in the framework of the interacting boson model. The use of large number of bosons renders additional studies of chaos possible, that can provide a direct comparison with similar classical studies of chaos. We intend to provide complete quantum chaotic dynamics at zero angular momentum in the vicinity of the arc of regularity and link the results of the study of chaos using statistical measures with those of the study of chaos using classical measures. Statistical measures of chaos are applied on the spectrum and the transition intensities of 0+ states in the framework of the interacting boson model. The energy dependence of chaos is provided for the first time using statistical measures of chaos. The position of the arc of regularity was also found to be stable in the limit of large boson numbers. The results of the study of chaos using statistical measures are consistent with previous studies using classical measures of chaos, as well as with studies using statistical measures of chaos, but for small number of bosons and states with angular momentum greater than 2.
nucl-thPRC(2015)·14 citations
05
Relative contributions of the weak, main and fission-recycling r-process
S. Shibagaki · T.Kajino · G. J. Mathews · S. Chiba · S. Nishimura · G. Lorusso
There has been a persistent conundrum in attempts to model the nucleosynthesis of heavy elements by rapid neutron capture (the $r$ -process). Although the location of the abundance peaks near nuclear mass numbers 130 and 195 identify an environment of rapid neutron capture near closed nuclear shells, the abundances of elements just above and below those peaks are often underproduced by more than an order of magnitude in model calculations. At the same time there is a debate in the literature as to what degree the $r$ -process elements are produced in supernovae or the mergers of binary neutron stars. In this paper we propose a novel solution to both problems. We demonstrate that the underproduction of elements above and below the $r$ -process peaks characteristic in the main or weak $r$ -process events (like magnetohydrodynamic jets or neutrino-driven winds in core-collapse supernovae) can be supplemented via fission fragment distributions from the recycling of material in a neutron-rich environment such as that encountered in neutron star mergers. In this paradigm, the abundance peaks themselves are well reproduced by a moderately neutron rich, main $r$ -process environment such as that encountered in the magnetohydrodynamical jets in supernovae supplemented with a high-entropy, weakly neutron rich environment such as that encountered in the neutrino-driven-wind model to produce the lighter $r$ -process isotopes. Moreover, we show that the relative contributions to the $r$ -process abundances in both the solar-system and metal-poor stars from the weak, main, and fission-recycling environments required by this proposal are consistent with estimates of the relative Galactic event rates of core-collapse supernovae for the weak and main $r$ -process and neutron star mergers for the fission-recycling $r$ -process.
↳ astro-ph.SRastro-ph.HEnucl-thApJ(2016)·73 citations
06
Reaction rates of $^{64}$ Ge( $p, γ$ ) $^{65}$ As and $^{65}$ As( $p, γ$ ) $^{66}$ Se and the extent of nucleosynthesis in type I X-ray bursts
Y. H. Lam · J. J. He · A. Parikh · H. Schatz · B. A. Brown · M. Wang · B. Guo · Y. H. Zhang · X. H. Zhou · H. S. Xu
The extent of nucleosynthesis in models of type I X-ray bursts and the associated impact on the energy released in these explosive events are sensitive to nuclear masses and reaction rates around the $^{64}$ Ge waiting point. Using the well known mass of $^{64}$ Ge, the recently measured $^{65}$ As mass, and large-scale shell model calculations, we have determined new thermonuclear rates of the $^{64}$ Ge( $p$ , $γ$ ) $^{65}$ As and $^{65}$ As( $p$ , $γ$ ) $^{66}$ Se reactions with reliable uncertainties. The new reaction rates differ significantly from previously published rates. Using the new data we analyze the impact of the new rates and the remaining nuclear physics uncertainties on the $^{64}$ Ge waiting point in a number of representative one-zone X-ray burst models. We find that in contrast to previous work, when all relevant uncertainties are considered, a strong $^{64}$ Ge $r p$ -process waiting point cannot be ruled out. The nuclear physics uncertainties strongly affect X-ray burst model predictions of the synthesis of $^{64}$ Zn, the synthesis of nuclei beyond $A = 64$ , energy generation, and burst light curve. We also identify key nuclear uncertainties that need to be addressed to determine the role of the $^{64}$ Ge waiting point in X-ray bursts. These include the remaining uncertainty in the $^{65}$ As mass, the uncertainty of the $^{66}$ Se mass, and the remaining uncertainty in the $^{65}$ As( $p$ , $γ$ ) $^{66}$ Se reaction rate, which mainly originates from uncertain resonance energies.
↳ astro-ph.SRnucl-thApJ(2016)·26 citations
07
Studying re-scattering effect in heavy-ion collision through $K^{*}$ Production
Subhash Singha🇺🇸 · Bedangadas Mohanty🇮🇳 · Zi-Wei Lin🇺🇸
We have studied the $K^{*}$ production within A Multi-Phase Transport model (AMPT) for Au+Au collisions at $s_{N N}$ = 200 GeV to understand the hadronic re-scattering effect on the measured yields of the resonance. The hadronic re-scattering of the $K^{*}$ decay daughter particles ( $π$ and K) will alter their momentum distribution thereby making it difficult to reconstruct the $K^{*}$ signal through the invariant mass method. An increased hadronic re-scattering effect thus leads to a decrease in the reconstructed yield of $K^{*}$ in heavy-ion collisions. Through this simulation study we argue that a decrease in $K^{*}$ /K ratio with increase in collision centrality necessarily reflects the hadronic re-scattering effect. Since the re-scattering occurs in the hadronic phase and $K^{*}$ has a lifetime of 4 fm/c, we present a toy model based discussion on using measured $K^{*}$ /K to put a lower limit on the hadronic phase lifetime in high energy nuclear collisions.
↳ nucl-exhep-phnucl-thIJMPE(2015)·23 citations
08
Ab initio calculation of the $n p \to d γ$ radiative capture process
Silas R. Beane🇺🇸 · Emmanuel Chang🇺🇸 · William Detmold🇺🇸 · Kostas Orginos🇺🇸 · Assumpta Parreño🇪🇸 · Martin J. Savage🇺🇸 · Brian C. Tiburzi🇺🇸
Lattice QCD calculations of two-nucleon systems are used to isolate the short-distance two-body electromagnetic contributions to the radiative capture process $n p \to d γ$ , and the photo-disintegration processes $γ^{(*)} d \to n p$ . In nuclear potential models, such contributions are described by phenomenological meson-exchange currents, while in the present work, they are determined directly from the quark and gluon interactions of QCD. Calculations of neutron-proton energy levels in multiple background magnetic fields are performed at two values of the quark masses, corresponding to pion masses of $m_{π} \sim 450$ and 806 MeV, and are combined with pionless nuclear effective field theory to determine these low-energy inelastic processes. Extrapolating to the physical pion mass, a cross section of $σ^{l q c d} (n p \to d γ) = 332.4 (+ 5.4 - 4.7) mb$ is obtained at an incident neutron speed of $v = 2, 200 m / s$ , consistent with the experimental value of $σ^{e x pt} (n p \to d γ) = 334.2 (0.5) mb$ .
↳ hep-lathep-phnucl-thPRL(2015)·96 citations
09
Local Gauge Transformation for the Quark Propagator in an SU(N) Gauge Theory
M. Jamil Aslam🇵🇰 · A. Bashir🇲🇽 · L.X. Gutierrez-Guerrero🇲🇽
In an SU(N) gauge field theory, the n-point Green functions, namely, propagators and vertices, transform under the simultaneous local gauge variations of the gluon vector potential and the quark matter field in such a manner that the physical observables remain invariant. In this article, we derive this intrinsically non perturbative transformation law for the quark propagator within the system of covariant gauges. We carry out its explicit perturbative expansion till O(g_s^6) and, for some terms, till O(g_s^8). We study the implications of this transformation for the quark-anti-quark condensate, multiplicative renormalizability of the massless quark propagator, as well as its relation with the quark-gluon vertex at the one-loop order. Setting the color factors C_F=1 and C_A=0, Landau-Khalatnikov-Fradkin transformation for the abelian case of quantum electrodynamics is trivially recovered.
↳ hep-thhep-phnucl-thPRD(2016)·28 citations
10
Event-by-event fluctuations in perturbative QCD + saturation + hydro model: pinning down QCD matter shear viscosity in ultrarelativistic heavy-ion collisions
H. Niemi🇩🇪 · K. J. Eskola🇫🇮 · R. Paatelainen🇪🇸
We introduce an event-by-event perturbative-QCD + saturation + hydro ("EKRT") framework for ultrarelativistic heavy-ion collisions, where we compute the produced fluctuating QCD-matter energy densities from next-to-leading order perturbative QCD using a saturation conjecture to control soft particle production, and describe the space-time evolution of the QCD matter with dissipative fluid dynamics, event by event. We perform a simultaneous comparison of the centrality dependence of hadronic multiplicities, transverse momentum spectra, and flow coefficients of the azimuth-angle asymmetries, against the LHC and RHIC measurements. We compare also the computed event-by-event probability distributions of relative fluctuations of elliptic flow, and event-plane angle correlations, with the experimental data from Pb+Pb collisions at the LHC. We show how such a systematic multi-energy and multi-observable analysis tests the initial state calculation and the applicability region of hydrodynamics, and in particular how it constrains the temperature dependence of the shear viscosity-to-entropy ratio of QCD matter in its different phases in a remarkably consistent manner.
↳ hep-phnucl-thPRC(2016)·381 citations
11
Evaluation of the proton charge radius from e-p scattering
John Arrington🇺🇸 · Ingo Sick🇨🇭
In light of the proton radius puzzle, the discrepancy between measurements of the proton charge radius from muonic hydrogen and those from electronic hydrogen and electron-proton scattering measurements, we reexamine the charge radius extractions from electron scattering measurements. We provide a recommended value for the proton RMS charge radius, $r_{E} = 0.879 \pm 0.011$ fm, based on a global examination of elastic e-p scattering data. The uncertainties include contributions to account for tension between different data sets and inconsistencies between radii using different extraction procedures.
↳ nucl-exhep-phnucl-thphysics.atom-phJ.Phys.Chem.Ref.Data(2015)·67 citations
12
FELIX-1.0: A finite element solver for the time dependent generator coordinate method with the Gaussian overlap approximation
D. Regnier · M. Verrière · N. Dubray · N. Schunck
We describe the software package FELIX that solves the equations of the time-dependent generator coordinate method (TDGCM) in N-dimensions (N $\geq$ 1) under the Gaussian overlap approximation. The numerical resolution is based on the Galerkin finite element discretization of the collective space and the Crank-Nicolson scheme for time integration. The TDGCM solver is implemented entirely in C++. Several additional tools written in C++, Python or bash scripting language are also included for convenience. In this paper, the solver is tested with a series of benchmarks calculations. We also demonstrate the ability of our code to handle a realistic calculation of fission dynamics.
↳ physics.comp-phnucl-thComput.Phys.Commun.(2016)·27 citations
13
Hadron mass corrections in semi-inclusive deep-inelastic scattering
J. V. Guerrero🇺🇸 · J. J. Ethier🇺🇸 · A. Accardi🇺🇸 · S. W. Casper🇺🇸 · W. Melnitchouk🇺🇸
The spin-dependent cross sections for semi-inclusive lepton-nucleon scattering are derived in the framework of collinear factorization, including the effects of masses of the target and produced hadron at finite momentum transfer squared Q^2. At leading order the cross sections factorize into products of parton distribution and fragmentation functions evaluated in terms of new, mass-dependent scaling variables. The size of the hadron mass corrections is estimated at kinematics relevant for future semi-inclusive deep-inelastic scattering experiments.
↳ hep-phhep-exnucl-thJHEP(2015)·28 citations

Affiliations

first authorsco-authorsvia INSPIRE