Nuclear Theory·nucl-th

Tuesday·March 8, 2016

18 papers—9 primary·9 cross-listed

01
Low-energy $^{6}$ He scattering in a microscopic model
P. Descouvemont
A microscopic version of the Continuum Discretized Coupled Channel (CDCC) method is used to investigate $^{6}$ He scattering on $^{27}$ Al, $^{58}$ Ni, $^{120}$ Sn, and $^{208}$ Pb at energies around the Coulomb barrier. The $^{6}$ He nucleus is described by an antisymmetric 6-nucleon wave function, defined in the Resonating Group Method. The $^{6}$ He continuum is simulated by square-integrable positive-energy states. The model is based only on well known nucleon-target potentials, and is therefore does not depend on any adjustable parameter. I show that experimental elastic cross sections are fairly well reproduced. The calculation suggests that breakup effects increase for high target masses. For a light system such as $^{6}$ He+ $^{27}$ Al, breakup effects are small, and a single-channel approximation provides fair results. This property is explained by a very simple model, based on the sharp-cut-off approximation for the scattering matrix. I also investigate the $^{6}$ He-target optical potentials, which confirm that breakup channels are more and more important when the mass increases. At large distances, polarization effects increase the Coulomb barrier, and provide a long-tail absorption component in the imaginary part of the nucleus-nucleus interaction.
nucl-thPRC(2016)·11 citations
02
Separation of elastic and inelastic processes in the relaxation time approximation for collision integral
Wojciech Florkowski🇵🇱 · Radoslaw Ryblewski🇵🇱
We introduce a generalised relaxation-time-approximation form of the collision term in the Boltzmann kinetic equation that allows for using different relaxation times for elastic and inelastic collisions. The efficacy of the proposed framework is demonstrated with the numerical calculations that describe systems with different relations between the two relaxation times and the evolution time of the system.
nucl-thhep-phPRC(2016)·25 citations
03
Extracting the resonance parameters from experimental data on scattering of charged particles
P. Vaandrager · S. A. Rakityansky
A new parametrization of the multi-channel S-matrix is used to fit scattering data and then to locate the resonances as its poles. The S-matrix is written in terms of the corresponding "in" and "out" Jost matrices which are expanded in the Taylor series of the collision energy E around an appropriately chosen energy E0. In order to do this, the Jost matrices are written in a semi-analytic form where all the factors (involving the channel momenta and Sommerfeld parameters) responsible for their "bad behaviour" (i.e. responsible for the multi-valuedness of the Jost matrices and for branching of the Riemann surface of the energy) are given explicitly. The remaining unknown factors in the Jost matrices are analytic and single-valued functions of the variable E and are defined on a simple energy plane. The expansion is done for these analytic functions and the expansion coefficients are used as the fitting parameters. The method is tested on a two-channel model, using a set of artificially generated data points with typical error bars and a typical random noise in the positions of the points.
nucl-thnucl-exIJMPE(2016)·6 citations
04
Consistency between the monopole strength of the Hoyle state determined by structural calculation and that extracted from reaction observables
Kosho Minomo · Kazuyuki Ogata
We analyze the $α$ - $^{12}$ C inelastic scattering to the $0_{2}^{+}$ state of $^{12}$ C, the Hoyle state, in a fully microscopic framework. With no free adjustable parameter, the inelastic cross sections at forward angles are well reproduced by the microscopic reaction calculation using the transition density of $^{12}$ C obtained by the resonating group method and the nucleon-nucleon $g$ matrix interaction developed by the Melbourne group. It is thus shown that the monopole transition strength obtained by the structural calculation is consistent with that extracted from the reaction observable, suggesting no missing monopole strength of the Hoyle state.
nucl-thPRC(2016)·20 citations
05
Open Questions On Nuclear Collective Motion
S. Frauendorf
The status of the macroscopic and microscopic description of the collective quadrupole modes is reviewed, where limits due to non-adiabaticity and decoherence are exposed. The microscopic description of the yrast states in vibrator-like nuclei in the framework of the rotating mean field is presented.
nucl-thAIP Conf.Proc.(2016)·3 citations
06
Study of compound nucleus formation via bremsstrahlung emission in proton $α$ -particle scattering
Sergei P. Maydanyuk (1 and 2)🇺🇦 · Peng-Ming Zhang (1 and 3) ((1) Institute of Modern Physics, Chinese Academy of Sciences, (2) Institute for Nuclear Research, National Academy of Sciences of Ukraine, (3) State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences)🇨🇳
In this paper a role of many-nucleon dynamics in formation of the compound $^{5} Li$ nucleus in the scattering of protons off $α$ -particles at the proton incident energies up to 20 MeV is investigated. We propose a bremsstrahlung model allowing to extract information about probabilities of formation of such nucleus on the basis of analysis of experimental cross-sections of the bremsstrahlung photons. In order to realize this approach, the model includes elements of microscopic theory and also probabilities of formation of the short-lived compound nucleus. Results of calculations of the bremsstrahlung spectra are in good agreement with the experimental cross-sections.
nucl-thhep-phnucl-ex0 citations
07
Heavy baryonic resonances, multistrange hadrons, and equilibration at energies available at the GSI Schwerionensynchrotron, SIS18
J. Steinheimer🇩🇪 · M. Lorenz🇩🇪 · F. Becattini🇮🇹 · R. Stock🇩🇪 · M. Bleicher🇩🇪
We study the details and time dependence of particle production in nuclear collisions at a fixed target beam energy of $E_{lab} = 1.76$ A GeV with the UrQMD transport model. We find that the previously proposed production mechanism for multi strange hadrons, $ϕ$ and $Ξ$ , are possible due to secondary interactions of incoming nuclei of the projectile and target with already created nuclear resonances, while the Fermi momenta of the nuclei play only a minor role. We also show how the centrality dependence of these particle multiplicities can be used to confirm the proposed mechanism, as it strongly depends on the number of participants in the reaction. Furthermore we investigate the time dependence of particle production in collisions of Ca+Ca at this beam energy, in order to understand the origins of the apparent chemical equilibration of the measured particle yields. We find that indeed the light hadron yields appear to be in equilibrium already from the very early stage of the collision while in fact no local equilibration, through multi collision processes, takes place. The apparent equilibrium is reached only through the decay of the resonances according to available phase space.
nucl-thPRC(2016)·19 citations
08
The hard-sphere model of strongly interacting fermion systems
Angela Mecca🇮🇹
The formalism based on Correlated Basis Functions (CBF) and the cluster-expansion technique has been recently employed to derive an effective interaction from a realistic nuclear Hamiltonian. One of the main objectives of the work described in this Thesis is establishing the accuracy of this novel approach--that allows to combine the flexibility of perturbation theory in the basis of eigenstates of the noninteracting system with a realistic description of short-range correlations in coordinate space--by focusing on the hard-sphere fermion system. As a first application of the formalism, the quasiparticle properties of hard spheres of degeneracy four have been determined from the two-point Green's function. The calculation has been performed carrying out a perturbative expansion of the self-energy, up to the second order in the CBF effective interaction. The main results of this study are the momentum distributions, the quasiparticle spectra and their description in terms of effective mass. The investigation of the hard-sphere fermion fluid has been extended to study the shear viscosity and thermal conductivity coefficients of the system with degeneracy two, that can be regarded as a model of pure neutron matter. The resulting transport coefficients show a strong sensitivity to the quasiparticle effective mass, reflecting the effect of second order contributions to the self-energy which are not taken into account in nuclear matter studies available in the literature. The difference between first and second order results is likely to play an important role in astrophysical applications and needs to be carefully investigated extending our analysis to nuclear matter.
nucl-th0 citations
09
Fluctuations as a test of chemical non-equilibrium at the LHC
Viktor Begun🇵🇱
It is shown that large chemical potential leads to the significant increase of multiplicity fluctuations for bosons, and makes the fluctuations infinite in the case of Bose-Einstein condensation. It allows to distinguish between the models that explain the anomalous proton to pion ratio and the low transverse momentum enhancement of pion spectra in Pb+Pb collisions at the LHC within chemical equilibrium or non-equilibrium models. The effects of resonance decays, finite size of the system, requirements to the event statistics, different momentum cuts, and limited detector acceptance are considered. The obtained results show the possibility to observe a substantial increase of the normalized kurtosis for positively or negatively charged pions in the case of non-equilibrium or partial pion condensation using currently measured data.
nucl-thhep-phnucl-exPRC(2016)·28 citations
10
Neutron Star Mass-Radius Constraints of the Quiescent Low-mass X-ray Binaries X7 and X5 in the Globular Cluster 47 Tuc
Slavko Bogdanov · Craig O. Heinke · Feryal Özel · Tolga Güver
We present Chandra ACIS-S sub-array observations of the quiescent neutron star low-mass X-ray binaries X7 and X5 in the globular cluster 47 Tuc. The large reduction in photon pile-up compared to previous deep exposures enables a substantial improvement in the spectroscopic determination of the neutron star radius and mass of these neutron stars. Modeling the thermal emission from the neutron star surface with a non-magnetized hydrogen atmosphere and accounting for numerous sources of uncertainties, we obtain for the neutron star in X7 a radius of $R = 11. 1_{- 0.7}^{+ 0.8}$ km for an assumed stellar mass of $M = 1.4$ M $_{⊙}$ (68% C.L.). We argue, based on astrophysical grounds, that the presence of a He atmosphere is unlikely for this source. Due to eclipses and variable absorption, the quiescent low-mass X-ray binary X5 provides less stringent constraints, leading to a radius of $R = 9. 6_{- 1.1}^{+ 0.9}$ km, assuming a hydrogen atmosphere and a mass of $M = 1.4$ M $_{⊙}$ . When combined with all other existing spectroscopic radius measurements, these measurements strongly favor radii in the 9.9-11.2 km range for a ~1.5 M $_{⊙}$ neutron star and point to a dense matter equation of state that is somewhat softer than the nucleonic ones that are consistent with laboratory experiments at low densities.
↳ astro-ph.HEnucl-thApJ(2016)·113 citations
11
Nuclear fusion induced by X-rays in a crystal
V. B. Belyaev · M. B. Miller · J. Otto · S. A. Rakityansky
The nuclei that constitute a crystalline lattice, oscillate relative to each other with a very low energy that is not sufficient to penetrate through the Coulomb barriers separating them. An additional energy, which is needed to tunnel through the barrier and fuse, can be supplied by external electromagnetic waves (X-rays or the synchrotron radiation). Exposing to the X-rays the solid compound LiD (lithium-deuteride) for the duration of 111 hours, we have detected 88 events of the nuclear fusion d+Li6 ---> Be8*. Our theoretical estimate agrees with what we observed. One of possible applications of the phenomenon we found, could be the measurements of the rates of various nuclear reactions (not necessarily fusion) at extremely low energies inaccessible in accelerator experiments.
↳ nucl-exnucl-thPRC(2016)·2 citations
12
A new insight into neutrino energy loss by electron capture of iron group nuclei in magnetars surface
Jing-Jing Liu🇨🇳 · Wei-Min Gu🇨🇳
Based on the relativistic mean-field effective interactions theory, and Lai dong model \citep{b37, b38, b39}, we discuss the influences of superstrong magnetic fields (SMFs) on electron Fermi energy, nuclear blinding energy, and single-particle level structure in magnetars surface. By using the method of Shell-Model Monte Carlo (SMMC), and the Random Phase Approximation (RPA) theory, we detailed analyze the neutrino energy loss rates(NELRs) by electron capture (EC) for iron group nuclei in SMFs.
↳ astro-ph.HEastro-ph.SRnucl-thAstrophys.J.Suppl.(2016)·17 citations
13
Parton distribution functions probed in ultraperipheral collisions at the CERN Large Hadron Collider
J. Thomas🇺🇸 · C.A. Bertulani🇺🇸 · N. Brady🇺🇸 · D. B. Clark🇺🇸 · E. Godat🇺🇸 · F. Olness🇺🇸
Vector meson production in ultra-peripheral pA and AA collisions at the CERN Large Hadron Collider (LHC) are very sensitive to Parton Distribution Functions (PDF) as well as to their leading-order, next-to-leading-order, and medium corrections. This process is a complimentary tool to explore the effects of different PDFs in particle production in proton-nucleus and nucleus-nucleus central collisions. Existing and forthcoming data available, e.g., from ALICE and CMS, may be used in conjunction with our theoretical predictions to constrain the PDFs. We make predictions for rapidity distributions and for cross sections of J/ $ψ$ , $ψ (2 S)$ and $Υ$ production at $s_{N N} = 2.76$ TeV and $s_{N N} = 5$ TeV. We use the second energy as representative for the Run 2 of PbPb collisions at the LHC.
↳ hep-phnucl-th4 citations
14
Full jet evolution in quark-gluon plasma and nuclear modification of jet production and jet shape in Pb+Pb collisions at 2.76 ATeV at the LHC
Ning-Bo Chang🇨🇳 · Guang-You Qin🇨🇳
We study the evolution of full jet shower in quark-gluon plasma via solving a set of coupled differential transport equations for the three-dimensional momentum distributions of quarks and gluons contained in the full jets. In our jet evolution equations, we include all partonic splitting processes as well as the collisional energy loss and transverse momentum broadening for both the leading and radiated partons of the full jets. Combining with a realistic (2+1)-dimensional viscous hydrodynamic simulation for the space-time profiles of the hot and dense nuclear medium produced in heavy-ion collisions, we apply our formalism to calculate the nuclear modification of single inclusive full jet spectra, the momentum imbalance of photon-jet and dijet pairs, and jet shape function (at partonic level) in Pb+Pb collisions at 2.76 ATeV. The roles of various jet-medium interaction mechanisms on the full jet modification are studied. We find that the nuclear modification of jet shape is sensitive to the interplay of different interaction mechanisms as well as the energies of the full jets.
↳ hep-phnucl-exnucl-thPRC(2016)·77 citations
15
Model discrimination in pseudoscalar-meson photoproduction
J. Nys🇧🇪 · J. Ryckebusch🇧🇪 · D. G. Ireland🇬🇧 · D. I. Glazier🇬🇧
To learn about a physical system of interest, experimental results must be able to discriminate among models. We introduce a geometrical measure to quantify the distance between models for pseudoscalar-meson photoproduction in amplitude space. Experimental observables, with finite accuracy, map to probability distributions in amplitude space, and the characteristic width scale of such distributions needs to be smaller than the distance between models if the observable data are going to be useful. We therefore also introduce a method for evaluating probability distributions in amplitude space that arise as a result of one or more measurements, and show how one can use this to determine what further measurements are going to be necessary to be able to discriminate among models.
↳ hep-phnucl-thPLB(2016)·15 citations
16
Fluctuations in Charged Particle Multiplicities in Relativistic Heavy-Ion Collisions
Maitreyee Mukherjee🇮🇳 · Sumit Basu🇮🇳 · Subikash Choudhury🇮🇳 · Tapan K. Nayak🇮🇳
Multiplicity distributions of charged particles and their event-by-event fluctuations have been compiled for relativistic heavy-ion collisions from the available experimental data at Brookhaven National Laboratory and CERN and also by the use of an event generator. Multiplicity fluctuations are sensitive to QCD phase transition and to the presence of critical point in the QCD phase diagram. In addition, multiplicity fluctuations provide baselines for other event-by-event measurements. Multiplicity fluctuation expressed in terms of the scaled variance of the multiplicity distribution is an intensive quantity, but is sensitive to the volume fluctuation of the system. The importance of the choice of narrow centrality bins and the corrections of centrality bin width effect for controlling volume fluctuations have been discussed. It is observed that the mean and width of the multiplicity distributions monotonically increase as a function of increasing centrality at all collision energies, whereas the multiplicity fluctuations show minimal variations with centrality. The beam energy dependence shows that the multiplicity fluctuations have a slow rise at lower collision energies and remain constant at higher energies.
↳ nucl-exhep-exhep-phnucl-thJ.Phys.G(2016)·17 citations
17
Functional renormalization group analysis of the soft mode at the QCD critical point
Takeru Yokota🇯🇵 · Teiji Kunihiro🇯🇵 · Kenji Morita🇯🇵
We make an intensive investigation of the soft mode at the quantum chromodynamics (QCD) critical point on the basis of the functional renormalization group (FRG) method in the local potential approximation. We calculate the spectral functions $ρ_{σ, π} (ω, p)$ in the scalar ( $σ$ ) and pseudoscalar ( $π$ ) channels beyond the random phase approximation in the quark--meson model. At finite baryon chemical potential $μ$ with a finite quark mass, the baryon-number fluctuation is coupled to the scalar channel and the spectral function in the $σ$ channel has a support not only in the time-like ( $ω > p$ ) but also in the space-like ( $ω < p$ ) regions, which correspond to the mesonic and the particle--hole phonon excitations, respectively. We find that the energy of the peak position of the latter becomes vanishingly small with the height being enhanced as the system approaches the QCD critical point, which is a manifestation of the fact that the phonon mode is the {\em soft mode} associated with the second-order transition at the QCD critical point, as has been suggested by some authors. Moreover, our extensive calculation of the spectral function in the $(ω, p)$ plane enables us to see that the mesonic and phonon modes have the respective definite dispersion relations $ω_{σ . ph} (p)$ , and it turns out that $ω_{σ} (p)$ crosses the light-cone line into the space-like region, and then eventually merges into the phonon mode as the system approaches the critical point more closely. This implies that the sigma-mesonic mode also becomes soft at the critical point. We also provide numerical stability conditions that are necessary for obtaining the accurate effective potential from the flow equation.
↳ hep-phnucl-thPTEP(2016)·42 citations
18
White Paper on Nuclear Astrophysics
Almudena Arcones🇩🇪 · Dan W. Bardayan🇺🇸 · Timothy C. Beers🇺🇸 · Lee A. Berstein🇺🇸 · Jeffrey C. Blackmon🇺🇸 · Bronson Messer🇺🇸 · B. Alex Brown🇺🇸 · Edward F. Brown🇺🇸 · Carl R. Brune🇺🇸 · Art E. Champagne🇺🇸 · Alessandro Chieffi · Aaron J. Couture🇺🇸 and 31 other authors
This white paper informs the nuclear astrophysics community and funding agencies about the scientific directions and priorities of the field and provides input from this community for the 2015 Nuclear Science Long Range Plan. It summarizes the outcome of the nuclear astrophysics town meeting that was held on August 21-23, 2014 in College Station at the campus of Texas A&M University in preparation of the NSAC Nuclear Science Long Range Plan. It also reflects the outcome of an earlier town meeting of the nuclear astrophysics community organized by the Joint Institute for Nuclear Astrophysics (JINA) on October 9- 10, 2012 Detroit, Michigan, with the purpose of developing a vision for nuclear astrophysics in light of the recent NRC decadal surveys in nuclear physics (NP2010) and astronomy (ASTRO2010). The white paper is furthermore informed by the town meeting of the Association of Research at University Nuclear Accelerators (ARUNA) that took place at the University of Notre Dame on June 12-13, 2014. In summary we find that nuclear astrophysics is a modern and vibrant field addressing fundamental science questions at the intersection of nuclear physics and astrophysics. These questions relate to the origin of the elements, the nuclear engines that drive life and death of stars, and the properties of dense matter. A broad range of nuclear accelerator facilities, astronomical observatories, theory efforts, and computational capabilities are needed. With the developments outlined in this white paper, answers to long standing key questions are well within reach in the coming decade.
↳ astro-ph.SRnucl-exnucl-thPPNP(2017)·55 citations

Affiliations

first authorsco-authorsvia INSPIRE