Nuclear Theory·nucl-th

Tuesday·August 18, 2015

16 papers—7 primary·9 cross-listed

01
Nuclear Level Density: Shell Model vs Mean Field
Roman Sen'kov · Vladimir Zelevinsky
The knowledge of the nuclear level density is necessary for understanding various reactions including those in the stellar environment. Usually the combinatorics of Fermi-gas plus pairing is used for finding the level density. Recently a practical algorithm avoiding diagonalization of huge matrices was developed for calculating the density of many-body nuclear energy levels with certain quantum numbers for a full shell-model Hamiltonian. The underlying physics is that of quantum chaos and intrinsic thermalization in a closed system of interacting particles. We briefly explain this algorithm and, when possible, demonstrate the agreement of the results with those derived from exact diagonalization. The resulting level density is much smoother than that coming from the conventional mean-field combinatorics. We study the role of various components of residual interactions in the process of thermalization, stressing the influence of incoherent collision-like processes. The shell-model results for the traditionally used parameters are also compared with standard phenomenological approaches.
nucl-thPRC(2016)·46 citations
02
New Measurements and Phase Shift Analysis of p16O Elastic Scattering at Astrophysical Energies
Sergey Dubovichenko · Nasurlla Burtebaev · Albert Dzhazairov-Kakhramanov · Denis Zazulin · Zhambyl Kerimkulov · Maulen Nassurlla · Chingis Omarov · Alesya Tkachenko · Tatyana Shmygaleva · Stanislaw Kliczewski · Turlan Sadykov
The results of new experimental measurements of p16O elastic scattering in the energy range of 0.6-1.0 MeV at angles of 40-160 deg. are given. Phase shift analysis of p16O elastic scattering was made using these and other experimental data on differential cross sections in excitation functions and angular distributions at energies of up to 2.5 MeV.
nucl-thCPC(2017)·9 citations
03
Event-by-event distribution of magnetic field energy over initial fluid energy density in $s_{NN}$ = 200 GeV Au-Au collisions
Victor Roy🇩🇪 · Shi Pu🇩🇪
We estimate the event-by-event (e-by-e) distribution of the ratio ( $σ$ ) of the magnetic field energy to the fluid energy density in the transverse plane of Au-Au collisions at $s_{NN}$ = 200 GeV. A Monte-Carlo (MC) Glauber model is used to calculate the $σ$ in the transverse plane for impact parameter b=0, 12 fm at time $τ_{i} \sim$ 0.5 fm. The fluid energy density is obtained by using Gaussian smoothing with two different smoothing parameter $σ_{g}$ =0.25 , 0.5 fm. For $b = 0 fm$ collisions $σ$ is found to be $≪$ 1 in the central region of the fireball and $σ ≳$ 1 at the periphery. For b=12 fm collisions $σ ≳$ 1. The e-by-e correlation between $σ$ and the fluid energy density ( $ε$ ) is studied. We did not find strong correlation between $σ$ and $ε$ at the centre of the fireball, whereas they are mostly anti-correlated at the periphery of the fireball.
nucl-thhep-phPRC(2015)·73 citations
04
ND^(*) and NB^(*) interactions in a chiral quark model
Dan Yang🇨🇳 · Jing Liu🇨🇳 · Dan Zhang🇨🇳
ND and ND^* interactions become a hot topic after the observation of new charmed hadrons \Sigma_c(2800) and \Lambda_c(2940)^+. In this letter, we have preliminary investigated S-wave ND and ND^* interactions with possible quantum numbers in the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving the resonating group method equation. The numerical results show that the interactions between N and D or N and D^* are both attractive, which are mainly from \sigma exchanges between light quarks. Further bound-state studies indicate the attractions are strong enough to form ND or ND^* molecules, except for (ND)_{J=3/2} and (ND^*)_{J=3/2} in the chiral SU(3) quark model. In consequence ND system with J=1/2 and ND^* system with J=3/2 in the extended SU(3) quark model could correspond to the observed \Sigma_c(2800) and \Lambda_c(2940)^+, respectively. Naturally, the same method can be applied to research NB and NB^* interactions, and similar conclusions obtained, i.e. NB and NB^* attractive forces may achieve bound states, except for (NB^*)_{J=3/2} in the chiral SU(3) quark model. Meanwhile, S partial wave phase shifts of ND^{(*)} and NB^{(*)} elastic scattering are illustrated, which are qualitatively consistent with results from bound state problem.
nucl-thhep-ph5 citations
05
Heavy flavor in relativistic heavy-ion collisions
E. L. Bratkovskaya🇩🇪 · T. Song🇩🇪 · H. Berrehrah🇩🇪 · D. Cabrera🇩🇪 · J. M. Torres-Rincon🇫🇷 · L. Tolos🇩🇪 · W. Cassing🇩🇪
We study charm production in ultra-relativistic heavy-ion collisions by using the Parton-Hadron-String Dynamics (PHSD) transport approach. The initial charm quarks are produced by the PYTHIA event generator tuned to fit the transverse momentum spectrum and rapidity distribution of charm quarks from Fixed-Order Next-to-Leading Logarithm (FONLL) calculations. The produced charm quarks scatter in the quark-gluon plasma (QGP) with the off-shell partons whose masses and widths are given by the Dynamical Quasi-Particle Model (DQPM), which reproduces the lattice QCD equation-of-state in thermal equilibrium. The relevant cross sections are calculated in a consistent way by employing the effective propagators and couplings from the DQPM. Close to the critical energy density of the phase transition, the charm quarks are hadronized into $D$ mesons through coalescence and/or fragmentation. The hadronized $D$ mesons then interact with the various hadrons in the hadronic phase with cross sections calculated in an effective lagrangian approach with heavy-quark spin symmetry. The nuclear modification factor $R_{AA}$ and the elliptic flow $v_{2}$ of $D^{0}$ mesons from PHSD are compared with the experimental data from the STAR Collaboration for Au+Au collisions at $s_{N N}$ =200 GeV and to the ALICE data for Pb+Pb collisions at $s_{N N}$ =2.76 TeV. We find that in the PHSD the energy loss of $D$ mesons at high $p_{T}$ can be dominantly attributed to partonic scattering while the actual shape of $R_{AA}$ versus $p_{T}$ reflects the heavy-quark hadronization scenario, i.e. coalescence versus fragmentation. Also the hadronic rescattering is important for the $R_{AA}$ at low $p_{T}$ and enhances the $D$ -meson elliptic flow $v_{2}$ .
nucl-thhep-phJ.Phys.Conf.Ser.(2016)·5 citations
06
Interferometry for rotating sources
S. Velle🇳🇴 · S. Mehrabi Pari🇳🇴 · L.P. Csernai🇳🇴
The two particle interferometry method to determine the size of the emitting source after a heavy ion collision is extended. Following the extension of the method to spherical expansion dynamics, here we extend the method to rotating systems. It is shown that rotation of a cylindrically symmetric system leads to modifications, which can be perceived as spatial asymmetry by the "azimuthal HBT" method. We study an exact rotating and expanding solution of the fluid dynamical model of heavy ion reactions. We consider a source that is azimuthally symmetric in space around the axis of rotation, and discuss the features of the resulting two particle correlation function. This shows the azimuthal asymmetry arising from the rotation. We show that this asymmetry leads to results similar to those given by spatially asymmetric sources.
nucl-thPLB(2016)·7 citations
07
Superdeformed band in the $N = Z + 4$ nucleus $^{40}$ Ar: A projected shell model analysis
Ying-Chun Yang · Yan-Xin Liu · Yang Sun · Mike Guidry
It has been debated whether the experimentally-identified superdeformed rotational band in $^{40}$ Ar [E. Ideguchi, et al., Phys. Lett. B 686 (2010) 18] has an axially or triaxially deformed shape. Projected shell model calculations with angular-momentum-projection using an axially-deformed basis are performed up to high spins. Our calculated energy levels indicate a perfect collective-rotor behavior for the superdeformed yrast band. However, detailed analysis of the wave functions reveals that the high-spin structure is dominated by mixed 0-, 2-, and 4-quasiparticle configurations. The calculated electric quadrupole transition probabilities reproduce well the known experimental data and suggest a reduced, but still significant, collectivity in the high spin region. The deduced triaxial deformation parameters are small throughout the entire band, suggesting that triaxiality is not very important for this superdeformed band.
nucl-thEPJA(2018)·2 citations
08
Intrinsic Fluctuations of the Proton Saturation Momentum Scale in High Multiplicity p+p Collisions
Larry McLerran🇺🇸 · Prithwish Tribedy🇺🇸
High multiplicity events in p+p collisions are studied using the theory of the Color Glass Condensate. We show that intrinsic fluctuations of the proton saturation momentum scale are needed in addition to the sub-nucleonic color charge fluctuations to explain the very high multiplicity tail of distributions in p+p collisions. The origin of such intrinsic fluctuations are presumably non-perturbative in nature. Classical Yang Mills simulations using the IP-Glasma model are performed to make quantitative estimations. We find that fluctuations as large as $O$ (1) of the average values of the saturation momentum scale can lead to rare high multiplicity events seen in p+p data at RHIC and LHC energies. Using the available data on multiplicity distributions we try to constrain the distribution of the proton saturation momentum scale and make predictions for the multiplicity distribution in 13 TeV p+p collisions.
↳ hep-phhep-exnucl-exnucl-thNPA(2016)·66 citations
09
Two-photon exchange correction in elastic unpolarized electron-proton scattering at small momentum transfer
O. Tomalak🇩🇪 · M. Vanderhaeghen (JGU Mainz)🇩🇪
We evaluate the two-photon exchange (TPE) correction to the unpolarized elastic electron-proton scattering at small momentum transfer $Q^{2}$ . We account for the inelastic intermediate states approximating the double virtual Compton scattering by the unpolarized forward virtual Compton scattering. The unpolarized proton structure functions are used as input for the numerical evaluation of the inelastic contribution. Our calculation reproduces the leading terms in the $Q^{2}$ expansion of the TPE correction and goes beyond this approximation by keeping the full $Q^{2}$ dependence of the proton structure functions. In the range of small momentum transfer, our result is in good agreement with the empirical TPE fit to existing data.
↳ hep-phnucl-thPRD(2016)·51 citations
10
Making a soft relativistic mean-field equation of state stiffer at high density
K.A. Maslov · E.E. Kolomeitsev · D.N. Voskresensky
We study relativistic mean-field (RMF) models including nucleons interacting with scalar, vector and iso-vector mean fields and self- and cross- mean-field interaction terms. Usually, in such a models the magnitude of the scalar field increases monotonically with the nucleon density, and the nucleon effective mass decreases. We demonstrate that the latter quantity stops to decrease and the equation of state stiffens, provided the mean-field self-interaction potential rises sharply in a narrow vicinity of the values of mean fields corresponding to nucleon densities $n > n_{*} > n_{0}$ , where $n_{0}$ is the nuclear saturation density. As the result the limiting neutron star mass increases. This procedure offers a simple way to stiffen the equation of state at densities above $n_{*}$ without altering it at densities $n \leq n_{0}$ . The developed scheme allows an application to neutron stars of the RMF models, which are well fitted to finite nuclei but do not fulfill the experimental constraint on the limiting neutron star mass. The exemplary application of the method to the well-known FSUGold model allows us to increase the limiting neutron star mass from $1.72 M_{⊙}$ to $M \geq 2.01 M_{⊙}$ .
↳ astro-ph.HEnucl-thPRC(2015)·48 citations
11
Pentaquarks from intrinsic charms in $Λ_{b}$ decays
Y.K. Hsiao🇹🇼 · C.Q. Geng🇨🇳
We study the three-body $Λ_{b}$ decays of $Λ_{b} \to J / ψ pM$ with $M = K^{-}$ and $π^{-}$ . The two new states $P_{c 1} \equiv P_{c} (4380)^{+}$ and $P_{c 2} \equiv P_{c} (4450)^{+}$ observed recently as the resonances in the $J / ψ p$ invariant mass spectrum of $Λ_{b} \to J / ψ p K^{-}$ can be identified to consist of five quarks, $uu d c c ˉ$ , being consistent with the existence of the pentaquark states. We argue that, in the doubly charmful $Λ_{b}$ decays of $Λ_{b} \to J / ψ p K^{-}$ through $b \to c c ˉ s$ , apart from those through the non-resonant $Λ_{b} \to p K^{-}$ and resonant $Λ_{b} \to Λ^{*} \to p K^{-}$ transitions, the third contribution with the non-factorizable effects is not the dominant part for the resonant $Λ_{b} \to K^{-} P_{c 1, c 2}, P_{c 1, c 2} \to J / ψ p$ processes, such that we propose that the $P_{c 1, c 2}$ productions are mainly from the charmless $Λ_{b}$ decays through $b \to u ˉ u s$ , in which the $c c ˉ$ content in $P_{c 1, c 2}$ arises from the intrinsic charms within the $Λ_{b}$ baryon. We hence predict the observables related to the branching ratios and the direct CP violating asymmetries to be $B (Λ_{b} \to π^{-} (P_{c 1, c 2} \to) J / ψ p) / B (Λ_{b} \to K^{-} (P_{c 1, c 2} \to) J / ψ p) = 0.8 \pm 0.1$ , $A_{C P} (Λ_{b} \to π^{-} (P_{c 1, c 2} \to) J / ψ p) = (- 3.9 \pm 0.2) %$ , and $A_{C P} (Λ_{b} \to K^{-} (P_{c 1, c 2} \to) J / ψ p) = (5.8 \pm 0.2) %$ , which can alleviate the inconsistency between the theoretical expectations from the three contributions in the doubly charmful $Λ_{b}$ decays and the observed data.
↳ hep-phhep-exnucl-thPLB(2015)·30 citations
12
Nontopological Soliton in the Polyakov Quark Meson Model
Jinshuang Jin🇨🇳 · Hong Mao🇨🇳
Within a mean field approximation, we study a nontopological soliton solution of the Polyakov quark-meson model in the presence of a fermionic vacuum term with two flavors at finite temperature and density. The profile of the effective potential exhibits a stable soliton solution below a critical temperature $T \leq T_{χ}^{c}$ for both the crossover and the first-order phase transitions, and these solutions are calculated here with appropriate boundary conditions. However, it is found that only if $T \leq T_{d}^{c}$ ,the energy of the soliton $M_{N}$ is less than the energy of the three free constituent quarks $3 M_{q}$ . As $T > T_{d}^{c}$ , there is an instant delocalization phase transition from hadron matter to quark matter. The phase diagram together with the location of a critical end point (CEP) has been obtained in $T$ and $μ$ plane. We notice that two critical temperatures always satisfy $T_{d}^{c} \leq T_{χ}^{c}$ . Finally, we present and compare the result of thermodynamic pressure at zero chemical potential with lattice data.
↳ hep-phnucl-thPRC(2016)·8 citations
13
Electric dipole moments of superheavy elements - A case study on copernicium
Laima Radžiūtė · Gediminas Gaigalas · Per Jönsson · Jacek Bieroń
The multiconfiguration Dirac-Hartree-Fock (MCDHF) method was employed to calculate atomic electric dipole moments (EDM) of the superheavy element copernicium (Cn, $Z = 112$ ). The EDM enhancement factors of Cn, here calculated for the first time, are about one order of magnitude larger than those of Hg. The exponential dependence of enhancement factors on atomic number $Z$ along group 12 of the periodic table was derived from the EDMs of the entire homolog series, $_{30}^{69}$ Zn, $_{148}^{111}$ Cd, $_{180}^{199}$ Hg, $_{112}^{285}$ Cn, and $_{162}^{482}$ Uhb. These results show that superheavy elements with sufficiently large half-lives are good candidates for EDM searches.
↳ physics.atom-phnucl-exnucl-thPRA(2016)·8 citations
14
The Pion-Cloud Contribution to the Electromagnetic Nucleon Form Factors
Daniel Kupelwieser🇦🇹 · Wolfgang Schweiger🇦🇹
We study the electromagnetic structure of the nucleon within a hybrid constituent-quark model that comprises, in addition to the $3 q$ valence component, also a $3 q$ + $π$ non-valence component. To this aim we employ a Poincaré-invariant multichannel formulation based on the point-form of relativistic quantum mechanics. With a simple 3-quark wave function for the bare nucleon, i.e. the $3 q$ -component, we obtain reasonable results for the nucleon form factors and predict the meson-cloud contribution to be significant only below $Q^{2} ≲ 0.5$ \,GeV $^{2}$ amounting to about 10\% for $Q^{2} \to 0$ , in accordance with the findings of other authors.
↳ hep-phnucl-thEPJ Web Conf.(2016)·4 citations
15
Vector meson spectral function and dilepton rate in the presence of strong entanglement effect between the chiral and the Polyakov loop dynamics
Chowdhury Aminul Islam🇮🇳 · Sarbani Majumder🇮🇳 · Munshi G. Mustafa🇮🇳
In this work we have re-explored our earlier study on the vector meson spectral function and its spectral property in the form of dilepton rate in a two-flavour Polyakov loop extended Nambu-Jona-Lasinio (PNJL) model in presence of a strong entanglement between the chiral and Polyakov loop dynamics. The entanglement considered here is generated through the four-quark scalar type interaction in which the coupling strength depends on the Polyakov loop and runs with temperature and chemical potential. The entanglement effect is also considered for the four-quark vector type interaction in the same manner. We observe that the entanglement effect relatively enhances the color degrees of freedom due to the running of the both scalar and vector couplings. This modifies the vector meson spectral function and thus the spectral property such as the dilepton production rate in low invariant mass also gets modified.
↳ hep-phnucl-thPRD(2015)·7 citations
16
Superconductivity and Superfluidity as Universal Emergent Phenomena
Mike Guidry · Yang Sun
Superconductivity (SC) or superfluidity (SF) is observed across a remarkably broad range of fermionic systems: in BCS, cuprate, iron-based, organic, and heavy-fermion superconductors, and superfluid helium-3 in condensed matter; in a variety of SC/SF phenomena in low-energy nuclear physics; in ultracold, trapped atomic gases; and in various exotic possibilities in neutron stars. The range of physical conditions and differences in microscopic physics defy all attempts to unify this behavior in any conventional picture. Here we propose a unification through the shared symmetry properties of the emergent condensed states, with microscopic differences absorbed into parameters. This, in turn, forces a rethinking of specific occurrences of SC/SF such as cuprate high-temperature superconductivity, which becomes far less mysterious when seen as part of a continuum of behavior shared by a variety of other systems.
↳ cond-mat.supr-concond-mat.str-elnucl-thFront.Phys.(Beijing)(2015)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE