Nuclear Theory·nucl-th

Monday·January 8, 2018

18 papers—11 primary·7 cross-listed

01
Nucleon Effective Masses in Neutron-Rich Matter
Bao-An Li🇺🇸 · Bao-Jun Cai🇨🇳 · Lie-Wen Chen🇨🇳 · Jun Xu🇨🇳
Various kinds of isovector nucleon effective masses are used in the literature to characterize the momentum/energy dependence of the nucleon symmetry potential or self-energy due to the space/time non-locality of the underlying isovector strong interaction in neutron-rich nucleonic matter. The multifaceted studies on nucleon isovector effective masses are multi-disciplinary in nature. Besides structures, masses and low-lying excited states of nuclei as well as nuclear reactions, studies of the isospin dependence of short-range correlations in nuclei from scatterings of high-energy electrons and protons on heavy nuclei also help understand nucleon effective masses especially the so-called E-mass in neutron-rich matter. A thorough understanding of all kinds of nucleon effective masses has multiple impacts on many interesting issues in both nuclear physics and astrophysics. We review some of the significant progresses made in recent years by the nuclear physics community in resolving some of the hotly debated and longstanding issues regarding nucleon effective masses especially in dense neutron-rich matter.
nucl-thastro-ph.HEhep-exhep-ph+1PPNP(2018)·220 citations
02
Does Compound Nucleus remember its Isospin- An Evidence from the Fission Widths
Swati Garg · Ashok Kumar jain
We present an evidence of isospin effects in nuclear fission by comparing the fission widths for reactions involving different isospin states of the same compound nucleus (CN). Yadrovsky suggested this possibility in 1975. Yadrovsky obtained the fission widths for two reaction data sets, namely $^{206}$ Pb( $α$ ,f) and $^{209}$ Bi(p,f), both leading to same CN, and concluded that "a nucleus remembers the isospin value of the nuclear states leading to fission". We obtain the fission decay widths for both the $T_{0} + 1/2$ and $T_{0} - 1/2$ states of CN by using two appropriate reaction data sets. We then compare the fission widths for the two isospin states of CN. More specifically, we have chosen the combination of $^{206}$ Pb( $α$ ,f) and $^{209}$ Bi(p,f) same as presented in Yadrovsky's paper and $^{235}$ U(d,f) and $^{236}$ U(p,f) reaction data sets in this study. A significant difference between the ratios of fission decay widths to total decay widths for different isospin values suggests that isospin plays an important role in fission.
nucl-thEPJ Web Conf.(2018)·3 citations
03
Examining empirical evidence of the effect of superfluidity on the fusion barrier
Guillaume Scamps
Background: Several Time-Dependent Hartree-Fock-Bogoliubov (TDHFB) calculations predict that the super- fluidity enhances the fluctuations of the fusion barrier. This effect is not fully understood and not yet revealed experimentally. Purpose: The goal of this study is to investigate empirically the effect of the superfluidity on the fusion barrier width. Method: First, the local regression method is introduce and used to determine the barrier distribution more precisely. A second method that requires only the calculation of an integral of the cross section is developed to determine accurately the fluctuations of the barrier. A benchmark is done between this two methods and with the fitting method usually used. This integral method showing a better agreement in a test case, it is applied systematically in a selection of 115 fusion reactions. Results: The fluctuations of the barrier for superfluid systems are on average larger than for magic or semi-magic nuclei. This is due to the deformation effects and the effect of the superfluidity. To disentangle those two effects, we compare the experimental width to the width estimated from a model that takes into account the tunneling, the deformation and the vibration effect. The deviation of the experimental width from this theory for reaction between superfluid nuclei shows that the superfluidity enhance the fusion barrier width. Conclusions: This analysis shows that the predicted effect of the superfluidity on the width of the barrier is real and is of the order of 1 MeV.
nucl-thnucl-exPRC(2018)·20 citations
04
Structures of $p$ -shell double- $Λ$ hypernuclei studied with microscopic cluster models
Yoshiko Kanada-En'yo
$0 s$ -orbit $Λ$ states in $p$ -shell double- $Λ$ hypernuclei ( $_{ΛΛ}^{A} Z$ ), $_{ΛΛ}^{8} Li$ , $_{ΛΛ}^{9} Li$ , $_{ΛΛ}^{10, 11, 12} Be$ , $_{ΛΛ}^{12, 13} B$ , and $_{ΛΛ}^{14} C$ are investigated. Microscopic cluster models are applied to core nuclear part and a potential model is adopted for $Λ$ particles. The $Λ$ -core potential is a folding potential obtained with effective $G$ -matrix $Λ$ - $N$ interactions, which reasonably reproduce energy spectra of $_{Λ}^{A - 1} Z$ . System dependence of the $Λ$ - $Λ$ binding energies is understood by the core polarization energy from nuclear size reduction. Reductions of nuclear sizes and $E 2$ transition strengths by $Λ$ particles are also discussed.
nucl-thPRC(2018)·8 citations
05
Three-body radiative capture reactions
J. Casal · M. Rodríguez-Gallardo · J. M. Arias · J. Gómez-Camacho
Radiative capture reaction rates for $^{6}$ He, $^{9}$ Be and $^{17}$ Ne formation at astrophysical conditions are studied within a three-body model using the analytical transformed harmonic oscillator method to calculate their states. An alternative procedure to estimate these rates from experimental data on low-energy breakup is also discussed
nucl-thEPJ Web Conf.(2017)·1 citation
06
Two-nucleon emitters within a pseudostate method: The case of $^{6}$ Be and $^{16}$ Be
J. Casal
Background: Since the first experimental observation, two-nucleon radioactivity has gained renewed attention over the past fifteen years. The $^{6}$ Be system is the lightest two-proton ground-state emitter, while $^{16}$ Be has been recently proposed to be the first two-neutron ground-state emitter ever observed. A proper understanding of their properties and decay modes requires a reasonable description of the three-body continuum. Purpose: Study the ground-state properties of $^{6}$ Be and $^{16}$ Be within a general three-body model and investigate their nucleon-nucleon correlations in the continuum. Method: The pseudostate (PS) method in hyperspherical coordinates, using the analytical transformed harmonic oscillator (THO) basis for three-body systems, is used to construct the $^{6}$ Be and $^{16}$ Be ground-state wave functions. These resonances are approximated as a stable PS around the known two-nucleon separation energy. Effective core- $N$ potentials, constrained by the available experimental information on the binary subsystems $^{5}$ Li and $^{15}$ Be, are employed in the calculations. Results: The ground state of $^{16}$ Be is found to present a strong dineutron configuration, with the valence neutrons occupying mostly an $l = 2$ state relative to the core. The results are consistent with previous $R$ -matrix calculations for the actual continuum. The case of $^{6}$ Be shows a clear symmetry with respect to its mirror partner, the two-neutron halo $^{6}$ He: The diproton configuration is dominant, and the valence protons occupy an $l = 1$ orbit. Conclusions: The PS method is found to be a suitable tool in describing the properties of unbound $core + N + N$ ground states. For both $^{16}$ Be and $^{6}$ Be, the results are consistent with previous theoretical studies and confirm the dominant dinucleon configuration. This favors the picture of a correlated two-nucleon emission.
nucl-thPRC(2018)·23 citations
07
Chiral-partner D mesons in a heat bath within QCD sum rules
Thomas Buchheim🇩🇪 · Thomas Hilger🇦🇹 · Burkhard Kampfer🇩🇪 · Stefan Leupold🇸🇪
Utilizing QCD sum rules, we extract the temperature dependences of the spectral properties of the pseudo-scalar and scalar D mesons regarded as chiral partners. Besides the masses also decay constants are analyzed as the D meson yields in heavy-ion collisions may be sensitive to their altered decay properties in an ambient strongly interacting medium. Our findings are ( $i$ ) a decreasing scalar D meson mass for growing temperatures while its pseudo-scalar partner meson seems hardly affected, which is in qualitative agreement with hadronic model calculations; ( $ii$ ) inferring an equally weak temperature dependence of the pseudo-scalar D meson decay properties the decreasing residua and decay constants of the scalar particle point towards partial chiral restoration. As a bonus of our analysis in the pseudo-scalar sector we determine the pseudo-scalar decay constant at vanishing temperature. Due to the connection to particular leptonic branching fractions this decay constant is of great interest allowing for the determination of the off-diagonal CKM matrix element $∣ V_{c d} ∣$ at zero temperature.
nucl-thJ.Phys.G(2018)·8 citations
08
Nambu--Jona-Lasinio model in a parallel electromagnetic field
Lingxiao Wang🇨🇳 · Gaoqing Cao🇨🇳 · Xu-Guang Huang🇨🇳 · Pengfei Zhuang🇨🇳
We explore the features of the $U_{A} (1)$ and chiral symmetry breaking of the Nambu--Jona-Lasinio model without the Kobayashi-Maskawa-'t Hooft determinant term in the presence of a parallel electromagnetic field. We show that the electromagnetic chiral anomaly can induce both finite neutral pion condensate and isospin-singlet pseudo-scalar $η$ condensate and thus modifies the chiral symmetry breaking pattern. In order to characterize the strength of the $U_{A} (1)$ symmetry breaking, we evaluate the susceptibility associated with the $U_{A} (1)$ charge. The result shows that the susceptibility contributed from the chiral anomaly is consistent with the behavior of the corresponding $η$ condensate. The spectra of the mesonic excitations are also studied.
nucl-thhep-phhep-thPLB(2018)·20 citations
09
Covariant kinetic theory for effective fugacity quasi particle model and first order transport coefficients for hot QCD matter
Sukanya Mitra🇮🇳 · Vinod Chandra🇮🇳
An effective relativistic kinetic theory has been constructed for an interacting system of quarks, anti-quarks and gluons within a quasi-particle description of hot QCD medium at finite temperature and baryon chemical potential, where the interactions are encoded in the gluon and quark effective fugacities with non-trivial energy dispersions. The local conservations of stress-energy tensor and number current require the introduction of a mean field term in the transport equation which produces non-vanishing contribution to the first order transport coefficients. Such contribution has been observed to be significant for the temperatures which are closer to the QCD transition tem- perature, however, induces negligible contributions beyond a few times the transition temperature. As an implication, impact of the mean field contribution on the the temperature dependence of the shear viscosity, bulk viscosity and thermal conductivity of a hot QCD medium in the presence of binary, elastic collisions among the constituents, has been investigated. Visible effects have been observed for the temperature regime closer to the QCD transition temperature.
nucl-thPRD(2018)·41 citations
10
Bulk Properties of the Matter Produced at Energies of the Beam Energy Scan Program
Yu. B. Ivanov🇷🇺 · A. A. Soldatov🇷🇺
Recent STAR data on the bulk observables in the energy range of the Beam-Energy Scan Program at the Relativistic Heavy-Ion Collider are analyzed within the model of the three-fluid dynamics (3FD). The simulations are performed with different equations of state (EoS). The purely hadronic EoS fails to reproduce the data. A good, though imperfect, overall reproduction of the data is found within the deconfinement scenarios. The crossover EoS turns out to be slightly preferable. For this reproduction a fairly strong baryon stopping in the quark-gluon phase is required. The 3FD model does not need two separate freeze-outs (i.e. kinetic and chemical ones) to describe the STAR data. A unified freeze-out is applied at all energies.
nucl-thhep-phnucl-exPRC(2018)·15 citations
11
Collective motion in triaxial nuclei within minimal length concept
M. Chabab🇲🇦 · A. El Batoul🇲🇦 · A. Lahbas🇲🇦 · M. Oulne🇲🇦
The concept of minimal length, inspired by Heisenberg algebra, is applied to the geometrical collective Bohr- Mottelson model (BMM) of nuclei. With the deformed canonical commutation relation and the Pauli-Podolsky prescription, we have derived the quantized Hamiltonian operator for triaxial nuclei as we have previously done for axial prolate $γ$ -rigid ones (M. Chabab et al., Phys. Lett. B 758 (2016) 212-218). By considering an infinite square well like potential in $β$ collective shape variable, the eigenvalues of the Hamiltonian are obtained in terms of zeros of Bessel functions of irrational order with an explicit dependence on the minimal length parameter. Moreover, the associated symmetry with the model that we have constructed here can be considered as a new quasi-dynamical critical point symmetries (CPSs) in nuclear structure. The theoretical results indicate a dramatic contribution (Low effect) of the minimal length to energy levels for lower values of the angular momentum and regular (significant effect) for higher values. In fact, these features show that the minimal length scenario which is useful in recognizing the properties of real deformed nuclei having high spins or strong rotations. Finally, numerical calculations are performed for some nuclei such as $^{124, 128, 130}$ Xe and $^{114}$ Pd revealing a qualitative agreement with the experimental data.
nucl-thNucl.Theor.(2017)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE