Nuclear Theory·nucl-th

Tuesday·April 14, 2020

20 papers—10 primary·10 cross-listed

01
Correlation between global polarization, angular momentum and flow in heavy-ion collisions
Yu. B. Ivanov🇷🇺 · A. A. Soldatov🇷🇺
Possible correlations of the global polarization of $Λ$ hyperons with the angular momentum and transverse flow in the central region of colliding nuclei are studied based on refined estimate of the global polarization. Simulations of Au+Au collisions at collision energies $s_{N N} =$ 6-40 GeV are performed within the model of the three-fluid dynamics. Within the crossover and first-order-phase-transition scenarios this refined estimate quite satisfactorily reproduces the experimental STAR data. Hadronic scenario fails at high collision energies, $s_{N N} >$ 10 GeV, and even predicts opposite sign of the global polarization. It is found that the global polarization correlates with neither the angular momentum accumulated in the central region nor with directed and elliptic flow. At the same time we observed correlation between the angular momentum and directed flow in both their time and collision-energy dependence. These results suggest that, although initially the angular momentum is the driving force for the vortex generation, later the angular momentum and vortex motion become decorrelated in the midrapidity region. Then the midrapidity angular momentum is determined by the pattern of the directed flow and even becomes negative when the antiflow occurs. At the freeze-out stage, the dominant part of the participant angular momentum is accumulated in the fragmentation regions.
nucl-thhep-phPRC(2020)·39 citations
02
Proto-Strange Quark Star Structure
Gholam Hossein Bordbar🇮🇷 · Fatemeh Sadeghi🇮🇷 · Fatemeh Kayanikhoo🇮🇷 · Ahmad Poostforush🇮🇷
In this paper, we investigate the newborn strange quark stars with constant entropy. We also use the MIT bag model to calculate the thermodynamic properties in two cases; the density-dependent bag constant and the fixed bag constant (B = 90 MeV). We show that the equation of state becomes stiffer by using the density dependent bag constant and by increasing the entropy. Furthermore, we show that the adiabatic index of the system reaches to 4/3 at high densities. Later, we calculate the structure of a strange quark star using the equation of state and the general relativistic equations of hydrostatic equilibrium, the Tolman-Oppenheimer-Volkoff (TOV) equations. We show that the gravitational mass of the star decreases by increasing the entropy and the maximum gravitational mass is larger when we use the density-dependent bag constant at fixed central energy density. It is shown that the mass-radius relation for this system obeys M R^ 3 for different cases of the calculations. Finally, we show that for a given stellar mass considering the fixed bag constant, the maximum gravitational red shift of a strange quark star occurs at larger values of entropy.
nucl-thgr-qchep-phIndian J.Phys.(2021)·11 citations
03
Chiral Effective Field Theory Calculations of Weak Transitions in Light Nuclei
G. B. King · L. Andreoli · S. Pastore · M. Piarulli · R. Schiavilla · R. B. Wiringa · J. Carlson · S. Gandolfi
We report Quantum Monte Carlo calculations of weak transitions in $A \leq 10$ nuclei, based on the Norfolk two- and three-nucleon chiral interactions, and associated one- and two-body axial currents. We find that the contribution from two-body currents is at the $2$ - $3%$ level, with the exception of matrix elements entering the rates of $^{8}$ Li, $^{8}$ B, and $^{8}$ He beta decays. These matrix elements are suppressed in impulse approximation based on the (leading order) Gamow Teller transition operator alone; two-body currents provide a $20$ - $30%$ correction, which is, however, insufficient to bring theory in agreement with experimental data. For the other transitions, the agreement with the data is satisfactory, and the results exhibit a negligible to mild model dependence when different combinations of Norfolk interactions are utilized to construct the nuclear wave functions. We report a complete study of two-body weak transition densities which reveals the expected universal behavior of two-body currents at short distances throughout the range of $A$ = $3$ to $A$ = $10$ systems considered here.
nucl-thPRC(2020)·85 citations
04
Momentum-dependent potential and collective flows within the relativistic quantum molecular dynamics approach based on relativistic mean-field theory
Yasushi Nara🇯🇵 · Tomoyuki Maruyama🇯🇵 · Horst Stoecker🇩🇪
Relativistic quantum molecular dynamics based on the relativistic mean field theory (RQMD.RMF) is extended by including momentum-dependent potential. The equation of state (EoS) dependence of the directed and the elliptic flow of protons in the beam energy range of $2.3 < s_{N N} < 20$ GeV is examined. It is found that the directed flow depends strongly on the optical potential at high energies, $s_{N N} > 3$ GeV, where no information is available experimentally. The correlation between effective mass at saturation density and the optical potential is found: smaller values of effective mass require smaller strengths of the optical potential to describe the directed flow data.This correlation can also be seen in the beam energy dependence of the elliptic flow at $s_{N N} > 3$ GeV, although its effect is rather weak. On the other hand, stiff EoS is required to describe the elliptic flow at lower energies.Experimental constraints on the optical potential from $p A$ collisions will provide important information on the EoS at high energies.The proton directed and the elliptic flow are well described in the RQMD.RMF model from $s_{N N} = 2.3$ to 8.8 GeV. In contrast,to reproduce the collapse of the directed flow above 10 GeV, pressure has to be reduced, which indicates a softening of the EoS around $s_{N N} = 10$ GeV.
nucl-thhep-phnucl-exPRC(2020)·68 citations
05
Investigation of Nuclear Structures of Self-conjugate Zn, Ge, Se, Kr, Sr Nuclei
Serkan Akkoyun · Tuncay Bayram
Nuclear structures of the atomic nuclei can be theoretically investigated by using nuclear shell model. Generally, a doubly closed-shell nucleus has been considered as inert core and the nucleons outside the core are taken into account in the calculation. It is assumed that the nucleons in the inert core do not move but each valance nucleon out of the core moves under an average potential created by the others. The self-conjugate (N=Z) moderate mass nuclei region is one of the region for the investigation of several phenomena because of the maximum spatial overlap of neutrons and protons. In this study, the nuclear structures of the moderate mass N=Z have been analyzed in the scope of the nuclear shell model by using KSHELL computer code. In the calculations, doubly magic 56Ni were taken as core and p3/2, f5/2 and p1/2 single particle orbits were used as valance orbits. Different two-body interactions have been taken into account. The results have been compared with each other and the available values existing in the literature.
nucl-th0 citations
06
Investigation of Nuclear Structures of Ne Isotopes by Nuclear Shell Model
Serkan Akkoyun · Tuncay Bayram
One of the common methods used to investigate the nuclear structures of atomic nuclei is the nuclear shell model. Similar to the placement of atomic electrons into orbits, in the nuclear shell model, protons and neutrons are thought to fill the orbits within the nucleus, following the principle of Pauli's exclusion. These orbits are grouped together to form shells, which are said to be closed if all possible places in a shell are full. Atomic nuclei with closed shells are very stable and valence nucleons that are more than these nuclei are included in the nuclear shell model calculations. In this study, the nuclear shell model was used to investigate the nuclear structure of even-even Ne nuclei by considering the 16O core as a closed shell nuclei. Single particle orbits d5/2, s1/2 and d3/2 are taken into account and different parameter sets are used for two-body interactions between valance nucleons. The results were compared with each other and with current literature values. It was seen that the closest results to the experimental values were obtained with parameter sets of usdb and sdnn.
nucl-th0 citations
07
The QCD critical point from the Nambu-Jona-Lasino model with a scalar-vector interaction
Kai-Jia Sun🇺🇸 · Che-Ming Ko🇺🇸 · Shanshan Cao🇺🇸 · Feng Li🇨🇳
We study the critical point in the QCD phase diagram in the Nambu-Jona-Lasino (NJL) model by including a scalar-vector coupled interaction. We find that varying the strength of this interaction, which has no effect on the vacuum properties of QCD, can significantly affect the location of the critical point in the QCD phase diagram, particularly the value of the cirtical temperature. This provides a convenient way to use the NJL-based transport or hydrodynamic model to extract information about the QCD phase diagram from relativistic heavy-ion collisions.
nucl-thhep-phPRD(2021)·18 citations
08
Yrast band in the heavy $N = Z$ nucleus $^{88}$ Ru: $α$ -cluster approach
Peter Mohr
The yrast band in the heavy $N = Z$ nucleus $^{88}$ Ru is studied in the framework of the $α$ -cluster model in combination with double-folding potentials. It is found that the excitation energies of the yrast band in $^{88}$ Ru can be nicely described within the $α$ -cluster approach using a smooth and mildly $L$ -dependent adjustment of the potential strength. This result is similar to well-established $α$ -cluster states in nuclei with a (magic core $\otimes$ $α$ ) structure. Contrary, the yrast bands in neighboring $N \neq = Z$ nuclei deviate from such a typical $α$ -cluster behavior. Finally, the $α$ -cluster model predicts reduced transition strengths of about 10 Weisskopf units for intraband transitions between low-lying states in the yrast band of $^{88}$ Ru.
nucl-thEPJA(2020)·3 citations
09
Calculation of the $^{6}$ Li ground state within the hyperspherical harmonic basis
Alex Gnech🇮🇹 · Michele Viviani🇮🇹 · Laura Elisa Marcucci🇮🇹
We have studied the solution of the six-nucleon bound state problem using the hyperspherical harmonic (HH) approach. For this study we have considered only two-body nuclear forces. In particular we have used a chiral nuclear potential evolved with the similarity renormalization group unitary transformation. A restricted basis has been selected by performing a careful analysis of the convergence of different HH classes. Finally, the binding energy and other properties of $^{6}$ Li ground state are calculated and compared with the results obtained by other techniques. Then, we present a calculation of matrix elements relevant for direct dark matter search involving $^{6}$ Li. The results obtained demonstrate the feasibility of using the HH method to perform calculation beyond $A = 4$ .
nucl-thPRC(2020)·22 citations
10
EMC effect, few-nucleon systems and Poincaré covariance
Emanuele Pace (Università di Roma "Tor Vergata'' and INFN, Sezione di Roma Tor Vergata, Italy)🇮🇹 · Matteo Rinaldi (Università di Perugia and INFN, Sezione di Perugia, Italy)🇮🇹 · Giovanni Salmè (INFN, Sezione di Roma, Italy)🇮🇹 · Sergio Scopetta (Università di Perugia and INFN, Sezione di Perugia, Italy)🇮🇹
An approach for a Poincaré covariant description of nuclear structure and of lepton scattering off nuclei is proposed within the relativistic Hamiltonian dynamics in the light-front form. Indeed a high level of accuracy is needed for a comparison with the increasingly precise present and future experimental data at high momentum transfer. Therefore, to distinguish genuine QCD effects or effects of medium modified nucleon structure functions from conventional nuclear structure effects, the commutation rules between the Poincaré generators should be satisfied. For the first time in this paper a proper hadronic tensor for inclusive deep inelastic scattering of electrons off nuclei is derived in the impulse approximation in terms of the single nucleon hadronic tensor. Our approach is based : i) on a light-front spectral function for nuclei, obtained taking advantage of the successful non-relativistic knowledge of nuclear interaction, and ii) on the free current operator that, if defined in the Breit reference frame with the momentum transfer, $q$ , parallel to the $z$ axis, fulfills Poincaré covariance and current conservation. Our results can be generalized : i) to exclusive processes or to semi-inclusive deep inelastic scattering processes; ii) to the case where the final state interaction is considered through a Glauber approximation; iii) to finite momentum transfer kinematics. As a first test, the hadronic tensor is applied to obtain the nuclear structure function F $_{2}^{A}$ and to evaluate the EMC effect for $^{3} H e$ in the Bjorken limit. Encouraging results including only the two-body part of the light-front spectral function are presented.
nucl-thPhys.Scripta(2020)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE