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Nuclear Theory·nucl-th

Tuesday·April 14, 2020

20 papers—10 primary·10 cross-listed

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  1. 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 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 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, 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
  2. 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
  3. 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 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 - level, with the exception of matrix elements entering the rates of Li, B, and 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 - 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 = to = systems considered here.

    nucl-thPRC(2020)·85 citations
  4. 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 GeV is examined. It is found that the directed flow depends strongly on the optical potential at high energies, 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 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 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 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 GeV.

    nucl-thhep-phnucl-exPRC(2020)·68 citations
  5. 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
  6. 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
  7. 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
  8. 08

    Yrast band in the heavy nucleus Ru: -cluster approach

    Peter Mohr

    The yrast band in the heavy nucleus Ru is studied in the framework of the -cluster model in combination with double-folding potentials. It is found that the excitation energies of the yrast band in Ru can be nicely described within the -cluster approach using a smooth and mildly -dependent adjustment of the potential strength. This result is similar to well-established -cluster states in nuclei with a (magic core ) structure. Contrary, the yrast bands in neighboring nuclei deviate from such a typical -cluster behavior. Finally, the -cluster model predicts reduced transition strengths of about 10 Weisskopf units for intraband transitions between low-lying states in the yrast band of Ru.

    nucl-thEPJA(2020)·3 citations
  9. 09

    Calculation of the 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 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 Li. The results obtained demonstrate the feasibility of using the HH method to perform calculation beyond .

    nucl-thPRC(2020)·22 citations
  10. 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, , parallel to the 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 and to evaluate the EMC effect for 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
  11. 11

    plus jets production via double parton scattering in collisions at the LHC

    B. Blok🇮🇱 · F. A. Ceccopieri (Technion)🇮🇱

    We present results on Zjj production via double parton scattering in pA collisions at the LHC. We perform the analysis at leading and next-leading order accuracy with different sets of cuts on jet transverse momenta and accounting for the single parton scattering background. By exploiting the experimental capability to measure the centrality dependence of the cross section, we discuss the feasibility of DPS observation in already collected data at the LHC and in future runs.

    ↳ hep-phhep-exnucl-exnucl-thEPJC(2020)·4 citations
  12. 12

    Non-equilibrium attractor in high-temperature QCD plasmas

    Dekrayat Almaalol🇺🇸 · Aleksi Kurkela🇨🇭 · Michael Strickland🇺🇸

    We establish the existence of a far-from-equilibrium attractor in weakly-coupled gauge theory undergoing one-dimensional Bjorken expansion. We demonstrate that the resulting far-from-equilibrium evolution is insensitive to certain features of the initial condition, including both the initial momentum-space anisotropy and initial occupancy. We find that this insensitivity extends beyond the energy-momentum tensor to the detailed form of the one-particle distribution function. Based on our results, we assess different procedures for reconstructing the full one-particle distribution function from the energy-momentum tensor along the attractor and discuss implications for the freeze-out procedure used in the phenomenological analysis of ultra-relativistic nuclear collisions.

    ↳ hep-phnucl-thPRL(2020)·92 citations
  14. 14

    First measurement of direct photoproduction of the meson on the proton

    A. Celentano · M. Battaglieri · R. De Vita · L. Marsicano · V. Mathieu · A. Pilloni · A. Szczepaniak (for the CLAS collaboration)

    We present the first measurement of the exclusive reaction in the photon energy range - GeV and four-momentum transfer squared GeV. Data were collected with the CEBAF Large Acceptance Spectrometer at the Thomas Jefferson National Accelerator Facility. The neutral resonance was detected by measuring the reaction and reconstructing the invariant mass. The differential cross section was extracted at different beam energies in each bin. The most prominent feature of the differential cross section is a dip at GeV. This can be well described in the framework of Regge phenomenology, where the exchange degeneracy hypothesis predicts a zero in the reaction amplitude for this value of the four-momentum transfer.

    ↳ nucl-exhep-exnucl-thPRC(2020)·12 citations
  15. 15

    Nonequilibrium pion distribution within the Zubarev approach

    David Blaschke🇵🇱 · Gerd Röpke🇷🇺 · Dmitry N. Voskresensky🇷🇺 · Vladimir G. Morozov🇷🇺

    We discuss how the nonequilibrium process of pion production within the Zubarev approach of the nonequilibrium statistical operator leads to a theoretical foundation for the appearance of a nonequilibrium pion chemical potential for the pion distribution function for which there is experimental evidence in experiments at the CERN LHC.

    ↳ hep-phcond-mat.stat-mechnucl-thParticles(2020)·8 citations
  16. 16

    Classical excluded volumes of loosely bound light (anti)nuclei and their chemical freeze-out in heavy ion collisions

    B. E. Grinyuk🇺🇦 · K. A. Bugaev🇺🇦 · V. V. Sagun🇵🇹 · O. I. Ivanytskyi🇵🇹 · D. L. Borisyuk🇺🇦 · A. S. Zhokhin🇺🇦 · G. M. Zinovjev🇺🇦 · D. B. Blaschke🇵🇱 · L. V. Bravina🇳🇴 · E. E. Zabrodin🇳🇴 · E. G. Nikonov🇷🇺 · G. Farrar🇺🇸 and 3 other authors

    From the analysis of light (anti)nuclei multiplicities that were measured recently by the ALICE collaboration in Pb+Pb collisions at the center-of-mass collision energy TeV there arose a highly non-trivial question about the excluded volume of composite particles. Surprisingly, the hadron resonance gas model (HRGM) is able to perfectly describe the light (anti)nuclei multiplicities under various assumptions. Thus, one can consider the (anti)nuclei with a vanishing hard-core radius (as the point-like particles) or with the hard-core radius of proton, but the fit quality is the same for these assumptions. It is clear, however, that such assumptions are unphysical. Hence we obtain a formula for the classical excluded volume of loosely bound light nuclei consisting of A baryons. To implement a new formula into the HRGM we have to modify the induced surface tension concept to treat the hadrons and (anti)nuclei on the same footing. We perform a simultaneous analysis of hadronic and (anti)nuclei multiplicities measured by the ALICE collaboration. The HRGM with the induced surface tension allows us to verify different assumptions on the values of hard-core radii and different scenarios of chemical freeze-out of light (anti)nuclei. It is shown that the unprecedentedly high quality of fit is achieved, if the chemical freeze-out temperature of hadrons is about MeV, while the one for all (anti)nuclei is MeV.

    ↳ hep-phnucl-exnucl-thIJMPE(2020)·7 citations
  17. 17

    Non-Hermitian Ferromagnetism in an Ultracold Fermi Gas

    Hiroyuki Tajima · Kei Iida

    We develop a non-Hermitian effective theory for a repulsively interacting Fermi gas in the excited branch. The on-shell -matrix is employed as a complex-valued interaction term, which describes a repulsive interaction between atoms in the excited branch and a two-body inelastic decay to the attractive branch. To see the feature of this model, we have addressed, in the weak coupling regime, the excitation properties of a repulsive Fermi polaron as well as the time-dependent number density. The analytic expressions obtained for these quantities qualitatively show a good agreement with recent experiments. By calculating the dynamical transverse spin susceptibility in the random phase approximation, we show that a ferromagnetic system with nonzero polarization undergoes a dynamical instability and tends towards a heterogeneous phase.

    ↳ cond-mat.quant-gasnucl-thJ.Phys.Soc.Jap.(2021)·3 citations
  18. 18

    Heavy-hadron molecules from light-meson-exchange saturation

    Fang-Zheng Peng🇨🇳 · Ming-Zhu Liu🇨🇳 · Mario Sánchez Sánchez🇫🇷 · Manuel Pavon Valderrama🇨🇳

    In the effective field theory framework the interaction between two heavy hadrons can be decomposed into a long- and a short-range piece. The long-range piece corresponds to the one-pion-exchange potential and is relatively well-known. The short-range piece is given by a series of contact-range interactions with unknown couplings, which substitute the less well-known short-range dynamics. While the general structure of the short-range potential between heavy hadrons is heavily constrained from heavy-quark symmetry, the couplings are still free parameters. Here we argue that the relative strength and the sign of these couplings can be estimated from the hypothesis that they are saturated by the exchange of light mesons, in particular the vector mesons and , i.e. from resonance saturation. However, we propose a novel saturation procedure that effectively removes form-factor artifacts. From this we can determine in which spin and isospin configurations the low-energy constants are most attractive for specific two-heavy-hadron systems. In general the molecular states with lower isospins and higher spins will be more attractive and thus more probable candidates to form heavy-hadron molecules. This pattern is compatible with the interpretation of the and as molecular states, but it is not applicable to states with maximum isospin like the .

    ↳ hep-phhep-exhep-latnucl-thPRD(2020)·37 citations
  19. 19

    Relativistic Borromean States

    Ziyue Wang🇨🇳 · Shao-Jian Jiang🇨🇳 · Yin Jiang🇨🇳

    In this work the existence of Borromean states has been discussed for bosonic and fermionic cases in both the relativistic and non-relativistic limits from the 3-momentum shell renormalization. With the linear bosonic model we checked the existence of Efimov-like states in the bosonic system. In both limits a geometric series of singularities are found in the 3-boson interaction vertex, while the energy ratio is reduced by around 70\% in the relativistic limit because of the anti-particle contribution. Motivated by the quark-diquark model in heavy baryon studies, we have carefully examined the p-wave quark-diquark interaction and found an isolated Borromean pole at finite energy scale. This may indicate a special baryonic state of light quarks in high energy quark matters. In other cases trivial results are obtained as expected. In relativistic limit, for both bosonic and fermionic cases, potential Borromean states are independent of the mass, which means the results would be valid even in zero-mass limit as well.

    ↳ hep-phcond-mat.quant-gashep-thnucl-thCPC(2021)·0 citations
  20. 20

    NS 1987A in SN 1987A

    Dany Page · Mikhail V. Beznogov · Iván Garibay · James M. Lattimer · Madappa Prakash · Hans-Thomas Janka

    The possible detection of a compact object in the remnant of SN 1987A presents an unprecedented opportunity to follow its early evolution. The suspected detection stems from an excess of infrared emission from a dust blob near the compact object's predicted position. The infrared excess could be due to the decay of isotopes like 44Ti, accretion luminosity from a neutron star or black hole, magnetospheric emission or a wind originating from the spindown of a pulsar, or thermal emission from an embedded, cooling neutron star (NS 1987A). It is shown that the last possibility is the most plausible as the other explanations are disfavored by other observations and/or require fine-tuning of parameters. Not only are there indications the dust blob overlaps the predicted location of a kicked compact remnant, but its excess luminosity also matches the expected thermal power of a 30 year old neutron star. Furthermore, models of cooling neutron stars within the Minimal Cooling paradigm readily fit both NS 1987A and Cas A, the next-youngest known neutron star. If correct, a long heat transport timescale in the crust and a large effective stellar temperature are favored, implying relatively limited crustal n-1S0 superfluidity and an envelope with a thick layer of light elements, respectively. If the locations don't overlap, then pulsar spindown or accretion might be more likely, but the pulsar's period and magnetic field or the accretion rate must be rather finely tuned. In this case, NS 1987A may have enhanced cooling and/or a heavy-element envelope.

    ↳ astro-ph.HEnucl-thApJ(2020)·85 citations

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