Nuclear Theory·nucl-th

Friday·July 6, 2018

8 papers—4 primary·4 cross-listed

01
On the effect of high order empirical parameters on the nuclear equation of state
J. Margueron🇺🇸 · F. Gulminelli🇫🇷
A quantitative knowledge of the nuclear Equation of State (EoS) requires an accurate estimation of the uncertainties on the EoS parameters and their mutual correlations. Such correlations are empirically observed in a large set of EoS models by different authors, but they are not always fully understood. We show that some of these correlations can be interpreted from basic physical constraints imposed on a simple Taylor expansion of the binding energy around saturation density. In particular, we investigate the correlations among the following empirical parameters: the symmetry energy $E_{sy m}$ , the slope and curvature of the symmetry energy $L_{sy m}$ and $K_{sy m}$ , and the curvature and skewness of the binding energy in symmetric matter $K_{s a t}$ and $Q_{s a t}$ . The uncertainties on these correlations is estimated through analytical modelling as well as a meta-modelling analysis of the EoS subject to physical constraints. We show that a huge dispersion of the correlations among low order empirical parameters is induced by the unknown higher order empirical parameters, such as $K_{sy m}$ (second order) and $Q_{s a t}$ and $Q_{sy m}$ (third order). We also propose an explanation of the reason why $Q_{s a t}$ is weakly constrained by present experimental data. We conclude that selective observables on high order parameters, such as $K_{sy m}$ and $Q_{s a t}$ , should be better determined before the present uncertainties on the EoS can be further reduced.
nucl-thastro-ph.HEPRC(2019)·59 citations
02
Revisiting the isospin relaxation time in intermediate-energy heavy-ion collisions
Han-Sheng Wang · Jun Xu · Bao-An Li · Wen-Qing Shen
Isospin relaxation times characterizing isospin transport processes between the projectile and the target with different $N / Z$ ratios and that between the neck and the spectator with different isospin asymmetries and densities in intermediate-energy heavy-ion collisions are studied within an isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model using the lattice Hamiltonian approach. The respective roles and time scales of the isospin diffusion and drift as the major mechanisms of isospin transport in intermediate-energy heavy-ion collisions are discussed. Effects of nuclear symmetry energy and neutron-proton effective mass splitting on the isospin relaxation times are examined.
nucl-thnucl-exPRC(2018)·7 citations
03
Heavy-ions collisions and fission dynamics with the time-dependent Hartree-Fock theory and its extensions
C. Simenel · A.S. Umar
Microscopic methods and tools to describe nuclear dynamics have considerably been improved in the past few years. They are based on the time-dependent Hartree-Fock (TDHF) theory and its extensions to include pairing correlations and quantum fluctuations. The TDHF theory is the lowest level of approximation of a range of methods to solve the quantum many-body problem, showing its universality to describe many-fermion dynamics at the mean-field level. The range of applications of TDHF to describe realistic systems allowing for detailed comparisons with experiment has considerably increased. For instance, TDHF is now commonly used to investigate fusion, multi-nucleon transfer and quasi-fission reactions. Thanks to the inclusion of pairing correlations, it has also recently led to breakthroughs in our description of the saddle to scission evolution, and, in particular, the non-adiabatic effects near scission. Beyond mean-field approaches such as the time-dependent random-phase approximation (TDRPA) and stochastic mean-field methods have reached the point where they can be used for realistic applications. We review recent progresses in both techniques and applications to heavy-ion collision and fission.
nucl-thnucl-exPPNP(2018)·180 citations
04
Finite resonance widths influence the thermal-model description of hadron yields
Volodymyr Vovchenko🇩🇪 · Mark I. Gorenstein🇩🇪 · Horst Stoecker🇩🇪
Different scenarios for modeling resonances in a thermal model description of hadron yields measured in heavy-ion collisions are explored: the zero-width approximation, the energy independent Breit-Wigner scheme, and the energy dependent Breit-Wigner (eBW) scheme. Application of the eBW scheme leads to a notable suppression in the proton yields, stemming mainly from a reduced feeddown from $Δ$ resonances because of the threshold effects. A significantly improved agreement of thermal model with hadron yields measured in Pb-Pb collisions at $s_{_{N N}} = 2.76$ TeV by the ALICE collaboration is obtained in the eBW scheme at $T ≃ 155$ MeV, indicating a possible resolution of the so-called 'proton anomaly'. The results obtained show that there are significant systematic uncertainties in the thermal model due to the modeling of broad resonances.
nucl-thhep-phPRC(2018)·71 citations
05
Systematics of azimuthal anisotropy harmonics in proton-nucleus collisions at the LHC from the Color Glass Condensate
Mark Mace🇺🇸 · Vladimir V. Skokov🇺🇸 · Prithwish Tribedy🇺🇸 · Raju Venugopalan🇺🇸
Simple power counting arguments in the dilute-dense framework of the Color Glass Condensate (CGC) Effective Field Theory predict that even and odd azimuthal anisotropy harmonics of two-particle correlations in proton-nucleus collisions at the LHC will respectively satisfy v^2_{2n} ~ N_{ch}^0 and v^2_{2n+1} ~ N_{ch}, where N_{ch} denotes the number of charged particles. We show that these expectations are borne out qualitatively, and even quantitatively, within systematic uncertainties, for v_2 and v_4 in comparisons with data from the ATLAS collaboration. We also observe that ATLAS data for the v_3 azimuthal harmonic are in excellent agreement with our qualitative expectation; quantitative comparisons are numerically challenging at present. The lessons from this study fully complement those gained by the recent comparison of the CGC dilute-dense framework [arXiv:1805.09342] to data from the PHENIX collaboration on small system collisions at RHIC.
↳ hep-phnucl-exnucl-thPLB(2019)·65 citations
06
General thermodynamic equilibrium with axial chemical potential for the free Dirac field
M. Buzzegoli (U. Florence)🇮🇹 · F. Becattini (U. Florence)🇮🇹
We calculate the constitutive equations of the stress-energy tensor and the currents of the free massless Dirac field at thermodynamic equilibrium with acceleration and rotation and a conserved axial charge by using the density operator approach. We carry out an expansion in thermal vorticity to the second order with finite axial chemical potential $μ_{A}$ . The obtained coefficients of the expansion are expressed as correlators of angular momenta and boost operators with the currents. We confirm previous observations that the axial chemical potential induces non-vanishing components of the stress-energy tensor at first order in thermal vorticity due to breaking of parity invariance of the density operator with $μ_{A} \neq = 0$ . The appearance of these components might play an important role in chiral hydrodynamics.
↳ hep-thgr-qcnucl-thJHEP(2018)·42 citations
07
Ordered arrays of Baryonic tubes in the Skyrme model in (3+1) dimensions at finite density
Fabrizio Canfora🇨🇱
A consistent ansatz for the Skyrme model in (3+1)-dimensions which is able to reduce the complete set of Skyrme field equations to just one equation for the profile in situations in which the Baryon charge can be arbitrary large is introduced: moreover, the field equation for the profile can be solved explicitly. Such configurations describe ordered arrays of Baryonic tubes living in flat space-times at finite density. The plots of the energy density (as well as of the Baryon density) clearly show that the regions of maximal energy density have the shape of a tube: the energy density and the Baryon density depend periodically on two spatial directions while they are constant in the third spatial direction. Thus, these topologically non-trivial crystal-like solutions can be intepreted as configurations in which most of the energy density and the baryon density are concentrated within tube-shaped regions. The positions of the energy-density peaks can be computed explicitly and they manifest a clear crystalline order. A non-trivial stability test is discussed.
↳ hep-thhep-phnucl-thEPJC(2018)·57 citations
08
Effect of flavor-dependent partonic transverse momentum on the determination of the $W$ boson mass in hadronic collisions
Alessandro Bacchetta🇮🇹 · Giuseppe Bozzi🇮🇹 · Marco Radici🇳🇱 · Mathias Ritzmann🇺🇸 · Andrea Signori🇺🇸
Within the framework of transverse-momentum-dependent factorization, we investigate for the first time the impact of a flavor-dependent intrinsic transverse momentum of quarks on the production of $W^{\pm}$ bosons in proton-proton collisions at $s$ = 7 TeV. We estimate the shift in the extracted value of the $W$ boson mass $M_{W}$ induced by different choices of flavor-dependent parameters for the intrinsic quark transverse momentum by means of a template fit to the transverse-mass and the lepton transverse-momentum distributions of the $W$ -decay products. We obtain $- 6 \leq Δ M_{W^{+}} \leq 9$ MeV and $- 4 \leq Δ M_{W^{-}} \leq 3$ MeV with a statistical uncertainty of $\pm 2.5$ MeV. Our findings call for more detailed investigations of flavor-dependent nonperturbative effects linked to the proton structure at hadron colliders.
↳ hep-phhep-exnucl-exnucl-thPLB(2019)·54 citations

Affiliations

first authorsco-authorsvia INSPIRE