Nuclear Theory·nucl-th

Tuesday·April 17, 2018

17 papers—12 primary·5 cross-listed

01
Non-resistive dissipative magnetohydrodynamics from the Boltzmann equation in the 14-moment approximation
Gabriel S. Denicol🇧🇷 · Xu-Guang Huang🇨🇳 · Etele Molnár🇩🇪 · Gustavo M. Monteiro🇧🇷 · Harri Niemi🇩🇪 · Jorge Noronha🇧🇷 · Dirk H. Rischke🇩🇪 · Qun Wang🇨🇳
We derive the equations of motion of relativistic, non-resistive, second-order dissipative magnetohydrodynamics from the Boltzmann equation using the method of moments. We assume the fluid to be composed of a single type of point-like particles with vanishing dipole moment or spin, so that the fluid has vanishing magnetization and polarization. In a first approximation, we assume the fluid to be non-resistive, which allows to express the electric field in terms of the magnetic field. We derive equations of motion for the irreducible moments of the deviation of the single-particle distribution function from local thermodynamical equilibrium. We analyze the Navier-Stokes limit of these equations, reproducing previous results for the structure of the first-order transport coefficients. Finally, we truncate the system of equations for the irreducible moments using the 14-moment approximation, deriving the equations of motion of relativistic, non-resistive, second-order dissipative magnetohydrodynamics. We also give expressions for the new transport coefficients appearing due to the coupling of the magnetic field to the dissipative quantities.
nucl-thhep-phphysics.flu-dynPRD(2018)·102 citations
02
Hadronic effects on the $cc q ˉ q ˉ$ tetraquark state in relativistic heavy ion collisions
Juhee Hong🇰🇷 · Sungtae Cho🇰🇷 · Taesoo Song🇩🇪 · Su Houng Lee🇰🇷
We study the hadronic effects on the $cc q ˉ q ˉ$ tetraquark state by focusing on the $T_{cc} (1^{+})$ meson during the hadronic stage of relativistic heavy ion collisions. We evaluate the absorption cross section of the $T_{cc}$ meson by pions in the quasi-free approximation, and investigate the time evolution of the $T_{cc}$ abundance in the hadronic medium based on the effective volume and temperature of the hadronic phase at both RHIC and LHC modelled by hydrodynamic calculations with the lattice equation of state. We probe two possible scenarios for the structure of $T_{cc}$ , where it is assumed to be either a compact multiquark state or a larger sized molecular configuration composed of DD*. Our numerical results suggest that the hadronic effects on the $T_{cc}$ production is insignificant, and its final abundance depends on the initial yield of $T_{cc}$ produced from the quark-gluon plasma phase, which will depend on the assumed structure of the state.
nucl-thPRC(2018)·30 citations
03
Monte Carlo Glauber model with meson cloud: predictions for 5.44 TeV Xe+Xe collisions
B.G. Zakharov🇷🇺
We study, within the Monte-Carlo Glauber model, centrality dependence of the midrapidity charged multiplicity density $d N_{c h} / d η$ and of the anisotropy coefficients $ε_{2, 3}$ in Pb+Pb collisions at $s = 5.02$ TeV and in Xe+Xe collisions at $s = 5.44$ TeV. Calculations are performed for versions with and without nucleon meson cloud. The fraction of the binary collisions, $α$ , has been fitted to the data on $d N_{c h} / d η$ in Pb+Pb collisions. We obtain $α \approx 0.09 (0.13)$ with (without) meson cloud. The effect of meson cloud on the $d N_{c h} / d η$ is relatively small. For Xe+Xe collisions for $0$ - $5$ \% centrality bin we obtain $d N_{c h} / d η \approx 1149$ and $1134$ with and without meson cloud, respectively. We obtain $ε_{2} (\mbox X e) / ε_{2} (\mbox P b) \sim 1.45$ for most central collisions, and $ε_{2} (\mbox X e) / ε_{2} (\mbox P b)$ close to unity at $c ≳ 20$ \%. We find a noticeable increase of the eccentricity in Xe+Xe collisions at small centralities due to the prolate shape of the Xe nucleus. The triangularity in Xe+Xe collisions is bigger than in Pb+Pb collisions at $c ≲ 70$ \%. We obtain $ε_{3} (\mbox X e) / ε_{3} (\mbox P b) \sim 1.3$ at $c ≲ 1$ \%.
nucl-thhep-phEPJC(2018)·14 citations
04
Scission Dynamics with K Partitions
G.F. Bertsch · W. Younes · L.M. Robledo
We propose a framework to calculate the dynamics at the scission point of nuclear fission, based as far as possible on a discrete representation of orthogonal many-body configurations. Assuming axially symmetric scission shapes, we use the $K$ orbital quantum number to build a basis of wave functions. Pre-scission configurations are stable under mean-field dynamics while post-scission configurations evolve to separated fragments. In this first exploratory study, we analyze a typical fission trajectory through to scission in terms of these configurations. We find that there is a major rearrangement of the $K$ occupancy factors at scission. Interestingly, very different fragment shapes occur in the post-scission configurations, even starting from the same pre-scission configuration.
nucl-thPRC(2018)·16 citations
05
Simulation study of elliptic flow of charged hadrons produced in Au + Au collisions at the Facility for Antiproton and Ion Research
Soumya Sarkar🇮🇳 · Provash Mali🇮🇳 · Amitabha Mukhopadhyay🇮🇳
Centrality and system geometry dependence of azimuthal anisotropy of charged hadrons measured in terms of the elliptic flow parameter are investigated using Au+Au event samples at incident beam energy $20$ A GeV and $40$ A GeV generated by Ultrarelativistic Quantum Molecular Dynamics and A Multiphase Transport models. The Monte Carlo Glauber model is employed to estimate the eccentricity of the overlapping zone at an early stage of the collisions. Anisotropies present both in the particle multiplicity distribution and in the kinetic radial expansion are examined by using standard statistical and phenomenological methods. In the context of upcoming Compressed Baryonic Matter experiment to be held at the Facility for Antiproton and Ion Research, the present set of simulated results provide us not only with an opportunity to examine the expected collective behavior of hadronic matter at high baryon density and moderate temperature environment, but when compared with similar results obtained from Relativistic Heavy Ion Collider and Large Hadron Collider experiments, they also allow us to investigate how anisotropy of hadronic matter may differ or agree with its low baryon density and high temperature counterpart.
nucl-thhep-phPRC(2017)·15 citations
06
Azimuthal anisotropy in particle distribution in A Multi-phase Transport Model
Soumya Sarkar🇮🇳 · Provash Mali🇮🇳 · Amitabha Mukhopadhyay🇮🇳
Anisotropic flow of hadronic matter is considered as a sensitive tool to detect the early stage dynamics of high-energy heavy-ion collisions. Taking the event by event fluctuations of the collision geometry into account, the elliptic flow parameter and the triangular flow parameter derived from the azimuthal distribution of produced hadrons, are investigated within the framework of a multiphase transport (AMPT) model, at a collision energy that in near future will typically be available at the Facility for Antiproton and Ion Research. The dependence of elliptic and triangular flow parameters on initial fluctuations, on parton scattering cross-sections, their mass ordering on different hadron species and on the constituent quark number scaling are examined. The AMPT simulation can not exactly match the elliptic flow results on Pb + Pb collision at 40A GeV of the NA49 experiment. The simulation results presented in this work are expected to provide us with an insight to study flow properties at high baryonic density but moderate temperature, and also with an opportunity to compare similar results available from RHIC and LHC experiments.
nucl-thhep-phPRC(2017)·8 citations
07
Possible generation of $π$ -condensation in a free space by collisions between photons and protons
Qi-Ren Zhang
A sharply peaked structure is found in the angular distribution of emitted $π^{+}$ mesons from the photon-proton collisions. It offers a possible way for generating a $π^{+}$ -condensation in free space. To make the stimulated emission of $π^{+}$ -mesons efficient, a ring resonator is designed.
nucl-thChin.Phys.B(2018)·0 citations
08
Diffusive dynamics of critical fluctuations near the QCD critical point
Marlene Nahrgang (SUBATECH, Nantes)🇫🇷 · Marcus Bluhm (Wroclaw U.)🇵🇱 · Thomas Schaefer (North Carolina State U.)🇺🇸 · Steffen A. Bass (Duke U.)🇺🇸
A quantitatively reliable theoretical description of the dynamics of fluctuations in non-equilibrium is indispensable in the experimental search for the QCD critical point by means of ultra-relativistic heavy-ion collisions. In this work we consider the fluctuations of the net-baryon density which becomes the slow, critical mode near the critical point. Due to net-baryon number conservation the dynamics is described by the fluid dynamical diffusion equation, which we extend to contain a white noise stochastic current. Including nonlinear couplings from the 3d Ising model universality class in the free energy functional, we solve the fully interacting theory in a finite size system. We observe that purely Gaussian white noise generates non-Gaussian fluctuations, but finite size effects and exact net-baryon number conservation lead to significant deviations from the expected behavior in equilibrated systems. In particular the skewness shows a qualitative deviation from infinite volume expectations. With this benchmark established we study the real-time dynamics of the fluctuations. We recover the expected dynamical scaling behavior and observe retardation effects and the impact of critical slowing down near the pseudo-critical temperature.
nucl-thhep-phPRD(2019)·131 citations
09
Scaling behavior of anisotropic flow harmonics in the far from equilibrium regime
Nicolas Borghini🇩🇪 · Steffen Feld🇩🇪 · Nina Kersting🇩🇪
We consider the development of anisotropic flow in an expanding system of particles undergoing very few rescatterings, using a kinetic-theoretical description with a nonlinear collision term. We derive the scaling behaviors of the harmonic coefficients $v_{n}$ with the initial-state eccentricities and the mean number of rescatterings, and argue that hexagonal flow $v_{6}$ should follow a nontrivial behavior, different from that of the lower harmonics. Our findings should be observable in experimental data for small systems.
nucl-thhep-phnucl-exEPJC(2018)·27 citations
10
Further studies of multiplicity derivative in models of heavy ion collision at intermediate energies as a probe for phase transition
S Das Gupta · S. Mallik · G. Chaudhuri
In conjunction with models, the experimental observable total multiplicity can be used to check if the data contain the signature of phase transition and if it is first order. Two of the models reach similar conclusions. The third one is quite different.
nucl-thnucl-exPRC(2018)·13 citations
11
Phase diagram of an extended Agassi model
J.E. García-Ramos · J. Dukelsky · P. Pérez-Fernández · J.M. Arias
Background: The Agassi model is an extension of the Lipkin-Meshkov-Glick model that incorporates the pairing interaction. It is a schematic model that describes the interplay between particle-hole and pair correlations. It was proposed in the 1960's by D. Agassi as a model to simulate the properties of the quadrupole plus pairing model. Purpose: The aim of this work is to extend a previous study by Davis and Heiss generalizing the Agassi model and analyze in detail the phase diagram of the model as well as the different regions with coexistence of several phases. Method: We solve the model Hamiltonian through the Hartree-Fock-Bogoliubov (HFB) approximation, introducing two variational parameters that play the role of order parameters. We also compare the HFB calculations with the exact ones. Results: We obtain the phase diagram of the model and classify the order of the different quantum phase transitions appearing in the diagram. The phase diagram presents broad regions where several phases, up to three, coexist. Moreover, there is also a line and a point where four and five phases are degenerated, respectively. Conclusions: The phase diagram of the extended Agassi model presents a rich variety of phases. Phase coexistence is present in extended areas of the parameter space. The model could be an important tool for benchmarking novel many-body approximations.
nucl-thquant-phPRC(2018)·9 citations
12
From cluster structures to nuclear molecules: the role of nodal structure of the single-particle wave functions
A.V. Afanasjev · H. Abusara
The nodal structure of the density distributions of the single-particle states occupied in rod-shaped, hyper- and megadeformed structures of non-rotating and rotating $N \sim Z$ nuclei has been investigated in detail. The single-particle states with the Nilsson quantum numbers of the $[N N 0] 1/2$ (with $N$ from 0 to 5) and $[N, N - 1, 1] Ω$ (with $N$ from 1 to 3 and $Ω = 1/2$ , 3/2) types are considered. These states are building blocks of extremely deformed shapes in the nuclei with mass numbers $A \leq 50$ . Because of (near)axial symmetry and large elongation of such structures, the wave functions of the single-particle states occupied are dominated by a single basis state in cylindrical basis. This basis state defines the nodal structure of the single-particle density distribution. The nodal structure of the single-particle density distributions allows to understand in a relatively simple way the necessary conditions for $α$ -clusterization and the suppression of the $α$ -clusterization with the increase of mass number. It also explains in a natural way the coexistence of ellipsoidal mean-field type structures and nuclear molecules at similar excitation energies and the features of particle-hole excitations connecting these two types of the structures. Our analysis of the nodal structure of the single-particle density distributions does not support the existence of quantum liquid phase for the deformations and nuclei under study.
nucl-thPRC(2018)·18 citations
13
Charm quarks are more hydrodynamic than light quarks in final-state elliptic flow
Hanlin Li🇨🇳 · Zi-Wei Lin🇨🇳 · Fuqiang Wang🇨🇳
We study the charm quark elliptic flow ( $v_{2}$ ) in heavy ion as well as small system collisions by tracking the evolution history of quarks of different flavors within a multi-phase transport model. The charm quark $v_{2}$ is studied as a function of the number of collisions the charm quark suffers with other quarks and then compared to the $v_{2}$ of lighter quarks. We find that the common escape mechanism is at work for both the charm and light quark $v_{2}$ . However, contrary to the naive expectation, the hydrodynamics-type flow is found to contribute more to the final state charm $v_{2}$ than light quark $v_{2}$ . This could be explained by the smaller average deflection angle the heavier charm quark undergoes in each collision, so that heavy quarks need more scatterings to accumulate a significant $v_{2}$ , while lighter quarks can more easily change directions with scatterings with their $v_{2}$ coming more from the escape mechanism. Our finding thus suggests that the charm $v_{2}$ is a better probe for studying the hydrodynamic properties of the quark-gluon plasma.
↳ hep-phnucl-exnucl-thPRC(2019)·25 citations
14
In depth analysis of the combined HERA data in the dipole models with and without saturation
Heikki Mäntysaari🇫🇮 · Pia Zurita🇺🇸
We present an updated impact parameter dependent saturation model (IPsat) determined trough a fit to the combined HERA I and I+II reduced cross section data. The same HERA data are used to fit the linearized (IPnonsat) version of the applied dipole amplitude, which makes it possible to estimate the magnitude of the saturation effects in various experiments. We find that both parametrizations provide comparable descriptions of the considered data when an effective confinement scale dynamics is incorporated with quark masses. Moreover, it is possible to consistently determine the light and charm quark masses. The role of potentially non-perturbatively large dipoles is examined in detail, with the result that, especially in case of the structure function $F_{2}$ , their contribution is numerically significant. Potential to discriminate between the two models in future $e + p$ and $e + A$ experiments is also illustrated.
↳ hep-phnucl-thPRD(2018)·92 citations
15
Enhanced nuclear spin dependent parity violation effects using the 199HgH molecule
A. J. Geddes🇦🇺 · L. V. Skripnikov🇷🇺 · A. Borschevsky🇳🇱 · J. C. Berengut🇦🇺 · V. V. Flambaum🇦🇺 · T. P. Rakitzis🇬🇷
Electron interactions with the nuclear-spin-dependent (NSD) parity non-conserving (PNC) anapole moment are strongly enhanced within heteronuclear diatomic molecules. A novel, low-energy optical rotation experiment is being proposed with the aim of observing NSD PNC interactions in HgH. Based on the relativistic coupled cluster method we present a complete calculation of the circular polarization parameter $P = 2 Im (E 1_{P N C}) / M 1 \approx 3 \times 1 0^{- 6} κ$ for the $^{2} Σ_{1/2} \to^{2} Π_{1/2}$ optical transition of HgH, where $κ$ is a dimensionless constant determined by the nuclear anapole moment. This provides an improvement in sensitivity to NSD PNC by 2 -- 3 orders of magnitude over the leading atomic Xe, Hg, Tl, Pb and Bi optical rotation experiments, and shows that the proposed measurement will be sensitive enough to extract the $^{199}$ Hg anapole moment and shed light on the underlying theory of hadronic parity violation.
↳ physics.atom-phnucl-thPRA(2018)·12 citations
16
Effective Stellar $β$ -Decay Rates of Nuclei with Long-lived Isomers: $^{26}$ Al and $^{34}$ Cl
Projjwal Banerjee · G. Wendell Misch · Surja K. Ghorui · Yang Sun
Isotopes with low-lying long-lived isomers can behave very differently from other isotopes in astrophysical environments. In particular, the assumption of thermal equilibrium in computing the temperature-dependent $β$ -decay rates of such isotopes can fail below certain temperatures. We focus on the $β$ -decay of $^{26}$ Al since it is one of the most important isotopes in observational astrophysics and has a low-lying isomeric state; we compare and contrast these results with $^{34}$ Cl. We rule out recently reported $^{26}$ Al effective $β$ -decay rates that showed large differences from previous calculations, finding that we agree with the earlier results. We conclude that in general, effective $β$ -decay rates should be defined separately for the ground and isomeric states at temperatures where thermal equilibrium cannot be achieved.
↳ astro-ph.HEnucl-thPRC(2018)·15 citations
17
Centrality dependence of freeze-out temperature fluctuations in Pb-Pb collisions at the LHC
Dariusz Prorok🇵🇱
Many data in the High Energy Physics are, in fact, sample means. It is shown that when this exact meaning of the data is taken into account and the most weakly bound states are removed from the hadron resonance gas, the whole spectra of pions, kaons and protons measured at midrapidity in Pb-Pb collisions at $s_{N N} = 2.76$ TeV can be fitted simultaneously. The invariant distributions are predicted with the help of the single-freeze-out model in the chemical equilibrium framework. The method is applied to the measurements in centrality bins of Pb-Pb collisions and gives acceptable fits for all but peripheral bins. The comparison with the results obtained in the framework of the original single-freeze-out model is also presented. Some more general, possible implications of this approach are pointed out.
↳ hep-phhep-exnucl-exnucl-thEPJA(2019)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE