Nuclear Theory·nucl-th

Wednesday·August 8, 2018

9 papers—4 primary·5 cross-listed

01
Estimating initial state and quark-gluon plasma medium properties using a hybrid model with nucleon substructure calibrated to $p$ -Pb and Pb-Pb collisions at $s_{NN} = 5.02$ TeV
J. Scott Moreland🇺🇸 · Jonah E. Bernhard🇺🇸 · Steffen A. Bass🇺🇸
We posit a unified hydrodynamic and microscopic description of the quark-gluon plasma (QGP) produced in ultrarelativistic $p$ -Pb and Pb-Pb collisions at $s_{NN} = 5.02$ TeV and evaluate our assertion using Bayesian inference. Specifically, we model the dynamics of both collision systems using initial conditions with parametric nucleon substructure, a pre-equilibrium free-streaming stage, event-by-event viscous hydrodynamics, and a microscopic hadronic afterburner. Free parameters of the model which describe the initial state and QGP medium are then simultaneously calibrated to fit charged particle yields, mean $p_{T}$ , and flow cumulants. We argue that the global agreement of the calibrated model with the experimental data strongly supports the existence of hydrodynamic flow in small collision systems at ultrarelativistic energies, and that the flow produced develops at length scales smaller than a single proton. Posterior estimates for the model's input parameters are obtained, and new insights into the temperature dependence of the QGP transport coefficients and event-by-event structure of the proton are discussed.
nucl-thnucl-exPRC(2020)·168 citations
02
Strangeness and $Δ$ resonance in compact stars with relativistic-mean-field models
Ting-Ting Sun🇨🇳 · Shi-Sheng Zhang🇨🇳 · Qiu-Lan Zhang🇨🇳 · Cheng-Jun Xia🇨🇳
We explore the effects of strangeness and $Δ$ resonance in baryonic matter and compact stars within the relativistic-mean-field (RMF) models. The covariant density functional PKDD is adopted for $N$ - $N$ interaction, parameters fixed based on finite hypernuclei and neutron stars are taken for the hyperon-meson couplings, and the universal baryon-meson coupling scheme is adopted for the $Δ$ -meson couplings. In light of the recent observations of GW170817 with the dimensionless combined tidal deformability $197 \leq Λ ˉ \leq 720$ , we find it is essential to include the $Δ$ resonances in compact stars, and small $Δ$ - $ρ$ coupling $g_{ρ Δ}$ is favored if the mass $2.27_{- 0.15}^{+ 0.17} M_{⊙}$ of PSR J2215+5135 is confirmed.
nucl-thastro-ph.HEPRD(2019)·42 citations
03
Short-range and tensor correlations in 4He and 8Be studied with antisymmetrized quasi cluster model
N. Itagaki🇯🇵 · H. Matsuno🇯🇵 · Y. Kanada-En'yo🇯🇵
We apply tensor version of antisymmetrized quasi cluster model (AQCM-T) to 4He and 8Be while focusing on the NN correlations in alpha clusters. We adopt the NN interactions including realistic ones containing a repulsive core for the central part in addition to the tensor part. In 4He, the pn pair in the 3D channel has been known to play a decisive role in the tensor correlation and the framework is capable of treating not only this channel but also the NN correlations in the 1S and 3S channels. In 8Be, when two alpha clusters approach, the 3D pair is suppressed because of the Pauli blocking effect, which induces the decrease of the 3S component through the 3S-3D coupling. This effect results in the reduction of the attractive effect of the central-even interaction in the middle-range region.
nucl-thPTEP(2019)·4 citations
04
Nuclear systems under extreme conditions: isospin asymmetry and strong B-fields
Martin Stein🇩🇪
This thesis explores nuclear systems under extreme conditions of isospin asymmetry and strong magnetic fields. Its first chapter is devoted to the phase diagram of isospin-asymmetrical nuclear matter in the density-temperature plane. Four competing phases of matter are included into the consideration: the unpaired phase, the ordinary Bardeen-Cooper-Schrieffer (BCS) phase, a phase where normal fluid and superfluid separate into distinct domains and the superfluid phase with a non-zero total momentum of Cooper pairs. The evolution of these phases from the weakly BCS limit to the strongly coupled Bose-Einstein-Condensate limit is studied by varying the density from high to low values at various temperatures and asymmetries. The emergence of tri-critical points (including a Lifshitz point) and various intrinsic properties of the condensate (pair wave-function, occupation numbers, quasiparticle spectra) are discussed. The second chapter studies the nuclei $^{12}$ C, $^{16}$ O, and $^{20}$ Ne in a magnetic field $B \approx 1 0^{17}$ G by utilizing the SKY3D code, suitably extended to include the magnetic field. Our solutions of time-independent Hartree-Fock equations on a Cartesian three-dimensional grid with a Skyrme interaction demonstrate a number of interesting phenomena, such as level splitting in the magnetic field, spontaneous rearrangement of energy levels, changes in the nuclear shape, etc. The third chapter studies the pairing in low-density neutron matter in the presence of a strong magnetic field. In particular, we find the limiting field for the destruction of the superfluidity of neutrons in the crust and outer core of magnetars. This field is density-dependent but is generally of the order of $B \geq 1 0^{17}$ G. The phase diagram of spin-polarized neutron matter is constructed in the case where only the BCS phase is allowed along with the (spin-polarized) normal phase.
nucl-th0 citations
05
Gluon Quasi-PDF From Lattice QCD
Zhou-You Fan🇺🇸 · Yi-Bo Yang🇺🇸 · Adam Anthony🇺🇸 · Huey-Wen Lin🇺🇸 · Keh-Fei Liu🇺🇸
We present the first attempt to access the $x$ -dependence of the gluon unpolarized parton distribution function (PDF), based on lattice simulations using the large-momentum effective theory (LaMET) approach. The lattice calculation is carried out with pion masses of 340 and 678 MeV on a 2+1-flavor DWF configuration with lattice spacing $a = 0.111$ ~fm, for the gluon quasi-PDF matrix element with the nucleon momentum up to 0.93 GeV. Taking the normalization from similar matrix elements in the rest frame of the nucleon and pion, our results for these matrix elements are consistent with the Fourier transform of the global fit CT14 and PDF4LHC15 NNLO of the gluon PDF, within statistical uncertainty and the systematic one up to power corrections, perturbative $O (α_{s})$ matching and the mixing from the quark PDFs.
↳ hep-lathep-phnucl-thPRL(2018)·107 citations
06
Impact of unitarization on the $J / ψ$ -light meson cross section
L. M. Abreu🇧🇷 · E. Cavalcanti🇧🇷 · A. P. C. Malbouisson🇧🇷
Hidden charm mesons continue playing an essential role as relevant probes to understand the evolution of partonic matter. It is expected that the charmonia that survived the quark-gluon plasma phase suffer collisions with other particles composing the hadronic matter. In this work, we intend to contribute on this subject by presenting an updated study about the interactions of $J / ψ$ with surrounding hadronic medium. The meson-meson interactions are described with a $S U (4)$ effective Lagrangian, and within the framework of unitarized coupled channel amplitudes projected onto s-wave. The symmetry is explicitly broken to $S U (3)$ by suppression of the interactions driven by charmed mesons. We calculate the cross sections for $J / ψ$ scattering by light pseudoscalar mesons ( $π, K, η$ ) and vector mesons ( $ρ, K^{*}, ω$ ), as well as their inverse processes. Keeping the validity of this present approach in the low CM energy range, the most relevant channels are evaluated and a comparison of the findings with existing literature is performed.
↳ hep-phnucl-thNPA(2018)·3 citations
07
Studies of the Giant Dipole Resonance in $^{27}$ Al, $^{40}$ Ca, $^{56}$ Fe, $^{58}$ Ni and $^{208}$ Pb with high energy-resolution inelastic proton scattering under 0 $^{\circ}$
M. Jingo (1,2) · E.Z. Buthelezi (3) · J. Carter (1) · G.R.J. Cooper (4) · R.W. Fearick (5) · S.V. Förtsch (3) · C.O. Kureba (1) · A.M. Krumbholz (6) · P. von Neumann-Cosel (6) · R. Neveling (3) · P. Papka (7) · I. Poltoratska (6) and 7 other authors
A survey of the fine structure of the Isovector Giant Dipole Resonance (IVGDR) was performed, using the recently commissioned zero-degree facility of the K600 magnetic spectrometer at iThemba LABS. Inelastic proton scattering at an incident energy of 200 MeV was measured on $^{27}$ Al, $^{40}$ Ca, $^{56}$ Fe, $^{58}$ Ni and $^{208}$ Pb. A high energy resolution ( $Δ E ≃$ 40 keV FWHM) could be achieved after utilising faint-beam and dispersion-matching techniques. Considerable fine structure is observed in the energy region of the IVGDR and characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The comparison with Quasiparticle-Phonon Model (QPM) calculations provides insight into the relevance of different giant resonance decay mechanisms. Photoabsorption cross sections derived from the data assuming dominance of relativistic Coulomb excitation are in fair agreement with previous work using real photons.
↳ nucl-exnucl-thEPJA(2018)·16 citations
08
Using Steady State Behavior to Assess Treatments of Nuclear Isomers in Astrophysical Environments
G. Wendell Misch🇨🇳 · Surja K. Ghorui🇨🇳 · Yang Sun🇨🇳
Differing reaction rates of long-lived nuclear states can force the level occupations out of thermal equilibrium, causing calculations of overall rates which rely on thermal equilibrium to be inaccurate. Therefore, nucleosynthesis calculations which include nuclei with isomers must use techniques that do not assume thermal equilibrium, and it is imperative that such techniques appropriately account for transitions between the ground and isomeric states via higher-lying levels. We develop a formalism to compute the steady state occupations of nuclear levels and apply it to the examples 26Al, 34Cl, and 85Kr. We show that this approach is useful both for assessing the required number of nuclear levels and for determining the temperature above which thermal equilibrium rates are appropriate.
↳ astro-ph.HEnucl-th2 citations
09
Radial Flow and Differential Freeze-out in Proton-Proton Collisions at $s = 7$ TeV at the LHC
Arvind Khuntia🇮🇳 · Himanshu Sharma🇮🇳 · Swatantra Kumar Tiwari🇮🇳 · Raghunath Sahoo🇮🇳 · Jean Cleymans🇿🇦
We analyse the transverse momentum ( $p_{T}$ )-spectra as a function of charged-particle multiplicity at midrapidity ( $∣ y ∣ < 0.5$ ) for various identified particles such as $π^{\pm}$ , $K^{\pm}$ , $K_{S}^{0}$ , $p + p$ , $ϕ$ , $K^{* 0} + K^{* 0}$ , and $Λ$ + $Λ ˉ$ in proton-proton collisions at $s$ = 7 TeV using Boltzmann-Gibbs Blast Wave (BGBW) model and thermodynamically consistent Tsallis distribution function. We obtain the multiplicity dependent kinetic freeze-out temperature ( $T_{kin}$ ) and radial flow ( $β$ ) of various particles after fitting the $p_{T}$ -distribution with BGBW model. Here, $T_{kin}$ exhibits mild dependence on multiplicity class while $β$ shows almost independent behaviour. The information regarding Tsallis temperature and the non-extensivity parameter ( $q$ ) are drawn by fitting the $p_{T}$ -spectra with Tsallis distribution function. The extracted parameters of these particles are studied as a function of charged particle multiplicity density ( $d N_{c h} / d η$ ). In addition to this, we also study these parameters as a function of particle mass to observe any possible mass ordering. All the identified hadrons show a mass ordering in temperature, non-extensive parameter and also a strong dependence on multiplicity classes, except the lighter particles. It is observed that as the particle multiplicity increases, the $q$ -parameter approaches to Boltzmann-Gibbs value, hence a conclusion can be drawn that system tends to thermal equilibrium. The observations are consistent with a differential freeze-out scenario of the produced particles.
↳ hep-phhep-exnucl-exnucl-thEPJA(2019)·48 citations

Affiliations

first authorsco-authorsvia INSPIRE