Nuclear Theory·nucl-th

Wednesday·April 8, 2020

12 papers—8 primary·4 cross-listed

01
Gamow Shell Model description of Li isotopes and their mirror partners
X. Mao · J. Rotureau · W. Nazarewicz · N. Michel · R.M. Id Betan · Y. Jaganathen
Background: Weakly bound and unbound nuclei close to particle drip lines are laboratories of new nuclear structure physics at the extremes of neutron/proton excess. The comprehensive description of these systems requires an open quantum system framework that is capable of treating resonant and nonresonant many-body states on equal footing. Purpose: In this work, we construct the minimal complex-energy configuration interaction approach to describe binding energies and spectra of selected 5 $\leq$ A $\leq$ 11 nuclei. Method: We employ the complex-energy Gamow shell model (GSM) assuming a rigid $^{4}$ He core. The effective Hamiltonian, consisting of a core-nucleon Woods-Saxon potential and a simplified version of the Furutani-Horiuchi-Tamagaki interaction with the mass-dependent scaling, is optimized in the sp space. To diagonalize the Hamiltonian matrix, we employ the Davidson method and the Density Matrix Renormalization Group technique. Results: Our optimized GSM Hamiltonian offers a good reproduction of binding energies and spectra with the root-mean-square (rms) deviation from experiment of 160 keV. Since the model performs well when used to predict known excitations that have not been included in the fit, it can serve as a reliable tool to describe poorly known states. A case in point is our prediction for the pair of unbound mirror nuclei $^{10}$ Li- $^{10}$ N in which a huge Thomas-Ehrman shift dramatically alters the pattern of low-energy excitations. Conclusion: The new model will enable comprehensive studies of structure and reactions aspects of light drip-line nuclei.
nucl-thPRC(2020)·27 citations
02
High-Energy Phase Diagrams with Charge and Isospin Axes under Heavy-Ion Collision and Stellar Conditions
K. Aryal🇺🇸 · C. Constantinou🇺🇸 · R. L. S. Farias🇧🇷 · V. Dexheimer🇺🇸
We investigate the phase transition from hadron to quark matter in the general case without the assumption of chemical equilibrium. The effects of net strangeness on charge and isospin fractions, chemical potentials, and temperature are studied in the context of the Chiral Mean Field (CMF) model that incorporates chiral symmetry restoration and deconfinement. The extent to which these quantities are probed during deconfinement in conditions expected to exist in protoneutron stars, binary neutron-star mergers, and heavy-ion collisions is analyzed via the construction of 3-dimensional phase diagrams.
nucl-thastro-ph.HEastro-ph.SRhep-phPRD(2020)·35 citations
03
Nuclear modification factor in Pb-Pb and p-Pb collisions using Boltzmann transport equation
L. Qiao🇨🇳 · G. Che🇨🇳 · J. Gu🇨🇳 · H. Zheng🇨🇳 · W.C. Zhang🇨🇳
We investigate the nuclear modification factor ( $R_{AA}$ ) of identified particles as a function of transverse momentum ( $p_{T}$ ) in Pb-Pb collisions at $s_{NN} =$ 2.76 and 5.02 TeV, as well as p-Pb collision at 5.02 TeV in the framework of Boltzmann transport equation with relaxation time approximation. In this framework, the initial distribution of particles is chosen as the Tsallis distribution and the local equilibrium distribution as the Boltzmann-Gibbs blast-wave distribution. The non-extensive parameter $q_{pp}$ , the Tsallis temperature $T_{pp}$ and the equilibrium temperature $T_{e q}$ are set to be in common for all particles, while the ratio of kinetic freeze-out time to relaxation time $t_{f} / τ$ is different for different particles when we performed a combined fit to the $R_{AA}$ spectra of different particles at a given centrality. We observe that the fitted curves describe the spectra well up to $p_{T} \approx$ 3 GeV/c. $q_{pp}$ and $T_{e q}$ ( $t_{f} / τ$ ) decrease (increases) with centrality nonlinearly, while $T_{pp}$ is almost independent of centrality. The dependence of the rate at which $q_{pp}$ , $T_{e q}$ or $t_{f} / τ$ changes with centrality on the energy and the size of the colliding system is discussed.
nucl-thJ.Phys.G(2020)·13 citations
04
Temperature fluctuations and Tsallis statistics in Relativistic Heavy Ion collisions
Abhisek Saha🇮🇳 · Soma Sanyal🇮🇳
We study temperature fluctuations in the initial stages of the relativistic heavy ion collision using a multiphase transport model. We consider the plasma in the initial stages after collision before it has a chance to equilibrate. We have considered Au + Au collision with a center of mass energy of 200 GeV. We use the non extensive Tsallis statistics to find the entropic index in the partonic stages of the relativistic heavy ion collisions. We find that the temperature and the entropic index have a linear relationship during the partonic stages of the heavy ion collision. This has already been observed in the hadronic phase. A detailed analysis of the dependence of the entropic index on the system shows that for increasing space time rapidity, the entropic index of the partonic system increases. The entropic index also depends on the beam collision energy. The calculation of the entropic index from the experimental data fitting of the transverse momenta deals with the hadronic phase. However, our current study shows that the behaviour of the entropic index in the initial non-equilibrium stage of the collision is very similar to the behaviour of the entropic index in the hadronic stage.
nucl-thMod.Phys.Lett.A(2021)·5 citations
05
The Non-perturbative Interaction of the Pseudovector Coupling for the Pion-nucleon Scattering
Susumu Kinpara🇯🇵
The effect of the non-perturbative term is investigated for the pion-nucleon scattering. Including the self-energy of nucleon the cross section of the elastic scattering results in a constant value at the laboratory momentum $p_{L} \to \infty$ . The amplitude of the forward direction is applied to the dispersion relation.
nucl-thhep-ph1 citation
06
Tensor and pairing interactions within the QMC energy density functional
Kay Marie L. Martinez🇦🇺 · Anthony William Thomas🇦🇺 · Pierre A. M. Guichon🇫🇷 · Jirina R. Stone🇬🇧
In the latest version of the QMC model, QMC $π$ -III-T, the density functional is improved to include the tensor component quadratic in the spin-current and a pairing interaction derived in the QMC framework. Traditional pairing strengths are expressed in terms of the QMC parameters and the parameters of the model optimised. A variety of nuclear observables are calculated with the final set of parameters. The inclusion of the tensor component improves the predictions for ground-state bulk properties, while it has a small effect on the single-particle spectra. Further, its effect on the deformation of selected nuclei is found to improve the energies of doubly-magic nuclei at sphericity. Changes in the energy curves along the Zr chain with increasing deformation are investigated in detail. The new pairing functional is also applied to the study of neutron shell gaps, where it leads to improved predictions for subshell closures in the superheavy region.
nucl-thPRC(2020)·20 citations
07
Seebeck effect in a thermal QCD medium in the presence of strong magnetic field
Debarshi Dey🇮🇳 · Binoy Krishna Patra🇮🇳
The strongly interacting partonic medium created post ultrarelativistic heavy ion collision experiments exhibits a significant temperature-gradient between the central and peripheral regions of the collisions, which in turn, is capable of inducing an electric field in the medium; a phenomenon known as Seebeck effect. The effect is quantified by the magnitude of the induced electric field per unit temperature-gradient - the Seebeck coefficient ( $S$ ). We study the coefficient, $S$ in the relativistic Boltzmann transport equation in relaxation-time approximation, as a function of temperature ( $T$ ) and chemical potential ( $μ$ ), wherein we find that with current quark masses, the magnitude of $S$ for individual flavours as well as that for the medium as a whole decreases with $T$ and increases with $μ$ , with the electric charge of the flavour deciding the sign of $S$ . The emergence of a strong magnetic field ( $B$ ) in the non-central collisions at heavy-ion collider experiments motivates us to study the effect of $B$ on Seebeck effect. The strong $B$ affects $S$ in multifold ways, via : a) modification of phase-space due to the dimensional reduction, b) dispersion relation in lowest Landau level (occupation probability), and c) relaxation-time. We find that a strong $B$ not only decreases the magnitudes of $S$ 's of individual species, it also flips their signs. This leads to a faster reduction of the magnitude of $S$ of the medium than its counterpart at $B = 0$ . We then explore how the interactions among partons in perturbative thermal QCD in the quasiparticle framework affect Seebeck effect, where we find that even in strong B, there is no more a flip of the sign of $S$ for individual species and an enhancement of the magnitudes of $S$ of individual species as well as that of the medium, compared to current quark mass description at either $B = 0$ or $B \neq = 0$ .
nucl-thcond-mat.mes-hallhep-phPRD(2020)·25 citations
08
Transverse momentum dependent decorrelation in Pb-Pb collisions at LHC
De-Xian Wei🇨🇳
Based on A Multi-Phase Transport (AMPT) model simulations, the transverse momentum dependent decorrelation has been studied in Pb-Pb collisions at $s_{N N}$ = 2.76 and 5.02 TeV, respectively. It has been found that the mix-order factorization ratio $r_{m, n}$ value deviates significantly from unity in noncentral collisions. Such effect becomes stronger with an increase in the $p_{T}$ difference $p_{T}^{a} - p_{T}^{b}$ . These decorrelations are not only between the same order harmonic but also between the different order harmonic, which as a result of the initial fluctuations appear between the different phase spaces. It has also been found that the correlations involving higher powers of the flow vector yield stronger decorrelation, $r_{m ∣ n; 3} < r_{m ∣ n; 2} < r_{m ∣ n; 1} (m = 2, 3; n = 2, 3, 4, 5)$ , except for the weighted factorization ratio $r_{3∣4; k}$ . The breaking phenomenon of these factorization ratios indicated that it provides a possible observation for studying the initial fluctuation properties of heavy-ion collisions.
nucl-thIJMPE(2020)·0 citations
09
Model Independent Extraction of the Proton Charge Radius from PRad data
Gil Paz🇺🇸
The proton radius puzzle has motivated several new experiments that aim to extract the proton charge radius and resolve the puzzle. Recently PRad, a new electron-proton scattering experiment at Jefferson Lab, reported a proton charge radius of $0.831 \pm 0.00 7_{statistical} \pm 0.01 2_{systematic}$ . The value was obtained by using a rational function model for the proton electric form factor. We perform a model-independent extraction using $z$ -expansion of the proton charge radius from PRad data. We find that the model-independent statistical error is more than 50\% larger compared to the statistical error reported by PRad.
↳ hep-phhep-exnucl-exnucl-thMod.Phys.Lett.A(2021)·7 citations
10
Heavy quarkonia in a bulk viscous medium
Lata Thakur🇰🇷 · Najmul Haque🇮🇳 · Yuji Hirono🇰🇷
We study the properties of heavy quarkonia in a quark-gluon plasma in the presence of bulk viscous effects. Within the hard thermal loop approximation at one-loop, the dielectric permittivity of quark-gluon plasma is computed, where the bulk viscous effect enters through the deformation of the distribution functions of thermal quarks and gluons. Based on the modified dielectric permittivity, we compute the in-medium heavy quark potential, that includes non-pertubative string-like terms as well as the perturbative Coulombic term. We discuss how the bulk viscous effect modifies the real and imaginary parts of the in-medium potential. Several prescriptions are examined as to how to include the string-like non-perturbative potentials. Using the deformed potential, we compute the wave functions, binding energies, and decay widths of heavy quarkonia in a bulk viscous medium, and study their sensitivity to the strength of the bulk viscous effect. An estimate of the melting temperatures is given.
↳ hep-phnucl-thJHEP(2020)·31 citations
11
Large-Momentum Effective Theory
Xiangdong Ji🇺🇸 · Yu-Sheng Liu🇨🇳 · Yizhuang Liu🇨🇳 · Jian-Hui Zhang🇨🇳 · Yong Zhao🇺🇸
Since the parton model was introduced by Feynman more than fifty years ago, we have learned much about the partonic structure of the proton through a large body of high-energy experimental data and dedicated global fits. However, calculating the partonic observables such as parton distribution function (PDFs) from the fundamental theory of strong interactions, QCD, has made limited progress. Recently, the authors have advocated a formalism, large-momentum effective theory (LaMET), through which one can extract parton physics from the properties of the proton travelling at a moderate boost-factor, e.g., $γ \sim (2 - 5)$ . The key observation behind this approach is that Lorentz symmetry allows the standard formalism of partons in terms of light-front operators to be replaced by an equivalent one with large-momentum states and time-independent operators of a universality class. With LaMET, the PDFs, generalized PDFs or GPDs, transverse-momentum-dependent PDFs, and light-front wave functions can all be extracted in principle from lattice simulations of QCD (or other non-perturbative methods) through standard effective field theory matching and running. Future lattice QCD calculations with exa-scale computational facilities can help to understand the experimental data related to the hadronic structure, including those from the upcoming Electron-Ion Colliders dedicated to exploring the partonic landscape of the proton. Here we review the progress made in the past few years in development of the LaMET formalism and its applications, particularly on the demonstration of its effectiveness from initial lattice QCD simulations.
↳ hep-phhep-latnucl-thRMP(2021)·382 citations
12
Non-perturbative renormalization scheme for the CP-odd three-gluon operator
Vincenzo Cirigliano🇺🇸 · Emanuele Mereghetti🇺🇸 · Peter Stoffer🇺🇸
We define a regularization-independent momentum-subtraction scheme for the $C P$ -odd three-gluon operator at dimension six. This operator appears in effective field theories for heavy physics beyond the Standard Model, describing the indirect effect of new sources of $C P$ -violation at low energies. In a hadronic context, it induces permanent electric dipole moments. The hadronic matrix elements of the three-gluon operator are non-perturbative objects that should ideally be evaluated with lattice QCD. We define a non-perturbative renormalization scheme that can be implemented on the lattice and we compute the scheme transformation to $MS$ at one loop. Our calculation can be used as an interface to future lattice-QCD calculations of the matrix elements of the three-gluon operator, in order to obtain theoretically robust constraints on physics beyond the Standard Model from measurements of the neutron electric dipole moment.
↳ hep-phhep-exhep-latnucl-thJHEP(2020)·28 citations

Affiliations

first authorsco-authorsvia INSPIRE