Nuclear Theory·nucl-th

Tuesday·May 5, 2020

12 papers—2 primary·10 cross-listed

01
Second virial coefficients of light nuclear clusters and their chemical freeze-out in nuclear collisions
K. A. Bugaev🇺🇦 · O. V. Vitiuk🇺🇦 · B. E. Grinyuk🇺🇦 · V. V. Sagun🇺🇦 · N. S. Yakovenko🇺🇦 · O. I. Ivanytskyi🇺🇦 · G. M. Zinovjev🇺🇦 · D. B. Blaschke🇵🇱 · E. G. Nikonov🇷🇺 · L. V. Bravina🇳🇴 · E. E. Zabrodin🇳🇴 · S. Kabana🇨🇱 and 4 other authors
Here we develop a new strategy to analyze the chemical freeze-out of light (anti)nuclei produced in high energy collisions of heavy atomic nuclei within an advanced version of the hadron resonance gas model. It is based on two different, but complementary approaches to model the hard-core repulsion between the light nuclei and hadrons. The first approach is based on an approximate treatment of the equivalent hard-core radius of a roomy nuclear cluster and pions, while the second approach is rigorously derived here using a self-consistent treatment of classical excluded volumes of light (anti)nuclei and hadrons. By construction, in a hadronic medium dominated by pions, both approaches should give the same results. Employing this strategy to the analysis of hadronic and light (anti)nuclei multiplicities measured by ALICE at $s_{N N} = 2.76$ TeV and by STAR at $s_{N N} = 200$ GeV, we got rid of the existing ambiguity in the description of light (anti)nuclei data and determined the chemical freeze-out parameters of nuclei with high accuracy and confidence. At ALICE energy the nuclei are frozen prior to the hadrons at the temperature $T = 175. 1_{- 3.9}^{+ 2.3}$ MeV, while at STAR energy there is a single freeze-out of hadrons and nuclei at the temperature $T = 167.2 \pm 3.9$ MeV. We argue that the found chemical freeze-out volumes of nuclei can be considered as the volumes of quark-gluon bags that produce the nuclei at the moment of hadronization.
nucl-thhep-phEPJA(2020)·19 citations
02
Extracing the number of short-range corerlated nucleon pairs from inclusive electron scattering data
R. Weiss🇮🇱 · A.W. Denniston🇺🇸 · J.R. Pybus🇺🇸 · O. Hen🇺🇸 · E. Piasetzky🇮🇱 · A. Schmidt🇺🇸 · L.B. Weinstein🇺🇸 · N. Barnea🇮🇱
The extraction of the relative abundances of short-range correlated (SRC) nucleon pairs from inclusive electron scattering is studied using the generalized contact formalism (GCF) with several nuclear interaction models. GCF calculations can reproduce the observed scaling of the cross-section ratios for nuclei relative to deuterium at high- $x_{B}$ and large- $Q^{2}$ , $a_{2} = (σ_{A} / A) / (σ_{d} /2)$ . In the non-relativistic instant-form formulation, the calculation is very sensitive to the model parameters and only reproduces the data using parameters that are inconsistent with ab-initio many-body calculations. Using a light-cone GCF formulation significantly decreases this sensitivity and improves the agreement with ab-initio calculations. The ratio of similar mass isotopes, such as $^{40}$ Ca and $^{48}$ Ca, should be sensitive to the nuclear asymmetry dependence of SRCs, but is found to also be sensitive to low-energy nuclear structure. Thus the empirical association of SRC pair abundances with the measured $a_{2}$ values is only accurate to about $20%$ . Improving this will require cross-section calculations that reproduce the data while properly accounting for both nuclear structure and relativistic effects.
nucl-thnucl-exPRC(2021)·33 citations
03
Effect of magnetic field on the charge and thermal transport properties of hot and dense QCD matter
Shubhalaxmi Rath🇮🇳 · Binoy Krishna Patra🇮🇳
We have studied the effect of strong magnetic field on the charge and thermal transport properties of hot QCD matter at finite chemical potential. For this purpose, we have calculated the electrical ( $σ_{el}$ ) and thermal ( $κ$ ) conductivities using kinetic theory in the relaxation time approximation, where the interactions are subsumed through the distribution functions within the quasiparticle model at finite temperature, strong magnetic field and finite chemical potential. This study helps to understand the impacts of strong magnetic field and chemical potential on the local equilibrium by the Knudsen number ( $Ω$ ) through $κ$ and on the relative behavior between thermal conductivity and electrical conductivity through the Lorenz number ( $L$ ) in the Wiedemann-Franz law. We have observed that, both $σ_{el}$ and $κ$ get increased in the presence of strong magnetic field, and the additional presence of chemical potential further increases their magnitudes, where $σ_{el}$ shows decreasing trend with the temperature, opposite to its increasing behavior in the isotropic medium, whereas $κ$ increases slowly with the temperature, contrary to its fast increase in the isotropic medium. The variation in $κ$ explains the decrease of the Knudsen number with the increase of the temperature. However, in the presence of strong magnetic field and finite chemical potential, $Ω$ gets enhanced and approaches unity, thus, the system may move slightly away from the equilibrium state. The Lorenz number ( $κ / (σ_{el} T))$ in the abovementioned regime of strong magnetic field and finite chemical potential shows linear enhancement with the temperature and has smaller magnitude than the isotropic one, thus, it describes the violation of the Wiedemann-Franz law for the hot and dense QCD matter in the presence of a strong magnetic field.
↳ hep-phhep-thnucl-thEPJC(2020)·27 citations
04
Medium modifications of girth distributions for inclusive jets and $Z^{0} + jet$ in relativistic heavy-ion collisions at the LHC
Jun Yan🇨🇳 · Shi-Yong Chen🇨🇳 · Wei Dai🇨🇳 · Ben-Wei Zhang🇨🇳 · Enke Wang🇨🇳
In this paper we investigate the medium modifications of girth distributions for inclusive jets and $Z^{0}$ tagged jets with small radius ( $R = 0.2$ ) in Pb+Pb collisions with $s = 2.76$ TeV at the LHC. The partonic spectrum in the initial hard scattering of elementary collisions are obtained by a event generator POWHEG+PYTHIA, which matches the next-to-leading (NLO) matrix elements with parton showering, and energy loss of faster parton traversing in hot/dense QCD medium is calculated by Monte Carlo simulation within Higher-Twist formalism of jet quenching in heavy-ion collisions. We present the model calculations of event normalized girth distributions for inclusive jets in p+p and Pb+Pb collisions at $s = 2.76$ TeV, which give nice descriptions of ALICE measurements. It is shown that the girth distributions of inclusive jets in Pb+Pb are shifted to lower girth region relative to that in p+p. Thus the nuclear modification factor of girth distributions for inclusive jets is larger than unity at small girth region, while smaller than one at large girth region. This behavior results from more soft fragments inside a jet as well as the fraction alteration of gluon/quark initiated jets in heavy-ion collisions. We further predict the girth distributions for $Z^{0}$ boson tagged jets in Pb+Pb collisions at $s = 2.76$ TeV, and demonstrate that the medium modification on girth distributions for $Z^{0}$ tagged jets is less pronounced as compared to that for inclusive jets because the dominant components of $Z^{0}$ tagged jets are quark-initiated jets.
↳ hep-phnucl-thCPC(2021)·22 citations
05
Probing nucleon strange and charm distributions with lattice QCD
Rui Zhang🇺🇸 · Huey-Wen Lin🇺🇸 · Boram Yoon🇺🇸
We present the first lattice-QCD calculation of the unpolarized strange and charm parton distribution functions using large-momentum effective theory (LaMET). We use a lattice ensemble with 2+1+1 flavors of highly improved staggered quarks (HISQ) generated by MILC collaboration, with lattice spacing $a \approx 0.12$ fm and $M_{π} \approx 310$ MeV, and clover valence fermions with two valence pion masses: 310 and 690 MeV. We use momentum-smeared sources to improve the signal up to nucleon boost momentum $P_{z} = 2.18$ GeV, and determine nonperturbative renormalization factors in RI/MOM scheme. We compare our lattice results with the matrix elements obtained from matching the PDFs from CT18NNLO and NNPDF3.1NNLO global fits. Our data support the assumptions of strange-antistrange and charm-anticharm symmetry that are commonly used in global PDF fits, and we find smaller than expected parton distribution at mid to small $x$ .
↳ hep-lathep-phnucl-thPRD(2021)·48 citations
06
Tritonlike molecules of three identical baryons
Li Ma🇨🇳
In nuclear physics, triton and helium-3 nucleus can be understood as three-body hadronic molecules. Analogous to the loosely bound structures for the triton and helium-3 nucleus, whether there is a bound state formed by three hadrons leaves us an open issue. Based on the one-boson exchange model as well as the adoption of the variational approach, we make a comprehensive investigation on the tritonlike systems of three identical baryons $N N N$ , $ΛΛΛ$ , $ΞΞΞ$ and $ΣΣΣ$ . We predict that the three-body molecular states for the systems of three identical hadrons of baryon octet are probably existent as long as their two-body subsystems have bound states. The numerical results of this work may be helpful for the theoretical and experimental researches on the tri-hadron molecules in future.
↳ hep-phnucl-thAdv.High Energy Phys.(2022)·0 citations
07
Covariant kinetic theory and transport coefficients for Gribov plasma
Amaresh Jaiswal🇮🇳 · Najmul Haque🇮🇳
Gribov quantization is a method to improve the infrared dynamics of Yang-Mills theory. We study the thermodynamics and transport properties of a plasma consisting of gluons whose propagator is improved by the Gribov prescription. We first construct thermodynamics of Gribov plasma using the gauge invariant Gribov dispersion relation for interacting gluons. When the Gribov parameter in the dispersion relation is temperature dependent, one expects a mean field correction to the Boltzmann equation. We formulate covariant kinetic theory for the Gribov plasma and determine the mean-field contribution in the Boltzmann equation. This leads to a quasiparticle like framework with a bag correction to pressure and energy density which mimics confinement. The temperature dependence of the Gribov parameter and bag pressure is fixed by matching with lattice results for a system of gluons. Finally we calculate the temperature dependence of the transport coefficients, i.e., bulk and shear viscosities.
↳ hep-phhep-thnucl-thPLB(2020)·28 citations
08
An Improved Hadronic Model for Pion Electroproduction
Robert J. Perry🇹🇼 · Ayse Kızılersu🇦🇺 · Anthony W. Thomas🇦🇺
Current measurements of the high energy behavior of the pion form factor are obtained from pion electroproduction data. These values are model dependent, utilizing the Vanderhaeghen, Guidal and Laget Regge (VGL) Model for their extraction. Recent work which examined the implementation of gauge invariance in that model suggested that it might lead to extracted pion form factors larger than the true values. Here we introduce a new model which preserves the successes of the VGL Model but implements gauge invariance in a new way. To demonstrate the validity of this new approach, we first use it to extract the pion form factor in a simple toy model. When compared with the previous extraction method, the improved model leads to a more reliable extraction. The success in this simple model leads us to reanalyse the electroproduction cross section data, where we obtain comparable values for the pion form factor to those obtained using the VGL procedure.
↳ hep-phhep-latnucl-thPLB(2020)·5 citations
09
Few-body bound states and resonances in finite volume
Sebastian König🇩🇪
Since the pioneering work of Lüscher in the 1980s it is well known that considering quantum systems in finite volume, specifically, finite periodic boxes, can be used as a powerful computational tool to extract physical observables. While this formalism has been worked out in great detail in the two-body sector, much effort is currently being invested into deriving analogous relations for systems with more constituents. This work is relevant not only for nuclear physics, where lattice methods are now able to calculate few- and many-nucleon states, but also for other fields such as simulations of cold atoms. This article discusses recent progress regarding the extraction of few-body bound-state and resonance properties from finite-volume calculations of systems with an arbitrary number of constituents.
↳ hep-latnucl-thFew Body Syst.(2020)·24 citations
10
Generating spin polarization from vorticity through nonlocal collisions
Nora Weickgenannt🇩🇪 · Enrico Speranza🇩🇪 · Xin-li Sheng🇨🇳 · Qun Wang🇨🇳 · Dirk H. Rischke🇩🇪
We derive the collision term in the Boltzmann equation using the equation of motion for the Wigner function of massive spin-1/2 particles. To next-to-lowest order in $ℏ$ it contains a nonlocal contribution, which is responsible for the conversion of orbital into spin angular momentum. In a proper choice of pseudo-gauge the antisymmetric part of the energy-momentum tensor arises solely from this nonlocal contribution. We show that the collision term vanishes only in global equilibrium and that the spin potential is then equal to the thermal vorticity. In the nonrelativistic limit, the equations of motion for the energy-momentum and spin tensors reduce to the well-known form for hydrodynamics for micropolar fluids.
↳ hep-phnucl-thPRL(2021)·214 citations
11
The X(3872) as a mass distribution
E. Ruiz Arriola🇪🇸 · P. Garcia Ortega🇪🇸
All existing experimental evidence of the bound state nature of the X(3872) relies on considering its decay products with a finite experimental spectral mass resolution which is typically $Δ m \geq 2$ MeV and much larger than its alleged binding energy, $B_{X} = 0.00 (18)$ MeV. On the other hand, there is a neat cancellation in the $1^{++}$ channel for the invariant $D D ˉ^{*}$ mass around the threshold between the continuum and bound state contribution. We discuss the impact of this effect for X(3872) at finite temperature, in prompt production in pp collisions data with a finite $p_{T}$ or the lineshapes of specific production experiments of exotic states involving triangle singularities
↳ hep-phnucl-thActa Phys.Polon.Supp.(2021)·2 citations
12
Exclusive tensor meson photoproduction
JPAC Collaboration: V. Mathieu🇪🇸 · A. Pilloni🇮🇹 · M. Albaladejo🇺🇸 · L. Bibrzycki🇺🇸 · A. Celentano🇮🇹 · C. Fernandez-Ramirez🇲🇽 · A.P. Szczepaniak🇺🇸
We study tensor meson photoproduction outside of the resonance region, at beam energies of few GeVs. We build a model based on Regge theory that includes the leading vector and axial exchanges. We consider two determinations of the unknown helicity couplings, and fit to the recent a2 photoproduction data from CLAS. Both choices give a similar description of the a2 cross section, but result in different predictions for the parity asymmetries and the f2 photoproduction cross section. We conclude that new measurements of f2 photoproduction in the forward region are needed to pin down the correct production mechanism. We also extend our predictions to the 8.5 GeV beam energy, where current experiments are running.
↳ hep-phnucl-exnucl-thPRD(2020)·28 citations

Affiliations

first authorsco-authorsvia INSPIRE