Nuclear Theory·nucl-th

Monday·September 6, 2021

8 papers—4 primary·4 cross-listed

01
Dynamics of light hypernuclei in collisions of $^{197}$ Au+ $^{197}$ Au at GeV energies
Zhao-Qing Feng🇨🇳
The dynamics of light hypernuclei and nuclear clusters produced in $^{197}$ Au+ $^{197}$ Au collisions has been investigated thoroughly with a microscopic transport model. All possible channels of hyperon production and transportation of hyperons in nuclear medium are implemented into the model. The light complex fragments are recognized with the Wigner density approach at the stage of freeze out in nuclear collisions. The isospin diffusion in the collisions is responsible for the neutron-rich cluster formation. The collective flows of nuclear clusters are consistent with the experimental data from FOPI collaboration. It is found that the influence of the hyperon-nucleon potential on the free hyperons is negligible, but available for the light hypernuclide formation. The directed and elliptic flows of $_{Λ}^{3}$ H and $_{Λ}^{4}$ H at incident energies of 2, 2.5, 3, 3.5 and 4 GeV/nucleon are investigated thoroughly and manifest the same structure with the nuclear clusters. The hypernuclear yields are produced in a wide rapidity and momentum regime with increasing the beam energy.
nucl-thEPJA(2021)·5 citations
02
Bayesian evaluation of residual production cross sections in proton induced spallation reactions
Peng Dan · Hui-Ling Wei · Xi-Xi Chen · Xiao-Bao Wei · Yu-Ting Wang · Jie Pu · Kai-Xuan Cheng · Chun-Wang Ma
The Bayesian neural network (BNN) method is used to construct a predictive model for fragment prediction of proton induced spallation reactions with the guidance of a simplified EPAX formula. Compared to the experimental data, it is found that the BNN + sEPAX model can reasonably extrapolate with less information compared with BNN method. The BNN + sEPAX method provides a new approach to predict the energy-dependent residual cross sections produced in proton-induced spallation reactions from tens of MeV/u up to several GeV/u.
nucl-thnucl-exJ.Phys.G(2022)·19 citations
03
Diffusion matrix associated with the diffusion processes of multiple conserved charges in a hot and dense hadronic matter
Arpan Das🇵🇱 · Hiranmaya Mishra🇮🇳 · Ranjita K. Mohapatra🇮🇳
Bulk matter produced in heavy ion collisions has multiple conserved quantum numbers like baryon number, strangeness and electric charge. The diffusion process of these charges can be described by a diffusion matrix describing the interdependence of diffusion of different charges. The diffusion coefficient matrix is estimated here from the Boltzmann kinetic theory for the hadronic phase within relaxation time approximation. In the derivation for the same, we impose the Landau-Lifshitz conditions of fit. This leads to e.g. the diagonal diffusion coefficients to be manifestly positive definite. The explicit calculations are performed within the ambit of hadron resonance gas model with and without excluded volume corrections. It is seen that the off-diagonal components can be significant to affect the charge diffusion in a fluid with multiple conserved charges. The excluded volume correction effects is seen to be not significant in the estimation of the elements of the diffusion matrix.
nucl-thhep-phPRD(2022)·17 citations
04
Evidence of quadrupole and octupole deformations in $^{96}$ Zr+ $^{96}$ Zr and $^{96}$ Ru+ $^{96}$ Ru collisions at ultra-relativistic energies
Chunjian Zhang🇺🇸 · Jiangyong Jia🇺🇸
In the hydrodynamic model description of heavy ion collisions, the elliptic flow $v_{2}$ and triangular flow $v_{3}$ are sensitive to the quadrupole deformation $β_{2}$ and octupole deformation $β_{3}$ of the colliding nuclei. The relations between $v_{n}$ and $β_{n}$ have recently been clarified and were found to follow a simple parametric form. The STAR Collaboration have just published precision $v_{n}$ data from isobaric $^{96}$ Ru+ $^{96}$ Ru and $^{96}$ Zr+ $^{96}$ Zr collisions, where they observe large differences in central collisions $v_{2, Ru} > v_{2, Zr}$ and $v_{3, Ru} < v_{3, Zr}$ . Using a transport model simulation, we show that these orderings are a natural consequence of $β_{2, Ru} ≫ β_{2, Zr}$ and $β_{3, Ru} ≪ β_{3, Zr}$ . We reproduce the centrality dependence of the $v_{2}$ ratio qualitatively and $v_{3}$ ratio quantitatively, and extract values of $β_{2}$ and $β_{3}$ that are consistent with those measured at low energy nuclear structure experiments. STAR data provide the first direct evidence of strong octupole correlations in the ground state of $^{96}$ Zr in heavy ion collisions. Our analysis demonstrates that flow measurements in high-energy heavy ion collisions, especially using isobaric systems, are a new precision tool to study nuclear structure physics.
nucl-thhep-phnucl-exPRL(2022)·160 citations
05
Bayesian Monte Carlo extraction of sea asymmetry with SeaQuest and STAR data
C. Cocuzza🇺🇸 · W. Melnitchouk🇺🇸 · A. Metz🇺🇸 · N. Sato🇺🇸
We perform a global QCD analysis of unpolarized parton distributions within a Bayesian Monte Carlo framework, including the new $W$ -lepton production data from the STAR Collaboration at RHIC and Drell-Yan di-muon data from the SeaQuest experiment at Fermilab. We assess the impact of these two new measurements on the light antiquark sea in the proton, and the $d ˉ - u ˉ$ asymmetry in particular. The SeaQuest data are found to significantly reduce the uncertainty on the $d ˉ / u ˉ$ ratio at large parton momentum fractions $x$ , strongly favoring an enhanced $d ˉ$ sea up to $x \approx 0.4$ , in general agreement with nonperturbative calculations based on chiral symmetry breaking in QCD.
↳ hep-phhep-exnucl-thPRD(2021)·50 citations
06
Revisit the isospin violating decays of $X (3872)$
Lu Meng🇩🇪 · Guang-Juan Wang🇯🇵 · Bo Wang🇨🇳 · Shi-Lin Zhu🇨🇳
In this work, we revisit the isospin violating decays of $X (3872)$ in a coupled-channel effective field theory. In the molecular scheme, the $X (3872)$ is interpreted as the bound state of $D ˉ^{* 0} D^{0} / D ˉ^{0} D^{* 0}$ and $D^{*-} D^{+} / D^{-} D^{*+}$ channels. In a cutoff-independent formalism, we relate the coupling constants of $X (3872)$ with the two channels to the molecular wave function. The isospin violating decays of $X (3872)$ are obtained by two equivalent approaches, which amend some deficiencies about this issue in literature. In the quantum field theory approach, the isospin violating decays arise from the coupling constants of $X (3872)$ to two di-meson channels. In the quantum mechanics approach, the isospin violating is attributed to wave functions at the origin. We illustrate that how to cure the insufficient results in literature. Within the comprehensive analysis, we bridge the isospin violating decays of $X (3872)$ to its inner structure. Our results show that the proportion of the neutral channel in $X (3872)$ is over $80%$ . As a by-product, we calculate the strong decay width of $X (3872) \to D ˉ^{0} D^{0} π^{0}$ and radiative one $X (3872) \to D ˉ^{0} D^{0} γ$ . The strong decay width and radiative decay width are about 30 keV and 10 keV, respectively, for the binding energy from $- 300$ keV to $- 50$ keV.
↳ hep-phhep-exhep-latnucl-thPRD(2021)·36 citations
07
The QCD Equation of State in Small Systems
W. A. Horowitz🇿🇦 · Alexander Rothkopf🇳🇴
We present first results on finite system size corrections to the equation of state, trace anomaly, and speed of sound for two model systems: 1) free, massless scalar theory and 2) quenched QCD with periodic boundary conditions (PBC). We further present work-in-progress results for quenched QCD with Dirichlet boundary conditions.
↳ hep-phhep-latnucl-thSciPost Phys.Proc.(2022)·12 citations
08
Do Minimal Parity Solutions to the Strong CP Problem Work?
Jordy de Vries🇳🇱 · Patrick Draper🇺🇸 · Hiren H. Patel🇺🇸
One class of solutions to the strong CP problem relies on generalized parity symmetries. A minimal model of this type, constructed by Babu and Mohapatra and based on a softly broken parity symmetry, has the remarkable property that effective QCD vacuum angle $θ ˉ$ vanishes up to one-loop order. We compute the leading two-loop contributions to $θ ˉ$ in this model and estimate subleading contributions. In contrast to previous estimates, we argue that $θ ˉ$ is not suppressed by the weak scale, and we find contributions of order $1 0^{- 3}$ - $1 0^{- 2}$ multiplying unknown mixing angles and phases. Thus the model does not generically address the strong CP problem, but it might be made consistent with $θ ˉ < 1 0^{- 10}$ in some corners of parameter space. For such non-generic parameters, $θ ˉ$ is still likely to be just below present bounds, and therefore provides the dominant source of hadronic EDMs. We discuss the resulting EDM phenomenology.
↳ hep-phnucl-th39 citations

Affiliations

first authorsco-authorsvia INSPIRE