Nuclear Theory·nucl-th

Thursday·June 30, 2022

11 papers—5 primary·6 cross-listed

01
Isospin-symmetry implications for nuclear two-body distributions and short-range correlations
R. Weiss🇺🇸 · A. Lovato🇺🇸 · R. B. Wiringa🇺🇸
We study the implications of isospin symmetry in nuclear systems on two-body distributions and derive relations between different densities or momentum distributions of a given nucleus or of different nuclei in the same isospin multiplet. A connection between neutrinoless double beta decay transition of mirror nuclei and two-body densities is also obtained. The relations are numerically verified by means of quantum Monte Carlo calculations. We discuss the relevance of these results to the analysis of nuclear short-range correlations and also show that isospin symmetry allows us to extract information about the spectator nucleons when a short-range correlated pair is formed.
nucl-thnucl-exPRC(2022)·2 citations
02
Microscopic-macroscopic level densities for low excitation energies
A.G. Magner · A.I. Sanzhur · S.N. Fedotkin · A.I. Levon · U.V. Grygoriev · S. Shlomo
Level density $ρ (E, Q)$ is derived within the micro-macroscopic approximation (MMA) for a system of strongly interacting Fermi particles with the energy $E$ and additional integrals of motion $Q$ , in line with several topics of the universal and fruitful activity of A.S. Davydov. Within the extended Thomas Fermi and semiclassical periodic orbit theory beyond the Fermi-gas saddle-point method we obtain $ρ \propto I_{ν} (S) / S^{ν}$ , where $I_{ν} (S)$ is the modified Bessel function of the entropy $S$ . For small shell-structure contribution one finds $ν = κ /2 + 1$ , where $κ$ is the number of additional integrals of motion. This integer number is a dimension of $Q$ , $Q = {N, Z, ...}$ for the case of two-component atomic nuclei, where $N$ and $Z$ are the numbers of neutron and protons, respectively. For much larger shell structure contributions, one obtains, $ν = κ /2 + 2$ . The MMA level density $ρ$ reaches the well-known Fermi gas asymptote for large excitation energies, and the finite micro-canonical combinatoric limit for low excitation energies. The additional integrals of motion can be also the projection of the angular momentum of a nuclear system for nuclear rotations of deformed nuclei, number of excitons for collective dynamics, and so on. Fitting the MMA total level density, $ρ (E, Q)$ , for a set of the integrals of motion $Q = {N, Z}$ , to experimental data on a long nuclear isotope chain for low excitation energies, one obtains the results for the inverse level-density parameter $K$ , which differs significantly from those of neutron resonances, due to shell, isotopic asymmetry, and pairing effects.
nucl-thLow Temp.Phys.(2022)·3 citations
03
Investigating the coalescence-inspired sum rule for light nuclei and hypernuclei in heavy-ion collisions
Ashik Ikbal Sheikh🇺🇸
A data-driven idea is presented to test if light nuclei and hypernuclei obey the coalescence-inspired sum rule, i.e., to test if the flow of a light nucleus or hypernucleus is the summed flow of each of its constituents. Here, the mass difference and charge difference among the constituents of light nuclei and hypernuclei are treated appropriately. The idea is applied to the available data for $s_{N N} = 3$ GeV fixed-target Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC), published by the STAR collaboration. It is found that the sum rule for light nuclei is approximately valid near mid-rapidity ( $- 0.3 < y < 0$ ), but there is a clear violation of the sum rule at large rapidity ( $y < - 0.3$ ). The Jet AA Microscopic Transport Model (JAM), with baryonic mean-field plus nucleon coalescence, generates a similar pattern as obtained from the experimental data. In the present approach, the rapidity dependence of directed flow of the hypernuclei $_{Λ}^{3} H$ and $_{Λ}^{4} H$ is predicted in a model-independent way for $s_{N N} = 3$ GeV Au+Au collisions, which will be explored by ongoing and future measurements from STAR.
nucl-thhep-exhep-phnucl-exPRC(2022)·2 citations
04
Quasi-bound state in the $K ˉ N N N$ system
N.V. Shevchenko🇨🇿
The paper is devoted to the $K ˉ N N N$ system, which is an exotic system consisting of an antikaon and three nucleons. Dynamically exact four-body Faddeev-type equations were solved and characteristics of the quasi-bound state in the system were evaluated. Three antikaon-nucleon and three nucleon-nucleon potentials were used, so the dependence of the four-body pole positions on the two-body interaction models was studied. The resulting binding energies $B_{K^{-} pp n}^{Chiral} \sim 30.5 - 34.5$ MeV obtained with chirally motivated and $B_{K^{-} pp n}^{SIDD} \sim 46.4 - 52.0$ MeV obtained with phenomenological antikaon-nucleon potentials are close to those obtained for the $K^{-} pp$ system with the same $K ˉ N$ and $N N$ potentials, while the four-body widths $Γ_{K^{-} pp n} \sim 38.2 - 50.9$ MeV are smaller.
nucl-thPRC(2022)·6 citations
05
Two-photon exchange in (muonic) deuterium at N3LO in pionless effective field theory
Vadim Lensky (JGU Mainz)🇩🇪 · Franziska Hagelstein (JGU Mainz and PSI Villigen)🇩🇪 · Vladimir Pascalutsa (JGU Mainz)🇩🇪
We present a study of the two-photon-exchange ( $2 γ$ -exchange) corrections to the $S$ -levels in muonic ( $μ$ D) and ordinary (D) deuterium within the pionless effective field theory (pionless EFT). Our calculation proceeds up to next-to-next-to-next-to-leading order (N3LO) in the pionless EFT expansion. The only unknown low-energy constant entering the calculation at this order corresponds to the coupling of a longitudinal photon to the nucleon-nucleon system. To minimise its correlation with the deuteron charge radius, it is extracted using the information about the hydrogen-deuterium isotope shift. We find the elastic $2 γ$ -exchange contribution in $μ$ D larger by several standard deviations than obtained in other recent calculations. This discrepancy ameliorates the mismatch between theory and experiment on the size of $2 γ$ -exchange effects, and is attributed to the properties of the deuteron elastic charge form factor parametrisation used to evaluate the elastic contribution. We identify a correlation between the deuteron charge and Friar radii, which can help one to judge how well a form factor parametrisation describes the low-virtuality properties of the deuteron. We also evaluate the higher-order $2 γ$ -exchange contributions in $μ$ D, generated by the single-nucleon structure and expected to be the most important terms beyond N3LO. The uncertainty of the theoretical result is dominated by the truncation of the pionless EFT series and is quantified using a Bayesian approach. The resulting extractions of the deuteron charge radius from the $μ$ D Lamb shift, the $2 S - 1 S$ transition in D, and the $2 S - 1 S$ hydrogen-deuterium isotope shift, with the respective $2 γ$ -exchange effects evaluated in a unified pionless EFT approach, are in perfect agreement.
nucl-thhep-phnucl-exphysics.atom-phEPJA(2022)·6 citations
06
Towards Powerful Probes of Neutrino Self-Interactions in Supernovae
Po-Wen Chang🇺🇸 · Ivan Esteban🇺🇸 · John F. Beacom🇺🇸 · Todd A. Thompson🇺🇸 · Christopher M. Hirata🇺🇸
Neutrinos remain mysterious. As an example, enhanced self-interactions ( $ν$ SI), which would have broad implications, are allowed. At the high neutrino densities within core-collapse supernovae, $ν$ SI should be important, but robust observables have been lacking. We show that $ν$ SI make neutrinos form a tightly coupled fluid that expands under relativistic hydrodynamics. The outflow becomes either a burst or a steady-state wind; which occurs here is uncertain. Though the diffusive environment where neutrinos are produced may make a wind more likely, further work is needed to determine when each case is realized. In the burst-outflow case, $ν$ SI increase the duration of the neutrino signal, and even a simple analysis of SN 1987A data has powerful sensitivity. For the wind-outflow case, we outline several promising ideas that may lead to new observables. Combined, these results are important steps towards solving the 35-year-old puzzle of how $ν$ SI affect supernovae.
↳ hep-phastro-ph.COastro-ph.HEhep-ex+1PRL(2023)·66 citations
07
Effect of thermal gluon absorption and medium fluctuations on heavy flavour nuclear modification factor at RHIC and LHC energies
Ashik Ikbal Sheikh🇺🇸
The presence of thermal gluons reduces the stimulated gluon emission off a heavy quark propagating in the quark-gluon plasma (QGP) while absorption causes reduction of the radiative energy loss. On the other hand, the chromo-electromagnetic field fluctuations present in the QGP lead to collisional energy gain of the heavy quark. The net effect of the thermal gluon absorption and field fluctuations is a reduction of the total energy loss of the heavy quark, prominent at the lower momenta. We consider both kind of the energy gains along with the usual losses, and compute the nuclear modification factor ( $R_{AA}$ ) of heavy mesons, viz., $D$ and $B$ mesons. The calculations have been compared with the experimental measurements in Au-Au collisions at $s_{N N} = 200$ GeV from STAR and PHENIX experiments at the RHIC and Pb-Pb collisions at $s_{N N} = 2.76$ TeV and $5.02$ TeV from CMS and ALICE experiments at the LHC. We find a significant effect of the total energy gain due to thermal gluon absorption and field fluctuations on heavy flavour suppression, especially at the lower transverse momenta.
↳ hep-phnucl-exnucl-thEPJA(2021)·1 citation
08
Quantum Chromodynamics Resolution of the ATOMKI Anomaly in $^{4} He$ Nuclear Transitions
Valery Kubarovsky🇺🇸 · Jennifer Rittenhouse West🇺🇸 · Stanley J. Brodsky🇺🇸
Observations of anomalous angular correlations in electron-positron pairs produced from excited states of $^{4}$ He, $^{8}$ Be and $^{12}$ C nuclei have been suggested as due to the creation and subsequent decay of a new light particle of mass $\sim$ 17 MeV. In this work, we investigate the possibility that the source of the observed signals is a set of new excitation channels created by the 12-quark hidden-color Fock state within the $^{4} He$ nuclear wavefunction dubbed the ``hexadiquark.'' We calculate the invariant $e^{+} e^{-}$ mass spectrum for the electromagnetic transition from a new excitation of $^{4}$ He, estimating its differential and total decay width. We find that we can fit the shape of the anomalous signal with the QCD Fock state at excitation energy $E^{*} = 17.9 \pm 1$ MeV and a Gaussian form factor for the electromagnetic decay. We address the physical issues with the fit parameters using properties of the hexadiquark state, in particular the three weakly repulsive $6_{C}$ interactions of $SU (3)_{C}$ between diquark pairs. Experimental tests of our model are described in detail. In light of this work, we emphasize the need for independent experimental confirmation or refutation of the ATOMKI results as well as dedicated experiments to search for the proposed new excitations of $^{4} He$ and other $α$ -cluster nuclei.
↳ hep-phnucl-exnucl-thPRC(2025)·16 citations
09
Theoretical study on the contributions of $ω$ meson to the $X (3872) \to J / ψ π^{+} π^{-}$ and $J / ψ π^{+} π^{-} π^{0}$ decays
Hao-Nan Wang🇨🇳 · Qian Wang🇨🇳 · Ju-Jun Xie🇨🇳
With the newly measurements of $X (3872) \to J / ψ π^{+} π^{-}$ from LHCb Collaboration, in addition to the dominant contribution from the $ρ^{0}$ meson, we perform a theoretical study on the contribution of $ω$ meson in the $X (3872) \to J / ψ π^{+} π^{-}$ and $X (3872) \to J / ψ π^{+} π^{-} π^{0}$ processes. It is found that the recent experimental measurements on the $π^{+} π^{-}$ invariant mass distributions can be well reproduced, and the ratio of the couplings between $X (3872) \to J / ψ ρ^{0}$ and $X (3872) \to J / ψ ω$ is also evaluated. Within the parameters extracted from the $π^{+} π^{-}$ invariant mass distributions of the $X (3872) \to J / ψ π^{+} π^{-}$ process, the branching fractions of the $X (3872) \to J / ψ ω$ channel relative to that of the $X (3872) \to J / ψ π^{+} π^{-} π^{0}$ channel and the $π^{+} π^{-} π^{0}$ invariant mass distributions of the $X (3872) \to J / ψ π^{+} π^{-} π^{0}$ decay are calculated, which gives a hint for the further high-statistic experiment.
↳ hep-phhep-exnucl-exnucl-thPRD(2022)·7 citations
10
Spectral and transport properties from lattice QCD
Olaf Kaczmarek🇩🇪 · Hai-Tao Shu🇩🇪
In these lecture notes we will discuss recent progress in extracting spectral and transport properties from lattice QCD. We will focus on results of probes of the thermal QCD medium as well as transport coefficients which are important ingredients for hydrodynamic and transport models that describe the evolution of the produced medium. These include electromagnetic probes, like the rates of emitted photons and dileptons, quarkonium spectral functions as well as transport coefficients like the electrical conductivity or heavy flavor diffusion coefficients of the quark gluon plasma (QGP). All these real time quantities are encoded in the vector meson spectral function. A direct determination of the spectral functions is not possible in Euclidean lattice QCD calculations but they can be analytically continued from imaginary to real time. Therefore it is possible to relate the spectral function to the corresponding Euclidean correlation functions. In the following sections we will discuss the procedure to determine the required correlation functions and the extraction of the spectral functions from lattice QCD correlators. We will illustrate the concepts and methods to obtain spectral functions and related physical observables from continuum extrapolated correlation functions. We will focus here on results obtained from continuum extrapolated lattice correlation functions, which requires large and fine lattices, which so far was only possible in quenched approximation. We will only give a brief introduction to lattice QCD and refer to the textbooks [1,2,3,4] and lecture notes [5] for more detailed introductions to lattice field theory. For the topics addressed in this lecture note we also like to refer to the overview articles on QCD thermodynamics and the QCD phase transition [5,6,7] and quarkonium in extreme conditions [8].
↳ hep-lathep-phnucl-thLect.Notes Phys.(2022)·13 citations
11
The role of electron polarization on nuclear spin diffusion
Alessandro Chessari · Samuel F. Cousin · Sami Jannin · Quentin Stern
Dynamic nuclear polarization (DNP) is capable of boosting signals in nuclear magnetic resonance by orders of magnitude by creating out-of-equilibrium nuclear spin polarization. The diffusion of nuclear spin polarization in the vicinity of paramagnetic dopants is a crucial step for DNP and remains yet not well understood. In this Letter, we show that the polarization of the electron spin controls the rate of proton spin diffusion in a DNP sample at 1.2 K and 7 T; at increasingly high electron polarization, spin diffusion vanishes. We rationalize our results using a 2 nucleus - 1 electron model and Lindblad s Master equation, which generalizes preexisting models in the literature and qualitatively accounts for the experimental observed spin diffusion dynamics.
↳ cond-mat.othernucl-thPRB(2023)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE