Nuclear Theory·nucl-th

Wednesday·June 30, 2021

10 papers—6 primary·4 cross-listed

01
Solving the puzzle of nuclear stopping power
Marek Jeżabek🇵🇱 · Andrzej Rybicki🇵🇱
This paper reviews our recent findings on the dynamics of transport of baryon number in proton-induced reactions at the CERN SPS. These are put in a more general context of the present understanding of baryon stopping phenomena up to LHC and cosmic ray energies. The implications of our studies, advantages to be provided by modern and high quality experimental data, and perspectives of new measurements are shortly discussed.
nucl-thhep-phActa Phys.Polon.B(2021)·4 citations
02
Ground-state properties of light $4 n$ self-conjugate nuclei in $ab$ $ini t i o$ no-core Monte Carlo shell model calculations with nonlocal $N N$ interactions
T. Abe · P. Maris · T. Otsuka · N. Shimizu · Y. Utsuno · J. P. Vary
We report $J^{π} = 0^{+}$ ground-state energies and point-proton radii of $^{4}$ He, $^{8}$ Be, $^{12}$ C, $^{16}$ O and $^{20}$ Ne nuclei calculated by the $ab$ $ini t i o$ no-core Monte Carlo shell model with the JISP16 and Daejeon16 nonlocal $N N$ interactions. Ground-state energies are obtained in the basis spaces up to seven oscillator shells ( $N_{shell} = 7$ ) with several oscillator energies ( $ℏ ω$ ) around the optimal oscillator energy for the convergence of ground-state energies. These energy eigenvalues are extrapolated to obtain estimates of converged ground state energies in each basis space using energy variances of computed energy eigenvalues. We further extrapolate these energy-variance-extrapolated energies obtained in the finite basis spaces to infinite basis-space results with an empirical exponential form. This form features a dependence on the basis-space size but is independent of the value of $ℏ ω$ used for the harmonic-oscillator basis functions. Point-proton radii for these states of atomic nuclei are also calculated following techniques employed for the energies. From these results, it is found that the Daejeon16 $N N$ interaction provides good agreement with experimental data up to approximately $^{16}$ O, while the JISP16 $N N$ interaction provides good agreement with experimental data up to approximately $^{12}$ C. Beyond these nuclei, the interactions produce overbinding accompanied by radii that are too small. These findings suggest and encourage further revisions of nonlocal $N N$ interactions towards the investigation of nuclear structure in heavier-mass regions.
nucl-thPRC(2021)·16 citations
03
Model selection for $K^{+} Σ^{-}$ photoproduction within isobar model
Petr Bydžovský🇨🇿 · Aleš Cieplý🇨🇿 · Dimitrios Petrellis🇨🇿 · Dalibor Skoupil🇨🇿 · Nicholas Zachariou🇬🇧
We utilise an isobar model to investigate the $K^{+} Σ^{-}$ photoproduction off a neutron in the resonance region. Except for the Born terms, we include high-spin (spin-3/2 and spin-5/2) nucleon resonances in the consistent formalism together with a few $Δ$ and kaon resonances to achieve an acceptable agreement with data. Interestingly, we reveal that no hyperon resonances are needed to achieve a reasonable description of data. On the other hand the $N (1720) 3/ 2^{+}$ resonance was found to be very important for correct description of data. The free parameters of the model were fitted to experimental data from the LEPS and CLAS Collaborations on either differential cross sections or photon beam asymmetry. The novel feature of the fitting procedure is the use of a regularization method, the Least Absolute Shrinkage Selection Operator, and information criteria in order to choose the best fit.
nucl-thPRC(2021)·16 citations
04
Negative R-parity scissors modes in the Two-Rotors Model
Fabrizio Palumbo
In a previous work I constructed R-negative scissors states in the Two-Rotors Model in which the rotors are two-sided classical bodies. Such states have |K| = 1; 0 components and negative space parity. Here I extend this work including reflections in a plane through the rotors symmetry axes obtaining also R-negative states of positive parity. I then associate reflections and R-operations with corresponding operations on internal noncollective variables of the rotors. I evaluate the em transition strengths of these states and compare them with the corresponding strengths of R-positive scissors modes.
nucl-th0 citations
05
Questioning the wobbling interpretation of low-spin bands in $γ$ -soft nuclei within the interacting boson-fermion model
K. Nomura🇭🇷 · C. M. Petrache🇫🇷
An alternative interpretation of the recently reported low-lying excited bands in $γ$ -soft odd-mass nuclei as wobbling bands is presented in terms of the interacting boson-fermion model. The model Hamiltonian is determined based on the mean-field calculations with the nuclear energy density functionals. The predicted mixing ratios of the $Δ I = 1$ electric quadrupole to magnetic dipole transition rates between yrast bands and those yrare bands previously interpreted as wobbling bands in $^{135}$ Pr, $^{133}$ La, $^{127}$ Xe, and $^{105}$ Pd are consistently smaller in magnitude than the experimental values on which the wobbling interpretation is based. These calculated mixing ratios indicate predominant magnetic character in agreement with the new experimental data. The earlier wobbling assignments are severely questioned.
nucl-thnucl-exPRC(2022)·17 citations
06
Fast & accurate emulation of two-body scattering observables without wave functions
J. A. Melendez🇺🇸 · C. Drischler🇺🇸 · A. J. Garcia🇺🇸 · R. J. Furnstahl🇺🇸 · Xilin Zhang🇺🇸
We combine Newton's variational method with ideas from eigenvector continuation to construct a fast & accurate emulator for two-body scattering observables. The emulator will facilitate the application of rigorous statistical methods for interactions that depend smoothly on a set of free parameters. Our approach begins with a trial $K$ or $T$ matrix constructed from a small number of exact solutions to the Lippmann--Schwinger equation. Subsequent emulation only requires operations on small matrices. We provide several applications to short-range potentials with and without the Coulomb interaction and partial-wave coupling. It is shown that the emulator can accurately extrapolate far from the support of the training data. When used to emulate the neutron-proton cross section with a modern chiral interaction as a function of 26 free parameters, it reproduces the exact calculation with negligible error and provides an over 300x improvement in CPU time.
nucl-thcond-mat.mtrl-scihep-lathep-ph+1PLB(2021)·54 citations
07
Angularity in DIS at next-to-next-to-leading log accuracy
Jiawei Zhu🇨🇳 · Daekyoung Kang🇨🇳 · Tanmay Maji🇨🇳
Angularity is a class of event-shape observables that can be measured in deep-inelastic scattering. With its continuous parameter $a$ one can interpolate angularity between thrust and broadening and further access beyond the region. Providing such systematic way to access various observables makes angularity attractive in analysis with event shapes. We give the definition of angularity for DIS and factorize the cross-section by using soft-collinear effective theory. The factorization is valid in a wide range of $a$ below and above thrust region but invalid in broadening limit. It contains an angularity beam function, which is new result and we give the expression at $O (\as)$ . We also perform large log resummation of angularity and make predictions at various values of $a$ at next-to-next-to-leading log accuracy.
↳ hep-phnucl-thJHEP(2021)·16 citations
08
Porter-Thomas fluctuations in complex quantum systems
K. Hagino🇯🇵 · G.F. Bertsch🇺🇸
The Gaussian Orthogonal Ensemble (GOE) of random matrices has been widely employed to describe diverse phenomena in strongly coupled quantum systems. An important prediction is that the decay rates of the GOE eigenstates fluctuate according to the distribution for one degree of freedom, as derived by Brink and by Porter and Thomas. However, we find that the coupling to the decay channels can change the effective number of degrees of freedom from $ν = 1$ to $ν = 2$ . Our conclusions are based on a configuration-interaction Hamiltonian originally constructed to test the validity of transition-state theory, also known as Rice-Ramsperger-Kassel-Marcus (RRKM) theory in chemistry. The internal Hamiltonian consists of two sets of GOE reservoirs connected by an internal channel. We find that the effective number of degrees of freedom $ν$ can vary from one to two depending on the control parameter $ρ Γ$ , where $ρ$ is the level density in the first reservoir and $Γ$ is the level decay width. The $ν = 2$ distribution is a well-known property of the Gaussian Unitary ensemble (GUE); our model demonstrates that the GUE fluctuations can be present under much milder conditions. Our treatment of the model permits an analytic derivation for $ρ Γ ≳ 1$ .
↳ quant-phnucl-thphysics.chem-phPRE(2021)·10 citations
09
Phenomenological study of quarkonium suppression and the impact of the energy gap between singlets and octets
Jean-Paul Blaizot🇫🇷 · Miguel Ángel Escobedo🇪🇸
The study of heavy quarkonium suppression in heavy-ion collisions represents an important source of information about the properties of the quark-gluon plasma produced in such collisions. In a previous paper, we have considered how to model the evolution of a quarkonium in such a way that the solution of the resulting equations evolves toward the correct thermal equilibrium distribution for an homogeneous and static medium. We found that it is crucial to take into account the energy gap between singlet and octet configurations when the temperature is not much greater than this energy gap. In this manuscript, we explore in more detail the phenomenological consequences of this observation in the more realistic situation of an expanding system. We consider two different scenarios, based on the same approximation scheme, but on different choices of parameters. In the first case, we rely on a Hard Thermal Loop approximation, while the second case is based on a recent determination of the static potential in lattice QCD. In both cases, we compute the decay width and the nuclear modification factor, both taking the energy gap into account and ignoring it. We find that the impact on the predictions is as large in the expanding medium as it is in the static case. Our conclusion is that this energy gap should be taken into account in phenomenological studies.
↳ hep-phnucl-thPRD(2021)·27 citations
10
Two- and three-particle nonflow contributions to the chiral magnetic effect measurement by spectator and participant planes in relativistic heavy ion collisions
Yicheng Feng🇺🇸 · Jie Zhao🇺🇸 · Hanlin Li🇨🇳 · Hao-jie Xu🇨🇳 · Fuqiang Wang🇺🇸
Correlation measurements with respect to the spectator and participant planes in relativistic heavy ion collisions were proposed to extract the chiral magnetic effect (CME) from background dominated azimuthal correlators. This paper investigates the effects of two- and three-particle nonflow correlations on the extracted CME signal fraction, $f_{CME}$ . It is found, guided by a multiphase transport (AMPT) model and the heavy ion jet interaction generator (HIJING) together with experimental data, that the nonflow effects amount to approximately $(4 \pm 5)$ % and $(- 5 \pm 3)$ % without and with pseudorapidity gaps, respectively, in 20-50% centrality Au+Au collisions at $s_{NN} = 200 GeV$ .
↳ nucl-exnucl-thPRC(2022)·33 citations

Affiliations

first authorsco-authorsvia INSPIRE