Nuclear Theory·nucl-th

Thursday·September 16, 2021

10 papers—7 primary·3 cross-listed

01
Baryon diffusion near the QCD critical point
Lipei Du (Ohio State U.)🇺🇸 · Xin An (North Carolina U.)🇺🇸 · Ulrich Heinz (Ohio State U.)🇺🇸
Fireballs created in relativistic heavy-ion collisions at different beam energies have been argued to follow different trajectories in the QCD phase diagram in which the QCD critical point serves as a landmark. Using a (1+1)-dimensional model setting with transverse homogeneity, we study the complexities introduced by the fact that the evolution history of each fireball cannot be characterized by a single trajectory but rather covers an entire swath of the phase diagram, with the finally emitted hadron spectra integrating over contributions from many different trajectories. Studying the phase diagram trajectories of fluid cells at different space-time rapidities, we explore how baryon diffusion shuffles them around, and how they are affected by critical dynamics near the QCD critical point. We find a striking insensitivity of baryon diffusion to critical effects. Its origins are analyzed and possible implications discussed.
nucl-thhep-phnucl-exPoS(2022)·4 citations
02
From Nuclear to Unnuclear Physics
Thomas Schaefer · Gordon Baym
We provide a brief commentary on recent work by Hammer and Son on the scaling behavior of nuclear reactions involving the emission of several loosely bound neutrons. In this work they discover a regime, termed unnuclear physics, in which these reactions are governed by an approximate conformal symmetry of the nuclear force. Remarkably, the scaling exponents that govern nuclear reactions can be related to the energies of ultracold atomic drops confined in harmonic potentials. We also comment on the importance and the limitations of this approximate symmetry in the physics of neutron stars.
nucl-thcond-mat.quant-gasProc.Nat.Acad.Sci.(2021)·5 citations
03
Pure quantum extension of the semiclassical Boltzmann-Uehling-Uhlenbeck equation
A. Bulgac
The Boltzmann equation is the traditional framework in which one extends the time-dependent mean field classical description of a many-body system to include the effect of particle-particle collisions in an approximate manner. A semiclassical extension of this approach to quantum many body systems was suggested by Uehling and Uhlenbeck in 1933 for both Fermi and Bose statistics, and many further developments of this approach are known as the BoltzmannUehling-Uhlenbeck (BUU) equations. Here I introduce a pure quantum version of the BUU type of equations, which is mathematically equivalent to a generalized Time-Dependent Density Functional Theory extended to superfluid systems. As expected, during non-equilibrium processes the quantum Boltzmann one body entropy increases during evolution.
nucl-thcond-mat.stat-mechPRC(2022)·15 citations
04
Inclusive electron scattering in the quasielastic region with Korea-IBS-Daegu-SKKU density functional
Hana Gil · Chang Ho Hyun · Kyungsik Kim
With the framework of KIDS (Korea-IBS-Daegu-SKKU) density functional model, the isoscalar and isovector effective masses of nucleon and the effect of symmetry energy in nuclear medium are investigated in inclusive $(e, e^{'})$ reaction in quasielastic region. The effective masses are varied in the range $(0.7 \sim 1.0) M$ with free nucleon mass $M$ , and the symmetry energy is varied within the uncertainty allowed by nuclear data and neutron star observation. The wave functions of nucleons inside target nucleus are generated by solving Hartree-Fock equation with adjusting equation of state, binding energy and radius of various stable nuclei, and effective mass of nucleon in the KIDS model. With the obtained wave functions, we calculate the differential cross section for the inclusive $(e, e^{'})$ reaction and compare the theoretical results with Bates, Saclay, and SLAC experimental data. Our model describes experimental data better at SLAC-type high incident electron energy than those measured from Bates and Saclay. The influence of the effective mass and symmetry energy appears to be precise on the longitudinal cross section.
nucl-thnucl-exPRC(2022)·13 citations
05
Nuclear giant quadruple resonance within transport approach and its constraint on nucleon effective mass
Yi-Dan Song · Rui Wang · Zhen Zhang · Yu-Gang Ma
We study the nuclear iso-scalar giant quadruple resonance~(ISGQR) based on the Boltzmann-Uehling-Uhlenbeck~(BUU) transport equation. The mean-field part of the BUU equation is described by the Skyrme nucleon-nucleon effective interaction, and its collision term, which embodies the two-particle-two-hole ( $2$ p- $2$ h) correlation, is implemented through the stochastic approach. We find that the width of ISGQR for heavy nuclei is exhausted dominated by collisional damping, which is incorporated into the BUU equation through its collision term, and it can be well reproduced through employing a proper in-medium nucleon-nucleon cross section. Based on further Vlasov and BUU calculations with a number of representative Skyrme interactions, the iso-scalar nucleon effective mass at saturation density is extracted respectively as $m_{s, 0}^{*} / m$ $=$ $0.83 \pm 0.04$ and $m_{s, 0}^{*} / m$ $=$ $0.82 \pm 0.03$ from the measured excitation energy $E_{x}$ of the ISGQR of $\isotope [208] P b$ . The small discrepancy between the two constraints indicates the negligible role of $2$ p- $2$ h correlation in constraining $m_{s, 0}^{*}$ with the ISGQR excitation energy.
nucl-thnucl-exPRC(2021)·10 citations
06
Systematic study of two-proton radioactivity half-lives within the two-potential approach with Skyrme-Hartree-Fock
Xiao Pan · You Tian Zou · Hong Ming Liu · Biao He · Xiao Hua Li · Xi Jun Wu · Zhen Zhang
In this work, we systematically study the two-proton( $2 p$ ) radioactivity half-lives using the two-potential approach while the nuclear potential is obtained by using Skyrme-Hartree-Fock approach with the Skyrme effective interaction of {SLy8}. For true $2 p$ radioactivity( $Q_{2 p}$ $>$ 0 and $Q_{p}$ $<$ 0, where the $Q_{p}$ and $Q_{2 p}$ are the released energy of the one-proton and two-proton radioactivity), the standard deviation between the experimental half-lives and our theoretical calculations is {0.701}. In addition, we extend this model to predict the half-lives of 15 possible $2 p$ radioactivity candidates with $Q_{2 p}$ $>$ 0 taken from the evaluated atomic mass table AME2016. The calculated results indicate that a clear linear relationship between the logarithmic $2 p$ radioactivity half-lives $log_{10} T_{1/2}$ and coulomb parameters [ ( $Z_{d}^{0.8}$ + $l^{0.25}$ ) $Q_{2 p}^{- 1/2}$ ] considered the effect of orbital angular momentum proposed by Liu $e t$ $a l$ [Chin. Phys. C \textbf{45}, 024108 (2021)] is also existed. For comparison, the generalized liquid drop model(GLDM), the effective liquid drop model(ELDM) and Gamow-like model are also used. Our predicted results are consistent with the ones obtained by the other models.
nucl-thCPC(2021)·12 citations
07
Longitudinal asymmetry in heavy ion collisions at RHIC
Sanchari Thakur🇮🇳 · Sumit Kumar Saha🇮🇳 · Sk Noor Alam🇮🇳 · Rupa Chatterjee🇮🇳 · Subhasis Chattopadhyay🇮🇳
The longitudinal asymmetry arises in relativistic heavy ion collisions due to fluctuation in the number of participating nucleons. This asymmetry causes a shift in the center of mass rapidity of the participant zone. The rapidity shift as well as the longitudinal asymmetry have been found to be significant at the top LHC energy for collisions of identical nuclei. We study the longitudinal asymmetry and its effect on charged particle rapidity distribution and anisotropic flow parameters at relatively lower RHIC energies using a model calculation. The rapidity shift is found to be more pronounced for peripheral collisions, smaller systems and also for lower beam energies due to longitudinal asymmetry. A detailed study has been done by associating the average rapidity shift to a polynomial relation where the coefficients of this polynomial characterize the effect of the asymmetry. We show that the rapidity shift may affect observables significantly at RHIC energies.
nucl-thnucl-exEPJA(2022)·3 citations
08
On the order of the QCD chiral phase transition for different numbers of quark flavours
Francesca Cuteri🇩🇪 · Owe Philipsen🇩🇪 · Alessandro Sciarra🇩🇪
The nature of the QCD chiral phase transition in the limit of vanishing quark masses has remained elusive for a long time, since it cannot be simulated directly on the lattice and is strongly cutoff-dependent. We report on a comprehensive ongoing study using unimproved staggered fermions with $N_{f} \in [2, 8]$ mass-degenerate flavours on $N_{τ} \in {4, 6, 8}$ lattices, in which we locate the chiral critical surface separating regions with first-order transitions from crossover regions in the bare parameter space of the lattice theory. Employing the fact that it terminates in a tricritical line, this surface can be extrapolated to the chiral limit using tricritical scaling with known exponents. Knowing the order of the transitions in the lattice parameter space, conclusions for approaching the continuum chiral limit in the proper order can be drawn. While a narrow first-order region cannot be ruled out, we find initial evidence consistent with a second-order chiral transition in all massless theories with $N_{f} \leq 6$ , and possibly up to the onset of the conformal window at $9 ≲ N_{f}^{*} ≲ 12$ . A reanalysis of already published $O (a)$ -improved $N_{f} = 3$ Wilson data on $N_{τ} \in [4, 12]$ is also consistent with tricritical scaling, and the associated change from first to second-order on the way to the continuum chiral limit. We discuss a modified Columbia plot and a phase diagram for many-flavour QCD that reflect these possible features.
↳ hep-lathep-phnucl-thJHEP(2021)·130 citations
09
First Measurement of the $B (E 2; 3/ 2^{-} \to 1/ 2^{-})$ Transition Strength in $^{7}$ Be: Testing Ab Initio Predictions for $A = 7$ Nuclei
S. L. Henderson · T. Ahn · M. A. Caprio · P. J. Fasano · A. Simon · W. Tan · P. O'Malley · J. Allen · D. W. Bardayan · D. Blankstein · B. Frentz · M. R. Hall and 6 other authors
Electromagnetic observables are able to give insight into collective and emergent features in nuclei, including nuclear clustering. These observables also provide strong constraints for ab initio theory, but comparison of these observables between theory and experiment can be difficult due to the lack of convergence for relevant calculated values, such as $E 2$ transition strengths. By comparing the ratios of $E 2$ transition strengths for mirror transitions, we find that a wide range of ab initio calculations give robust and consistent predictions for this ratio. To experimentally test the validity of these ab initio predictions, we performed a Coulomb excitation experiment to measure the $B (E 2; 3/ 2^{-} \to 1/ 2^{-})$ transition strength in $^{7}$ Be for the first time. A $B (E 2; 3/ 2^{-} \to 1/ 2^{-})$ value of $26 (6) (3) e^{2} fm^{4}$ was deduced from the measured Coulomb excitation cross section. This result is used with the experimentally known $^{7}$ Li $B (E 2; 3/ 2^{-} \to 1/ 2^{-})$ value to provide an experimental ratio to compare with the ab initio predictions. Our experimental value is consistent with the theoretical ratios within $1 σ$ uncertainty, giving experimental support for the value of these ratios. Further work in both theory and experiment can give insight into the robustness of these ratios and their physical meaning.
↳ nucl-exnucl-thPRC(2019)·20 citations
10
Definitive Detection of Orbital Angular Momentum States in Neutrons by Spin-polarized $^{3}$ He
Terrence Jach (National Institute of Standards and Technology)🇺🇸 · John Vinson (National Institute of Standards and Technology)🇺🇸
A standard method to detect thermal neutrons is the nuclear interaction $^{3}$ He(n,p) $^{3}$ H. The spin-dependence of this interaction is also the basis of a neutron spin-polarization filter using nuclear polarized $^{3}$ He. We consider the corresponding interaction for neutrons placed in an intrinsic orbital angular momentum (OAM) state. We derive the relative polarization-dependent absorption cross-sections for neutrons in an $L = 1$ OAM state. The absorption of those neutrons results in compound states $J^{π} = 0^{-}$ , $1^{-}$ , and $2^{-}$ . Varying the three available polarizations tests that an OAM neutron has been absorbed and probes which decay states are physically possible. We describe the energetically likely excited states of $^{4}$ He after absorption, due to the fact that the compound state has odd parity. This provides a definitive method for detecting neutron OAM states and suggests that intrinsic OAM states offer the possibility to observe new physics, including anomalous cross-sections and new channels of radioactive decay.
↳ quant-phnucl-thPRC(2022)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE