Nuclear Theory·nucl-th

Friday·May 1, 2020

13 papers—7 primary·6 cross-listed

01
Classification of Equation of State in Relativistic Heavy-Ion Collisions Using Deep Learning
Yu. Kvasiuk🇳🇴 · E. Zabrodin🇳🇴 · L. Bravina🇳🇴 · I. Didur🇺🇦 · M. Frolov🇺🇦
Convolutional Neural Nets, which is a powerful method of Deep Learning, is applied to classify equation of state of heavy-ion collision event generated within the UrQMD model. Event-by-event transverse momentum and azimuthal angle distributions of protons are used to train a classifier. An overall accuracy of classification of 98\% is reached for Au+Au events at $s_{N N} = 11$ GeV. Performance of classifiers, trained on events at different colliding energies, is investigated. Obtained results indicate extensive possibilities of application of Deep Learning methods to other problems in physics of heavy-ion collisions.
nucl-thcs.LGhep-phnucl-exJHEP(2020)·12 citations
02
Constraining the quadrupole deformation of atomic nuclei with relativistic nuclear collisions
Giuliano Giacalone🇫🇷
Preliminary data by the STAR collaboration at the BNL Relativistic Heavy Ion Collider shows that the elliptic flow, $v_{2}$ , and the average transverse momentum, $⟨ p_{t} ⟩$ , of final-state hadrons produced in high-multiplicity $^{238}$ U+ $^{238}$ U collisions are negatively correlated. This observation brings experimental evidence of a significant prolate deformation, $β \approx 0.3$ , in the colliding $^{238}$ U nuclei. I show that a quantitative description of this new phenomenon can be achieved within the hydrodynamic framework of heavy-ion collisions, and that thus such kind of data in the context of high-energy nuclear experiments can help constrain the quadrupole deformation of the colliding species.
nucl-thhep-exhep-phnucl-exPRC(2020)·71 citations
03
Moravcsik's theorem on complete sets of polarization observables reexamined
Y. Wunderlich🇩🇪 · P. Kroenert🇩🇪 · F. Afzal🇩🇪 · A. Thiel🇩🇪
We revisit Moravcsik's theorem on the unique extraction of amplitudes from polarization observables, which has been originally published in 1985. The proof is (re-) written in a more formal and detailed way and the theorem is corrected for the special case of an odd number of amplitudes (this case was treated incorrectly in the original publication). Moravcsik's theorem, in the modified form, can be applied in principle to the extraction of an arbitrary number of $N$ helicity amplitudes. The uniqueness theorem is then applied to hadronic reactions involving particles with spin. The most basic example is Pion-Nucleon scattering ( $N = 2$ ), the first non-trivial example is pseudoscalar meson photoproduction ( $N = 4$ ) and the most technically involved case treated here is given by pseudoscalar meson electroproduction ( $N = 6$ ). The application of Moravcsik's theorem to electroproduction yields new results, which for the first time provide insights into the structure and content of complete sets for this particular process. The uniqueness-statements for the various reactions are compared and an attempt is made to recognize general patterns, which emerge under the application of the theorem.
nucl-thPRC(2020)·11 citations
04
Microscopic calculation of proton and alpha-particle inelastic scattering to study the excited states of $^{6}$ He and $^{8}$ He
Yoshiko Kanada-En'yo · Kazuyuki Ogata
Elastic and inelastic cross sections of the $p +^{6} He$ , $p +^{8} He$ , and $α +^{8} He$ reactions were investigated using the Melbourne $g$ -matrix folding approach with the theoretical densities of $^{6} He$ and $^{8} He$ obtained by a microscopic structure model of antisymmetrized molecular dynamics (AMD). Microscopic coupled-channel (MCC) calculations of the $p +^{6} He$ and $p +^{8} He$ reactions were performed to investigate transition properties of the $^{6} He (2_{1}^{+})$ and $^{8} He (2_{1}^{+})$ states. The MCC+AMD calculations reproduced elastic cross sections of the $p +^{6} He$ reaction at $E = 40.9$ MeV/A and of the $p +^{8} He$ reaction at $E = 32.5$ and 72 MeV/A, which have both been measured by inverse kinematics experiments. For $p +^{6} He$ inelastic scattering to the $2_{1}^{+}$ state, the calculated result was in reasonable agreement with the $(p, p^{'})$ data at $E = 24.5$ and 40.9 MeV/A and supported the AMD prediction of the neutron transition matrix element $M_{n} = 7.9$ fm $^{2}$ . For the $p +^{8} He$ inelastic scattering to $^{8} He (2_{1}^{+})$ , the MCC+AMD calculation overshot the $(p, p^{'})$ cross sections at $E = 72$ MeV/A by a factor of three. According to a phenomenological model analysis, $M_{n}$ values in the range of 4--6 fm $^{2}$ were favored to reproduce the $^{8} He (2_{1}^{+})$ cross sections of the $p +^{8} He$ reaction at $E = 72$ MeV/A. For the $α +^{8} He$ reaction, the MCC+AMD calculation reproduced the elastic cross sections at $E = 26$ MeV/A. Theoretical predictions of the ( $p, p^{'}$ ) and ( $α, α^{'}$ ) cross sections to the $^{8} He (0_{2}^{+})$ , $^{8} He (1_{1}^{-})$ , $^{8} He (2_{3}^{+})$ and $^{8} He (3_{1}^{-})$ states are also given.
nucl-th2 citations
05
Determining $B (E 1)$ distributions of weakly bound nuclei from breakup cross sections using Continuum Discretized Coupled Channels calculations. Application to $^{11}$ Be
A.M. Moro · J.A. Lay · J.Gómez-Camacho
A novel method to extract the $B (E 1)$ strength of a weakly bound nucleus from experimental Coulomb dissociation data is proposed. The method makes use of continuum discretized coupled channels (CDCC) calculations, in which both nuclear and Coulomb forces are taken into account to all orders. This is a crucial advantage with respect to the standard procedure based on the Equivalent Photon Method (EPM) which does not properly take into account nuclear distortion, higher order coupling effects, or Coulomb-nuclear interference terms. The procedure is applied to the $^{11}$ Be nucleus using two sets of available experimental data at different energies, for which seemingly incompatible $B (E 1)$ have been reported using the EPM. We show that the present procedure gives consistent $B (E 1)$ strengths, thus solving the aforementioned long-standing discrepancy between the two measurements.
nucl-thnucl-exPLB(2020)·18 citations
06
$^{8}$ He and $^{9}$ Li cluster structures in light nuclei
Naoyuki Itagaki · Tokuro Fukui · Junki Tanaka · Yuma Kikuchi
The possibility of the $^{8}$ He and $^{9}$ Li clusters in atomic nuclei is discussed. Until now most of the clusters in the conventional models have been limited to the closures of the three-dimensional harmonic oscillators, such as $^{4}$ He, $^{16}$ O, and $^{40}$ Ca. In the neutron-rich nuclei, however, the neutron to proton ratio is not unity, and it is worthwhile to think about more neutron-rich objects with $N > Z$ as the building blocks of cluster structures. Here the nuclei with the neutron number six, which is the subclosure of the $p_{3/2}$ subshell of the $j j$ -coupling shell model, are assumed to be clusters, and thus we study the $^{8}$ He and $^{9}$ Li cluster structures in $^{16}$ Be ( $^{8}$ He+ $^{8}$ He), $^{17}$ B ( $^{8}$ He+ $^{9}$ Li), $^{18}$ C ( $^{9}$ Li+ $^{9}$ Li), and $^{24}$ C ( $^{8}$ He+ $^{8}$ He+ $^{8}$ He). Recent progress of the antisymmetrized quasi cluster model (AQCM) enables us to utilize $j j$ -coupling shell model wave functions as the clusters rather easily. It is shown that the $^{8}$ He+ $^{9}$ Li and $^{9}$ Li+ $^{9}$ Li cluster configurations cover the lowest shell-model states of $^{17}$ B and $^{18}$ C, respectively. To predict the cluster states with large relative distances, we increase the expectation value of the principal quantum numbers by adding the nodes to the lowest states under the condition that the total angular momentum is unchanged (equal to $J^{π} = 0$ ). As a result, developed cluster states are obtained around the corresponding threshold energies. The rotational band structure of $^{24}$ C, which reflect the symmetry of equilateral triangular configuration ( $D_{3 h}$ symmetry) of three $^{8}$ He clusters, also appears around the threshold energy.
nucl-thPRC(2020)·12 citations
07
Quantifying alpha clustering in light nuclei from binding energies
K. Fossez
What is the origin of nuclear clustering and how does it emerge from the nuclear interaction? While there is ample experimental evidence for this phenomenon, its theoretical characterization directly from nucleons as degrees of freedom remains a challenge, making it difficult to improve nuclear forces using clustering observables. In this work, a simple ratio of energies based on effective scale arguments is proposed to assess the quality of nuclear forces on alpha clustering ( $^{4} He$ ) in bound and narrow ground-state nuclei. The proposed clustering ratio is parameter-free and correctly identify basic alpha clustering features in light nuclei. It is found that in nuclei ranging from $^{6} Li$ to $^{14} C$ , state-of-the-art \textit{ab initio} nuclear forces underestimate the degree of alpha clustering in key nuclei such as $^{8} Be$ and $^{12} C$ . Stringent constraints on binding energies are then provided by back-propagating 10\% relative uncertainties on the experimental clustering ratios using a parallel Markov chain Monte Carlo algorithm. It is demonstrated that the binding energies of the nuclei $^{6, 7}$ Li, $^{7}$ Be, $^{10, 11}$ B, and $^{11}$ C need to be obtained within tens of keV precision by nuclear forces to ensure a proper reproduction of basic alpha clustering features in light nuclei. This study provides a new and practical path to guide future optimizations of nuclear forces with a potential impact for medium-mass nuclei.
nucl-thnucl-ex1 citation
08
On the canonical formulation of gauge field theories and Poincare transformations
Daniel N. Blaschke🇺🇸 · Francois Gieres🇫🇷
We address the Hamiltonian formulation of classical gauge field theories while putting forward results some of which are not entirely new, though they do not appear to be well known. We refer in particular to the fact that neither the canonical energy momentum vector $(P^{μ})$ nor the gauge invariant energy momentum vector $(P_{inv}^{μ})$ do generate space-time translations of the gauge field by means of the Poisson brackets: In a general gauge, one has to consider the so-called kinematical energy momentum vector and, in a specific gauge (like the radiation gauge in electrodynamics), one has to consider the Dirac brackets rather than the Poisson brackets. Similar arguments apply to rotations and to Lorentz boosts and are of direct relevance to the "nucleon spin crisis" since the spin of the proton involves a contribution which is due to the angular momentum vector of gluons and thereby requires a proper treatment of the latter. We conclude with some comments on the relationships between the different approaches to quantization (canonical quantization based on the classical Hamiltonian formulation, Gupta-Bleuler, path integrals, BRST, covariant canonical approaches).
↳ hep-thhep-phnucl-thNPB(2021)·11 citations
09
Thermodynamic properties and transport coefficients of QCD matter within the non-extensive Polyakov-Nambu-Jona-Lasinio model
Ya-Peng Zhao🇨🇳
We present a non-extensive version of the Polyakov-Nambu-Jona-Lasinio model which is based on the non-extentive statistical mechanics. This new statistics is characterized by a dimensionless non-extensivity parameter $q$ that accounts for all possible effects violating the assumptions of the Boltzmann-Gibbs statistics (when $q \to 1$ , it returns to the Boltzmann-Gibbs case). Using this q-Polyakov-Nambu-Jona-Lasinio model and including two different Polyakov-loop potentials, we discussed the influence of the parameter $q$ on chiral and deconfinement phase transition, various thermodynamic quantities and transport coefficients at finite temperature and zero quark chemical potential. We found that the Stefan-Boltzmann limit is actually related to the choice of statistics. For example, in the Tsallis statistics, the thermodynamic quantities $\frac{ϵ}{T ^{4}}$ , $\frac{p}{T ^{4}}$ and $\frac{s}{T ^{3}}$ all increase with $q$ , exceed their usual Stefan-Boltzmann limits and tend to a new $q$ -related Tsallis limit at temperature high enough. Interestingly, however, due to a surprising cancellation, the high temperature limit of $c_{s}^{2}$ is still its SB limit $1/3$ . In addition, we found some similarities between the non-extensive effect and the finite-size effect. For example, as $q$ increases (size decreases), the criticality of $\frac{c _{v}}{T ^{3}}$ and $c_{s}^{2}$ gradually disappears. Besides, in order to better study the non-extensive effect, we defined a new susceptibility and calculated the response of thermodynamic quantities and transport coefficients to $q$ . And found that their response patterns are different.
↳ hep-phnucl-thPRD(2020)·37 citations
10
QCD Hidden-Color Hexa-diquark in the Central Core of Nuclei
Jennifer Rittenhouse West🇺🇸 · Stanley J. Brodsky🇺🇸 · Guy F. de Teramond🇨🇷 · Alfred S. Goldhaber🇺🇸 · Ivan Schmidt🇨🇱
Hidden-color configurations are a key prediction of QCD with important physical consequences. In this work we examine a QCD color-singlet configuration in nuclei formed by combining six scalar $[u d]$ diquarks in a strongly bound $SU (3)_{C}$ channel. The resulting hexadiquark state is a charge-2, spin-0, baryon number-4, isospin-0, color-singlet state. It contributes to alpha clustering in light nuclei and to the additional binding energy not saturated by ordinary nuclear forces in \he as well as the alpha-nuclei sequence of interest for nuclear astrophysics. We show that the strongly bound combination of six scalar isospin-0 $[u d]$ diquarks within the nuclear wave function - relative to free nucleons - provides a natural explanation of the EMC effect measured by the CLAS collaboration's comparison of nuclear parton distribution function ratios for a large range of nuclei. These experiments confirmed that the EMC effect; i.e., the distortion of quark distributions within nuclei, is dominantly identified with the dynamics of neutron-proton (``isophobic'') short-range correlations within the nuclear wave function rather than proton-proton or neutron-neutron correlations.
↳ hep-phnucl-exnucl-thNPA(2021)·20 citations
11
Spin versus Helicity Equilibration Times and Lagrangian for Strange Quarks in Rotating Quark-Gluon Plasma
Joseph I. Kapusta🇺🇸 · Ermal Rrapaj🇺🇸 · Serge Rudaz🇺🇸
Measurements of the net polarization of $Λ$ and $Λ ˉ$ hyperons at the Relativistic Heavy Ion Collider (RHIC) have stimulated much interest in how strange quarks might align their spin with the vorticity of the matter created in heavy ion collisions. We calculate the Lagrangian in the rest frame of a fluid element undergoing rotation with angular velocity $ω$ including photon and gluon fields. There is an additional coupling between the quarks and the gauge fields proportional to $ω$ , but this vertex does not change the spin of the quarks. We also show that the times to equilibrate quark helicity and spin parallel to the vorticity are the same so long as $ω$ is small compared to the temperature.
↳ hep-thnucl-thPRC(2020)·24 citations
12
One-loop Matching for Spin-Dependent Quasi-TMDs
Markus A. Ebert🇺🇸 · Stella T. Schindler🇺🇸 · Iain W. Stewart🇺🇸 · Yong Zhao🇺🇸
Transverse momentum dependent parton distribution functions (TMDPDFs) provide a unique probe of the three-dimensional spin structure of hadrons. We construct spin-dependent quasi-TMDPDFs that are amenable to lattice QCD calculations and that can be used to determine spin-dependent TMDPDFs. We calculate the short-distance coefficients connecting spin-dependent TMDPDFs and quasi-TMDPDFs at one-loop order. We find that the helicity and transversity distributions have the same coefficient as the unpolarized TMDPDF. We also argue that the same is true for pretzelosity and that this spin universality of the matching will hold to all orders in $α_{s}$ . Thus, it is possible to calculate ratios of these distributions as a function of longitudinal momentum and transverse position utilizing simpler Wilson line paths than have previously been considered.
↳ hep-phhep-latnucl-thJHEP(2020)·55 citations
13
Transport coefficients of nucleon neutron star cores for various nuclear interactions within the Brueckner-Hartree-Fock approach
Peter Shternin · Marcello Baldo
We consider the thermal conductivity, shear viscosity, and momentum relaxation rates in the nucleon cores of the neutron stars. We study how the choice of the nuclear interaction and the model for three-body forces may affect these transport coefficients calculated within the Brueckner-Hartree-Fock many-body nuclear theory. We find that at relatively large densities the model dependence of the results is substantial. In addition we provide the analytical approximations which allow to incorporate our results in practical simulations.
↳ astro-ph.HEnucl-thPRD(2020)·11 citations

Affiliations

first authorsco-authorsvia INSPIRE