Nuclear Theory·nucl-th

Tuesday·August 13, 2019

12 papers—5 primary·7 cross-listed

01
Radiative parton energy loss and baryon stopping in $AA$ collisions
B.G. Zakharov🇷🇺
We study the radiative energy loss contribution to proton stopping in $AA$ collisions. The analyses is performed within the light-cone path integral approach to induced gluon emission. We have found that the radiative correction can fill in partly the midrapidity dip in the net proton rapidity distribution in $AA$ collisions at $s \sim 10$ GeV. We argue that at $s \sim 10$ GeV the net proton fluctuations at midrapidity may be dominated by the initial fluctuations of the proton flow, which, to a good accuracy, should be binomial.
nucl-thhep-phJETP Lett.(2019)·3 citations
02
Above-barrier heavy-ion fusion cross-sections using the relativistic mean-field approach: case of spherical colliding nuclei
Maria V. Chushnyakova · Mrutunjaya Bhuyan · Igor I. Gontchar · Natalya A. Khmyrova
The double folding (DF) approach is one of the widely used methods for finding nucleus-nucleus interaction potential. In the present work, the influence of the nuclear matter density on the DF potential and on the Coulomb barrier parameters is studied systematically for collisions of spherical nuclei. The value of the parameter $B_{Z} = Z_{P} Z_{T} / (A_{P}^{1/3} + A_{T}^{1/3})$ (estimating the Coulomb barrier height) varies in these calculations from 10 MeV up to 150 MeV. The novel feature of this study is that the nuclear densities came from the Relativistic Mean Field approach (RMF). For the nucleon-nucleon effective interaction, the M3Y forces with the finite range exchange term and density dependence are employed. The above barrier fusion cross sections are calculated within the framework of the trajectory model with surface friction. Results are compared with the previous study in which the nuclear density came from the Hartree-Fock (HF) calculations and with the high precision experimental data. This comparison demonstrates that i) agreement between the theoretical and experimental cross sections obtained with RMF and HF densities is of the same quality and ii) the values of the only adjustable parameter (friction strength) obtained with RMF and HF densities strongly correlate.
nucl-thNPA(2020)·6 citations
03
Testing the energy diffusion approximation for the escape of a Brownian particle from a potential pocket
Igor I. Gontchar · Maria V. Chushnyakova
For the first time, the energy diffusion approximation is confronted at the percent level with the exact numerical modeling of thermal decay of a metastable state. The latter is performed using the quasistationary decay rates resulting from the Langevin equations for the coordinate and conjugated momentum. For the energy (or action) diffusion approach, a Langevin-type equation for the action is constructed, validated, and solved numerically. The comparison of two approaches is performed for four potentials (two of which are anharmonic) in a wide range of two dimensionless scaling parameters: the governing parameter $G$ reflecting how high is the barrier with respect to the temperature and the damping parameter $φ$ expressing the friction strength. It turns out that the action diffusion approach produces the rate which is in 50% agreement with the exact one only at $φ < 0.02$ contrary to $φ < 1$ as claimed in the literature.
nucl-thcond-mat.stat-mechChin.J.Phys.(2020)·0 citations
04
Puzzling Radii of Calcium Isotopes: $^{40} Ca \to^{44} Ca \to^{48} Ca \to^{52} Ca$ , and Duality in the Structure of $_{14}^{42} Si_{28}$ and $_{20}^{48} Ca_{28}$
Syed Afsar Abbas · Anisul Ain Usmani · Usuf Rahaman · Mohammad Ikram
In this paper we study the issue of the puzzle of the radii of calcium isotopes. Despite an excess of eight neutrons, strangely $^{48} Ca$ exhibits essentially the same charge radius as $^{40} Ca$ does. A fundamental microscopic description of this is still lacking. Also strange is a peak in charge radius of calcium at N = 24. The $^{52} Ca$ (N = 32) nucleus, well known to be doubly magical, amazingly has recently been found to have a very large charge radius. Also amazing is the property of $_{14}^{42} Si_{28}$ which simultaneously appears to be both magical/spherical and strongly deformed as well. We use a Quantum Chromodynamics based model, which treats triton as elementary entity to make up $_{14}^{42} Si_{28}$ . We show here how this QCD based model is able to provide a consistent physical understanding of simultaneity of magicity/sphericity and strong deformation of a single nucleus. This brings in an essential duality in the structure of $_{14}^{42} Si_{28}$ and subsequently also that of $_{20}^{48} Ca_{28}$ We also provide consistent understanding of the puzzling radii of calcium isotopes. We predict that the radius of $^{54} Ca$ should be even bigger than that of $^{52} Ca$ ; and also that the radius of $^{60} Ca$ should be the same as that of $^{40} Ca$ . In addition we also show wherefrom arises the neutron E2 effective charge of $\frac{1}{2}$ .
nucl-thnucl-ex0 citations
05
Influence of correlations between yields on the chemical freeze-out temperature
Dariusz Prorok🇵🇱
A statistical (thermal) model is applied to the description of hadron yields measured at central nucleus-nucleus collisions at the top RHIC energy $s_{N N} = 200$ GeV and the LHC energy $s_{N N} = 2.76$ TeV. In contrast to the previous analyzes a more general form of the least squares test statistic is used, which takes into account also possible correlations between different species of yields. In addition to hadrons also light nuclei are included in the fits. Because of the lack of data, a toy model is constructed where the correlation coefficients are just free parameters. Because of this the presented considerations are speculative and should be treated as an imperfect illustration of the problem. Within these limitations it is impossible to formulate any definite conclusion, it might be only mentioned that for the considered examples the dependence of the freeze-out temperature and baryon chemical potential on correlations turned out to be weak.
nucl-thhep-exhep-phnucl-exChin.J.Phys.(2021)·0 citations
06
Indirect Detection of Composite (Asymmetric) Dark Matter
Rakhi Mahbubani🇨🇭 · Michele Redi🇮🇹 · Andrea Tesi🇮🇹
Dark Matter can form bound states upon the emission of quanta of energy equal to the binding energy. The rate of this process is large for strongly-interacting Dark Matter, and further enhanced by long distance effects. The resulting monochromatic and diffuse $γ$ -rays can be tested in indirect detection experiments. If Dark Matter has electroweak charge, indirect signals include multiple observable photon lines for masses in the TeV range. Else if it couples only via a dark photon portal, diffuse spectra from dwarf galaxies and CMB reionization set powerful limits for masses below a TeV. This mechanism provides a powerful means of probing Asymmetric Dark Matter today.
↳ hep-phastro-ph.COhep-latnucl-thPRD(2020)·26 citations
07
Development and testing of an unstructured mesh method for whole plasma gyrokinetic simulations in realistic tokamak geometry
Z.X. Lu · Ph. Lauber · T. Hayward-Schneider · A. Bottino · M. Hoelzl
In this work, we have formulated and implemented a mixed unstructured mesh-based finite element (FE)-Fourier decomposition scheme for gyrokinetic simulations in realistic tokamak geometry. An efficient particle positioning (particle-triangle mapping) scheme for the charge deposition and field scattering using an intermediate grid as the search index for triangles has been implemented and a significant speed-up by a factor of $\sim 30$ is observed as compared with the brute force scheme for a medium-size simulation. The TRIMEG (TRIangular MEsh based Gyrokinetic) code has been developed. As an application, the ion temperature gradient (ITG) mode is simulated using the simplified gyrokinetic Vlasov-Poisson model. Our simulation and that using the ORB5 code for the DIII-D Cyclone case show reasonable agreement. As an additional application, ITG simulations using an ASDEX Upgrade equilibrium have been performed with density and temperature gradient profiles similar to the Cyclone case. Capabilities of the TRIMEG code for simulations with realistic experimental equilibria in the plasma core and in the whole plasma volume with open field lines are demonstrated.
↳ physics.plasm-phnucl-thphysics.comp-phPhys.Plasmas(2019)·0 citations
08
Constraints for stellar electron-capture rates on $^{86}$ Kr via the $^{86}$ Kr( $t$ , $^{3}$ He $+ γ$ ) $^{86}$ Br reaction and the implications for core-collapse supernovae
R. Titus · E.M. Ney · R.G.T. Zegers · D. Bazin · J. Belarge · P.C. Bender · B.A. Brown · C.M. Campbell · B. Elman · J. Engel · A. Gade · B. Gao and 11 other authors
In the late stages of stellar core-collapse, prior to core bounce, electron captures on medium-heavy nuclei drive deleptonization and simulations require the use of accurate reaction rates. Nuclei with neutron number near $N = 50$ , just above atomic number $Z = 28$ , play an important role, but rates used in astrophysical simulations rely primarily on a relatively simple single-state approximation. In order to improve the accuracy of astrophysical simulations, experimental data are needed to test the electron-capture rates and to guide the development of better theoretical models. This work presents the results of the $^{86}$ Kr( $t$ , $^{3}$ He+ $γ$ ) experiment at the NSCL, from which an upper limit for the Gamow-Teller strength up to an excitation energy in $^{86}$ Br of 5 MeV is extracted. The derived upper limit for the electron-capture rate on $^{86}$ Kr indicates that the rate estimated through the single-state approximation is too high and that rates based on Gamow-Teller strengths estimated in shell-model and QRPA calculations are more accurate. The QRPA calculations tested in this manner were used for estimating the electron capture rates for 78 isotopes near $N = 50$ and above $Z = 28$ . The impact of using these new electron-capture rates in simulations of supernovae instead of the rates based on the single-state approximation is investigated, indicating a significant reduction in the deleptonization that affects multi-messenger signals, such as the emission of neutrinos and gravitational waves.
↳ nucl-exastro-ph.HEastro-ph.SRnucl-thPRC(2019)·18 citations
09
Relativistic many body theory of the electric dipole moment of $^{129}$ Xe and its implications for probing new physics beyond the Standard Model
Akitada Sakurai🇯🇵 · B. K. Sahoo🇮🇳 · K. Asahi🇯🇵 · B. P. Das🇯🇵
We report the results of our theoretical studies of the time-reversal and parity violating electric dipole moment (EDM) of $^{129}$ Xe arising from the nuclear Schiff moment (NSM) and the electron-nucleus tensor-pseudotensor (T-PT) interaction based on the self-consistent and the normal relativistic coupled-cluster methods. The important many-body effects are highlighted and their contributions are explicitly presented. The uncertainties in the calculations of the correlation and relativistic effects are determined by estimating the contributions of the triples excitations, and the Breit interaction respectively, which together amount to about 0.7% for the NSM and 0.2% for the T-PT interactions. The results of our present work in combination with improved experimental limits for $^{129}$ Xe EDM in the future would tighten the constraints on the hadronic CP violating quantities, and this could provide important insights into new physics beyond the Standard Model of elementary particles.
↳ physics.atom-phhep-phnucl-thPRA(2019)·13 citations
10
Accelerating lattice quantum field theory calculations via interpolator optimization using NISQ-era quantum computing
A. Avkhadiev🇺🇸 · P. E. Shanahan🇺🇸 · R. D. Young🇦🇺
The only known way to study quantum field theories in non-perturbative regimes is using numerical calculations regulated on discrete space-time lattices. Such computations, however, are often faced with exponential signal-to-noise challenges that render key physics studies untenable even with next generation classical computing. Here, a method is presented by which the output of small-scale quantum computations on Noisy Intermediate-Scale Quantum era hardware can be used to accelerate larger-scale classical field theory calculations through the construction of optimized interpolating operators. The method is implemented and studied in the context of the 1+1-dimensional Schwinger model, a simple field theory which shares key features with the standard model of nuclear and particle physics.
↳ hep-lathep-phnucl-thPRL(2020)·41 citations
11
Event multiplicity, transverse momentum and energy dependence of charged particle production, and system thermodynamics in $pp$ collisions at the Large Hadron Collider
Rutuparna Rath🇮🇳 · Arvind Khuntia🇵🇱 · Raghunath Sahoo🇮🇳 · Jean Cleymans🇿🇦
In the present work, we study the recent collision energy and multiplicity dependence of the charged particle transverse momentum spectra as measured by the ALICE collaboration in $pp$ collisions at $s$ = 5.02 and 13 TeV using the non-extensive Tsallis distribution and the Boltzmann-Gibbs Blast Wave (BGBW) model. A thermodynamically consistent form of the Tsallis distribution is used to extract the kinetic freeze-out parameters from the transverse momentum spectra of charged particles at mid-rapidity. In addition, a comprehensive study of fitting range dependence of transverse momentum spectra on the freeze-out parameters is done using Tsallis statistics. The applicability of BGBW model is verified by fitting the transverse momentum spectra of the bulk part ( $\sim 2.5 GeV / c$ )for both 5.02 and 13 TeV energies and also in different multiplicity classes. The radial flow, $< β >$ is almost independent of collision energy and multiplicity whereas the behavior of kinetic freeze-out temperature significantly depends on multiplicity classes. It is found that the Tsallis distribution generally leads to a better description for the complete transverse momentum spectra whereas the BGBW model explains the bulk part of the system.
↳ hep-phhep-exnucl-exnucl-thJ.Phys.G(2020)·32 citations
12
Clustering of Four-Component Unitary Fermions
William G. Dawkins🇨🇦 · J. Carlson🇺🇸 · U. van Kolck🇫🇷 · Alexandros Gezerlis🇨🇦
Ab initio nuclear physics tackles the problem of strongly interacting four-component fermions. The same setting could foreseeably be probed experimentally in ultracold atomic systems, where two- and three-component experiments have led to major breakthroughs in recent years. Both due to the problem's inherent interest and as a pathway to nuclear physics, in this Letter we study four-component fermions at unitarity via the use of quantum Monte Carlo methods. We explore novel forms of the trial wave function and find one which leads to a ground state of the eight-particle system whose energy is almost equal to that of two four-particle systems. We investigate the clustering properties involved and also extrapolate to the zero-range limit. In addition to being experimentally testable, our results impact the prospects of developing nuclear physics as a perturbation around the unitary limit.
↳ cond-mat.quant-gasnucl-thphysics.atm-clusPRL(2020)·22 citations

Affiliations

first authorsco-authorsvia INSPIRE