Nuclear Theory·nucl-th

Thursday·December 12, 2019

16 papers—6 primary·10 cross-listed

01
Microscopic predictions for production of neutron rich nuclei in the reaction $^{176} Yb +^{176} Yb$
K. Godbey🇺🇸 · C. Simenel🇦🇺 · A.S. Umar🇺🇸
Background: Production of neutron-rich nuclei is of vital importance to both understanding nuclear structure far from stability and to informing astrophysical models of the rapid neutron capture process (r-process). Multinucleon transfer (MNT) in heavy-ion collisions offers a possibility to produce neutron-rich nuclei far from stability. Purpose: The $^{176} Yb +^{176} Yb$ reaction has been suggested as a potential candidate to explore the neutron-rich region surrounding the principal fragments. The current study has been conducted with the goal of providing guidance for future experiments wishing to study this (or similar) system. Methods: Time-dependent Hartree-Fock (TDHF) and its time-dependent random-phase approximation (TDRPA) extension are used to examine both scattering and MNT characteristics in $^{176} Yb +^{176} Yb$ . TDRPA calculations are performed to compute fluctuations and correlations of the neutron and proton numbers, allowing for estimates of primary fragment production probabilities. Results: Both scattering results from TDHF and transfer results from the TDRPA are presented for different energies, orientations, and impact parameters. In addition to fragment composition, scattering angles and total kinetic energies, as well as correlations between these observables are presented. Conclusions: $^{176} Yb +^{176} Yb$ appears to be an interesting probe for the mid-mass neutron-rich region of the chart of nuclides. The predictions of both TDHF and TDRPA are speculative, and will benefit from future experimental results to test the validity of this approach to studying MNT in heavy, symmetric collisions.
nucl-thPRC(2020)·41 citations
02
Ab initio nuclear thermodynamics
Bing-Nan Lu🇺🇸 · Ning Li🇺🇸 · Serdar Elhatisari🇹🇷 · Dean Lee🇺🇸 · Joaquín E. Drut🇺🇸 · Timo A. Lähde🇩🇪 · Evgeny Epelbaum🇩🇪 · Ulf-G. Meißner🇩🇪
We propose a new Monte Carlo method called the pinhole trace algorithm for {\it ab initio} calculations of the thermodynamics of nuclear systems. For typical simulations of interest, the computational speedup relative to conventional grand-canonical ensemble calculations can be as large as a factor of one thousand. Using a leading-order effective interaction that reproduces the properties of many atomic nuclei and neutron matter to a few percent accuracy, we determine the location of the critical point and the liquid-vapor coexistence line for symmetric nuclear matter with equal numbers of protons and neutrons. We also present the first {\it ab initio} study of the density and temperature dependence of nuclear clustering.
nucl-thcond-mat.stat-mechhep-latnucl-exPRL(2020)·61 citations
03
Delineating the properties of neutron star matter in cold, dense QCD
Toru Kojo🇨🇳
The properties of dense QCD matter are delineated through the construction of equations of state which should be consistent with the low and high density limits of QCD, nuclear laboratory experiments, and the neutron star observations. These constraints, together with the causality condition of the sound velocity, are used to develop the picture of hadron-quark continuity in which hadronic matter continuously transforms into quark matter (modulo small 1st order phase transitions). The resultant unified equation of state at zero temperature and $β$ -equilibrium, which we call Quark-Hadron-Crossover (QHC19), is consistent with the measured properties of neutron stars as well as the microphysics known for the hadron phenomenology. In particular to $\sim 10 n_{0}$ ( $n_{0}$ : saturation density) the gluons remain as non-perturbative as in vacuum and the strangeness can be as abundant as up- and down-quarks at the core of two-solar mass neutron stars. Within our modeling the maximum mass is found less than $≃ 2.35$ times solar mass and the baryon density at the core ranges in $\sim 5$ -8 $n_{0}$ .
nucl-thastro-ph.HEhep-latPoS(2019)·0 citations
04
Calculated solar-neutrino capture rate for a radiochemical 205 Tl-based solar-neutrino detector
Joel Kostensalo🇫🇮 · Jouni Suhonen🇫🇮 · Kai Zuber🇩🇪
Radiochemical experiments for low-energy solar-neutrino detection have been making headlines by exploiting the isotopes \iso{Cl}{37} and \iso{Ga}{71}. Such a very low-threshold measurement of this type can also be performed using \iso{Tl}{205}, which has been considered for decades for this purpose. A unique feature of this detector nucleus is the integration is the solar-neutrino flux over millions of years owing to its long-living daughter \iso{Pb}{205}. In this study we have calculated for the first time the cross section for the charged-current solar-neutrino scattering off \iso{Tl}{205}. Taking into account the solar-model-predicted neutrino fluxes and the electron-neutrino survival probabilities, a solar-neutrino capture rate of 62.2 $\pm 8.6$ SNU is determined, a value significantly smaller than in previous estimates.
nucl-thhep-phPRC(2020)·7 citations
05
Low-energy neutron scattering on light nuclei and $^{19}$ B as a $^{17}$ B- $n$ - $n$ three-body system in the unitary limit
Jaume Carbonell🇫🇷 · Emiko Hiyama🇯🇵 · Rimantas Lazauskas🇫🇷 · F. Miguel Marqués🇫🇷
We consider the evolution of the neutron-nucleus scattering length for the lightest nuclei. We show that, when increasing the number of neutrons in the target nucleus, the strong Pauli repulsion is weakened and the balance with the attractive nucleon-nucleon interaction results into a resonant virtual state in $^{18}$ B. We describe $^{19}$ B in terms of a $^{17}$ B- $n$ - $n$ three-body system where the two-body subsystems $^{17}$ B- $n$ and $n$ - $n$ are unbound (virtual) states close to the unitary limit. The energy of $^{19}$ B ground state is well reproduced and two low-lying resonances are predicted. Their eventual link with the Efimov physics is discussed. This model can be extended to describe the recently discovered resonant states in $^{20, 21}$ B.
nucl-thnucl-exquant-phSciPost Phys.Proc.(2020)·2 citations
06
Fission of relativistic nuclei with fragment excitation and reorientation
C.A. Bertulani🇺🇸 · Y. Kucuk🇹🇷 · R. Lozeva🇫🇷
Experimental studies of fission induced in relativistic nuclear collisions show a systematic enhancement of the excitation energy of the primary fragments by a factor of ~ 2, before their decay by fission and other secondary fragments. Although it is widely accepted that by doubling the energies of the single-particle states may yield a better agreement with fission data, it does not prove fully successful, since it is not able to explain yields for light and intermediate mass fragments. State-of-the-art calculations are successful to describe the overall shape of the mass distribution of fragments, but fail within a factor of 2-10 for a large number of individual yields. Here, we present a novel approach that provides an account of the additional excitation of primary fragments due to final state interaction with the target. Our method is applied to the 238U + 208Pb reaction at 1 GeV/nucleon (and is applicable to other energies), an archetype case of fission studies with relativistic heavy ions, where we find that the large probability of energy absorption through final state excitation of giant resonances in the fragments can substantially modify the isotopic distribution of final fragments in a better agreement with data. Finally, we demonstrate that large angular momentum transfers to the projectile and to the primary fragments via the same mechanism imply the need of more elaborate theoretical methods than the presently existing ones.
nucl-thnucl-exPRL(2020)·9 citations
07
Monte Carlo simulations of the S-shaped neutron guide
Luiz P. de Oliveira · Alexandre P.S. Souza · Fabiano Yokaichiya · Frederico A. Genezini · Margareth K.K.D. Franco
Neutron transport along guides is governed by the Liouville theorem and the technology involved has advanced in recent decades. Computer simulations have proven to be useful tools in the design and conception of neutron guide systems in facilities. In this study, we use a Monte Carlo method to perform simulations for an S-shaped neutron guide with different dimensions for a Small-Angle Neutron Scattering (SANS) instrument, through the MCSTAS software. A wavelength cutoff is observed and shown to be dependent on the geometrical parameters of the guide. Results for the neutron flux at sample position are presented and a greater sensitivity of cutoffs concerning the curvatures of the guides than to their lengths is noticed. Our results are in agreement with those obtained from the Acceptance Diagram method and we analyze the beam divergence behavior along the S-shaped guide.
↳ physics.ins-detnucl-exnucl-thJINST(2020)·2 citations
08
Hyperon resonances and meson-baryon interactions in isospin 1
K. P. Khemchandani🇧🇷 · A. Martinez Torres🇧🇷 · J. A. Oller🇪🇸
In this work we extend our formalism to study meson-baryon interactions by including $s$ - and $u$ -channel diagrams for pseudoscalar-baryon systems. We study the coupled systems with strangeness $- 1$ and focus on studying the isospin-1 resonance(s), especially in the energy region around 1400 MeV. By constraining the model parameters to fit the cross section data available on several processes involving relevant channels, we find resonances in the isoscalar as well as the isovector sector in the energy region around 1400 MeV.
↳ hep-phnucl-th1 citation
09
Renormalization of a Contact Interaction on a Lattice
Christopher Körber🇺🇸 · Evan Berkowitz🇩🇪 · Thomas Luu🇩🇪
Contact interactions can be used to describe a system of particles at unitarity, contribute to the leading part of nuclear interactions and are numerically non-trivial because they require a proper regularization and renormalization scheme. We explain how to tune the coefficient of a contact interaction between non-relativistic particles on a discretized space in 1, 2, and 3 spatial dimensions such that we can remove all discretization artifacts. By taking advantage of a latticized Lüscher zeta function, we can achieve a momentum-independent scattering amplitude at any finite lattice spacing.
↳ hep-latnucl-thphysics.comp-ph7 citations
10
Towards a full solution of relativistic Boltzmann equation for quark-gluon matter on GPUs
Jun-Jie Zhang🇨🇳 · Hong-Zhong Wu🇨🇳 · Shi Pu🇨🇳 · Guang-You Qin🇨🇳 · Qun Wang🇨🇳
We have developed a numerical framework for a full solution of the relativistic Boltzmann equations for the quark-gluon matter using the multiple Graphics Processing Units (GPUs) on distributed clusters. Including all the $2 \to 2$ scattering processes of 3-flavor quarks and gluons, we compute the time evolution of distribution functions in both coordinate and momentum spaces for the cases of pure gluons, quarks and the mixture of quarks and gluons. By introducing a symmetrical sampling method on GPUs which ensures the particle number conservation, our framework is able to perform the space-time evolution of quark-gluon system towards thermal equilibrium with high performance. We also observe that the gluons naturally accumulate in the soft region at the early time, which may indicate the gluon condensation.
↳ hep-phhep-exnucl-thphysics.comp-phPRD(2020)·11 citations
11
Dynamic Structure of Hadrons in ChPT
A. Aleksejevs🇨🇦 · S. Barkanova
The Chiral Perturbation Theory (ChPT) has been very successful in describing low-energy hadronic properties in the non-perturbative regime of Quantum Chromodynamics. The results of ChPT, many of which are currently under active experimental investigation, provide stringent predictions of many fundamental properties of hadrons, including quantities such as electromagnetic polarizabilities. The paper outlines our semi-automated calculations in ChPT, the corresponding results for the electric and magnetic polarizabilities of the proton and our predictions for Compton differential cross sections.
↳ hep-phnucl-thPoS(2019)·0 citations
12
Constraining the QCD phase diagram at finite temperature and density
Owe Philipsen🇩🇪
Neither the chiral limit nor finite baryon density can be simulated directly in lattice QCD, which severely limits our understanding of the QCD phase diagram. In this review I collect results for the phase structure in an extended parameter space of QCD, with varying numbers of flavours, quark masses, colours, lattice spacings, imaginary and isospin chemical potentials. Such studies help in understanding the underlying symmetries and degrees of freedom, and are beginning to provide a consistent picture constraining the possibilities for the physical phase diagram.
↳ hep-lathep-phnucl-thPoS(2019)·60 citations
13
Radiative contribution to $p_{⊥}$ -broadening of fast partons in a quark-gluon plasma
B.G. Zakharov🇷🇺
The contribution of radiative processes to $p_{⊥}$ -broadening of fast partons in a quark-gluon plasma is investigated. Calculations are performed beyond the soft gluon approximation. It is shown that the radiative correction to $⟨ p_{⊥}^{2} ⟩$ for conditions of heavy ion collisions at RHIC and LHC is negative and can be comparable in absolute value with the nonradiative contribution. This prediction differs radically from the essentially positive contribution of radiative processes to $p_{⊥}$ -broadening, which was predicted earlier in the literature.
↳ hep-phnucl-thJ.Exp.Theor.Phys.(2019)·6 citations
14
Chemical freeze-out conditions from net-kaon fluctuations at RHIC
Jamie M. Stafford🇺🇸
We compare the mean-over-variance ratio of the net-kaon distribution calculated within a state-of-the-art hadron resonance gas model to the latest experimental data from the Beam Energy Scan at RHIC by the STAR collaboration. Our analysis indicates that it is not possible to reproduce the experimental results using the freeze-out parameters from the existing combined fit of net-proton and net-electric charge mean-over-variance. The strange mesons need about 10-15 MeV higher temperatures than the light hadrons at the highest collision energies. In view of the recent lambda fluctuation measurements, we predict the net-lambda variance-over-mean at the light and strange chemical freeze-out parameters. We observe that the lambda fluctuations are sensitive to the difference in the freeze-out temperatures established in this analysis. Our results have implications for other phenomenological models in the field of relativistic heavy-ion collisions.
↳ hep-phnucl-thJ.Phys.Conf.Ser.(2020)·0 citations
15
Effect of color reconnection on forward-backward multiplicity and mean transverse momentum correlation
Sourav Kundu🇮🇳 · Bedangadas Mohanty🇮🇳 · Dukhishyam Mallick🇮🇳
Color reconnection (CR) mechanism in PYTHIA model has been reported to be essential to describe the flow-like collective effect observed in high multiplicity $p$ + $p$ and $p$ +Pb collisions. In this work, we test this mechanism towards explaining the Forward-Backward multiplicity correlation (b $_{cor}$ ) measurements in $p$ + $p$ collisions at the LHC energies. Out of the three different CR schemes implemented in PYTHIA, (a) MPI based CR (default mechanism), (b) QCD based CR and (c) Gluon moved CR, we found that the QCD based CR scheme describes relatively better the ALICE measurements of b $_{cor}$ in $p$ + $p$ collisions at $s$ = 0.9 and 7 TeV. In addition, we have tuned the parameters of the default CR mechanism in PYTHIA to describe simultaneously the measured charged particle multiplicity pseudo-rapidity ( $η$ ) distribution and b $_{cor}$ . We found that an average number of multipartonic interactions ( $⟨ N_{MPI} ⟩$ ) between 2.5 to 3 and CR range between 0.9 to 2.5 best describes the experimental data. Finally, we have presented a study using PYTHIA events for $p$ + $p$ collisions at $s$ = 7 TeV which shows that the strength of Forward-Backward mean transverse momentum correlation (b $_{cor}^{⟨ p_{T} ⟩ ⟨ p_{T} ⟩}$ ) is found to increase with CR in contrast to decrease of b $_{cor}$ values with CR effect. Hence, simultaneously studying the b $_{cor}^{⟨ p_{T} ⟩ ⟨ p_{T} ⟩}$ and b $_{cor}$ in the experiments will help in establishing the arguments either in favour or in disfavour of CR effect in the measurements.
↳ hep-phhep-exnucl-th8 citations
16
Nontrivially Topological Phase Structure of Ideal Bose Gas System within Different Boundary Conditions
Yonghui Xia · Hongtao Feng · Hongshi Zong
The phase structure of ideal Bose gas system within different boundary conditions, i.e., the periodic boundary condition and Dirichlet boundary condition in this work, in an infinite volume, is investigated. It is found that the ground states of ideal Bose gas within those two boundary conditions are both topologically nontrivial, which can not be classified by the traditional symmetry breaking theory. The ground states are different topological phases corresponding to those two boundary conditions, which can be distinguished by the off--diagonal particle number susceptibility. Moreover, this result is universal. The boundary condition may play an important role in pining the critical endpoint of QCD diagram on the approach of the lattice simulations and the computation of some solvable statistical models .
↳ cond-mat.quant-gasnucl-th0 citations

Affiliations

first authorsco-authorsvia INSPIRE