Nuclear Theory·nucl-th

Tuesday·September 24, 2019

14 papers—7 primary·7 cross-listed

01
Constraining level densities through quantitative correlations with cross-section data
G. P. A. Nobre · D. A. Brown · M. W. Herman · A. Golas
The adopted level densities (LD) for the nuclei produced through different reaction mechanisms significantly impact the calculation of cross sections for the many reaction channels. Common LD models make simplified assumptions regarding the overall behavior of the total LD and the intrinsic spin and parity distributions of the excited states. However, very few experimental constraints are taken into account: LD at neutron separation energy coming from average resonance spacings, whenever they have been previously measured, and the sometimes subjective extrapolation of discrete levels. These, however, constrain the LD only for very specific spins, parities and excitation energies. This work aims to establish additional experimental constraints on LD through quantitative correlations between cross sections and LD. This allows for the fitting and determination of detailed structures in LD. For this we use the microscopic Hartree-Fock-Bogoliubov (HFB) LD to associate variations predicted by the model with the structure observed in double-differential spectra at low outgoing neutron energy, which is dominated by the LD input. We also use \nuc{56}{Fe} ( $n, p$ ) as an example cross sections are extremely sensitive to LD. For comparison purposes we also perform calculations with the GC model. With this approach we are able to perform fits of the LD based on actual experimental data, constraining the model and ensuring its consistency. This approach can be particularly useful in extrapolating the LD to nuclei for which high-excited discrete levels and/or resonance spacings are unknown. It also predicts inelastic gamma cross sections that can significantly differ from more standard phenomenological LD.
nucl-thPRC(2020)·8 citations
02
Antiproton production in heavy-ion collisions at subthreshold energies
Zhao-Qing Feng🇨🇳
Within the framework of the Lanzhou quantum molecular dynamics model, the deep subthreshold antiproton production in heavy-ion collisions has been investigated thoroughly. The elastic scattering, annihilation and charge exchange reactions associated with antiproton channels are implemented in the model. The attractive antiproton potential extracted from the G-parity transformation of the nucleon selfenergies enhance the antiproton yields to some extent. The calculated invariant spectra are consistent with the available experimental data. The primordial antiproton yields increase with the mass number of colliding system. However, the annihilation reactions reduce the antiproton production and enable independent to colliding partners. Antiflow phenomena of antiprotons correlated to the mean-field potential and annihilation mechanism is found in comparison with proton flows.
nucl-thCPC(2020)·1 citation
03
Strangeness and hypernuclear production in fragmentation reactions induced by antikaons
Zhao-Qing Feng🇨🇳
Formation mechanism of hyperfragments with strangeness s=-1 and s=-2 in collisions of antikaons on nuclei has been investigated within a microscopic transport model. Dynamics of pseudoscalar mesons and hyperons is modeled within the transport model, in which all possible reaction channels for creating hyperons such as the elastic scattering, resonance production and decay, strangeness exchange reaction and direct strangeness production in meson-baryon and baryon-baryon collisions have been included. A coalescence approach is developed for constructing hyperfragments in phase space and the decay process is described with a statistical approach. It is found that the $Ξ^{-}$ production is correlated to the K $^{+}$ formation and the hyperons $Λ$ and $Σ$ are created within a broad rapidity region. The production cross sections of nucleonic fragments and hyperfragments weakly depends on the incident momentum. The yields of $Λ -$ hyperfragments are the six order of magnitude of $Ξ^{-} -$ hyperfragments.
nucl-thPRC(2020)·6 citations
04
Modeling photon--induced reactions on $^{233 - 238}$ U actinide targets
M. Sin · R. Capote · M.W. Herman · A. Trkov · B.V. Carlson
Comprehensive calculations of cross sections of photon induced reactions on $^{233 - 238}$ U targets for incident photon energies from 3 up to 30 MeV are undertaken with the statistical model code EMPIRE-3.2 Malta. Results are compared with the experimental data from EXFOR and with the current evaluations. The differences and the similarities between the models and parameters used in calculations of photon- and neutron-induced reactions on the same nuclei are discussed with focus on fission. The role of the extended optical model for fission in improving the description of the measured data and in determining consistent sets of barrier parameters is pointed out.
nucl-thPRC(2021)·6 citations
05
Signatures of octupole shape phase transitions in radioactive nuclei
Kosuke Nomura
We analyze the octupole deformations and the related collective excitations in medium-heavy and heavy nuclei based on the microscopic framework of the nuclear energy density functional theory. Constrained self-consistent mean-field calculation with a given energy density functional is performed to provide for each nucleus a potential energy surface with axial quadrupole and octupole shape degrees of freedom. Spectroscopic properties are computed by means of the interacting-boson Hamiltonian, which is determined by mapping the fermionic potential energy surface onto the bosonic counterpart. The overall systematics of the calculated spectroscopic observables exhibit phase transitional behaviors between stable octupole deformation and octupole vibration characteristic of the octupole-soft potential within the set of nuclei in light actinide and rare-earth regions, Th, Ra, Sm, Gd, and Ba isotopes, where octupole shapes are most likely to occur.
nucl-thJ.Phys.Conf.Ser.(2020)·0 citations
06
A quartet BCS-like theory
V. V. Baran · D. S. Delion
We introduce a BCS-like theory for the quartet correlations induced by the isovector pairing interaction. It is based on a coherent state of BCS type and, unlike usual mean field approaches, it displays a vanishing pair anomalous density $⟨ c^{†} c^{†} ⟩ = 0$ . We find good agreement between our theory and the exact results. We discuss how the pairing and quarteting correlations share some similar qualitative features within the BCS approach. However, there is no sharp quarteting phase transition. We also present various ways in which our theory may be further developed.
nucl-thPLB(2020)·23 citations
07
Quantifying multinucleon effect in Argon using high-pressure TPC
Jaydip Singh🇮🇳 · Srishti Nagu🇮🇳 · Jyotsna Singh🇮🇳 · R.B. Singh🇮🇳
Neutrino oscillation experiments use heavy nuclear targets to achieve sufficient interaction rates. Nuclear effects are introduced in the experimental environment by the use of these targets and need to be quantified as they add to the systematic errors. In the low energy region(around 1 GeV) multinucleon events are also present along with Quasi Elastic(QE) and Delta interactions. Therefore if these multinucleon events are not incorporated in the data set properly, we end up with an inaccurate reconstruction of neutrino energy. In our work, we have illustrated the importance of incorporation of multinucleon events for the reduction of systematic errors in physics predictions by DUNE-Near Detector(ND). To achieve this we have presented the event distribution ratio of Ar/C, Ar/Ar, and C/C as a function of squared four-momentum transfer by employing different nuclear models. This analysis recommends the addition of 2p2h or multinucleon events in the event sample and promotes model with Random Phase Approximations(RPA) effect for the analysis of the event sample to overcome or reduce the systematic uncertainties.
nucl-thhep-phNPB(2020)·11 citations
08
Analytic solutions of the Schrödinger equation with non-central generalized inverse quadratic Yukawa potential
C. O. Edet · P. O Okoi · S. O Chima
This study presents the solutions of Schrödinger equation for the Non-Central Generalized Inverse Quadratic Yukawa Potential within the framework of Nikiforov-Uvarov. The radial and angular part of the Schrödinger equation are obtained using the method of variable separation. More so, the bound states energy eigenvalues and corresponding eigenfunctions are obtained analytically. Numerical results were obtained for the Generalized Inverse Quadratic Yukawa Potential for comparison sake. It was found out that our results agree with existing literature.
↳ quant-phmath-phmath.MPnucl-thRev.Bras.Ens.Fis.(2020)·13 citations
09
Temperature Dependence of the Axion Mass in a Scenario Where the Restoration of Chiral Symmetry Drives the Restoration of the $U_{A} (1)$ Symmetry
Davor Horvatić🇭🇷 · Dalibor Kekez🇭🇷 · Dubravko Klabučar🇭🇷
The temperature ( $T$ ) dependence of the axion mass is predicted for $T$ 's up to $\sim 2.3 \times$ the chiral restoration temperature of QCD. The axion is related to the $U_{A} (1)$ anomaly. The squared axion mass $m_{a} (T)^{2}$ is, modulo the presently undetermined scale of spontaneous breaking of Peccei-Quinn symmetry $f_{a}$ (squared), equal to QCD topological susceptibility $χ (T)$ for all $T$ . We obtain $χ (T)$ by using quark condensates calculated in two effective Dyson-Schwinger models of nonperturbative QCD. They exhibit the correct chiral behavior, including the dynamical breaking of chiral symmetry and its restoration at high $T$ . This is reflected in the $U_{A} (1)$ symmetry breaking and restoration through $χ (T)$ . In our previous studies, such $χ (T)$ yields the $T$ -dependence of the $U_{A} (1)$ -anomaly-influenced masses of $η^{'}$ and $η$ mesons consistent with experiment. This in turn supports our prediction for the $T$ -dependence of the axion mass. Another support is a rather good agreement with the pertinent lattice results. This agreement is not spoiled by our varying $u$ and $d$ quark mass parameters out of the isospin limit.
↳ hep-phnucl-thUniverse(2019)·8 citations
10
Towards a combined analysis of inclusive/exclusive electroproduction
Astrid N. Hiller Blin🇩🇪 · Vitaly V. Chesnokov🇷🇺 · Victor I. Mokeev🇺🇸
In view of the major advances achieved by the CLAS experiments in studying the N* electroexcitation amplitudes, as well as further extension of these studies in the experiments with CLAS12, we present an approach for the evaluation of the resonant contributions to inclusive electron scattering off protons. For the first time, the resonant contributions are determined from the experimental results on N* electrocouplings available from the data analyses of exclusive meson electroproduction off protons. This is a useful benchmark for future endeavours on understanding the transition region between low and high-energy regions, strongly related to tests on quark-hadron duality.
↳ hep-phnucl-thEPJ Web Conf.(2020)·1 citation
11
The Hellmann-Feynman theorem at finite temperature
Marina Pons · Bruno Juliá-Díaz · Arnau Rios · Isaac Vidaña · Artur Polls
We present a simple derivation of the Hellmann-Feynman theorem at finite temperature. We illustrate its validity by considering three relevant examples which can be used in quantum mechanics lectures: the one-dimensional harmonic oscillator, the one-dimensional Ising model and the Lipkin model. We show that the Hellmann-Feynman theorem allows one to calculate expectation values of operators that appear in the Hamiltonian. This is particularly useful when the total free-energy is available, but there is not direct access to the thermal average of the operators themselves.
↳ quant-phcond-mat.quant-gascond-mat.stat-mechnucl-th+1Am.J.Phys.(2020)·5 citations
12
Consistency checks for two-body finite-volume matrix elements: I. Conserved currents and bound states
Raúl A. Briceño🇺🇸 · Maxwell T. Hansen🇨🇭 · Andrew W. Jackura🇺🇸
Recently, a framework has been developed to study form factors of two-hadron states probed by an external current. The method is based on relating finite-volume matrix elements, computed using numerical lattice QCD, to the corresponding infinite-volume observables. As the formalism is complicated, it is important to provide non-trivial checks on the final results and also to explore limiting cases in which more straightforward predications may be extracted. In this work we provide examples on both fronts. First, we show that, in the case of a conserved vector current, the formalism ensures that the finite-volume matrix element of the conserved charge is volume-independent and equal to the total charge of the two-particle state. Second, we study the implications for a two-particle bound state. We demonstrate that the infinite-volume limit reproduces the expected matrix element and derive the leading finite-volume corrections to this result for a scalar current. Finally, we provide numerical estimates for the expected size of volume effects in future lattice QCD calculations of the deuteron's scalar charge. We find that these effects completely dominate the infinite-volume result for realistic lattice volumes and that applying the present formalism, to analytically remove an infinite-series of leading volume corrections, is crucial to reliably extract the infinite-volume charge of the state.
↳ hep-lathep-phnucl-thPRD(2019)·39 citations
13
A new approach for open quantum systems based on a phonon number representation of a harmonic oscillator bath
M. Tokieda · K. Hagino
To investigate a system coupled to a harmonic oscillator bath, we propose a new approach based on a phonon number representation of the bath. Compared to the method of the hierarchical equations of motion, the new approach is computationally much less expensive in a sense that a reduced density matrix is obtained by calculating the time evolution of vectors, instead of matrices, which enables one to deal with large dimensional systems. As a benchmark test, we consider a quantum damped harmonic oscillator, and show that the exact results can be well reproduced. In addition to the reduced density matrix, our approach also provides a link to the total wave function by introducing new boson operators.
↳ quant-phcond-mat.stat-mechnucl-thAnnals Phys.(2020)·10 citations
14
Global fluid fits to identified particle transverse momentum spectra from heavy-ion collisions at the Large Hadron Collider
D. Devetak🇩🇪 · A. Dubla🇩🇪 · S. Floerchinger🇩🇪 · E. Grossi🇩🇪 · S. Masciocchi🇩🇪 · A. Mazeliauskas🇨🇭 · I. Selyuzhenkov🇩🇪
Transverse momentum spectra of identified particles produced in heavy-ion collisions at the Large Hadron Collider are described with relativistic fluid dynamics. We perform a systematic comparison of experimental data for pions, kaons and protons up to a transverse momentum of 3 GeV $/ c$ with calculations using the FluiduM code package to solve the evolution equations of fluid dynamics, the TrENTo model to describe the initial state and the FastReso code to take resonance decays into account. Using data in five centrality classes at the center-of-mass collision energy per nucleon pair $s_{NN} = 2.76 TeV$ , we determine systematically the most likely parameters of our theoretical model including the shear and bulk viscosity to entropy ratios, the initialization time, initial density and freeze-out temperature through a global search and quantify their posterior probability. This is facilitated by the very efficient numerical implementation of FluiduM and FastReso. Based on the most likely model parameters we present predictions for the transverse momentum spectra of multi-strange hadrons as well as identified particle spectra from Pb-Pb collisions at $s_{NN} = 5.02 TeV$ .
↳ hep-phnucl-exnucl-thJHEP(2020)·50 citations

Affiliations

first authorsco-authorsvia INSPIRE