Nuclear Theory·nucl-th

Tuesday·June 26, 2018

17 papers—10 primary·7 cross-listed

01
Astrophysical factors of $^{12} C +^{12} C$ fusion from Trojan horse method
A. M. Mukhamedzhanov · D. Y. Pang
Carbon-carbon burning plays an important role in many stellar environments. Recently, using the indirect Trojan horse method A. Tumino {\em et al.} reported [Nature {\bf 557} 687 (2018)] a strong rise of the astrophysical factor for the carbon-carbon fusion at low resonance energies. In this paper, we demonstrate that this rise is the artifact of using an invalid plane-wave approximation. It is shown that the calculated renormalization factor decreases the astrophysical factor from [A. Tumino {\em et al.}, Nature {\bf 557} 687 (2018)] at the resonance energies of $E = 0.8 - 0.9$ MeV by as much as $\approx 1 0^{3}$ times.
nucl-thPRC(2019)·43 citations
02
Semiclassical description of chiral geometry in triaxial nuclei
R. Budaca🇷🇴
A triaxial particle-rotor Hamiltonian for three mutually perpendicular angular momentum vectors corresponding to two high- $j$ quasiparticles and the rotation of a triaxial collective core, is treated within a time-dependent variational principle. The resulting classical energy function is used to investigate the rotational dynamics of the system. It is found that the classical energy function exhibits two minima starting from a critical angular momentum value which depends on the single-particle configuration and the asymmetry measure $γ$ . The emergence of the two minima is attributed to the breaking of the chiral symmetry. Quantizing the energy function for a given angular momentum, one obtains a Schrödinger equation with a coordinate dependent mass term for a symmetrical potential which changes from a single to a double well shape as the angular momentum pass the critical value. The energies of the chiral partner bands for a given angular momentum are then given by the lowest two eigenvalues. The procedure is exemplified for maximal triaxiality and two $h_{11/2}$ quasiparticles, with the results used for the description of the chiral doublet bands in $^{134}$ Pr.
nucl-thPRC(2018)·21 citations
03
A linearized Boltzmann--Langevin model for heavy quark transport in hot and dense QCD matter
Weiyao Ke🇺🇸 · Yingru Xu🇺🇸 · Steffen A. Bass🇺🇸
In relativistic heavy-ion collisions, the production of heavy quarks at large transverse momenta is strongly suppressed compared to proton-proton collisions. In addition an unexpectedly large azimuthal anisotropy was observed for the emission of charmed hadrons in non-central collisions. Both observations pose challenges to the theoretical understanding of the coupling between heavy quarks and the quark-gluon plasma produced in these collisions. Transport models for the evolution of heavy quarks in a QCD medium offer the opportunity to study these effects - two of the most successful approaches are based on the linearized Boltzmann transport equation and the Langevin equation. In this work, we develop a hybrid transport model that combines the strengths of both of these approaches: heavy quarks scatter with medium partons using matrix-elements calculated in perturbative QCD, while between these discrete hard scatterings they evolve using a Langevin equation with empirical transport coefficients to capture the non-perturbative soft part of the interaction. With the hybrid transport model coupled to a state-of-the-art event-by-event bulk evolution model based on 2+1D relativistic viscous fluid dynamics, we study the azimuthal anisotropy and nuclear modification factor of heavy quarks in Pb+Pb collisions at $s = 5.02$ TeV. The parameters of our model are calibrated using a Bayesian analysis comparing to available $D$ -meson and $B$ -meson data at the LHC. Using the calibrated model, we study the implications on heavy-flavor transport properties and predict novel observables.
nucl-thPRC(2018)·130 citations
04
The $S_{E 1}$ factor of radiative $α$ capture on $^{12}$ C in cluster effective field theory
Shung-Ichi Ando (Sunmoon U.)🇰🇷
The $S_{E 1}$ -factor of radiative $α$ -capture on $^{12}$ C is studied in effective field theory up to next-to-leading order. A modification of the counting rules for the radiative capture amplitudes is discussed. We find that only two unfixed parameters remain in the amplitudes, and those two parameters are fitted to the experimental $S_{E 1}$ data. An $S_{E 1}$ factor is calculated at the Gamow-peak energy as $S_{E 1} = 59 \pm 3$ keV $\cdot$ b, and the result is found to be about 30% smaller than the estimates reported recently. An uncertainty of the estimate in the present work is also discussed.
nucl-thnucl-exPRC(2019)·22 citations
05
{\it Ab initio} perturbation calculations of realistic effective interactions in the Hartree--Fock basis
Q. Wu🇨🇳 · F.R. Xu🇨🇳 · B.S. Hu🇨🇳 · J.G. Li🇨🇳
We perform two types of {\it ab initio} perturbation calculations of effective interactions in the Hartree--Fock (HF) basis instead of the harmonic-oscillator basis: one is called the Brillouin--Wigner (BW) perturbation and another is called the Rayleigh--Schrödinger (RS) perturbation. It is shown that the HF basis provides good convergences. We also benchmark the perturbation calculations with the in-medium similarity renormalization group (IM-SRG) which is a nonperturbative method. In the HF basis some-type perturbation diagrams can be cancelled out, while the cancellation does not happen in the harmonic-oscillator basis. We have investigated the {\it sd} shell using the chiral N $^{3}$ LO potential softened by $V_{low- k}$ . With the low-momentum N $^{3}$ LO potential, we first perform the spherical HF calculations for the $^{16}$ O core of the {\it sd} shell, and the realistic effective two-body interactions for the HF {\it sd}-shell space can be derived by the perturbation calculations. The calculations give simultaneously effective single-particle energies and excitation spectra of two valence particle systems (i.e., $^{18}$ O, $^{18}$ F, and $^{18}$ Ne in the {\it sd} shell). Convergences have been analyzed order by order. The perturbation calculations are in fairly good agreement with nonperturbative method IM-SRG. We find that the HF RS perturbation gives even better results compared with the BW perturbation. The HF realistic effective interactions derived by the perturbations can be used for further shell-model calculations.
nucl-thJ.Phys.G(2019)·8 citations
06
Heavy Quarkonia in a Potential Model: Binding Energy, Decay Width, and Survival Probability
P. K. Srivastava🇮🇳 · O. S. K. Chaturvedi🇮🇳 · Lata Thakur🇮🇳
Recently a lot of progress has been made in deriving the heavy quark potential within a QCD medium. In this article we have considered heavy quarkonium in a hot quark gluon plasma phase. The heavy-quark potential has been modeled properly for short as well as long distances. The potential at long distances is modeled as a QCD string which is screened at the same scale as the Coloumb field. We have numerically solved the 1+1-dimensional Schrodinger equation for this potential and obtained the eigen wavefunction and binding energy for the $1 S$ and $2 S$ states of charmonium and bottomonium. Further, we have calculated the decay width and dissociation temperature of quarkonium states in the QCD plasma. Finally, we have used our recently proposed unified model with these new values of decay widths to calculate the survival probability of the various quarkonium states with respect to centrality at relativistic heavy ion collider (RHIC) and large hadron collider (LHC) energies. This study provides a unified, consistent and comprehensive description of spectroscopic properties of various quarkonium states at finite temperatures along with their nuclear modification factor at different collision energies.
nucl-thhep-phEPJC(2018)·16 citations
07
Discrepancy in low transverse momentum dileptons from relativistic heavy-ion collisions
Taesoo Song🇩🇪 · Wolfgang Cassing🇩🇪 · Pierre Moreau🇩🇪 · Elena Bratkovskaya🇩🇪
The dilepton transverse momentum spectra and invariant mass spectra for low $p_{T} < 0.15$ ~GeV/c in Au+Au collisions of different centralities at $s_{N N}$ = 200 GeV are studied within the parton-hadron-string dynamics (PHSD) transport approach. The PHSD describes the whole evolution of the system on a microscopic basis, incorporates hadronic and partonic degrees-of-freedom, the dynamical hadronization of partons and hadronic rescattering. For dilepton production in p+p, p+A and A+A reactions the PHSD incorporates the leading hadronic and partonic channels (also for heavy flavors) and includes in-medium effects such as a broadening of the vector meson spectral functions in hadronic matter and a modification of initial heavy-flavor correlations by interactions with the partonic and hadronic medium. The transport calculations reproduce well the momentum integrated invariant mass spectra from the STAR Collaboration for minimum bias Au+Au collisions at $s_{N N}$ = 200 GeV, while the description of the STAR data - when gating on low $p_{T} < 0.15$ GeV/c - is getting worse when going from central to peripheral collisions. An analysis of the transverse momentum spectra shows that the data for peripheral (60-80\%) collisions are well reproduced for $p_{T} > 0.2$ GeV/c while the strong peak at low $p_{T} < 0.15$ GeV/c, that shows up in the experimental data for the mass bins ( $0.4 < M < 0.7$ GeV and $1.2 < M < 2.6$ GeV), is fully missed by the PHSD and cannot be explained by the standard in-medium effects. This provides a new puzzle for microscopic descriptions of low $p_{T}$ dilepton data from the STAR Collaboration.
nucl-thnucl-exPRC(2018)·9 citations
08
Pygmy resonances: what's in a name?
R.A. Broglia🇮🇹 · F. Barranco🇪🇸 · A. Idini🇸🇪 · G. Potel🇺🇸 · E. Vigezzi🇮🇹
The centroid, width and percentage of energy weighted sum rule of dipole resonances can be strongly affected by dynamical fluctuations and static deformations of the nuclear surface, deformations and fluctuations which, in turn, depend on pairing, and thus on Cooper pairs. Because of angular momentum conservation, such insight is restricted, to lowest order, to deformations of quadrupole and monopole type. The latter being closely connected with the neutron (excess) skin and thus with soft dipole modes. From the values $(N - Z) / A \approx 0.18$ , 0.21, and 0.45 for the nuclei $^{122}$ Sn, $^{208}$ Pb, and $^{11}$ Li, it is expected that the latter system, which is weakly bound by pairing effects (spatially extended single Cooper pair and odd proton acting as spectator), constitutes an attractive laboratory to study the properties of soft $E 1$ --modes and thus of isospin nuclear deformation. From the calculation of the full dipole response function in QRPA, discretizing the continuum in a spherical box of radius of 40 fm, one finds a GDR with centroid $E_{x} \approx 24$ MeV, width $Γ \approx$ 11 MeV and carrying 90\% of the EWSR, and a low--lying collective resonance characterized by $E_{X} = 0.75$ MeV, $Γ = 0.5$ MeV and $6.2%$ EWSR The wave function of the latter resonance is built out of about fifteen components (both protons and neutrons), typical of a collective mode. The transition densities indicate this soft $E 1$ --mode to be generated by surface density oscillation of the neutron skin ( $Δ r_{n p} \approx 1.71$ fm) relative to an approximately isospin--saturated core. Through a detailed study of the full dipole response of $^{11}$ Li we will draw a comparison between the soft $E 1$ --mode of this halo nucleus and the PDR of heavy stable nuclei, pointing to the physical similarities and also to the basic differences.
nucl-thPhys.Scripta(2019)·6 citations
09
Effective-field-theory predictions of the muon-deuteron capture rate
Bijaya Acharya🇩🇪 · Andreas Ekström🇸🇪 · Lucas Platter🇺🇸
We quantify the theoretical uncertainties of chiral effective-field-theory predictions of the muon-deuteron capture rate. Theoretical error estimates of this low-energy process is important for a reliable interpretation of forthcoming experimental results by the MuSun collaboration. Specifically, we estimate the three dominant sources of uncertainties that impact theoretical calculations of this rate: those resulting from uncertainties in the pool of fit data used to constrain the coupling constants in the nuclear interaction, those due to the truncation of the effective field theory, and those due to uncertainties in the axial radius of the nucleon. For the capture rate into the $^{1} S_{0}$ channel, we find an uncertainty of approximately $4.6 s^{- 1}$ due to the truncation in the effective field theory and an uncertainty of $3.9 s^{- 1}$ due to the uncertainty in the axial radius of the nucleon, both of which are similar in size to the targeted experimental precision.
nucl-thnucl-exPRC(2018)·14 citations
10
Global superscaling analysis of quasielastic electron scattering with relativistic effective mass
J.E. Amaro🇪🇸 · V.L. Martinez-Consentino🇪🇸 · E. Ruiz Arriola🇪🇸 · I. Ruiz Simo🇪🇸
We present a global analysis of the inclusive quasielastic electron scattering data with a superscaling approach with relativistic effective mass. The SuSAM* model exploits the approximation of factorization of the scaling function $f^{*} (ψ^{*})$ out of the cross section under quasifree conditions. Our approach is based on the relativistic mean field theory of nuclear matter where a relativistic effective mass for the nucleon encodes the dynamics of nucleons moving in presence of scalar and vector potentials. Both the scaling variable $ψ^{*}$ and the single nucleon cross sections include the effective mass as a parameter to be fitted to the data alongside the Fermi momentum $k_{F}$ . Several methods to extract the scaling function and its uncertainty from the data are proposed and compared. The model predictions for the quasielastic cross section and the theoretical error bands are presented and discussed for nuclei along the periodic table from $A = 2$ to $A = 238$ : $^{2}$ H, $^{3}$ H, $^{3}$ He, $^{4}$ He, $^{12}$ C, $^{6}$ Li, $^{9}$ Be, $^{24}$ Mg, $^{59}$ Ni, $^{89}$ Y, $^{119}$ Sn, $^{181}$ Ta, $^{186}$ W, $^{197}$ Au, $^{16}$ O, $^{27}$ Al, $^{40}$ Ca, $^{48}$ Ca, $^{56}$ Fe, $^{208}$ Pb, and $^{238}$ U. We find that more than 9000 of the total $\sim 20000$ data fall within the quasielastic theoretical bands. Predictions for $^{48}$ Ti and $^{40}$ Ar are also provided for the kinematics of interest to neutrino experiments.
nucl-thnucl-exPRC(2018)·23 citations
11
Modeling the nonperturbative contributions to the complex heavy-quark potential
Yun Guo🇨🇳 · Lihua Dong🇨🇳 · Jisi Pan🇨🇳 · Manoel R. Moldes🇪🇸
In this paper, we construct a simple model for the complex heavy quark potential which is defined through the Fourier transform of the static gluon propagator. Besides the hard thermal loop resummed contribution, the gluon propagator also includes a non-perturbative term induced by the dimension two gluon condensate. Within the framework of thermal field theory, the real and imaginary parts of the heavy quark potential are determined in a consistent way without resorting to any extra assumption as long as the exact form of the retarded/advanced gluon propagator is specified. The resulting potential model has the desired asymptotic behaviors and reproduces the data from lattice simulation reasonably well. By presenting a direct comparison with other complex potential models on the market, we find the one proposed in this work shows a significant improvement on the description of the lattice results, especially for the imaginary part of the potential, in a temperature region relevant to quarkonium studies.
↳ hep-phnucl-thPRD(2019)·38 citations
12
In-medium loop corrections and longitudinally polarized gauge bosons in high-energy showers
Peter Arnold🇺🇸 · Shahin Iqbal🇵🇰
The splitting processes of bremsstrahlung and pair production in a medium are coherent over large distances in the very high energy limit, which leads to a suppression known as the Landau-Pomeranchuk-Migdal (LPM) effect. We continue study of the case when the coherence lengths of two consecutive splitting processes overlap (which is important for understanding corrections to standard treatments of the LPM effect in QCD), avoiding soft-emission approximations. In this particular paper, we show (i) how the "instantaneous" interactions of Light-Cone Perturbation Theory must be included in the calculation to account for effects of longitudinally-polarized gauge bosons in intermediate states, and (ii) how to compute virtual corrections to LPM emission rates, which will be necessary in order to make infrared-safe calculations of the characteristics of in-medium QCD showering of high-energy partons. In order to develop these topics in as simple a context as possible, we will focus in the current paper not on QCD but on large- $N_{f}$ QED, where $N_{f}$ is the number of electron flavors.
↳ hep-phnucl-thJHEP(2018)·22 citations
13
From Nuclei to the Cosmos: Tracing Heavy-Element Production with the Oldest Stars
Anna Frebel (MIT)🇺🇸
Understanding the origin of the elements has been a decades long pursuit, with many open questions still remaining. Old stars found in the Milky Way and its dwarf satellite galaxies can provide answers because they preserve clean elemental patterns of the nucleosynthesis processes that operated some 13 billion years ago. This enables the reconstruction of the chemical evolution of the elements. Here we focus on the astrophysical signatures of heavy neutron-capture elements made in the s-, i- and r-process found in old stars. A highlight is the recently discovered r-process galaxy Reticulum II that was apparently enriched by a neutron star merger. These results show that old stars in dwarf galaxies provide a novel means to constrain the astrophysical site of the r-process, ushering in much needed progress on this major outstanding question. This nuclear astrophysics work complements the many nuclear physics efforts into heavy-element formation, and aligns with recent results on the gravitational wave signature of a neutron star merger.
↳ astro-ph.SRnucl-exnucl-thAnn.Rev.Nucl.Part.Sci.(2018)·73 citations
14
Flavor-dependent EMC effect from a nucleon swelling model
Rong Wang🇫🇷 · Raphaël Dupre🇫🇷 · Yin Huang🇨🇳 · Baiyang Zhang🇭🇺 · Silvia Niccolai🇫🇷
We present our results for a flavor-dependent EMC effect based on the nIMParton nuclear PDFs, in which the $x$ -dependence is described with a nucleon swelling model. The nuclear correction from nucleon swelling is considered through a modification of the initial valence quark distributions instead of a dynamical rescaling. To probe the flavor-dependence of the model, the experimental observables are calculated applying nIMParton nuclear modifications for various experiments: parity-violating deep inelastic scattering on nuclear target, pion-induced Drell-Yan, and W-boson production in proton-nucleus collisions. In addition, we present the expected effect for the spectator-tagged deep inelastic scattering process, which will be performed by the CLAS12 collaboration with the ALERT detector.
↳ hep-phnucl-thPRC(2019)·11 citations
15
Deuteron and Antideuteron Production Simulation in Cosmic-ray Interactions
Diego-Mauricio Gomez-Coral🇲🇽 · Arturo Menchaca Rocha🇲🇽 · Varlen Grabski🇲🇽 · Amaresh Datta🇺🇸 · Philip von Doetinchem🇺🇸 · Anirvan Shukla🇺🇸
The study of the cosmic-ray deuteron and antideuteron flux receives an increasing interest in current astrophysics investigations. For both cases an important contribution is expected from the nuclear interactions of primary cosmic rays with intergalactic matter. In this work, deuteron and antideuteron production from 20 to 2.6 $\times$ 10 $^{7}$ GeV beam energy in p+p and p+A collisions were simulated using EPOS-LHC and Geant4's FTFP-BERT Monte Carlo models by adding an event-by-event coalescence model afterburner. These estimates depend on a single parameter ( $p_{0}$ ) obtained from a fit to the data. The $p_{0}$ for deuterons in this wide energy range was evaluated for the first time. It was found that $p_{0}$ for antideuterons is not a constant at all energies as previous works suggested and as a consequence the antideuteron production cross section can be at least 20 times smaller in the low collision energy region, than earlier estimations.
↳ astro-ph.HEhep-phnucl-thPRD(2018)·38 citations
16
Weak pion production off the nucleon in covariant chiral perturbation theory
De-Liang Yao🇪🇸 · Luis Alvarez-Ruso🇪🇸 · Astrid N. Hiller Blin🇩🇪 · M. J. Vicente Vacas🇪🇸
Weak pion production off the nucleon at low energies has been systematically investigated in manifestly relativistic baryon chiral perturbation theory with explicit inclusion of the $Δ$ (1232) resonance. Most of the involved low-energy constants have been previously determined in other processes such as pion-nucleon elastic scattering and electromagnetic pion production off the nucleon. For numerical estimates, the few remaining constants are set to be of natural size. As a result, the total cross sections for single pion production on neutrons and protons, induced either by neutrino or antineutrino, are predicted. Our results are consistent with the scarce existing experimental data except in the $ν_{μ} n \to μ^{-} n π^{+}$ channel, where higher-order contributions might still be significant. The $Δ$ resonance mechanisms lead to sizeable contributions in all channels, especially in $ν_{μ} p \to μ^{-} p π^{+}$ , even though the considered energies are close to the production threshold. The present study provides a well founded low-energy benchmark for phenomenological models aimed at the description of weak pion production processes in the broad kinematic range of interest for current and future neutrino-oscillation experiments.
↳ hep-phnucl-thPRD(2018)·36 citations
17
Multi-body correlations in SU(3) Fermi gases
Hiroyuki Tajima · Pascal Naidon
We investigate strong-coupling effects in a three-component atomic Fermi gas. It is a promising candidate for simulating quantum chromodynamics (QCD), and furthermore, the emergence of various phenomena such as color superfluidity and Efimov effect are anticipated in this system. In this paper, we study the effects of two-body and three-body correlations by means of the many-body $T$ -matrix approximation (TMA) as well as the Skorniakov-Ter-Martirosian (STM) equation with medium corrections. We investigate the effects of finite temperature and chemical potential on the trimer binding energy at the superfluid critical point of the unitarity limit.
↳ cond-mat.quant-gashep-phnucl-thJ.Low Temp.Phys.(2019)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE