Nuclear Theory·nucl-th

Friday·January 16, 2015

14 papers—11 primary·3 cross-listed

01
Uncertainty Quantification for Nuclear Density Functional Theory and Information Content of New Measurements
J.D. McDonnell · N. Schunck · D. Higdon · J. Sarich · S.M. Wild · W. Nazarewicz
Statistical tools of uncertainty quantification can be used to assess the information content of measured observables with respect to present-day theoretical models; to estimate model errors and thereby improve predictive capability; to extrapolate beyond the regions reached by experiment; and to provide meaningful input to applications and planned measurements. To showcase new opportunities offered by such tools, we make a rigorous analysis of theoretical statistical uncertainties in nuclear density functional theory using Bayesian inference methods. By considering the recent mass measurements from the Canadian Penning Trap at Argonne National Laboratory, we demonstrate how the Bayesian analysis and a direct least-squares optimization, combined with high-performance computing, can be used to assess the information content of the new data with respect to a model based on the Skyrme energy density functional approach. Employing the posterior probability distribution computed with a Gaussian process emulator, we apply the Bayesian framework to propagate theoretical statistical uncertainties in predictions of nuclear masses, two-neutron dripline, and fission barriers. Overall, we find that the new mass measurements do not impose a constraint that is strong enough to lead to significant changes in the model parameters. The example discussed in this study sets the stage for quantifying and maximizing the impact of new measurements with respect to current modeling and guiding future experimental efforts, thus enhancing the experiment-theory cycle in the scientific method.
nucl-thPRL(2015)·118 citations
02
Superfluid dynamics of 258Fm fission
Guillaume Scamps🇫🇷 · Cédric Simenel🇦🇺 · Denis Lacroix🇫🇷
Theoretical description of nuclear fission remains one of the major challenges of quantum many-body dynamics. The slow, mostly adiabatic motion through the fission barrier is followed by a fast, non-adiabatic descent of the potential between the fragments. The latter stage is essentially unexplored. However, it is crucial as it generates most of the excitation energy in the fragments. The superfluid dynamics in the latter stage of fission is obtained with the time-dependent Hartree-Fock theory including BCS dynamical pairing correlations. The fission modes of the 258Fm nucleus are studied. The resulting fission fragment characteristics show a good agreement with experimental data. Quantum shell effects are shown to play a crucial role in the dynamics and formation of the fragments. The importance of quantum fluctuations beyond the independent particle/quasi-particle picture is underlined and qualitatively studied.
nucl-thPRC(2015)·117 citations
03
Coulomb breakup of $^{37}$ Mg and its ground state structure
Neelam Shubhchintak · R. Chatterjee · R. Shyam · K. Tsushima
We calculate Coulomb breakup of the neutron rich nucleus $^{37}$ Mg on a Pb target at the beam energy of 244 MeV/nucleon within the framework of a finite range distorted wave Born approximation theory that is extended to include the effects of projectile deformation. In this theory, the breakup amplitude involves the full wave function of the projectile ground state. Calculations have been carried out for the total one-neutron removal cross section $(σ_{- 1 n})$ , the neutron-core relative energy spectrum, the parallel momentum distribution of the core fragment, the valence neutron angular, and energy-angular distributions. The calculated $σ_{- 1 n}$ has been compared with the recently measured data to put constraints on the spin parity, and the one-neutron separation energy ( $S_{n}$ ) of the $^{37}$ Mg ground state ( $^{37}$ Mg $_{g s}$ ). The dependence of $σ_{- 1 n}$ on the deformation of this state has also been investigated. While a spin parity assignment of $7/ 2^{-}$ for the $^{37}$ Mg $_{g s}$ is ruled out by our study, neither of the $3/ 2^{-}$ and $1/ 2^{+}$ assignments can be clearly excluded. Using the spectroscopic factor of one for both the $3/ 2^{-}$ and $1/ 2^{+}$ configurations and ignoring the projectile deformation effects, the $S_{n}$ values of $0.35 \pm 0.06$ MeV and $0.50 \pm 0.07$ MeV, respectively, are extracted for the two configurations. However, the extracted $S_{n}$ is strongly dependent on the spectroscopic factor and the deformation effects of the respective configuration. The narrow parallel momentum distribution of the core fragment and the strong forward peaking of the valence neutron angular distribution suggest a one-neutron halo configuration in either of the $2 p_{3/2}$ and $2 s_{1/2}$ configurations of the $^{37}$ Mg ground state.
nucl-thnucl-exNPA(2015)·21 citations
04
Pion Transverse Momentum Spectrum, Elliptic Flow and Interferometry in the Granular Source Model in Ultra-Relativistic Heavy Ion Collisions
Jing Yang🇨🇳 · Yan-Yu Ren🇨🇳 · Wei-Ning Zhang🇨🇳
We systematically investigate the pion transverse momentum spectrum, elliptic flow, and Hanbury-Brown-Twiss (HBT) interferometry in the granular source model of quark-gluon plasma droplets in ultra-relativistic heavy ion collisions. The granular source model can well reproduce the experimental results of the Au-Au collisions at $s_{N N} =$ 200 GeV and the Pb-Pb collisions at $s_{N N} =$ 2.76 TeV with different centralities. We examine the parameters of the granular source models with an uniform and Woods-Saxon initial energy distributions in a droplet. The parameters exhibit certain regularities for collision centrality and energy.
nucl-th3 citations
05
Accuracy of the new pairing theory and its improvement
L. Y. Jia
Recently I proposed a new method for solving the pairing Hamiltonian with the pair-condensate wavefunction ansatz based on the Heisenberg equations of motion for the density matrix operators. In this work an improved version is given by deriving the relevant equations more carefully. I evaluate both versions in a large ensemble with random interactions, and the accuracy of the methods is given statistically in terms of root-mean-square derivations from the exact results. The widely used variational calculation is also done and the results and computing-time costs are compared.
nucl-thPRC(2013)·8 citations
06
Solving for the Particle-Number-Projected HFB Wavefunction
L. Y. Jia
Recently we proposed a particle-number-conserving theory for nuclear pairing [Jia, Phys. Rev. C 88, 044303 (2013)] through the generalized density matrix formalism. The relevant equations were solved for the case when each single-particle level has a distinct set of quantum numbers and could only pair with its time-reversed partner (BCS-type Hamiltonian). In this work we consider the more general situation when several single-particle levels could have the same set of quantum numbers and pairing among these levels is allowed (HFB-type Hamiltonian). The pair condensate wavefunction (the HFB wavefunction projected onto good particle number) is determined by the equations of motion for density matrix operators instead of the variation principle. The theory is tested in the simple two-level model with factorizable pairing interactions and the semi-realistic model with the zero-range delta interaction.
nucl-thNPA(2015)·4 citations
07
The hypercentral Constituent Quark Model and its application to baryon properties
M. M. Giannini🇮🇹 · E. Santopinto🇮🇹
The hypercentral Constituent Quark Model (hCQM) for the baryon structure is reviewed and its applications are systematically discussed. The model is based on a simple form of the quark potential, which contains a Coulomb-like interaction and a confinement, both expressed in terms of a collective space coordinate, the hyperradius. The model has only three free parameters, determined in order to describe the baryon spectrum. Once the parameters have been fixed, the model, in its non relativistic version, is used to predict various quantities of physical interest, namely the elastic nucleon form factors, the photocouplings and the helicity amplitudes for the electromagnetic excitation of the baryon resonances. In particular, the $Q^{2}$ dependence of the helicity amplitude is quite well reproduced, thanks to the Coulomb-like interaction. The model is reformulated in a relativistic version by means of the Point Form hamilton dynamics. While the inclusion of relativity does not alter the results for the helicity amplitudes, a good description of the nucleon elastic form factors is obtained.
nucl-thhep-phChin.J.Phys.(2015)·145 citations
08
Particle Number Fluctuations for van der Waals Equation of State
V. Vovchenko · D. V. Anchishkin · M. I. Gorenstein
The van der Waals (VDW) equation of state describes a thermal equilibrium in system of particles, where both repulsive and attractive interactions between them are included. This equation predicts an existence of the 1st order liquid-gas phase transition and the critical point. The standard form of the VDW equation is given by the pressure function in the canonical ensemble (CE) with a fixed number of particles. In the present paper the VDW equation is transformed to the grand canonical ensemble (GCE). We argue that this procedure can be useful for new physical applications. Particularly, the fluctuations of number of particles, which are absent in the CE, can be studied in the GCE. For the VDW equation of state in the GCE the particle number fluctuations are calculated for the whole phase diagram, both outside and inside the liquid-gas mixed phase region. It is shown that the scaled variance of these fluctuations remains finite within the mixed phase and goes to infinity at the critical point. The GCE formulation of the VDW equation of state can be also an important step for its application to a statistical description of hadronic systems, where numbers of different particle species are usually not conserved.
nucl-thcond-mat.stat-mechJ.Phys.A(2015)·62 citations
09
The scissors mode from a different perspective
Matthew Harper · Larry Zamick
The scissors mode, a magnetic dipole excitation-mainly orbital is usually discussed in terms of a transition from a J=0^{+} ground state to a J=1^{+} excited state. This is understandable because it follows from the way the experiment is performed-e.g. inelastic electron scattering. Here however, we start with the excited 1^{+} state and consider all possible transitions to J=0,1 and 2 states.
nucl-thnucl-exphysics.atom-phPRC(2015)·8 citations
10
Yields of neutron-rich nuclei by actinide photofission in giant dipole resonance region
Debasis Bhowmick🇮🇳 · Debasis Atta🇮🇳 · D. N. Basu🇮🇳 · Alok Chakrabarti🇮🇳
Photofission of actinides is studied in the region of nuclear excitation energies that covers the entire giant dipole resonance (GDR) region. A comparative analysis of the behavior of the symmetric and asymmetric modes of photon induced fission as a function of the average excitation energy of the fissioning nucleus is performed. The mass distributions of $^{238}$ U photofission fragments are obtained at the endpoint bremsstrahlung energy of 29.1 MeV which corresponds to mean photon energy of 13.7 $\pm$ 0.3 MeV that coincides with GDR peak for $^{238}$ U photofission. The integrated yield of $^{238}$ U photofission as well as charge distribution of photofission products are calculated and its role in the production of neutron-rich nuclei and their exoticity is explored.
nucl-thPRC(2015)·7 citations
11
Two particle correlation effects and Differential HBT for rotation in heavy ion collisions
L.P. Csernai🇳🇴 · S. Velle🇳🇴 · D.J. Wang🇳🇴
Peripheral heavy ion reactions at ultra relativistic energies have large angular momentum that can be studied via two particle correlations using the Differential Hanbury Brown and Twiss method. We analyze the possibilities and sensitivity of the method in a rotating system. We also study an expanding solution of the fluid dynamical model of heavy ion reactions.
nucl-th0 citations
12
Electrical Conductivity of an Anisotropic Quark Gluon Plasma : A Quasiparticle Approach
P. K. Srivastava🇮🇳 · Lata Thakur🇮🇳 · Binoy Krishna Patra🇮🇳
The study of transport coefficients of strongly interacting matter got impetus after the discovery of perfect fluid ever created at ultrarelativistic heavy ion collision experiments. In this article, we have calculated one such coefficient viz. electrical conductivity of the quark gluon plasma (QGP) phase which exhibits a momentum anisotropy. Relativistic Boltzmann's kinetic equation has been solved in the relaxation-time approximation to obtain the electrical conductivity. We have used the quasiparticle description to define the basic properties of QGP. We have compared our model results with the corresponding results obtained in different lattice as well as other model calculations. Furthermore, we extend our model to calculate the electrical conductivity at finite chemical potential.
↳ hep-phnucl-thPRC(2015)·44 citations
13
X(3872), I^G(J^{PC})=0^+(1^{++}), as the \chi_{1c}(2P) charmonium
N.N. Achasov🇷🇺 · E.V. Rogozina🇷🇺
Contrary to almost standard opinion that the X(3872) resonance is the D^{*0}\bar D^0+c.c. molecule or the qc\bar q\bar c four-quark state, we discuss the scenario where the X(3872)resonance is the c\bar c = \chi_{c1}(2P) charmonium which "sits on" the D^{*0}\bar D^0 threshold. We explain the shift of the mass of the X(3872) resonance with respect to the prediction of a potential model for the mass of the \chi_{c1}(2P) charmonium by the contribution of the virtual D^*\bar D+c.c. intermediate states into the self energy of the X(3872) resonance. This allows us to estimate the coupling constant of the X(7872) resonance with the D^{*0}\bar D^0 channel, the branching ratio of the X(3872) \to D^{*0}\bar D^0 + c.c. decay, and the branching ratio of the X(3872) decay into all non-D^{*0}\bar D^0 + c.c. states. We predict a significant number of unknown decays of X(3872) via two gluon:X(3872)\to gluon\ gluon\to hadrons. We suggest a physically clear program of experimental researches for verification of our assumption.
↳ hep-phhep-exnucl-thMod.Phys.Lett.A(2015)·45 citations
14
Modeling the pion Generalized Parton Distribution
C. Mezrag🇫🇷
We compute the pion Generalized Parton Distribution (GPD) in a valence dressed quarks approach. We model the Mellin moments of the GPD using Ansätze for Green functions inspired by the numerical solutions of the Dyson-Schwinger Equations (DSE) and the Bethe-Salpeter Equation (BSE). Then, the GPD is reconstructed from its Mellin moment using the Double Distribution (DD) formalism. The agreement with available experimental data is very good.
↳ hep-phnucl-thInt.J.Mod.Phys.Conf.Ser.(2016)·2 citations

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first authorsco-authorsvia INSPIRE