arXiv subjects
Publications and source records attributed to Ryoichi Seki.
Nuclear effective field theory is applied to the effective range expansion of S-wave nucleon-nucleon scattering on a discrete lattice. Lattice regularization is demonstrated to yield the effective range expansion in the same way as in the usual continuous open space. The relation between the effective range parameters and the potential parameters is presented in the limit of a large lattice.
A quantitative understanding of the weak nuclear response is a prerequisite for the analyses of neutrino experiments such as K2K and MiniBOONE, which measure energy and angle of the muons produced in neutrino-nucleus interactions in the energy range $0.5-3$ GeV and reconstruct the incident neutrino energy to determine neutrino oscillations. In this paper we discuss theoretical calculations of electron- and neutrino-nucleus scattering, carried out within the impulse approximation scheme using realistic nuclear spectral functions.Comparison between electron scattering data and the calculated inclusive cross section off oxygen, at beam energies ranging between 700 and 1200 MeV, show that the Fermi gas model, widely used in the analysis of neutrino oscillation experiments,fails to provide a satisfactory description of the measured cross sections,and inclusion of nuclear dynamics is needed.
A brief overview is presented of various issues involved in phenomenological and theoretical works on charge-current neutrino-nucleus reactions associated with the quasi-free Delta(1232) production. An assessment of the present status of the works is made with respect to the objective of this conference, Sub-Dominant Oscillation Effects in Atmospheric Neutrino Experiments.
We carry out a relativistic calculation of the cross sections of electron-16O and -12C quasi-elastic scattering and quasi-free Delta production and compare with the (e,e') data systematically in the wide energy range of 0.5 - 1.5 GeV. Using the same formalism, we examine the mu-neutrino quasi-elastic scattering from 16O. The model incorporating the nuclear correlation effects agrees better with the electron-nucleus scattering data than a uniform Fermi-Gas model. In the neutrino quasi-elastic scattering, the nuclear correlation has an appreciable effect on the cross section of high-energy scattered leptons, and it may have an important consequence in the neutrino oscillation measurements aiming at a few % precision.
We demonstrate that the matter density distribution in the surface region is determined well by the use of the relatively low-intensity beams that become available at the upcoming radioactive beam facilities. Following the method used in the analyses of electron scattering, we examine how well the density distribution is determined in a model-independent way by generating pseudo data and by carefully applying statistical and systematic error analyses. We also study how the determination becomes deteriorated in the central region of the density, as the quality of data decreases. Determination of the density distributions of neutron-rich nuclei is performed by fixing parameters in the basis functions to the neighboring stable nuclei. The procedure allows that the knowledge of the density distributions of stable nuclei assists to strengthen the determination of their unstable isotopes.
We calculate cross sections of high energy electron inclusive scattering off nuclear matter in a new and consistent formulation based on the Green's function method with the Glauber approximation, which is an extension of our previous work on the nuclear transparency in (e, e'p) reaction. The comparison with other approaches is discussed. In this framework, we study the finite-range effect of the nucleon-nucleon interaction in the final-state interactions, and the effect of the nuclear short-range correlation. We propose a zero-range approximation, which works well when correlation and finite interaction-range effects are included. It greatly reduces the numerical work, while maintaining a reasonable accuracy.
We investigate a domain-structured source in the pion interferometry of relativistic nuclear collisions. The source emits coherent pions intermittently with the background of chaotic pions. The coherent pions examined are either of a general nature or of disoriented chiral condensate. Two- and three-pion correlations for the source are shown to agree well with the recent NA44 experimental data.
Three-pion interferometry is investigated for new information on the space-time structure of the pion source created in ultra-relativistic heavy-ion collisions. The two- and three-pion correlations are numerically computed for incoherent source functions based on the Bjorken hydrodynamical model, over a wide range of the kinematic variables. New information provided by three-pion interferometry, different from that provided by two-pion interferometry, should appear in the phases of the Fourier transform of the source function. Variables are identified that would be sensitive to the phases and suitable for observation. For a positive, chaotic source function, however, a variation of the three-pion phase is found to be difficult to extract from experiments. Effects of asymmetry of the source function are also examined.
Two- and three-pion correlation functions are investigated for a source that is not fully chaotic. Various models are examined to describe the source. The chaoticity and weight factor are evaluated in each model as measures of the strength of correlations and compared to experimental results. A new measure of three-pion correlation is also suggested.
Two- and three-pion correlations are investigated in cases when disoriented chiral condensate (DCC) occurs. A chaoticity and weight factor are used as measures of two- and three-pion correlations, and the various models for DCC are investigated. Some models are found to yield the chaoticity and weight factor in a reasonable agreement with recent experimental data.
We analyze the geometry of the species- and genotype-size distribution in evolving and adapting populations of single-stranded self-replicating genomes: here programs in the Avida world. We find that a scale-free distribution (power law) emerges in complex landscapes that achieve a separation of two fundamental time scales: the relaxation time (time for population to return to equilibrium after a perturbation) and the time between mutations that produce fitter genotypes. The latter can be dialed by changing the mutation rate. In the scaling regime, we determine the critical exponent of the distribution of sizes and strengths of avalanches in a system without coevolution, described by first-order phase transitions in single finite niches.
Spin-polarization response functions are examined for high-energy $(\vec{e},e'\vec{p})$ reaction by computing the full 18 response functions for the proton kinetic energy $T_{p'}=$ 0.515 GeV and 3.179 GeV with an 16O target. The Dirac eikonal formalism is applied to account for the final-state interactions. The formalism is found to yield the response functions in good agreement with those calculated by the partial-wave expansion method at 0.515 GeV. We identify the response functions that depend on the spin-orbital potential in the final-state interactions, but not on the central potential. Dependence on the Dirac- or Pauli-type current of the nucleon is investigated in the helicity-dependent response functions, and the normal-component polarization of the knocked-out proton, $P_n$, is computed.
We calculate, in chiral perturbation theory, the change in the self-energy of decuplet baryons in nuclear matter. These self-energy shifts are relevant in studies of meson-nucleus scattering and of neutron stars. Our results are leading order in an expansion in powers of the ratio of characteristic momenta to the chiral symmetry-breaking scale (or the nucleon mass). Included are contact diagrams generated by 4-baryon operators, which were neglected in earlier studies for the $Δ$ isomultiplet but contribute to the self-energy shifts at this order in chiral perturbation theory.
Nuclear transparency is calculated for high-energy, semi-inclusive $(e,e'p)$ reactions, by accounting for all orders of Glauber multiple-scattering and by using realistic finite-range $p N$ interaction and (dynamically and statistically) correlated nuclear wave functions. The nuclear correlation effect is reduced due to the $p N$ finite-range effect. The net effect is small, and depends sensitively on details of the nuclear correlations in finite nuclei, which are poorly known at present.