Ryoichi Seki

Observation of Kaonic Hydrogen K α X Rays

We have measured the shift and width of the kaonic hydrogen 1s state due to the {ovr K}N strong interaction. We have observed, for the first time, distinct K-series kaonic hydrogen x rays with good signal-to-noise ratio in the energy spectrum. The measured energy shift and width were determined to be {Delta}E(1s)=-323{plus_minus}63(stat){plus_minus}11(syst)eV (repulsive) and {Gamma}(1s)=407{plus_minus}208(stat){plus_minus}100(syst)eV,respectively. {copyright} {ital 1997} {ital The American Physical Society}

Electron- and neutrino-nucleus scattering in the impulse approximation regime

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 of 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.

Nuclear matter on a lattice

We investigate nuclear matter on a cubic lattice. An exact thermal formalism is applied to nucleons with a Hamiltonian that accommodates on-site and next-neighbor parts of the central, spin-, and isospin-exchange interactions. We describe the nuclear matter Monte Carlo methods which contain elements from shell model Monte Carlo methods and from numerical simulations of the Hubbard model. We show that energy and basic saturation properties of nuclear matter can be reproduced. Evidence of a first-order phase transition from an uncorrelated Fermi gas to a clustered system is observed by computing mechanical and thermodynamical quantities such as compressibility, heat capacity, entropy, and grand potential. We compare symmetry energy and first sound velocities with literature and find reasonable agreement.

Nuclear transparency in the Glauber impulse approximation

Abstract We carefully construct a formalism, called the Glauber impulse approximation, for describing nuclear transparency for the semi-exclusive process of high-energy proton quasi-elastic scattering from nuclei. The formalism is based on the conventional multiple-scattering theory and uses the Glauber theory with impulse approximation. In the heavy nuclear limit, our formalism yields the familiar formula for the process based on the mean-free-path argument, except that the reaction cross section appears instead of the total cross section. Our nuclear transparency is thus larger than what could naively have been expected. The nuclear transparency calculated for various nuclei, agrees with the observation in overall magnitude, but fails to explain the energy variation.

Effective field theory of nucleon-nucleon scattering on large discrete lattices

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.

Electron screening in molecular fusion reactions

Abstract Recent laboratory experiments have measured fusion cross sections at center-of-mass energies low enough for the effects of atomic and molecular electrons to be important. To extract the cross section for bare nuclei from these data (as required for astrophysical applications), it is necessary to understand these screening effects. We study electron screening effects in the low-energy collisions of Z = 1 nuclei with hydrogen molecules. Our model is based on a dynamical evolution of the electron wave functions within the TDHF scheme, while the motion of the nuclei is treated classically. We find that at the currently accessible energies the screening effects depend strongly on the molecular orientation. The screening is found to be larger for molecular targets than for atomic targets, due to the reflection symmetry in the latter. The results agree fairly well with data measured for deuteron collisions on molecular deuterium and tritium targets.

A unified analysis of pionic atoms and low-energy pion-nucleus scattering

Abstract The nature of the insensitivity of low-energy (⩽ 50 MeV, including π - -atoms) data to be detailed structure of the optical potential is established. By means of the effective nuclear density for the pion interaction, a phenomenological Kisslinger potential for the pionic atoms is microscopically shown to be extrapolated successfully to the low-energy scattering.

Spin-orbit potential in the Skyrme model

Abstract The full spin-orbit potential is calculated in the Skyrme model with a product ansatz. The magnitude of the potential agrees with conventional vector-meson exchange potentials in the asymptotic region. The isoscalar part has, however, the opposite sign to conventional potentials. This difficulty with the isoscalar part is similar to that of missing central attraction.

KAONIC HYDROGEN MEASUREMENT WITH DEAR AT DAΦNE

The DEAR (DAΦNE Exotic Atom Research) experiment1 measured the energy of X-rays emitted in the transitions to the ground states of kaonic hydrogen. The shift ∊ and the width Γ of the 1s state are sensitive quantities for tests of the current understanding of the low energy antikaon-nucleon interaction. We obtain ∊1s=-193±37 (stat.)±6 (syst.) and Γ1s=249±112 (stat.)±30 (syst.).

A new approach to measure kaonic hydrogen X-rays

Abstract Previous kaonic hydrogen X-ray experiments suffered from a poor signal-to-background level. This has been overcome in the present measurement through the use of a gaseous hydrogen target and the imposition of a two-charged-pion tagging requirement. In this paper a full technical description is given of the experimental methods employed.