K0 photoproduction on 12C in the threshold region
The γ n → K 0 Λ process plays an important role in the study of strangeness production by the electromagnetic interaction. We have investigated the quasi-free production reaction on a 12 C target in the threshold region ( E γ = 0.8 – 1.1 GeV ) at the Laboratory of Nuclear Science, Tohoku University. Preliminary results are presented.

title: Photoproduction of neutral kaons on a liquid deuterium target in the threshold region
abstract: The photoproduction process of neutral kaons on a liquid deuterium target is investigated near the threshold region, E{sub {gamma}}=0.8-1.1 GeV. K{sup 0} events are reconstructed from positive and negative pions, and differential cross sections are derived. Experimental momentum spectra are compared with those calculated in the spectator model using a realistic deuteron wave function. Elementary amplitudes as given by recent isobar models and a simple phenomenological model are used to study the effect of the new data on the angular behavior of the elementary cross section. The data favor a backward-peaked angular distribution of the elementary n({gamma},K{sup 0}){lambda} process, which provides additional constraints on current models of kaon photoproduction. The present study demonstrates that the n({gamma},K{sup 0}){lambda} reaction can provide key information on the mechanism of the photoproduction of strangeness.

title: Photoproduction of η-mesons off C and Cu nuclei for photon energies below 1.1 GeV
abstract: The η -meson photoproduction cross sections have been measured on C and Cu targets for the photon energies between 600 and 1100 MeV to investigate the behavior of the S 11 ( 1535 ) resonance in a nucleus. The excitation functions of the cross section as well as the angular and momentum distributions of η -mesons are in quantitative agreement with the Quantum Molecular Dynamics (QMD) model calculations in which the η -meson emission processes other than the S 11 ( 1535 ) resonance are also incorporated. It is shown that the η production in the γ N → π η N reaction and the D 15 ( 1675 ) resonance formation in the γ n → η n reaction play an important role for E γ > 900 MeV .

title: Study of double pion photoproduction on the deuteron
abstract: The π + π − photoproductions on the proton and deuteron have been studied in a photon energy range of 0.8–1.1 GeV at the Laboratory of Nuclear Science, Tohoku University. Charged pions and protons were detected using Neutral Kaon Spectrometer. We obtained the cross sections for the p ( γ , p π + π − ) and d ( γ , p π + π − ) n . The quasi-free process with a neutron spectator was extracted by the neutron momentum cut of p n > 0.3 GeV / c . The cross section for the Δ + + Δ − production was deduced in the non-quasi-free process of the γ d → p n π + π − . It was 13.4 ± 0.4 μb at E γ = 0.82 GeV .

title: S11(1535) Resonance in Nuclear Medium Observed with the (gamma, eta) Reactions

title: The 1.2 GeV photon tagging system at LNS-Tohoku
abstract: A tagged photon beam line has been constructed in the Stretcher–Booster ring (STB ring) at Tohoku University. The quasi-monochromatic photon beam is produced by the internal photon tagging system which consists of a solid fiber radiator and the compact tagging counter installed in a bending magnet of the STB ring. The energy range of the tagged photon is from 0.8 to 1.1 GeV with the electron energy of 1.2 GeV . The performance of the tagging system has been investigated. The system provides good quality of γ -rays for the nuclear and hadron physics experiments.

title: Dominant colliding beam cross-sections at high-energies
abstract: We report on our calculation of the energy and angular dependence of the cross sections for the production of various particles by two-photon annihilation processes in ${e}^{+}{e}^{\ensuremath{-}}$ and ${e}^{\ensuremath{-}}{e}^{\ensuremath{-}}$ colliding beams. For beam energy $E$ of more than 1 GeV, these cross sections [$\ensuremath{\sigma}\ensuremath{\propto}{\ensuremath{\alpha}}^{4}{(\mathrm{ln}E)}^{3}$] become increasingly more important than the usual one-photon cross sections [$\ensuremath{\sigma}\ensuremath{\propto}{\ensuremath{\alpha}}^{2}{(E)}^{\ensuremath{-}2}$] for hadron production.

title: Comment on the sign of the pseudoscalar pole contribution to the muon g 2
abstract: We correct the error in the sign of the pseudoscalar pole contribution to the muon g 2, which dominates the O( 3 ) hadronic light-by-light scattering eect. The error originates from the fact that the algebraic manipulation program FORM treats -tensor so as to satisfy 1 2 3 4 1 2 3 4 11 22 33 44 = 24, as opposed to the expected value 24 when Minkowski space-time metric is specied (at least in the version available before 1995). Replacing the part 1 2 3 4 1 2 3 4 by 1 1 2 2 3 3 4 4 in the FORM-formatted programs, we obtained a positive value for the pseudoscalar pole contribution, which agrees with the recent result obtained by Knecht et al.

title: The two-photon process for particle production in colliding beam experiments
abstract: Cross sections for particle production by the two-photon process for the reactions ee→ee X with X = π 0 or η and X = π + π − or π + π − are calculated exactly by numerical techniques and are compared with predictions of the double equivalent photon approximation (DEPA). Implications of these results as to the validity of the DEPA are discussed and an attempt is made to summarize and clarify some of the earlier criticisms of this approximation.

title: New approach to the separation of ultraviolet and infrared divergences of Feynman-parametric integrals
abstract: A scheme for systematically separating ultraviolet divergences of Feynman amplitudes in parametric space is developed. It is summarized by an explicit formula which enables us to incorporate readily the ultraviolet-finite remainders thus constructed into the usual renormalization scheme. It is shown further that infrared divergences can be treated in a very similar way. Our method is particularly suitable for numerical integration.

title: Quantum Electrodynamics and Its Predictions
abstract: The theories of (special) relativity and quantum mechanics are two of the most fundamental discoveries of modern physics. Since the former is really a property of space-time which is supposed to be obeyed by all physical laws, it was obvious from the beginning that quantum mechanics (which was not relativistic in its original form) must somehow be reformulated as a relativistic theory. This goal was attained by 1929 by means of the method of field quantization. The resulting theory was called quantum electrodynamics (QED) which described the interaction of electrons and photons satisfactorily in the lowest order of perturbation theory. It had, however, an annoying feature that higher order correction terms were always divergent and ruined completely whatever agreement that existed between experiments and lowest order calculations. Because of this difficulty, which originates from the high energy region of momentum space and hence is called an ultraviolet divergence, QED was not taken seriously for nearly 20 years.