The 1.2 GeV photon tagging system at LNS-Tohoku
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: S11(1535) Resonance in Nuclear Medium Observed with the (gamma, eta) Reactions

title: NEUTRAL KAON PHOTOPRODUCTION AT LNS, TOHOKU UNIVERSITY
abstract: The elementary photo-strangeness production process has been intensively studied based on the high-quality data of the charged kaon channel, γ + p → K+ + Λ(Σ0). However, there had been no reliable data for the neutral kaon channel γ + n → K0 + Λ(Σ0) and the theoretical investigations suffer seriously from the lack of the data. In order to have reliable data for the neutral kaon photo-production data, substantial effort has been made to measure the γ + n → K0 + Λ process in the π+π- decay channel, using a liquid deuterium target and a tagged photon beam (Eγ = 0.8-1.1 GeV) in the threshold region at the Laboratory of Nuclear Science (LNS), Tohoku University. We have taken exploratory data quite successfully with the use of Neutral Kaon Spectrometer (NKS) at LNS-Tohoku in 2003 and 2004. The data is compared to theoretical models and it indicates a hint that the K0 differential cross section has a backward peak in the energy region. The second generation of the experiment, NKS2, is designed to extend the NKS experiment by considerably upgrading the original neutral kaon spectrometer, fully replacing the spectrometer magnet, tracking detectors and all the trigger counters. The new spectrometer NKS2 has significantly larger acceptance for neutral kaons compared with NKS, particularly covering forward angles and much better invariant mass resolution. The estimated acceptance of NKS2 is three (ten) times larger for than that of NKS. The spectrometer is newly constructed and installed at the Laboratory of Nuclear Science, Tohoku University in 2005. The deuterium target data was taken with tagged photon beam in 2006-2007. We will report recent results of NKS2 in this paper. Additionally, a status of the upgrade project that gives us larger acceptance and capability of K0 + Λ coincidence measurement will be presented.

title: Photoproduction of neutral kaons at LNS

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: 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: 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: SIXTH-ORDER VACUUM-POLARIZATION CONTRIBUTION TO THE LAMB SHIFT OF MUONIC HYDROGEN
abstract: The sixth-order electron-loop vacuum-polarization contribution to the $2P_{1/2} - 2S_{1/2}$ Lamb shift of the muonic hydrogen ($\mu^{-} p^+$ bound state) has been evaluated numerically. Our result is 0.007608(1) meV. This eliminates the largest uncertainty in the theoretical calculation. Combined with the proposed precision measurement of the Lamb shift it will lead to a very precise determination of the proton charge radius.

title: Theory of Lepton Anomalous Magnetic Moments, 1947-1983

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: Status of G‐2 calculation for the electron and muon
abstract: The electron anomalous magnetic moment provides the most precise test of QED. The present precision is such that one must begin to seriously question the validity of theories of condensed‐matter physics underlying the determination of α. The muon anomalous magnetic moment will play a very important role in testing gauge theories of electroweak interaction at the one loop level. Electron and muon moments may also provide useful information on the possible internal structure of leptons. Experimental and theoretical works are under way to improve the precision of these tests. Here I report on the present status of theoretical progress.