NEUTRAL KAON PHOTOPRODUCTION AT LNS, TOHOKU UNIVERSITY
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: First beam test on a BSO electromagnetic calorimeter
abstract: A beam test has been performed on a prototype electromagnetic calorimeter of bismuth silicate BSO crystals for the first time using electrons of 0.5–3.0 GeV. The calorimeter consists of nine BSO crystals, 22 mm × 22 mm × 180 mm (15.6 radiation lengths), arranged in a 3 × 3 array. Each crystal is coupled to a small photomultiplier tube of 20 mm in diameter. The obtained energy resolution is σ E / E = ( 0.023 ± 0.003 ) / E ( GeV ) ⊕ ( 0.017 ± 0.002 ) for incident electrons of the energy E in GeV. The position information for an electron injected onto the center crystal of the calorimeter array is given with energy deposit signals from nine BSO crystals. The RMS position resolution σ x is parameterized as σ x = [ ( 3.2 ± 0.1 ) / E ( GeV ) ⊕ ( 1.3 ± 0.1 ) ] mm at the center of the crystal. Misidentification probability of pions to electrons is found to be ∼ 10 - 3 for the pion momentum ranging from 1.0 to 3.0 GeV/ c .

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

title: K0 photoproduction on 12C in the threshold region
abstract: 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: 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: 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: Asymptotic photon propagator and higher-order QED Callan-Symanzik β function
abstract: The QED Callan-Symanzik β function is calculated for a certain class of higher-order photon self-energy diagrams within the framework of perturbative QED. It is found that the formulation of de Rafael and Rosner is valid up to the sixth order but must be modified from the eighth order on. Correction terms are evaluated explicitly. The result, applied a renormalization group calculation of an eighth-order contribution to the muon anomalous magnetic moment, gives a good agreement with the exact numerical evaluation.

title: Quantum Electrodynamics — From a Personal Perspective —
abstract: Renormalized quantum electrodynamics is such a sturdy theory that its breakdown has not yet been witnessed, in spite of the most careful and extensive scrutinies it has undergone since its inception in 1947. In this talk I review the high precision tests at low energies in which I have participated for nearly 30 years, through calculation of higher-order radiative corrections to the anomalous magnetic moments of the electron and the muon and to the hyperfine structure of the ground state of muonium.

title: Tenth-Order Lepton Anomalous Magnetic Moment -- Second-Order Vertex Containing Two Vacuum Polarization Subdiagrams, One Within the Other
abstract: This paper reports the tenth-order QED contribution to the $g\ensuremath{-}2$ of electron and muon from two gauge-invariant sets: Set $\mathrm{I}(g)$ and Set $\mathrm{I}(h)$. In the case of electron $g\ensuremath{-}2$, Set $\mathrm{I}(g)$ consists of nine Feynman diagrams which have a fourth-order vacuum-polarization loop containing another fourth-order vacuum-polarization loop. Set $\mathrm{I}(h)$ consists of 30 Feynman diagrams which have a proper sixth-order vacuum-polarization loop containing a second-order vacuum-polarization loop. The results of numerical integration, including mass-dependent terms containing one closed loop of muon, are $0.028\text{ }597\text{ }(4)\text{ }(\ensuremath{\alpha}/\ensuremath{\pi}{)}^{5}$ for Set $\mathrm{I}(g)$ and $0.001\text{ }685\text(\ensuremath{\alpha}/\ensuremath{\pi}{)}^{5}$ for Set $\mathrm{I}(h)$, respectively. We also report the contributions of Set $\mathrm{I}(g)$ and Set $\mathrm{I}(h)$ to the muon anomaly. Diagrams included are those containing electron, muon, and tau-lepton loops. Their sums are $2.640\text{ }9\text{ }(4)(\ensuremath{\alpha}/\ensuremath{\pi}{)}^{5}$ and $\ensuremath{-}0.564\text{ }8\text{ }(11)(\ensuremath{\alpha}/\ensuremath{\pi}{)}^{5}$, respectively. The sum of contributions of Sets $\mathrm{I}(g)$ and $\mathrm{I}(h)$ containing only electron loops are in fair agreement with the recently obtained asymptotic analytic results.

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: Two-Photon Mechanism of Particle Production by High-Energy Colliding Beams
abstract: We report on the calculation of the cross sections for the production of positive-charge-conjugation states such as ${\ensuremath{\pi}}^{0}$, $\ensuremath{\eta}$, ${e}^{+}{e}^{\ensuremath{-}}$, ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, and ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ by a two-photon mechanism in ${e}^{\ensuremath{-}}{e}^{+}$ and ${e}^{\ensuremath{-}}{e}^{\ensuremath{-}}$ collisions. We give the precise relationship of the process $e+e\ensuremath{\rightarrow}e+e+X (X \mathrm{is}\mathrm{any} C=+ \mathrm{state})$ to the corresponding two-photon annihilation process $\ensuremath{\gamma}+\ensuremath{\gamma}\ensuremath{\rightarrow}X$, as well as a careful derivation of the equivalent-photon approximation. In the case of the ${\ensuremath{\pi}}^{0}$ production, we have found that, for the beam energy $E$ in the 1-3 GeV range, the exact total cross section is 20-30% larger than the one calculated previously in the equivalent-photon approximation. However, the introduction of form factors cuts down the exact total cross section, reducing it to within 10% of the equivalent-photon-approximation result. For $\ensuremath{\eta}$ production the agreement is even better. Thus it appears that the use of the equivalent-photon approximation is justified in most cases. We discuss detailed angular distributions in this approximation for the case of ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ production. One important problem which cannot be adequately studied in the equivalent-photon approximation is the degree of noncoplanarity of the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ (and the ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$) pair. We have studied this problem using the exact formula and found that, for $E=1$ GeV, typically 40-50% of pion pairs will be produced with the noncoplanarity angle greater than 12\ifmmode^\circ\else\textdegree\fi{}. We discuss the general structure of the $\ensuremath{\gamma}+\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$ amplitude as well as a simple model incorporating the $\ensuremath{\sigma}$ meson. We also give a rough estimate of multihadron production cross sections.