120487284
Improved Theory of the Muon Anomalous Magnetic Moment
A new theoretical value a/sub ..mu../ = 11 659 202(20) x 10/sup -10/ is reported for the muon anomalous moment, based on the first complete calculation of the ..cap alpha../sup 4/ QED term and improvements of the ..cap alpha../sup 3/ QED term and various hadronic contributions. The remaining error is mostly due to the experimental inputs needed for evaluation of the hadronic vacuum polarization effect. Further improvement of this error seems possible. Thus the electroweak theory may be tested at the one-loop level if measurement of a/sub ..mu../ is improved by an order of magnitude.
120292427
Automated calculation scheme for alpha**n contributions of QED to lepton g-2: Generating renormalized amplitudes for diagrams without lepton loops
Abstract Among 12 672 Feynman diagrams contributing to the electron anomalous magnetic moment at the tenth order, 6354 are the diagrams having no lepton loops, i.e., those of quenched type. Because the renormalization structure of these diagrams is very complicated, some automation scheme is inevitable to calculate them. We developed an algorithm to write down FORTRAN programs for numerical evaluation of these diagrams, where the necessary counterterms to subtract out ultraviolet subdivergence are generated according to Zimmermann's forest formula. Thus far we have evaluated crudely integrals of 2232 tenth-order vertex diagrams which require vertex renormalization only. Remaining 4122 diagrams, which have ultraviolet-divergent self-energy subdiagrams and infrared-divergent subdiagrams, are being evaluated by giving small mass λ to photons to control the infrared problem.
122384955
Power-counting theorem for infrared logarithms in non-Abelian gauge theories
We have developed a general diagrammatic method for precisely determining the power of infrared logarithms for diagrams of arbitrary order in non-Abelian gauge theories. It is applied specifically to the study of the infrared structure of the gauge-group singlet quark form factor for fixed momentum transfer and nonvanishing quark mass. All leading infrared logarithms of the form factor are found to arise from a class of planar quantum-electrodynamic-type diagrams in which, however, the gluon propagators are fully dressed by gluon and ghost loops. Thus the infrared behavior of the massive-quark sector reflects strongly that of the massless-gluon sector, which in turn is controlled by the ultraviolet structure of the gluon self-interaction.
3035381
Eighth-order magnetic moment of the electron. IV. Vertex diagrams containing photon-photon scattering subdiagrams.
We have evaluated the contribution to the eighth-order term of the anomalous magnetic moment of the electron arising from a class of 144 vertex diagrams all of which contain a photon- photon scattering subdiagram with various further radiative corrections. Our result is (-0.473 +- 0.015)(..cap alpha../..pi..)/sup 4/. The theoretical error represents the estimated accuracy (90% confidence limit) of the required numerical integration. This result is obtained from approximately 6000 CPU hours of computation on various large-scale (scalar and vector) computers and replaces our earlier preliminary result for this group of diagrams.
120958910
VIOLATION OF THE POMERANCHUK THEOREM AND ZEROS OF THE SCATTERING AMPLITUDES.
121956246
Eighth-order magnetic moment of the electron. III. Sixth-order vertices containing a second-order vacuum polarization subdiagram
We have calculated the contribution to the eighth-order anomalous magnetic moment of the electron arising from 150 Feynman diagrams, each generated by inserting a second-order vacuum polarization loop in the photon lines of sixth-order vertices of the three-photon-exchange type. Our result is 1.419(16)(..cap alpha../..pi..)/sup 4/. The theoretical error represents the estimated accuracy (90% confidence limit) of the required numerical integrations.
120952573
Photoproduction of neutral kaons on C in the threshold region
Abstract The measurement of neutral kaon photoproduction in the threshold region is in progress at Laboratory of Nuclear Science, Tohoku University. One of the purpose of the experiment is to study electromagnetic strangeness production mechanism, which is necessary for hypernuclear spectroscopy by electromagnetic probes. We have observed K 0 's produced on a carbon target in a commissioning run. Data taking will start in 2003.
121123072
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.
116682853
Narrow resonance at E(gamma) = 1020-MeV in the d (gamma, eta) p n reaction
Differential and total cross sections of the D(γ, η)pn reaction have been measured for photon energies between 600 and 1150 MeV. The data provide the information of the γn → ηn reaction above Eγ ≥ 800 MeV. The total cross section shows a narrow resonance structure peaked at Eγ = 1020 MeV. The angular distribution coefficients together with the total cross section are compared with the calculation of the isobar model by using the impulse approximation. Although the spin and parity of the resonance cannot be determined unambiguously, a negative parity assignment gives better fit to the data.
120762412
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 .
122810217
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.