17694103
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 .
106402542
Photoproduction of neutral kaons on a liquid deuterium target in the threshold region
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.
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 .
120479135
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 .
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.
116485131
S11(1535) Resonance in Nuclear Medium Observed with the (gamma, eta) Reactions
11527845
SIXTH-ORDER VACUUM-POLARIZATION CONTRIBUTION TO THE LAMB SHIFT OF MUONIC HYDROGEN
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.
125033752
High Precision Tests of Quantum Electrodynamics—An Overview
122590039
Two-Photon Mechanism of Particle Production by High-Energy Colliding Beams
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.
122863414
Dominant colliding beam cross-sections at high-energies
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.
117916352
Status of the BNL muon (g−2) experiment
The muon (g−2) experiment at Brookhaven has just completed a 3-month run for checkout and initial data-taking. In the first two months beam was taken in a parasitic mode where one out of ten AGS pulses was delivered for commissioning of the beam line, quadrupoles, detectors, and data acquisition system. This was followed by four weeks of dedicated data collection. The main components of the experiment, which include the pion/muon beam line, the superconducting inflector, the superferric storage ring with its pulsed electric quadrupoles and magnetic field measurement system, and the detector system based on lead-scintillating fiber electron calorimeters, have been satisfactorily commissioned. The muon (g−2) precession frequency is clearly seen as a large signal. It is estimaed that over 25×106 decay positrons with energies greater than 1.5 GeV have been detected.