Search

Coherent pion photoproduction from deuteron is studied by measuring the differential cross-sections at c.m. angles between 90° and 130° in a photon energy range from 500 to 1000 MeV. The experimental data are compared with a model calculation which takes into account two kinds of contributions, the nonresonant contribution consisting of pion photoproduction from single nucleons and pion rescattering and that from the dibaryon resonances3F3(2.26) and1G4(2.51). The model predictions for the photon asymmetry σ and the deuteron polarizationiT11 are also presented.

The linear polarization of the coherent bremsstrahlung from a single crystal of silicon was measured by observing the one-dimensionally projected angles of electron and positron pairs. The coherent bremsstrahlung was produced by injecting the 1153 MeV electrons to the silicon crystal nearly along the [110] axis. The emission angles, η + and η − , of pair particles were determined event by observing their tracks with a set of four wire spark chambers. From the ( η + , η − ) distribution of events, the polarization of photons was evaluated. The obtained polarization was consistent with the calculated values, and the technique gives a new approach to the measurement of the linear polarization of photons.

An experimental investigation of the reaction γ p → p p p at photon energies 4.7 ⩽ E γ ⩽ 6.6 GeV is described. The main results are the measurement of the cross section as a function of energy, a discussion of the main dynamical features of the reaction and the observation of a narrow p p mass state at 2.024 ± 0.005 GeV with a width of 29 ± 13 MeV.

The differential cross section of the reaction ( γ p → p φ ) has been measured in the t range 0 ⩽ t ⩽ 0.4 GeV 2 and for photon energies from 3.0 to 6.7 GeV. In particular for the small t region the measurement accuracy was better than 10%. We obtained for the slope parameter B in an exponential parametrization of the differential cross section d σ /d t = A e − Bt values of B ⋍ 6 ± 0.5 GeV −2 which are significantly larger than the slopes obtained by most other experiments at higher t values. This indicates a t dependence of B particularly in the small t region. An energy dependence of the optical point (d σ /d t ) t =0 , observed in our measurements, has been explained as a kinematic effect due to the VDM relation. A fit of our measurements is in excellent agreement with all other published values of (d σ /d t ) t =0 ( γ p → φ p), this implies that σ tot (φp) must be essentially energy independent in this energy range. Spin density matrix elements of the φ have been evaluated and an analysis of the helicity amplitudes has been carried out. This analysis confirmed s -channel helicity conservation. Moments of spherical harmonics of the K K angular decay distribution have been computed for 10 MeV K K mass-bins from threshold to 1.3 GeV. The mass dependence of the normalized moments is generally smooth. Contributing amplitudes have essentially only even moments. The moment 〈 Y 2 0 〉/〈 Y 0 0 〉 changes sign above the φ mass. Differential cross sections for the inelastic φ production γ p → φ X have been evaluated for the first time both with respect to t − t min and M K . The integrated inelastic cross sections are comparable in size with the elastic ones. The slopes of the differential cross sections d σ /d t appear to become flatter with increasing M X .

Differential cross sections of proton Compton scattering have been measured in the energy range between 375 MeV and 1150 MeV in steps of 25 MeV at c.m. angles of 130°, 100° and 70°. The recoil proton was detected with a magnetic spectrometer. In coincidence with the proton, the scattered photon was detected with a lead-glass Cerenkov counter of the total absorption type. Theoretical calculations based on an isobar model with two components, that is, the resonance plus the background, were practiced. The photon couplings of the second resonance region were determined from the proton Compton data for the firs time. The results were that the helicity 1 2 photon couplings of P11(1470) and S11(1535), and the helicity 3 2 photon coupling of D13(1520) were consistent with those determined from the single-pion photoproduction data; however, the helicity 1 2 photon coupling of D13(1520) required a somewhat larger value than that from the single-pion photoproduction data.

The π + and π − momentum spectrum of the reaction γ p → ππ N have been measured at lab angles 20°, 40°, 60° and 90° and photon energies 0.744, 0.844, 0.944 and 1.044 GeV with a magnetic spectrometer using the photon subtraction method. Both spectra show a peak corresponding to the production of the πΔ(1236) state. The analysis has been carried out with amplitudes for the quasi two-body process γ p → πΔ (1236) and a phase-space background so as to reproduce both π + and π − spectra. The ratio of cross sections σ ( γ p → π + Δ 0 )/ ( γ p → π − Δ ++ ) is found to vary 0.0 to 1.8, depending on kinematical conditions.

The recoil proton polarization of proton Compton scattering (γp→γp) was measured in the photon energy range from 500 MeV to 1000 MeV atθ ∗=100° and from 400MeV to 800 MeV atθ ∗=130°. A recoil proton and a scattered photon were detected in coincidence with a magnetic spectrometer and a photon detector. The recoil proton polarization was measured with a carbon polarimeter. The results are compared with a phenomenological analysis based on an isobar model and a dynamical analysis based on the dispersion relation.

The recoil proton polarization of the reaction γp → π0p was measured at a c.m. angle of 100° for incident photon energies between 451 and 1106 MeV, and at an angle of 130° for energies from 400 to 1142 MeV. One photon, decayed from a π0 meson, and a recoil proton were detected in coincidence. Two kinds of polarization analyzer were employed. In the range of proton kinetic energy less than 420 MeV and higher than 346 MeV, carbon plates and liquid hydrogen were used for determining the polarization, respectively. The data given by the two polarimeter systems are in good agreement. Results are compared with recent phenomenological analyses. From the comparison between the present data and the polarized target data, the invariant amplitude A3 can be estimated to be small.

Momentum distributions for inclusive photoemission of deuterons from nitrogen have been measured at laboratory angles of 43° and 50°, and for maximum energies of the bremsstrahlung photon beam of 725, 775 and 825 MeV. The double differential cross sections of deuterons emitted from nitrogen are obtained for photon energies of 750 and 800 MeV and for laboratory angles of 43° and 50°. The photon energy is determined by the photon subtraction method. Results are examined by a π 0 photoproduction process off a quasi-deuteron in nitrogen ( γ ″d″→ π 0 d) and by a two-step process. The two-step process means the following: first, a nucleon is produced by a photo-pion production process from a quasi-free nucleon in the nitrogen nucleus ( γ ″N″→ π N); second, the nucleon produced at the first step picks up another nucleon in the nucleus and then a deuteron is emitted (N+A→d+anything).

The differential cross sections for the reactions γ d → π 0 d have been measured for photons from 500 to 1000 MeV. We discuss the effect of the double scattering term and suggest no indication for the dibaryon resonances of the mass around 2.5 GeV.

Total absorption cross sections of photons in carbon, aluminium and titanium have been studied for photon energies at 250, 450, 700 and 1000MeV. The bremsstrahlung beam produced by the 1.3 GeV electron synchrotron at the Institute for Nuclear Study was used as the source of high energy photons. The detection of high energy photons was made by a magnetic pair spectrometer. Experimental results agree with theoretical calculations on the total absorption cross section for photons within experimental errors.

The total absorption cross sections of photons in copper, silver, tin, tantalum, tungsten and lead have been studied for photon energies at 450, 700 and 1000 MeV. A comparison is made between experimental and theoretical cross sections. The Hartree-Fock-Slater cross section agrees with experimental results with an accuracy of the order of 1%.

A new tagged-photon beam channel is under construction at the electron synchrotron laboratory of Institute for Nuclear Study, University of Tokyo. In this channel, the duty cycle of the extracted electron beam is expected to be 20% so that the effective tagged-photon intensity will be as high as 2 × 106 photons/second. To obtain the high-duty-cycle beam, magnetic fields of the components in the beam extraction system and in the beam transport system are modulated so as to follow the change of the magnetic field of the synchrotron. By introducing a largeacceptance spectrometer for the experiments with the tagged photon beam, the data-taking efficiency will be markedly improved. These high-duty beam will enable us to perform the experiment with the tagged and polarized photon beam by using a single crystal for the radiator material in the tagging system.