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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 .

A mass-dependent asymmetry was observed in the decay angular distribution of a photoproduced K+K− system near the K+K− threshold. The corresponding moments 〈Y10〉 have been evaluated. Interpreting the asymmetry as an S-P wave interface due to the states S993∗(0+) and o1019(1−) one can compute the moments 〈Y10〉 through an amplitude analysis. The theoretical calculation reproduces the experimental results well, if one assumes a real S-wave amplitude for the S993∗. The data cannot be explained by a non-resonant real S-wave. Other possibilities have been discussed. An estimate of the photoproduction cross section of the S∗ → K+K− can be given on the basis of the above hypothesis.

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 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.