Yojiro Murata

Photoproduction of η Mesons from Protons at Incident Energies below 1 GeV

Differential cross sections of the reaction γp→ηp have been measured by using a tagged photon beam in the energy range from 808 MeV to 1008 MeV at θ * η =45°C, 80°C, 100°C and 110°C. Photon couplings of nucleon resonances with masses below 1700 MeV are determined by a partial wave analysis of the reaction γp→ηp based on the isobar model. Results are compared with photon-couplings obtained by the analysis of the reaction γN→πN and by the quark model calculation.

Quasi-free pion photoproduction from carbon above 300 MeV

Abstract The momentum spectra of charged pions produced in the reaction 12 C( γ , π ± ) have been measured for incident photon energies in the interval between 300 and 850 MeV in steps of 50 MeV. Pions with relatively high momenta have been detected by a magnetic spectrometer set at the lab angles 28.4° and 44.2°. All these spectra exhibit a clear singly peaked structure. Detailed features of the structure are quantitatively investigated and compared with a plane-wave impulse-approximation calculation. Calculated results are found to reproduce the spectral shape very well and the absolute magnitude is also rather well fitted by introducing the pion absorption effect properly.

Investigation of Cascade Showers in Lead with X-Ray Films

By using x-ray films with different sensitivities, observations have been made on the lateral and longitudinal distributions of the energy Loss in showers developing in lead. The x-ray films inserted among lead Plates were irradiated by the electron beam with an energy of 200 MeV and by the bremsstrahlung gamma-ray beam with peak energies of 720 MeV and 200 MeV. There seems to be some difference between Kantz and Hofstadters results and ours in the lateral and longitudinal distributions of the energy loss in the electron-initiated shower. This difference is discussed in some detail. The results are also compared with the conventional shower theory. A fraction energy loss contained in various cylindrical volumes of lead is calculated from data obtained in the present experiment to facilitate a determination of the efficiency of a total absorption type detector

On the Momentum Spectrum of µ-Mesons near Sea-Level at 24°N

The momentum spectrum of µ-mesons near sea-level and at geo-magnetic latitude 24°N has been obtained by means of a magnet cloud chamber. Above 700 Mev/c the results are in agreement with the momentum spectrum derived from Olberts production spectrum at 24°N. At lower momenta, our spectrum is found to decrease more rapidly than the corresponding spectra derived from differential range measurements. This discrepancy, which is not understood, may be due to some systematic error in either the magnetic deflection or differential range method.

Quasi-free photoproduction of charged pions from copper and lead

Abstract The photoproduction of charged pions in the sub GeV region has been studied for two nuclear targets, copper and lead, by using a magnetic spectrometer. The photon energies are determined in steps of 50 MeV by a subtraction method for the bremsstrahlung spectrum. The observed pion momentum spectra reveal characteristic features of quasi-free production (QFP) even for such heavy nuclei as copper and lead. The data are compared with results obtained by a PWIA calculation, which give a good fit to the data. The QFP cross sections per relevant nucleon at 44.2° and the average photon energy 〈k〉 = 668 MeV are found to be approximately proportional to A − 1 3 .

On the Range Spectrum of µ-Mesons at Sea-Level at Geomagnetic Latitude 24°N

Differential intensities of µ-mesons at sea-level at 24°N have been measured for the residual range equivalent to from 44 to 430 g/cm 2 of the air using a delayed coincidence method. It was found that the obtained range spectrum was nearly flat for present ranges and was 20 percent lower than Rossis curve which should be valid at geomagnetic latitude greater than 45°. The effect of the lateral displacement as well as the angular deflection of particles in the absorber was taken into account for the scattering correction. Mesons locally produced in the absorber was found to be at most a few per cent of all mesons that stop and decay in the apparatus. This fact suggests that the discrepancy between µ-meson spectra by the absorption method and by the magnetic cloud chamber method can not be accounted for only by the local π-meson production.

Photoproduction of πΔ(1236) from protons below 1.1 GeV

Abstract 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.

Experimantal Study of Inclusive Reaction 12C(γ, π-) at 44.2°

It is found that, even at a considerably large jab angle 44.2°, momentum spectra of pions in the reaction 12 C(γ, π - ) show a clear singly-peaked structure throughout a photon energy range between 300 and 850 MeV. The peak momentum is always about 40 MeV/c less than that determined by free nucleon kinematics. The width increses almost inearly with photon energy. Differential cross section does not exhibit a marked variation with energy. These data are quite well explained by an impulse-approximation calculation.

Quasi-Free Pion Photoproduction from Copper and Lead

We have recently reported the experimental results of charged pion photoproduction from carbon in an energy range between 300 and 850 MeV of the incident photons1. Momentum spectra at lab angles 28.4° and 44.2° have been measured and in these spectra clearly revealed are the striking features characteristic of the quasi-free production (QFP) of the pions. The data have in fact been well reporduced by a plane-wave impulse approximation (PWIA) calculation in which pion absorption due to the final state interactions is properly taken into account.