I. Arai

Particle production in the target-rapidity region from hadron-nucleus reactions at several GeV

Abstract Highly inelastic processes in hadron-nucleus reactions at several GeV have been studied by measuring multi-particle emission in the target-rapidity region. Events with no leading particle(s) but with high multiplicities were observed up to 4 GeV. Proton spectra from such events were well reproduced with a single-moving-source model, which implied possible formation of a local source. The number of nucleons involved in the source was estimated to be (3–5)A 1 3 from the source velocity and the multiplicity of emitted protons. In those processes the incident energy flux seemed to be deposited totally or mostly (>62;75%) in the target nucleus to form the local source. The cross sections for the process were about 30% of the geometrical cross sections, with little dependence on incident energies up to 4 GeV and no dependence on projectiles (pions or protons). The E0 parameter in the invariant-cross-section formula E d3σ/dp3 = A exp (−E/E0) for protons from the source increases with incident energy from 1 to 4 GeV/c, but seems to saturate above 10 GeV at a value E0 = 60–70 MeV. Three components in the emitted nucleon spectra were observed which would correspond to three stages of the reaction process: primary, pre-equilibrium and equilibrium.

Stopping and energy deposition of GeV particles in target nuclei

Abstract In a study of hadron-nucleus reactions we were able to identify events in which leading particles were completely (or mostly) stopped and deposited their energies up to 4 GeV in target nuclei to form moving sources. Cross sections for such “stopped” events were nearly constant over the energy range from 2 to 4 GeV and amounted up to 30% of geometrical cross sections.

A phenomenological analysis of single pion photoproduction in the resonance region using fixed-t dispersion relations

Abstract An energy-dependent partial-wave analysis of single pion photoproduction from the first resonance region through the fourth resonance region has been made. 7768 data points on the processes γ p → π + n, γ p → π 0 p and γ n → π − p have been used. The method employed in this analysis is mostly similar to that of R.G. Moorhouse et al. (MOR), which is specified by using (i) fixed- t dispersion relations and (ii) K -matrix formalism. In addition to this framework, a Regge-like parametrization of the amplitudes was employed in the higher energy region and the partial waves from S-wave up to H-wave were included. The coupling constant for the radiative decay of the principal multiplets have been determined successfully and comparisons both with the results of previous analyses and with the quark model predictions are discussed.

Readout system for a cylindrical drift chamber “Michie”

Abstract A readout electronic system for a jet-chamber-type cylindrical drift chamber has been constructed for nuclear experiments at the KEK proton synchrotron. The system handles amplitude and timing information of signals from 384 resistive sense wires, and is able to record multiple hits up to 4 per wire. For detecting composite particles together with minimum ionizing particles, the system was designed to cover a wide dynamic range. A multiprocesser system with use of VERSAbus and MC68000 microprocessors has been developed for fast data handling and for communication with a host computer.

Measurement of the proton polarization in deuteron photodisintegration at photon energies between 350 and 700 MeV

Abstract The proton polarization in the γ d → pn reaction has been measured at a c.m. angle of 90° and photon energies between 350 and 700 MeV, using a carbon polarimeter. The magnitude of the polarization shows a sharp energy dependence with a peak of about −80% at around 500–550 MeV. This feature cannot be explained by conventional models and seems to indicate a new mechanism in the dibaryon system.

Deuteron emission from pion absorption at Tπ = 65 MeV

Abstract The angular distributions of high-energy deuterons and proton-deuteron coincident events were measured at T π = 65 MeV for C, Al and Cu. The angular distribution of the inclusive ( π + , d) cross section was similar to that of the inclusive ( π + , p?) reaction, but the ratios of the inclusive ( π + , pd?) cross section to the inclusive ( π + , pp) cross section had a strong angular dependence. These results support the idea that contributions from the three-nucleon absorption as well as those from the two-step process are important for the emission of high energy deuterons at T π = 65 MeV.

Measurmennt of recoil proton polarization in the process of π− photoproduction from neutrons in the energy range between 700 and 1200 MeV

Abstract The recoil proton polarization for γ n → π − p was measured around the third resonance region. Both momentum vectors of the proton and the pion were determined by the magnetic spectrometers. The proton polarization was measured by means of proton-carbon scattering in the polarization analyzer located behind the proton spectrometer. Below 900 MeV incident photon energy, our data are consistent with the other existing experimental data ( θ π ∗ = 90° ) and the predictions of partial-wave analyses. Above 1000 MeV, however, a large discrepancy was observed between our data and the predictions of the partial-wave analyses. The discrepancy stands out as the pion c.m. angle increases. A new partial-wave analysis was made for γ n → π − p including our polarization data, and the accuracy of the experimentally determined electromagnetic coupling constant of the third resonances were greatly improved. In particular, a finite amount of the helicity 3 2 amplitude for the γ n → F 15 (1688) resonance was obtained against the predictions of the quark models, by Copley, Karl and Obryk and by Feynman, Kislinger and Ravendal but in agreement with the relativistic quark models of Sugimoto and Toya, and Kubota and Ohta.

A proton spectrometer/polarimeter for photoreactions below 1 GeV

Abstract We describe the construction and performance of an apparatus to measure the polarization of protons in the kinetic energy range 100∼400 MeV, operated with an extracted electron beam and a high-intensity bremsstrahlung photon beam. It consists of four multiwire proportional chambers, a spectrometer magnet, ten wire spark chambers with magnetostrictive readout, a carbon scatterer of variable thickness and a range counter hodoscope. The multiwire proportional chambers are placed before the magnet and are directly exposed to intense electromagnetic background coming from a target. For this reason, special care is taken of the readout electronics. A method of polarization analysis is also described in detail.

Photoproduction of Negative Pions from Carbon in the Energy Range between 510 MeV and 750 MeV

The cross section of the photoproduction of pions from carbon at 41° in the laboratory system and in the incident energy region from 510 MeV to 750 MeV is measured by a magnetic spectrometer for pions and counter hodoscopes for recoil protons in coincidence with pions. A tagged photon beam is used. The results which show the production of pions from the quasi free nucleons inside the nucleus are analyzed in terms of the distorted wave impulse approximation.

Differential Cross Sections for Single Pion Photoproduction from Protons in the Energy Range between 500 MeV and 930 MeV

Differential cross sections of the reactions, γ+ p → p +π°, and γ+ p → n +π + , are measured at about 85° and 65°, respectively, in the incident energy range from 500 MeV to 930 MeV. A tagged photon is used as an incident photon beam. Overall features are consistent with the theoretical analyses by Moorhouse Oberlack and Rosenfeld, and by Metcalf and Walker.