G. von Holtey

PHOTOPRODUCTION OF NEUTRAL PIONS ON HYDROGEN AT PHOTON ENERGIES BETWEEN 200 AND 440 MeV.

The two measurements of the process γ+p→π0+p at the Bonn 500 MeV electron synchrotron are discussed and after correction of systematic deviations combined to one set of data. A comparison with other measurements and theoretical calculations is given.

Coherent π0-photoproduction on deuterium in the first resonance region

Differential cross sections for coherent π0-photoproduction from deuterium have been measured in the photon energy range from 240 to 400 MeV and for pion c.m. angles between 70 ° and 160 °. The recoil deuterons were analysed in angle and momentum by a magnetic spectrometer. The cross sections obtained were higher by a factor of about 2 compared with the results from Stanford [7], the only data available up to now in the first resonance region. Below the resonance the measured cross sections give a smooth extension to the low energy data from Glasgow [5] and Orsay [6].

Angular distributions of pions from γ+p→π++n at photon energies between 220 and 425 MeV

Earlier measurements of the differential cross section for π+ photoproduction on hydrogen at forward angles have been extended up to 180 °. The pions were analysed in angle and momentum by a magnetic spectrometer. Angular distributions have been measured at 16 energies between 220 and 425 MeV. Most of them cover the region between 15 ° and 180 ° in steps of 5 degree with a statistical error of about 3%. Moravcsik equivalent fits give a very good representation of the data.

THE 2.5 GeV ELECTRON SYNCHROTRON OF THE UNIVERSITY OF BONN.

Abstract From 1963 to 1967 a 2.5 GeV electron synchrotron with 50 Hz repetition rate has been built at the University of Bonn. Design, construction and first operation of the machine are described. Electrons are injected by a 25 MeV linear accelerator. The magnet ring has a mean radius of 11.08 m and consists of 12 magnets with the basic structure O/2 F D O/2. The frequency of the rf acceleration system is 499.670 MHz. A pure ceramic vacuum chamber is used. To achieve a high circulating beam current a special rf amplitude regulation system has been built to reduce the influence of beam loading. The maximum circulating beam intensity achieved up to now is 5 × 10 12 electrons/sec. About 60% of the circulating electron beam can be ejected with spill times up to 1 msec.

Photoproduction of positive pions on hydrogen at photon energies between 220 and 425 mev

Differential cross section for π+ photoproduction on hydrogen have been measured over a photon energy range from 220 to 425 MeV and for pion c.m. angles between 15° and 70°. The pions have been analysed in angle and momentum by a magnetic spectrometer.

The π−π+ ratio of photoproduction on deuterium for energies between 240 and 400 MeV

Abstract The π − π + ratio photoproduction on deuterons has been measured for photon energies between 240 and 400 MeV at CM-angles from 15° to 180°. Using the π + -photoproduction on protons, measured with the same apparatus, the π − -production on neutrons is calculated. Comparison with π + shows no isotensor contribution, whereas the inverse reaction deviates considerably in the resonance region.

Photoproduction of charged pions on deuterium in the first resonance region

Photoproduction of pi /sup +/ and pi /sup -/ on deuterium was measured in the photon energy range from 240 to 400 MeV and for pion c.m. angles between 15 deg and 180 deg . The pions were analyzed in angle and momentum by a magnetic spectrometer. From the measured pi /sup -// pi /sup +/ ratio, corrected for Coulomb interactions in the final state, differential cross sections of the reaction gamma + n yields pi /sup -/ + p were calculated. Together with the pi /sup +/ photoproduction the data show no isotensor contribution. Comparison of the data with the recent experiments done on the inverse reaction shows no evidence of a violation of time reversal invariance. With the measured pi /sup +/ photoproduction on deuterium, a test of the spectator model has been made. Using the closure-approximation of Chew and Lewis the data agree within a range of plus or minus 10%. (auth)

Photoproduction of neutral pions on hydrogen at photon energies between 200 and 440 MeV

At the Bonn 500 MeV electron synchrotron the differential cross section of the reaction γ+p → π0+p has been measured detecting the recoil proton by a magnetic spectrometer. Angular distributions between pion c.m. angles of 50 ° and 160 ° were taken at photon energies between 220 and 420 MeV.The two measurements of the process γ+p→π0+p at the Bonn 500 MeV electron synchrotron are discussed and after correction of systematic deviations combined to one set of data. A comparison with other measurements and theoretical calculations is given.

A determination of the pion-nucleon coupling constant from pion photoproduction

Three different methods for the determination of the pion nucleon coupling constant ƒ2 from single pion photoproduction data in the first resonance region are discussed. They all yield results for ƒ2 compatible with each other and with the results from investigations of πN and NN scattering. The determination from π+ data alone (independent of πN phase shifts) yield the value ƒ2 = (79.2 ± 3.9) × 10−3, while the determination using the Bonn multipole analysis (dependent on πN phase shifts) yields ƒ2 = (76.9 ± 4.5) × 10−3.