A. Hünger

Compton scattering by the proton through θcms = 75° and 90° in the Δ-resonance region

Abstract Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θ cms = 75° and θ cms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the resonance part of the M 1+ 3 2 photo-meson amplitude by (2.8 ± 0.9)% is required in comparison with the VPI analysis. The deduced value of the M 1+ 3 2 - photoproduction amplitude at the resonance energy of 320 MeV is: |M 1+ 3 2 | = (39.6 ± 0.4) × 10 −3 m π + −1 .

Scattering of photons by the proton through θcms = 90° in the Δ-resonance region☆

Abstract The differential cross section for the scattering of photons by the proton was measured in the energy range Eγ = 250−500 MeV at the scattering angle θcms = 90° ± 3°. The tagged photon beam of the MAMI accelerator was used and both the scattered photon and the recoil proton were detected. The data essentially are consistent with dispersion theories, and remove the discrepancy that has existed above 290 MeV between theory and earlier published experimental results.

Elastic and inelastic photon scattering from 12C

Abstract The elastic and inelastic photon scattering from 12 C was investigated in the energy range of the Δ-resonance ( E γ = 200–500 MeV) at a scattering angle of 40°. The experiment was performed with the tagged photon facility at the cw electron accelerator MAMI ( E e − = 855 MeV). By using a large NaI(Tl) detector having an energy resolution of 1.5%, the elastic scattering could be separated from the inelastic process to the first excited state ( E x = 4.44 MeV of 12 C. The differential cross section for the coherent scattering is compared with a simple static ansatz, that uses the known charge form factor, and with a recent Δ-hole calculation.

Compton scattering by the proton through θcms = 75° in the Δ-resonance region

Using the tagged-photon beam of MAMI (Mainz) differential cross-sections for Compton scattering by the proton through θcms = 75° have been measured for the Δ-resonance region from 200 to 410 MeV. The data put a new constraint on the M1+32 photoproduction amplitude in the resonance, |M1+32| = (39.6 ± 0.4) · 10−3mπ+−1 at 320 MeV, which is (2.8 ± 0.9) % less than given by the recent analysis SM95 of the Virginia group.

Compton scattering from 4He in the Δ(1232) resonance region

Differential cross sections for Compton scattering from 4He have been measured at θlah = 37° and Eγ = 120–510 MeV using the tagged photon beam of MAMI and the Mainz large NaI(Tl) detector. The shape of the cross section is qualitatively reproduced by a simple schematic model, which however underestimates the absolute scale. More profound calculations like the Δ-hole model also fail to describe the data quantitatively, in particular in the Δ-resonance region.

Program for computer simulation on photoproduction of mesons decaying into two photons

Experiments carried out using multi-detector arrays and wide-band taggers in general lead to large amounts of data which can only be meaningfully analysed if the experiment is accompanied by detailed computer simulations, being at least ten times as precise as the result of the experiment. For this reason we have developed a computer code for the simulation of photoproduction of mesons decaying into two photons which avoids Monte-Carlo procedures, and have applied this code to studies of possibilities to separate events of proton Compton scattering from events of the p(γ, π0)p reaction. Requiring only a very moderate computer time, our new code leads to predictions of photon spectra and angular distributions of recoil protons without the fluctuations typical for a Monte Carlo result.

Photoemission of protons from4He in theΔ-resonance region

High resolution proton energy spectra from the4He(γ,p) reaction have been measured with tagged photons in the range Eγ = 130−525 MeV using the large Mainz NaI(T1) spectrometer atΘplab=37.1°. Three separate reaction channels were identified, viz.4He(γ,p)t two-body breakup,4He photodisintegration via two-nucleon photon absorption processes and the quasifree pion production channel. Differential cross sections are presented for each of these channels as a function of photon energy. The sum of the two-nucleon photon absorption and the quasifree pion production differential cross sections, in the CM system, resembles that of the corresponding free-nucleon differential cross section when Fermi motion is taken into account.