J. Arends

Measurement of total photonuclear cross sections in the Δ-resonance region☆

Abstract Double differential cross sections for the photo-emission of photons and charged pion production were investigated for a number of target nuclei (He, Be, C, O, Ai, Ti, Cu, Sn, Pb) in the photon energy range k = (215−386) MeV. On the basis of these experimental results the total hadronic cross section was determined.

Photoproduction of positive pions from hydrogen with PHOENICS at ELSA

Abstract The differential cross section of the reaction γ p→ π + n has been measured with the PHOENICS detector at ELSA in Bonn. For the first time this cross section has been determined simultaneously over a large range of photon energies ( E γ = 220−900 MeV) and pion angles ( Θ c . m . pi = 35°−135°) with a tagged photon facility. The experimental set-up allowed a considerable kinematic overdetermination of the investigated reaction. Accordingly, the background contributions have been suppressed to below 1%. The measured differential cross section is in good agreement with existing data. The comparison with different model calculations is presented.

Experimental investigation of deuteron photodisintegration in the δ-resonance region

Abstract Differential cross sections for the deuteron photodisintegration process were measured for photon energies between 200 and 440 MeV using the tagged photon beam facility of the Bonn 500 MeV synchrotron. At eight angles between 18° and 145° charged particles were detected simultaneously in time-of-flight spectrometers consisting of scintillation counters. Above the resonance region the measured cross sections agree fairly well with earlier results, whereas there are larger discrepancies at low photon energies.

Measurement of the total cross section for 235U and 238U photofission in the δ-resonance region

Abstract The total cross section for the photoemission of fission fragments σ(γ, F) has been measured for 235U and 238U using tagged bremsstrahlung photons in the energy range 120–460 MeV. The fission fragments were detected in parallel plate avalanche detectors. The results are compared with other information on the photonuclear absorption cross section.

Experimental investigation of the reaction12C(γ, π0)X in the photon energy range between threshold and 450 MeV

The photoproduction of neutral pions on12C has been investigated between threshold and 450 MeV photon energy using the tagged photon beam at the Bonn 500 MeV synchrotron and a large acceptance detector. Theπ0 detector consists of cylindrical wire chambers covering a solid angle of nearly 4π. Using a scintillation counter as an active12C target an attempt was made to separate coherent and incoherentπ0 photoproduction. The measured total and differential cross sections are compared to corresponding theoretical calculations.

Inclusive charged pion photoproduction on12C using tagged photons in the energy range (200–390) MeV

The photoproduction of charged pions on12C has been investigated using the tagged photon beam facility at the Bonn 500 MeV synchrotron. Pions were detected in a broad range magnetic spectrometer. Double differential cross sections for pion emission at fixed photon energies are presented. The integration of the measured distributions yields the total cross section for inclusive pion production. The data are compared to the predictions of a simple model that takes the quasifree production of pions and their subsequent scattering and reabsorption into account.

A determination of the total photonuclear absorption cross section for Pb in the Δ-resonance region by means of a neutron multiplicity measurement

Abstract Multiple-neutron events ( γ , i n…) for Pb have been recorded according to their neutron multiplicity i , for i ⩾ 1 with a quasi-monoenergetic photon beam obtained by the annihilation in flight of monochromatic positrons. These experimental results, taken with photon energies E γ from 145 up to 440 MeV, are subsequently used to determine the partial sum σ (2) ( E γ )= Σ i ⩾2 σ ( γ , i n…) and to evaluate the ensuing total photonuclear absorption cross section σ (tot: Eγ ).

Measurement of total cross sections for π0 photoproduction on nuclei in the Δ-resonance region☆

Abstract Total cross sections for π 0 photoproduction on Be, C, Al, Cu, Sn and Pb have been measured in the photon energy range k = 220–450 MeV using the tagged photon beam of the Bonn 500 MeV synchrotron. The data show a broad maximum around k = 350 MeV. The A -dependence can be described by σ A ∝ A 0.66 . The results are compared to charged pion production and to total hadronic cross sections.

Photoproduction of positive pions from polarized protons

Abstract Target asymmetry data for single positive pion photoproduction from polarized protons have been obtained at the Bonn Electron Stretcher Accelerator ELSA. Data were taken in a wide kinematical range of E γ = 215–800 MeV and Θ CMS π = 35°–135° with the PHOENICS-detector. This detector permits a considerable kinematical overdetermination so that the nominal process could be clearly separated from the background. For the first time a combination of a frozen spin target with a tagged photon beam has been used. Butanol (C 4 H 9 OH) was used as target material with a maximum proton polarization of more than ±90%. Due to the simultaneous energy and angle coverage the systematical error in the order of ΔT sys = ±2.5% is common for all data points. The results at low photon energies show significant deviations from existing multipole analyses.

Cross sections and asymmetries for the p(p,π0)pp reaction from threshold to 1 GeV

Abstract Total cross sections, differential cross sections and asymmetries for the reaction p( p ,π 0 )pp from threshold to 1 GeV have been measured. The outgoing π0 was detected by a 4π neutral meson spectrometer. Our data are compared with the corresponding np→NNπ± reactions. The isoscalar partial cross sections are extracted from the relevant total cross sections. They are significant throughout the whole energy range. Below the Δ-region, energy-integrated differential cross sections show a large anisotropy difference between the neutral and charged pion channels, respectively. A partial-wave fit shows that the initial T = 0 state is dominated by the 3D1 wave in this energy region. Finally, predictions of phenomenological models give reasonable good account of the measured observables but cannot reproduce the sign of the asymmetries.