R. Beck

Properties of baryon resonances from a multichannel partial wave analysis

Properties of nucleon and Δ resonances are derived from a multichannel partial wave analysis of pion and photo-induced reactions off protons. This paper summarizes the latest results on masses, widths, and decay properties of nucleon and Δ resonances.

A focal plane system for the 855 MeV tagged photon spectrometer at MAMI-B

Abstract This paper describes a 352 element detector, designed for the focal plane of the 855 MeV electron spectrometer at the Institut fur Kernphysik in Mainz. The system tags bremsstrahlung photons in the energy range 40–800 MeV with a resolution of ∼2 MeV and an overall flux of ∼10 8 s −1 .

First measurement of the Gerasimov-Drell-Hearn integral for Hydrogen from 200 to 800 MeV

A direct measurement of the helicity dependence of the total photoabsorption cross section on the proton was carried out at MAMI (Mainz) in the energy range 200<E_gamma<800 MeV. The experiment used a 4

Measurement of the E2/M1 ratio in the N ---> Delta transition using the reaction p(gamma(pol.),p)pi0

\pi

Quasifree photoproduction of eta mesons off the neutron

detection system, a circularly polarized tagged photon beam and a frozen spin target. The contributions to the Gerasimov-Drell-Hearn sum rule and to the forward spin polarizability

New results on the Roper resonance and the P-11 partial wave

\gamma_0

In-medium modifications of the pi pi interaction in photon-induced reactions

determined from the data are 226 \pm 5 (stat)\pm 12(sys) \mu b and -187 \pm 8 (stat)\pm 10(sys)10^{-6} fm^4, respectively, for 200<E_\gamma<800 MeV.

Quasifree Photoproduction ofηMesons off the Neutron

The small electric quadrupole E2 amplitude of the predominantly magnetic dipole M1 p -> Delta(1232) transition has been measured using 270 to 420 MeV tagged linearly polarized photons in the p(gamma,p)pi0 reaction at the Mainz Microtron MAMI. Differential cross sections and photon asymmetries were determined by measuring the recoil proton in the cylindrically symmetric 4pi detector DAPHNE. From the proton angular distributions the ratio E2/M1 = -(2.5+-0.2+-0.2)% at the maximum of the Delta(1232) resonance has been derived.The small electric quadrupole E2 amplitude of the predominantly magnetic dipole M1 p{r_arrow}{Delta}(1232) transition has been measured using 270 to 420MeV tagged linearly polarized photons in the p({gamma}{searrow},p){pi}{sup o} reaction at the Mainz Microtron MAMI. Differential cross sections and photon asymmetries were determined by measuring the recoil proton in the cylindrically symmetric 4{pi} detector DAPHNE. From the proton angular distributions the ratio E2/M1=-(2.5{plus_minus}0.2{plus_minus}0.2){percent} at the maximum of the {Delta}(1232) resonance has been derived. {copyright} {ital 1997} {ital The American Physical Society}

Near-threshold photoproduction of η-mesons from the deuteron

Quasifree photoproduction of eta mesons off nucleons bound in the deuteron has been measured with the CBELSA/TAPS detector for incident photon energies up to 2.5 GeV at the Bonn ELSA accelerator. The eta mesons have been detected in coincidence with recoil protons and recoil neutrons, which allows a detailed comparison of the quasifree n(gamma,eta)n and p(gamma,eta)p reactions. The excitation function for eta production off the neutron shows a pronounced bumplike structure at W=1.68 GeV (E{gamma} approximately 1 GeV), which is absent for the proton.

Near threshold photoproduction of η-mesons from complex nuclei

Abstract Properties of the Roper resonance, the first scalar excitation of the nucleon, are determined. Pole positions and residues of the P 11 partial wave are studied in a combined analysis of pion- and photo-induced reactions. We find the Roper pole at { ( 1371 ± 7 ) − i ( 92 ± 10 ) } MeV and an elasticity of 0.61 ± 0.03 . The largest decay coupling is found for the Nσ ( σ = ( π π ) - S -wave). The analysis is based on new data on γ p → p π 0 π 0 for photons in the energy range from the two-pion threshold to 820 MeV from TAPS at Mainz and from 0.4 to 1.3 GeV from Crystal Barrel at Bonn and includes further data from other experiments. The partial wave analysis excludes the possibility that the Roper resonance is split into two states with different partial decay widths.