First measurement of the circular beam asymmetry in the gamma p --> pi0 eta p reaction

The circular photon asymmetry for pi0 eta photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the Delta(1700)D33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D33 amplitude.Comment: 11 pages, 3 figures, submitted to Phys.Lett.

Measurement of the helicity-dependent total cross-section for the gamma n -> p pi(-)pi(0) reaction

The helicity dependence of the total cross-section for the gamma n -> p pi(-)pi(0) reaction has been measured for the first time at incident photon energies from 450 to 800MeV. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. Both the measured unpolarized and the helicity-dependent observables are not well described by the existing theoretical models

Helicity dependence of the γd → πNN reactions in the Δ-resonance region

The helicity dependence of the differential cross-section for the gamma d -> pi NN reactions has been measured for the first time in the Delta-resonance region. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. The data show that the main reaction mechanisms for the pi(+/-) NN channels are the quasi-free N pi processes on one bound nucleon with nuclear dynamics playing a minor role. On the contrary, for the pi(0)np channel nuclear mechanisms involving the reabsorption of the photoproduced pi(0) by the np pair have to be taken into account to reproduce the experimental data

Measurement of the helicity-dependent total cross-section for the γ n → p π− π0 reaction

The helicity dependence of the total cross-section for the gamma n -> p pi(-)pi(0) reaction has been measured for the first time at incident photon energies from 450 to 800MeV. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. Both the measured unpolarized and the helicity-dependent observables are not well described by the existing theoretical models

First measurement of the helicity dependence for the gamma p -> p pi(+)pi(-) reaction

The helicity dependence of the total cross-section and the invariant-mass distributions in the (p pi(+/-)) and (pi(+) pi(-)) final states for the gamma p -> p pi(+)pi(-) reaction have been measured for the first time at incident photon energies from 400 to 800MeV. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. Although this channel is found to be predominantly excited by the intermediate production of a Delta pi state, both the measured unpolarized and the helicity-dependent observables are generally not well described by the existing theoretical models

First measurement of the helicity dependence for the gamma p -> p pi(+)pi(-) reaction

The helicity dependence of the total cross-section and the invariant-mass distributions in the (p pi(+/-)) and (pi(+) pi(-)) final states for the gamma p -> p pi(+)pi(-) reaction have been measured for the first time at incident photon energies from 400 to 800MeV. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. Although this channel is found to be predominantly excited by the intermediate production of a Delta pi state, both the measured unpolarized and the helicity-dependent observables are generally not well described by the existing theoretical models

Measurement of the Gerasimov-Drell-Hearn integrand for ²H from 200 to 800 MeV

A measurement of the helicity dependence of the total inclusive photoabsorption cross section on the deuteron was carried out at MAMI (Mainz) in the energy range 200<Eγ<800  MeV. The experiment used a 4π detection system, a circularly polarized tagged photon beam and a frozen-spin target which provided longitudinally polarized deuterons. The contribution to the Gerasimov-Drell-Hearn sum rule for the deuteron determined from the data is 407±20(stat)±24(syst)  μb for 200<Eγ<800  MeV