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Register a new userFirst measurement of target and beam-target asymmetries in the $gamma pto pi^0eta p$ reaction
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The first data on target and beam-target asymmetries for the $gamma ptopi^0eta p$ reaction at photon energies from 1050 up to 1450 MeV are presented. The measurements were performed using the Crystal Ball and TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. The general assumption that the reaction is dominated by the $Delta 3/2^-$ amplitude is confirmed. The data are in particular sensitive to small contributions from other partial waves.
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We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the $vec gamma vec ptoeta p$ reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indicating a significant impact on our understanding of the underlying dynamics of $eta$ meson photoproduction. The peculiar nodal structure observed in existing T data close to threshold is not confirmed.
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.
The data available from the A2 Collaboration at MAMI were analyzed to select the $gamma pto pi^0eta p$ reaction on an event-by-event basis, which allows for partial-wave analyses of three-body final states to obtain more reliable results, compared to fits to measured distributions. These data provide the worlds best statistical accuracy in the energy range from threshold to $E_{gamma}=1.45$ GeV, allowing a finer energy binning in the measurement of all observables needed for understanding the reaction dynamics. The results obtained for the measured observables are compared to existing models, and the impact from the new data is checked by the fit with the revised Mainz model.
The reaction $gamma pto ppi^0eta$ has been studied with the CBELSA detector at the tagged photon beam of the Bonn electron stretcher facility. The reaction shows contributions from $Delta^+(1232)eta$, $N(1535)^+pi^0$ and $pa_0(980)$ as intermediate states. A partial wave analysis suggests that the reaction proceeds via formation of six $Delta$ resonances, $Delta(1600)P_{33}$, $Delta(1920)P_{33}$, $Delta(1700)D_{33}$, $Delta(1940)D_{33}$, $Delta(1905)F_{35}$, $Delta(2360)D_{33}$, and two nucleon resonances $N(1880)P_{11}$ and $N(2200)P_{13}$, for which pole positions and decay branching ratios are given.
A measurement of the double-polarization observable $E$ for the reaction $gamma pto pi^0 p$ is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C$_4$H$_9$OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from $E_gamma =600$~MeV to $E_gamma =2310$~MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
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