0000000000547702
AUTHOR
M. Martinez-fabregate
Determination of the η-transition form factor in the γp→pη→pγe+e− reaction
The Dalitz decay η→γe+e− has been measured using the combined Crystal Ball and TAPS photon detector setup at the electron accelerator MAMI-C. Compared to the most recent transition form-factor measurement in the e+e− channel, statistics have been improved by one order of magnitude. The e+e− invariant mass distribution shows a deviation from the QED prediction for a point-like particle, which can be described by a form-factor. Using the usual monopole transition form-factor parameterization, F(m2)=(1−m2/Λ2)−1, a value of Λ−2=(1.92±0.35(stat)±0.13(syst)) GeV−2 has been determined. This value is in good agreement with a recent measurement of the η Dalitz decay in the μ+μ− channel and with rece…
Measurement of the Gerasimov-Drell-Hearn Integrand forH2from 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 $200l{E}_{\ensuremath{\gamma}}l800\text{ }\text{ }\mathrm{MeV}$. The experiment used a $4\ensuremath{\pi}$ 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 $407\ifmmode\pm\else\textpm\fi{}20(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}24(\mathrm{syst})\text{ }\text{ }\ensuremath{\mu}\mathrm{b}$ for $200l{E}_{\ensuremath{\gamma}}l800\text{ }\text{ }\m…
First measurement of the circular beam asymmetry in the γ→p→π0ηp reaction
Abstract The circular photon asymmetry for π 0 η 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 Δ ( 1700 ) D 33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D 33 amplitude.