Two neutral pion photoproduction off the proton between threshold and 800 MeV

The photoproduction of two neutral pions off the proton has been studied for incident photon energies between E-gamma = a 309 MeV (threshold) and 792 MeV with the TAPS photon spectrometer at the Mainz Microtron MAMI. Both 3 gamma- and 4 gamma-events have been analysed in order to deduce the total p(gamma, 2 pi(0))p cross section, The total cross section is less than 300 nb between threshold and similar or equal to 460 MeV, beyond which it starts to rise to a maximum value of about 11 mu b at around 750 MeV. For the highest energies it starts to decrease again, The 4 gamma-sample has been used to reconstruct 2 neutral pions from the above reaction channel by an invariant mass and a missing mass analysis, After reconstruction of the unobserved proton, a 2 has been obtained, which indicates that the decay chain includes the Delta(1232)-resonance as Dalitz-plot of m(pi 0 pi 0) vs. m(p pi 0)(2) an intermediate state.