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HK: Hadronen und Kerne
HK 26: Electromagnetic Probes IV, Electro-, Photoproduction
HK 26.8: Vortrag
Dienstag, 17. März 1998, 16:00–16:15, B
Photoproduction of neutral pion pairs from the proton — •Matthias Wolf — II. Physikalisches Institut, Universität Gießen
First measurements of the reaction p(γ,πoπo)p have been performed in 1992 with the photon spectrometer TAPS at the Mainz microtron MAMI [1]. This experiment revealed a dominant two-step production mechanism near the peak cross section (Eγ≈ 720 MeV) involving the excitation of the D13(1520) baryon resonance and the Δ(1232) as intermediate state. Due to the limited statistics the production cross section close to threshold (Eγ< 450 MeV) could not be extracted unambiguously. However, it is only in this energy regime that predictions of Chiral Pertubation Theory can be tested.
Therefore the experiment was redone in 1995 with significantly increased statistics. The new data allow to determine the total cross section from threshold up to the highest photon energies (309 – 820 MeV) with a reduced systematic error near threshold. Dalitz plots ranging to smaller cm–energies may provide further information of the production mechanism. Theories expect that the cross section near threshold is no longer dominated by a two–step mechanism but by the emission of correlated pion pairs from the P11(1440) resonance.
Preliminary results of the new experiment will be discussed.
[1] F. Härter et al., Physics Letters B 401 (1997) 229
[2] supported by BMBF and DFG (SFB 201)