Double π Photoproduction off the Proton at Threshold
نویسنده
چکیده
The reaction γp → ππp has been measured using the TAPS BaF2 calorimeter at the tagged photon facility of the Mainz Microtron accelerator. Chiral perturbation theory (ChPT) predicts that close to threshold this channel is significantly enhanced compared to double pion final states with charged pions. In contrast to other reaction channels, the lower order tree terms are strongly suppressed in 2π photoproduction. The consequence is the dominance of pion loops in the 2π channel close to threshold a result that opens new prospects for the test of ChPT and in particular its inherent loop terms. The present measurement is the first which is sensitive enough for a conclusive comparison with the ChPT calculation and is in agreement with its prediction. The data also show good agreement with a calculation in the unitary chiral approach. Preprint submitted to Elsevier Science 8 February 2008
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