First observation of the reactionγγ→π 2→π 0 π 0 π 0

The Crystal Ball detector has been used at the DORIS II storage ring at DESY to study the reactionγγ→π 0 π 0 π 0 in theπ 0 π 0 π 0 invariant mass range from 850 MeV/c2 to 2600 MeV/c2. An enhancement around 1750 MeV/c2 is attributed to theπ 2(1670) resonance. The observedπ 0 π 0 invariant mass distribution and theπ 0 angular distributions are consistent with those expected for the decay chainπ 2→π 0 f 2(1270)→π 0 π 0 π 0. From our measurements we find the following resonance parameters: two photon partial width $$\Gamma _{\pi _2 }^{\gamma \gamma } = (1.41 \pm 0.23 \pm 0.28)keV$$ , massM(π 2)=(1742±31±49)MeV/c2. and total width $$\Gamma _{\pi _2 }^{tot} = (236 \pm 49 \pm 36)MeV$$ .