Köln 2004 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 11: Poster Session: Electromagnetic and Hadronic Probes

HK 11.25: Poster

Tuesday, March 9, 2004, 13:30–15:30, Foyer

Investigation of the η→π⁰γγ decay — •Raghava Varma^1,2 and Ankhi Roy^1,2 — ¹II. Physikalisches Institut, Justus-Liebig-Universityät Gießen — ²Indian Institute of Technology,Bombay

In this poster, we present the investigation of the reaction η→π^∘γγ. The PDG assigns a width of 0.84±0.18 eV to this decay, based on GAMS2000 measurements Chiral perturbation theory (ChPT) calculations are problematic and underpredict the branching ratio for this decay. Recently, Oset et al. have taken a coherent sum of VMD and ChPT and have come up with a width of 0.47±0.10 eV which is in clear disagreement with published results but in remarkable agreement with recent experiment by the Crystal Ball group which also do not agree with earlier measurements. These calculations crucially depend on the shape of invariant mass of the two bachelor photons. To resolve the experimental discrepancy as well as to test the theory we have remeasured the width of this rare decay using tagged Bresstrahlung photons from 3.2 GeV electrons from ELSA@Bonn. A 5cm long LH₂ was used as a target. The experiment has been performed using an almost full 4π setup combining the Crystal Barrel with TAPS forming the forward wall. The analysis is going on. It involves eliminating the background consisting of η→ 3π^∘ (where two clusters overlap) and kinematically identical pγ→ pπ^∘π^∘ events. The results of the anaysis would be presented at the conference.