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Köln 2004 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 27: Electromagnetic and Hadronic Probes IV

HK 27.6: Talk

Wednesday, March 10, 2004, 12:15–12:30, E

Search for the γγ Decay of the σ-Meson at CELSIUS-WASA — •M. Bashkanov, H. Clement, E. Doroshkevich, M. Kaskulov, R. Meier, T. Skorodko, and G.J. Wagner — Physikalisches Institut, Universität Tübingen

The γγ decay of the σ meson, though likely to be extremely small, provides a key information about its nature, in particular its qq and qqqq contents. From the reverse reaction γγ→ ππ, which has been investigated by CLEO and Crystal Ball, estimates for σ → γγ have been obtained [1]. In the current study at WASA we consider the hadronic production of σ and its potentially successive γγ decay by pppp σ → ppγγ at Tp = 1360 MeV, i.e. at the energy, where most of the statistics has been accumulated so far. Between the π0 and η peaks in Mγγ we observe for Mγγ > 350 MeV a low-statistics continuum of counts which may be associated with incomplete detection of π0π0 production. However, near the π0π0 threshold and in particular below it we observe some structure, which in MC simulations cannot be explained by π0, π0π0 and η production or any detector features known so far. On the other hand, the shape of the observed structure would be consistent with a σ → γγ decay, where the strength above the π0π0 threshold is expected to be heavily quenched due to the opening of the overwhelmingly strong ππ decay channel.

[1] PDG, Phys. Rev. D66, 1 (2002) and references therein supported by BMBF (06 TU 201), DFG (Europ. Graduiertenkolleg) and Landesforschungsschwerpunkt (Quasiteilchen)

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