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 γ^∗γ^∗→ 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 pp → pp σ → ppγγ at T_p = 1360 MeV, i.e. at the energy, where most of the statistics has been accumulated so far. Between the π⁰ and η peaks in M_γγ we observe for M_γγ > 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)