Berlin 2005 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 9: Elektromagnetische und Hadronische Proben

HK 9.9: Vortrag

Freitag, 4. März 2005, 18:45–19:00, TU MA004

Investigation of 3π⁰ final states with the CELSIUS/WASA experiment^* — •C. Pauly¹, F. Cappellaro², L. Demirörs¹, I. Koch², and W. Scobel¹ — ¹Institut f. Experimentalphysik, Universität Hamburg — ²Dep. of Radiation Sciences, Uppsala University

In the WASA experiment (CELSIUS, Uppsala), decays of the η meson produced in pp and pd reactions are investigated. To obtain the necessary high luminosities a unique target of frozen Hydrogen pellets is used. A 4π CsI calorimeter together with a multilayered forward detector provides the necessary high acceptance and tagging accuracy.
In the last year, data were taken for the pp reaction with a mean luminosity of well above 5· 10³⁰ cm⁻² s⁻¹ and projectile energies of 1360 MeV and 1450 MeV corresponding to excess energies Q=41 MeV and 75 MeV, above the η production threshold (1254 MeV). Due to the high geometric acceptance, 3π⁰ → 6γ final states can be fully reconstructed with all 6 gammas being detected in the calorimeter, and thus providing a very clean event sample. The η → 3 π⁰ channel clearly stands out in the pp missing mass distribution; the η angular distribution will be shown and its Dalitz plot discussed in context with the slope parameter α as a measure of nonuniformity [1]. A cross section estimate for prompt 3π⁰ production can be deduced by decomposing the pp missing mass distribution of 6γ events based on MC simulations.

[1] W. B. Tippens et al., Phys. Rev. Lett. 87, 192001 (2001) ^* supported by BMBF (06HH152)