Leipzig 2002 – scientific programme

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T: Teilchenphysik

T 405: Seltene Zerf
älle

T 405.4: Talk

Thursday, March 21, 2002, 14:45–15:00, HS 14

Search for the decay K_S→π⁰γγ — •Lucia Masetti — Institut f"ur Physik, Johannes-Gutenberg-Universit"at Mainz

A search for the decay K_S→π⁰γγ has been made using the NA48 detector at the CERN SPS. The study of this decay is useful to test the predictions of the Chiral Perturbation Theory (χ PT) on branching ratios and q²-spectra. χ PT predicts a branching ratio for K_S→π⁰γγ of 3.8× 10⁻⁸ with the cut-off z=q²/m_K0²≥ 0.2, to avoid the region with the pion pole, which dominates the total rate. K_S→2π⁰ events are very similar to the signal and have a branching ratio ∼ 10⁷ times higher, therefore they are the main source of background due to misreconstructed photon energy, conversions, lost photons and in-time accidental activity in the detector. Using data collected in 1999 during a 40-hour run with a high-intensity K_S beam, an upper limit for the branching ratio BR(K_S →π⁰γγ)_{z≥ 0.2}<4.4×10⁻⁷, at 90% confidence level has been obtained.