Speaker
Cristina Lazzeroni
(University of Birmingham (GB))
Description
We report the first observation of the very rare decay K+- -> pi+- pi0 e+ e- by the NA48/2 experiment. From a clean sample of almost 2000 reconstructed signal events, we have determined the branching fraction with high precision and measured the e+ e- invariant mass distribution, which allows to differentiate between different decay models.
Besides, the NA48/2 experiment has recently published a detailed study of the
Ke4 decay mode K —> pi0 pi0 e nu based on 65000 candidates with a low 1% background contamination. The achieved experimental precision brings evidence for isospin breaking mass effects and final state pi pi scattering. Theoretical calculations will have to face a new precision challenge when using such improved inputs to extract for example low energy constants of Chiral Perturbation Theory.
Author
Cristina Lazzeroni
(University of Birmingham (GB))
