PoS - Proceedings of Science
Volume 414 - 41st International Conference on High Energy physics (ICHEP2022) - Quark and Lepton Flavour Physics
Precise measurement of the Decay K± ➞ π0 π0 µ± ν
D. Madigozhin*  on behalf of the NA48/2 Collaboration
Full text: pdf
Pre-published on: November 16, 2022
Published on: June 15, 2023
We report the first observation of the decay $K^{\pm} \rightarrow \pi^{0} \pi^{0} \mu^{\pm} \nu$ ($K^{00}_{\mu4}$)
by the NA48/2 experiment at the CERN SPS. From 2437 detected signal candidates with a S/B ratio of about 6,
the branching ratio of the decay is determined with high precision. In the region of squared dilepton mass
above $0.03$~GeV$^2/c^4$, the branching ratio is found to be $BR(K^{00}_{\mu 4},S_l>0.03) = (0.65 \pm 0.03) \times 10^{-6}$.
The full phase space result $BR(K^{00}_{\mu 4}) = (3.4 \pm 0.2) \times 10^{-6}$, depending on the decay model
extrapolation, is in a reasonable agreement with the R form factor prediction from 1-loop Chiral Perturbation Theory.
DOI: https://doi.org/10.22323/1.414.0723
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