Speaker
Description
The NA62 experiment at CERN collected the world’s largest dataset of charged
kaon decays in 2016-2018, leading to the first measurement of the Branching
Fraction of the ultra-rare K+ → π+ν¯ν decay, based on 20 candidates. This
provides evidence for the very rare K+ → π+ν¯ν decay, observed with a significance
of 3.4σ. This measurement is also used to set limits on BR(K+ → π+X),
where X is a scalar or pseudo-scalar particle. The analysis of the full 2016-2018
data sample and future NA62 plans and prospects are reviewed.
More recent results from NA62 analyses of K+ → π0e+νγ, K+ → π+μ+μ−
and K+ → π+γγ decays, using data samples recorded in 2017–2018, are also
reported. The radiative kaon decay K+ → π0e+νγ (Ke3g) is studied with a
data sample of O(100k) Ke3g candidates with sub-percent background contaminations.
Preliminary results with the most precise measurements of the Ke3g
branching ratios and T-asymmetry are presented. The K+ → π+μ+μ− sample
comprises about 27k signal events with negligible background contamination,
and the presented analysis results include the most precise determination of the
branching ratio and the form factor. The K+ → π+γγ sample contains about
4k signal events with 10% background contamination, and the analysis improves
the precision of the branching ratio measurement by a factor of 3 with respect
to the previous measurements. An overview of the latest NA62 results and the
future prospect of the experiment are presented.
The first observation of the decay K± → π0π0μ±ν (K00μ4) by the NA48/2
experiment at the CERN and the preliminary measurement of the branching
ratio are also presented. The result is converted into a first measurement of
the R form factor in Kl4 decays and compared with the prediction from 1-loop
Chiral Perturbation Theory.
