Experiment E949 at Brookhaven National Laboratory has observed three new events
consistent with the decay K+→ π+ ν ν in the pion momentum region 140< P π< 199 MeV/c in an …

Three events for the decay K+→ π+ ν ν have been observed in the pion momentum region
below the K+→ π+ π 0 peak, 140< P π< 199 MeV/c, with an estimated background of 0.93±…

A new measurement of the π+→ e+ ν branching ratio gives R π e ν= Γ (π→ eν+ π→ eνγ)/Γ (π→
μν+ π→ μνγ)=[1.2265±0.0034 (stat)±0.0044 (sys)]× 10− 4. This result is in agreement …

A precision measurement of the ratio R K of the rates of kaon leptonic decays K ± →e ± ν
and K ± →μ ± ν with the full data sample collected by the NA62 experiment at CERN in 2007–…

An additional event near the upper kinematic limit for K+→ π+ ν ν has been observed by
experiment E949 at Brookhaven National Laboratory. Combining previously reported and new …

Evidence of massive neutrinos was sought in the π+→ e+ ν decay spectrum with the background
from the π→ μ→ e decay chain highly suppressed. Upper limits (90% CL) were set on …

Additional evidence for the rare kaon decay K+→ π+ ν ν has been found in a new data set
with comparable sensitivity to the previously reported result. One new event was observed in …

A search for heavy neutral lepton (N) production in K + → e + N decays using the data sample
collected by the NA62 experiment at CERN in 2017–2018 is reported. Upper limits of the …

Evidence of a heavy neutrino, ν H, in the K+→ μ+ ν H decays was sought using the E949
experimental data with an exposure of 1.70× 1 0 12 stopped kaons. With the major background …

A search for heavy neutral lepton production in K + decays using a data sample collected with
a minimum bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits …