Search for lepton number and flavour violation in K+ and pi0 decays

The NA62 experiment at CERN collected a large sample of charged kaon decays into final states with multiple charged particles in 2016-2018. This sample provides sensitivities to rare decays with branching ratios as low as 10 −11 . Searches for the lepton number violating K + → π − µ + e+ decay and the lepton flavour violating K + → π + µ − e + and π 0 → µ − e + decays are reported. No evidence for these decays is found and upper limits of the branching ratios are obtained at 90% confidence level. These results improve by one order of magnitude over previous results for these decay modes

New measurement of the radiative decay Ke3g at the NA62 experiment at CERN

The NA62 experiment at CERN reports new results from the study of the radiative kaon decay K+→π0e+νγ (Ke3γ ), using a data sample recorded in 2017 and 2018. Preliminary results with the most precise measurement of the Ke3γ branching ratio, and a T-asymmetry measurement in the Ke3γ decay, are presented

Searches for heavy neutral lepton production at the NA62 experiment

Searches for heavy neutral lepton production in K+ ? e+N and K+ ? µ+N decays using the data set collected by the NA62 experiment at CERN in 2016-18 are presented. Upper limits on the elements of the extended neutrino mixing matrix and are established at the levels of 10-9 and 10-8, respectively, improving on the earlier searches for heavy neutral lepton production and decays in the kinematically accessible mass range. Searches for the K+ ? µ+vvv and K+ ? µ+vX decays, where X is a new light invisible particle, are also reported

Searches for lepton flavour/number violation in K⁺ and π⁰ decays at the NA62 experiment

Searches for the lepton number violating K+ → π−μ+e+ decay and lepton flavour violating decays K+ → π+μ−e+ and π0 → μ−e+ are reported, using NA62 data collected in 2017 and 2018. In the absence of a significant excess above the background in each channel, upper limits on the branching ratios are established at 90% confidence level: B(K+ → π−μ+e+) < 4.2 × 10−11, B(K+ → π+μ−e+) < 6.6 × 10−11, and B(π0 → μ−e+) < 3.2 × 10−1

Search for K⁺ decays to a lepton and invisible particles

Searches for heavy neutral leptons N in the K+ → e+N and K+ → μ+N decay channels using the dataset collected by the NA62 experiment at CERN between 2016-2018 are presented. Upper limits on the corresponding mixing matrix elements are reported at the level of O(10−9) and O(10−8), respectively. This represents an improvement of at least an order of magnitude on previous measurement, as well as an extension to higher masses than previously covered. Related searches set upper limits on the rate of the K+ → μ+νν(Equation presented) and K+ → μ+νX decay channels, with X an invisible scalar or vector boson

Search for dark photon decays to μ + μ − at NA62

Abstract The NA62 experiment at CERN, designed to study the ultra-rare decay K + → π + ν ν ¯ $$\nu \overline{\nu}$$ , has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to μ + μ − pairs is reported, based on a sample of 1.4 × 1017 protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV/c 2

New measurement of radiative decays at the NA62 Experiment at CERN: (Ke3γ) K+→ π0 e+νγ,

The NA62 experiment at CERN reports new results from studies of radiative kaon decaysK+→ π0e+νγ(Ke3γ), using a data sample collected in 2017-2018. The sample comprises O(100k) Ke3γ candidates with sub-percent background contaminations. Preliminary results including the most precise measurement of the Ke3γ branching ratios and theT -asymmetry measurement in the Ke3γ decay, are presented

Search for lepton number and flavour violation in K+ and π0 decays

The NA62 experiment at CERN collected a large sample of charged kaon decays into the final states with multiple charged particles in 2016-2018. This sample provides the sensitivities to rare decays with branching ratios as low as 10−11. The results from the searches for lepton flavour/number violating decays of the charged kaon and the neutral pion to the final states containing a lepton pair based on this data set are presented