Development of a new CEDAR for kaon identification at the NA62 experiment at CERN

The NA62 experiment at CERN utilises a differential Cherenkov counter with achromatic ring focus (CEDAR) for tagging kaons within an unseparated monochromatic beam of charged hadrons. The CEDAR-H detector was developed to minimise the amount of material in the path of the beam by using hydrogen gas as the radiator medium. The detector was shown to satisfy the kaon tagging requirements in a test-beam before installation and commissioning at the experiment. The CEDAR-H performance was measured using NA62 data collected in 2023

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

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

Measurement of the very rare K+ → π+ν ¯ν decay at the NA62 experiment

The K+ -> pi(+) nu(nu) over bar decay, with a very precisely predicted branching ratio of less than 10(-10), is among the best processes to reveal indirect effects of new physics. The NA62 experiment reports the branching ratio measurement BR(K+ -> pi(+) nu(nu) over bar) = (1.06(-0.34)(+0.40)vertical bar(stat) +/- 0.09 vertical bar syst) . 10(-10) at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016-2018. This provides evidence for the very rare K+ -> pi(+)nu(nu) over bar decay, observed with a significance of 3.4 sigma. This measurement is also used to set limits on BR(K+ -> pi(+) X), where X is a new feebly interacting scalar or pseudo-scalar particle, foreseen in several new physics scenarios

Development of a new CEDAR for kaon identification at the NA62 experiment at CERN

The NA62 experiment at CERN utilises a differential Cherenkov counter with achromatic ring focus (CEDAR) for tagging kaons within an unseparated monochromatic beam of charged hadrons. The CEDAR-H detector was developed to minimise the amount of material in the path of the beam by using hydrogen gas as the radiator medium. The detector was shown to satisfy the kaon tagging requirements in a test-beam before installation and commissioning at the experiment. The CEDAR-H performance was measured using NA62 data collected in 2023

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

High level performance of the NA62 RICH detector

NA62 is the last generation kaon experiment at the CERN SPS aiming to measure the branching ratio of the ultra-rare decay with 10% accuracy. The challenging aspect of NA62 is the suppression of background decay channels with branching ratios up to 10 orders of magnitude higher than the signal and with similar experimental signature: one of the main backgrounds comes from the decay, therefore a highly powerful pion/muon separation is needed. To this purpose good identification (PID) is required. A key element of PID in NA62 is the Ring-Imaging Cherenkov (RICH) detector. According to the NA62 requirements, the RICH identifies and in the momentum range between 15 and 35 GeV/c with a muon rejection factor of . It also measures the arrival time of charged particles with a precision better than 100 ps and is one of the main components of the NA62 trigger system. The RICH detector has been successfully operated during the 2016, 2017 and 2018 data taking periods of NA62, being essential in the analysis leading to the first evidence for the observation of the decay. NA62 data taking was resumed in 2021. The main design aspects and operational characteristics of the detector are described and a detailed report of its performance concerning the separation is presented, together with preliminary results about its basic performance in 2021