Limits on Heavy Neutrinos at NA48/2 and NA62

Large samples of charged kaon decays have been collected by the NA48/2 (2003-2004), the NA62-RK (2007) and the NA62 (2015) experiments at CERN SPS. This proceedings summarizes upper limits on heavy neutrino production measured by these experiments. The results from the 2015 data analysis at the NA62 experiment are preliminary

Measurement of K+→π+μ+μ−K^+ \to \pi^+ \mu^+ \mu^− Decay Form Factor and Evaluation of Muon Veto and Charged Hodoscope Efficiencies at NA62 Experiment at CERN

The main focus of the presented thesis is the measurement of form factor parameters and branching fraction of a rare kaon decay $K^+ \to \pi^+ \mu^+ \mu^- (K_{\pi\mu\mu})$ at the NA62 experiment, using a sub-sample of data collected in 2017. In addition to the main $K_{\pi\mu\mu}$ analysis, efficiency evaluation studies for sub-detectors MUV3 and CHOD carried out by the author are summarized in the thesis. The measured efficiencies were monitored during the NA62 data taking in 2016–2018 using the developed tools

Reconstruction of neutral mesons using photon conversions

The main subject of this project were feasibility studies for the reconstruction of $\eta$ and $\omega$ mesons in p-Pb collisions, employing the different techniques used in ALICE, focusing on the detection channels in which the PCM method can improve the extraction of the mesons. However, studies combining PCM photons with photons detected in the calorimeters were also performed as well as studies where both photons were detected in the calorimeters. Outputs of this project are corrected yields for $\eta$ and $\omega$ mesons for various $p_T$

Search for Lepton Number and Flavour Violation in K+K^+ and π0\pi^0 Decays

The NA62 experiment at CERN collected a large sample of charged kaon decays into final states with multiple charged particles in Run 1 from 2016 to 2018. This sample provides sensitivities to rare decays with branching fractions as low as 10−11. Results of searches for the lepton number and/or flavour violating decays K+→π±μ∓e+ and π0→μ−e+ are reported. No evidence of these decays is found, and upper limits on the branching fractions are obtained 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+)<3.2×10−10. These results improve by approximately one order of magnitude over previous results for these decay modes

Search for Heavy Neutral Lepton production in K+K^+ decays at NA62

Large samples of charged kaon decays have been collected by the NA62-R$_K$ (2007) and the NA62 (2015) experiments at CERN SPS. This proceedings summarizes upper limits on heavy neutrino production measured by these experiments

Search for heavy neutral lepton production in K+K^+ decays

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 at the $10^{-7}$ to $10^{-6}$ level are established on the elements of the extended neutrino mixing matrix $|U_{\ell 4}|^2$ ($\ell=e,\mu$) for heavy neutral lepton mass in the range $170-448~{\rm MeV}/c^2$. This improves on the results from previous production searches in $K^+$ decays, setting more stringent limits and extending the mass range.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 at the 10−7 to 10−6 level are established on the elements of the extended neutrino mixing matrix |Ue4|2 and |Uμ4|2 for heavy neutral lepton mass in the ranges 170–448 MeV/ c2 and 250–373 MeV/ c2 , respectively. This improves on the previous limits from HNL production searches over the whole mass range considered for |Ue4|2 , and above 300 MeV/ c2 for |Uμ4|2

Search for leptonic decays of the dark photon at NA62

International audienceThe NA62 experiment at CERN, configured in beam-dump mode, has searched for dark photon decays in flight to electron-positron pairs using a sample of $1.4\times 10^{17}$ protons on dump collected in 2021. No evidence for a dark photon signal is observed. The combined result for dark photon searches in lepton-antilepton final states is presented and a region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon mass values between 50 and 600 MeV$/c^2$ and coupling values in the range $10^{-6}$ to $4\times10^{-5}$. An interpretation of the $e^+ e^-$ search result in terms of the emission and decay of an axion-like particle is also presented

Search for dark photon decays to μ+μ−\mu^+\mu^- at NA62

International audienceThe NA62 experiment at CERN, designed to study the ultra-rare decay $K^+ \to \pi^+\nu\overline{\nu}$, 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 $\mu^+\mu^-$ pairs is reported, based on a sample of $1.4 \times 10^{17}$ 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$/c^2$

Search for leptonic decays of the dark photon at NA62

International audienceThe NA62 experiment at CERN, configured in beam-dump mode, has searched for dark photon decays in flight to electron-positron pairs using a sample of $1.4\times 10^{17}$ protons on dump collected in 2021. No evidence for a dark photon signal is observed. The combined result for dark photon searches in lepton-antilepton final states is presented and a region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon mass values between 50 and 600 MeV$/c^2$ and coupling values in the range $10^{-6}$ to $4\times10^{-5}$. An interpretation of the $e^+ e^-$ search result in terms of the emission and decay of an axion-like particle is also presented

First search for K+→π+ννˉK^+\rightarrow\pi^+\nu\bar{\nu} using the decay-in-flight technique

International audienceThe NA62 experiment at the CERN SPS reports the first search for K+→π+νν¯ using the decay-in-flight technique, based on a sample of 1.21×1011 K+ decays collected in 2016. The single event sensitivity is 3.15×10−10 , corresponding to 0.267 Standard Model events. One signal candidate is observed while the expected background is 0.152 events. This leads to an upper limit of 14×10−10 on the K+→π+νν¯ branching ratio at 95% CL