Measurement of the very rare K+→π+ννˉK^+ \to \pi^+ \nu \bar\nu decay

The decay K+→π+νν¯ , 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 at CERN SPS is designed to study the K+→π+νν¯ decay and to measure its branching ratio using a decay-in-flight technique. NA62 took data in 2016, 2017 and 2018, reaching the sensitivity of the Standard Model for the K+→π+νν¯ decay by the analysis of the 2016 and 2017 data, and providing the most precise measurement of the branching ratio to date by the analysis of the 2018 data. This measurement is also used to set limits on BR(K+→π+X ), where X is a scalar or pseudo-scalar particle. The final result of the BR(K+→π+νν¯ ) measurement and its interpretation in terms of the K+→π+X decay from the analysis of the full 2016-2018 data set is presented, and future plans and prospects are reviewed

Physics beyond the SM with kaons at NA62

The decay $K^{+} \rightarrow \pi^{+} v \overline{v}$, with a very precisely predicted branching ratio of less than $10^{-10}$, is one of the best candidates to reveal indirect effects of new physics at the highest mass scales. The NA62 experiment at the CERN SPS is designed to measure the branching ratio of the $K^{+} \rightarrow \pi^{+} v \overline{v}$ with a decay-in-flight technique. NA62 took data so far in 2016-2018. Statistics collected in 2016 allowed NA62 to reach the Standard Model sensitivity for $K^{+} \rightarrow \pi^{+} v \overline{v}$, entering the domain of $10^{-10}$ single event sensitivity and showing the proof of principle of the experiment. Thanks to the statistics collected in 2017, NA62 surpasses the present best sensitivity. The analysis strategy is reviewed and the preliminary result from the 2017 data set is presented.The NA62 experiment at CERN collected a large sample of charged kaon decays into final states with multiple charged particles in 2016-2018. The sensitivity to a range of lepton flavour and lepton number violating kaon decays provided by this data set improves over the previously reported measurements. Results from the searches for these processes with a partial NA62 data sample are presented

New result on the search for the K+→π+ννˉK^+ \to \pi^+ \nu\bar\nu decay at the NA62 experiment at CERN

The ultra-rare $K^{+} \rightarrow \pi^{+}\nu\overline{\nu}$ decay benefits from a precisely predicted branching ratio in the SM$BR(K^{+} \rightarrow \pi^{+}\nu\overline{\nu}) = (8.4\pm 1.0)\times10^{-11}$, being almost free from theoretical uncertainties, andmost importantly from a very high sensitivity to a variety ofbeyond-the-standard-model scenarios, making it one of the bestcandidates to reveal indirect effects of new physics in the flavoursector. The NA62 experiment at the CERN SPS, designed to measurethe branching ratio of $K^{+} \rightarrow \pi^{+}\nu\overline{\nu}$with a decay-in-flight technique, collected data in 2016-2018. Newresults from the analysis of 2018 data, the largest data set so farcollected, will be presented. The result will represent the mostaccurate measurement so far achieved of this ultra-rare decay

NA48/62 latest results

The NA62 experiment at the CERN SPS recorded in 2007 a large sample of $K^+ \to \mu^+ \nu_{\mu}$ decays. A peak search in the missing mass spectrum of this decay is performed. In the absence of observed signal, the limits obtained on $\mathscr{B}(K^+\to \mu^+ \nu_{h})$ and on the mixing matrix element $\mid U_{\mu 4}\mid$ are reported. The upgraded NA62 experiment started data taking in 2015. About $5 \times 10^{11}K^+$ decays have been recorded so far to measure the branching ratio of the $K^+ \to \pi^+ \nu\overline{\nu}$ decay. Preliminary results from the $K^+ \to \pi^+ \nu\overline{\nu}$ analysis based on about 5% of the 2016 statistics are reporte

Searches for lepton number violation and resonances in K±→πμμK^\pm \to \pi \mu \mu decays with the NA48/2 experiment

he NA48/2 experiment at CERN collected a large sample of charged kaon decays into final states with multiple charged particles in 2003-2004. An upper limit of 8 : 6 x 10-11 at 90 % CL is set on the branching ratio of the lepton number violating decay K ! p m m . Searches for two-body resonances like heavy neutral leptons and inflatons in the K ! p m m decays in the accessible range of masses and lifetimes are also presente

First measurement of the K+→π+νν‾K^{+} \rightarrow \pi^{+}\nu\overline{\nu} decay with the NA62 experiment at CERN

The decay $K^{+} \rightarrow \pi^{+}\nu\overline{\nu}$ with a very precisely predicted branching ratio of $8.4\times 10^{-10}$ is one of the best candidates to reveal indirect effects of new physics at the highest mass scales. The NA62 experiment at CERN SPS is designed to measure the branching ratio of the $K^{+} \rightarrow \pi^{+}\nu\overline{\nu}$ decay with a decay-in-flight technique, novel for this channel. The search for the $K^{+} \rightarrow \pi^{+}\nu\overline{\nu}$ decay is presented in this thesis, based on a sample of about $10^{11}$ $K^+$ decays collected in 2016 by the NA62 experiment. The Single Event Sensitivity is found to be $3\times 10^{-10}$ corresponding to about 0.26 $K^{+} \rightarrow \pi^{+}\nu\overline{\nu}$̄ and 0.15 background events expected. The analysis has revealed one candidate event compatible with the expectations. Interpreting the candidate as background leads to a 95$\%$ CL upper limit of $1.4\times10^{-9}$ on the $K^{+} \rightarrow \pi^{+}\nu\overline{\nu}$ branching ratio. Prospects for future developments are also reviewed

First measurement of the K+rightarrowpi+nuoverlinenuK^{+} rightarrow pi^{+}nuoverline{nu} decay with the NA62 experiment at CERN

The decay $K^{+} rightarrow pi^{+}nuoverline{nu}$ with a very precisely predicted branching ratio of $8.4times 10^{-10}$ is one of the best candidates to reveal indirect effects of new physics at the highest mass scales. The NA62 experiment at CERN SPS is designed to measure the branching ratio of the $K^{+} rightarrow pi^{+}nuoverline{nu}$ decay with a decay-in-flight technique, novel for this channel. The search for the $K^{+} rightarrow pi^{+}nuoverline{nu}$ decay is presented in this thesis, based on a sample of about $10^{11}$ $K^+$ decays collected in 2016 by the NA62 experiment. The Single Event Sensitivity is found to be $3times 10^{-10}$ corresponding to about 0.26 $K^{+} rightarrow pi^{+}nuoverline{nu}$̄ and 0.15 background events expected. The analysis has revealed one candidate event compatible with the expectations. Interpreting the candidate as background leads to a 95$$ CL upper limit of $1.4times10^{-9}$ on the $K^{+} rightarrow pi^{+}nuoverline{nu}$ branching ratio. Prospects for future developments are also reviewed.Der Zerfall $K^{+} rightarrow pi^{+}nuoverline{nu}$ mit einem sehr genau vorhergesagten Verzweigungsverh"{a}ltnis von $8.4times 10^{-10}$ ist einer der besten Kandidaten, um indirekte Effekte neuer Physik auf h"{o}chsten Massenskalen zu finden. Das NA62-Experiment am CERN SPS wurde entwickelt, um das Verzweigungsverh"{a}ltnis des $K^{+} rightarrow pi^{+}nuoverline{nu}$-Zerfalls mit einer f"{u}r diesen Kanal neuartigen textit{Decay-in-flight}-Technik zu messen. Die Suche nach dem $K^{+} rightarrow pi^{+}nuoverline{nu}$-Zerfall wird in dieser Arbeit mit einem Datensatz von etwa $10^{11}$ $K^+$-Zerf"{a}llen im Jahr 2016 mit dem NA62-Experiment aufgezeichnet wurden, durchgef"{u}hrt. Die Single-Event-Sensitivit"{a}t ist $3times 10^{-10}$ und entspricht etwa 0.26 $K^{+} rightarrow pi^{+}nuoverline{nu}$- und 0.15 Hintergrundereignissen. Die Analyse findet einen Kandidaten und ist mit dem Erwartungen vereinbar. Wenn man den gefundenen Kandidaten als Untergrund interpretiert, f"{u}hrt dies zu einer Obergrenze vom $1.4times 10^{-9}$ bei 95$$ CL auf das $K^{+} rightarrow pi^{+}nuoverline{nu}$-Verzweigungsverh"{a}ltnis. Aussichten f"{u}r zuk"{u}nftige Entwicklungen werden ebenfalls dargestellt