The Kaon identification system at the NA62 experiment at CERN

The NA62 experiment at CERN SPS aims to measure the branching ratio of the ultra-rare kaon decay $K^+\to\pi^+\nu\bar{\nu}$ with 10\% precision, collecting $\sim 100$ events, assuming the Standard Model~(SM) branching ratio of $8.4 \times 10^{-11}$, starting in 2016. The NA62 experiment uses a kaon decay-in-flight technique and is exposed to a 750~MHz high-energy unseparated charged hadron beam, in which kaons are a minor component (6\%). Kaon identification is therefore mandatory to reduce the interference of the dominant non-kaon component with the experimental measurements. The NA62 kaon identification system and its performances are presented.Comment: 6 pages. To be published in ICHEP 2016 conference proceeding

Searches for Lepton Number Violation and resonances in the K±→πμμK^{\pm} \to \pi\mu\mu decays at the NA48/2 experiment

The NA48/2 experiment at CERN collected a large sample of charged kaon decays into final states with multiple charged particles in 2003--2004. A new upper limit on the rate of the lepton number violating decay $K^{\pm} \to \pi^{\mp} \mu^{\pm} \mu^{\pm}$ obtained from this sample is reported: $\mathcal{B}(K^{\pm} \to \pi^{\mp} \mu^{\pm} \mu^{\pm})<8.6 \times 10^{-11}$ at 90\% CL. Searches for two-body resonances in the $K^{\pm} \to \pi\mu\mu$ decays (including heavy neutral leptons~$N_4$ and inflatons~$\chi$) in the accessible range of masses and lifetimes are also presented. In the absence of a signal, upper limits are set on the products of branching ratios~$\mathcal{B}(K^{\pm} \to \mu^{\pm} N_{4})\mathcal{B}(N_{4} \to \pi^{\mp}\mu^{\pm})$ and $\mathcal{B}(K^{\pm} \to \pi^{\pm} \chi)\mathcal{B}(\chi \to \mu^{+}\mu^{-})$ as functions of the resonance mass and lifetime. These limits are in the $10^{-10}-10^{-9}$ range for resonance lifetimes below 100~ps.Comment: 8 pages. To be published in Rencontres de Moriond 2016 conference proceeding

Studio di alcuni processi di background nell'esperimento NA62

L'esperimento NA62 al CERN SPS si propone di misurare il \emph{branching ratio} del decadimento ultra-raro~$K^+ \! \rightarrow \! \pi^+ \nu \bar{\nu}$ con maggiore precisione rispetto alla misura ottenuta dagli esperimenti BNL-AGS-E787/E949, al fine di testare in maniera più stringente la validità del Modello Standard. Il branching ratio misurato da tali esperimenti è pari a~$1.73^{+1.15}_{-1.05} \times 10^{-10}$, per cui è richiesta una soppressione del background estremamente elevata. Tale background è dato prevalentemente dagli altri canali di decadimento del~$K^+$, ma esiste anche una componente legata all'interazione del fascio di particelle con l'apparato sperimentale. In particolare, le principali fonti di tale background sono il gas residuo nella \emph{vacuum tank} ed i GigaTracker --- dei sottili rivelatori di silicio per la misura della posizione del fascio --- poiché questi sono gli unici materiali sulla linea del fascio di particelle a trovarsi prima o all'interno del volume fiduciale di decadimento. In questa tesi si è studiato tale background. Per fare ciò è stato utilizzato Flyo, un programma di simulazione Monte~Carlo creato a Pisa. Lo studio del background dovuto al gas residuo ha portato ad una stima della pressione massima tollerabile nella \emph{vacuum tank}; lo studio del background dovuto ai GigaTracker, invece, è servito per stimarne il rapporto segnale-rumore, parametro determinante per capire se tale fondo possa essere problematico

Kaon identification and Search for Lepton Number Violation in K±^± decay-in-flight experiments at CERN

A search for the Lepton Number Violating decay $K$$^±$ → $π$$^∓$$μ$$^±$$μ$$^±$ has been performed using the data collected by the NA48/2 experiment in 2003 and 2004. The signal event selection, the background rejection, the evaluation of the muon identification efficiency and the statistical methods used for the data interpretation are presented. Based on 1.8 x 10$^1$$^1$ kaon decays in the fiducial volume and using several models for the signal, upper limits for the branching ratio $B$($K$$^±$ → $π$$^∓$$μ$$^±$$μ$$^±$) of the order of 10$^-$$^1$$^0$ have been obtained for 90%, 95% and 99% confidence levels, improving the previous best limit of one order of magnitude. The Cherenkov differential counter used for kaon identification in the NA62 experiment, equipped with approximately 30% of the photo-detectors, was installed and tested during a Technical Run in 2012. The counter's ability of distinguishing between kaons and pions has been validated via pressure scan procedure. The data collected have been used for evaluating the kaon efficiency and time resolution. The extrapolation to the full-sized detector has been also estimated

Search for heavy neutral lepton production in 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 |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

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

Precision tests of the Standard Model with kaon decays at CERN

Recent results and prospects for precision tests of the Standard Model in kaon decay-in-flight experiments at CERN are presented. A measurement of the ratio of leptonic decay rates of the charged kaon at the level of 0.4% precision constrains the parameter space of new physics models with extended Higgs sector, a fourth generation of quarks and leptons or sterile neutrinos. Searches for heavy neutrino mass states and the dark photon in the ∼ 100 MeV/c(2) mass range based on samples collected in 2003-2007 are in progress and prospects will be discussed. The NA62 experiment, starting in 2014, will search for a range of lepton number and lepton flavour violating decays of the charged kaon and the neutral pion at improved sensitivities down to ∼ 10(-12), which will probe new physics scenarios involving heavy Majorana neutrinos or R-parity violating SUSY

Searches for lepton number violation and resonances in the K±→πμμK^{\pm}\rightarrow \pi \mu \mu decays at the NA48/2 experiment

The NA48/2 experiment at CERN collected a large sample of charged kaon decays into final states with multiple charged particles in 2003--2004. A new upper limit on the rate of the lepton number violating decay $K^{\pm}\to\pi^{\mp}\mu^{\pm}\mu^{\pm}$ obtained from this sample is reported: $\mathcal{B}(K^{\pm}\to\pi^{\mp}\mu^{\pm}\mu^{\pm})<8.6 \times 10^{-11}$ at 90\% CL. Searches for two-body resonances in the $K^{\pm}\to\pi\mu\mu$ decays (including heavy neutral leptons~$N_4$ and inflatons~$\chi$) in the accessible range of masses and lifetimes are also presented. In the absence of a signal, upper limits are set on the products of branching ratios~$\mathcal{B}(K^{\pm}\to\mu^{\pm}N_4)\mathcal{B}(N_4\to\pi\mu)$ and $\mathcal{B}(K^{\pm}\to\pi^{\pm}\chi)\mathcal{B}(\chi\to\mu^+\mu^-)$ as functions of the resonance mass and lifetime. These limits are in the $10^{-10}-10^{-9}$ range for resonance lifetimes below 100~ps

Kaon identification and Search for Lepton Number Violation in K±K^{\pm} decay-in-flight experiments at CERN

A search for the Lepton Number Violating decay $K^{\pm} \to \pi^{\pm} \mu^{\pm} \mu^{\pm}$ has been performed using the data collected by the NA48/2 experiment in 2003 and 2004. The signal event selection, the background rejection, the evaluation of the muon identifcation efficiency and the statistical methods used for the data interpretation are presented. Based on $1.8 \times 10 ^{11}$ kaon decays in the fiducial volume and using several models for the signal, upper limits for the branching fraction B($K^{\pm} \to \pi^{\pm} \mu^{\pm} \mu^{\pm}$) of the order of $10^{-10}$ have been obtained for 90%, 95% and 99% confidence levels, improving the previous best limit by one order of magnitude. The Cherenkov differential counter used for kaon identification in the NA62 experiment, equipped with approximately 30% of the photo-detectors, was installed and tested during a Technical Run in 2012. The counter's ability of distinguishing between kaons and pions has been validated via pressure scan procedure. The data collected have been used for evaluating the kaon identification efficiency and time resolution. The extrapolation to the full-sized detector has been also estimated