arXiv subjects

NA62 collaboration

Publications and source records attributed to NA62 collaboration.

12 recordsLinked to original sources

arXiv2024

First search for $K^+\to\pi^0\pi\mu e$ decays

The first search for the lepton number violating decay $K^+\to\pi^0\pi^-\mu^+e^+$ and lepton flavour violating decays $K^+\to\pi^0\pi^+\mu^-e^+$, $K^+\to\pi^0\pi^+\mu^+e^-$ has been performed using a dataset collected by the NA62 experiment at CERN in 2016-2018. Upper limits of $2.9\times 10^{-10}$, $3.1\times 10^{-10}$ and $5.0\times 10^{-10}$, respectively, are obtained at 90% CL for the branching ratios of the three decays on the assumption of uniform phase-space distributions.

hep-ex↗

arXiv2023

Search for $K^+$ decays into the $\pi^+e^+e^-e^+e^-$ final state

The first search for ultra-rare $K^+$ decays into the $\pi^+e^+e^-e^+e^-$ final state is reported, using a dataset collected by the NA62 experiment at CERN in 2017-2018. An upper limit of $1.4\times 10^{-8}$ at 90% CL is obtained for the branching ratio of the $K^+\to\pi^+e^+e^-e^+e^-$ decay, predicted in the Standard Model to be $(7.2\pm0.7)\times 10^{-11}$. Upper limits at 90% CL are obtained at the level of $10^{-9}$ for the branching ratios of two prompt decay chains involving pair-production of hidden-sector mediators: $K^+\to\pi^+aa$, $a\to e^+e^-$ and $K^+\to\pi^+S$, $S\to A^\prime A^\prime$, $A^\prime\to e^+e^-$.

hep-ex↗

arXiv2022

A search for the $K^+\to\mu^-\nu e^+e^+$ decay

A search for the $K^+\to\mu^-\nu e^+e^+$ decay, forbidden within the Standard Model by either lepton number or lepton flavour conservation depending on the flavour of the emitted neutrino, has been performed using the dataset collected by the NA62 experiment at CERN in 2016--2018. An upper limit of $8.1\times 10^{-11}$ is obtained for the decay branching fraction at 90% CL, improving by a factor of 250 over the previous search.

hep-ex↗

arXiv2022

Searches for lepton number violating $K^+\toπ^-(π^0)e^+e^+$ decays

Searches for lepton number violating $K^+\toπ^-e^+e^+$ and $K^+\toπ^-π^0e^+e^+$ decays have been performed using the complete dataset collected by the NA62 experiment at CERN in 2016-2018. Upper limits of $5.3\times 10^{-11}$ and $8.5\times 10^{-10}$ are obtained on the decay branching fractions at 90% confidence level. The former result improves by a factor of four over the previous best limit, while the latter result represents the first limit on the $K^+\toπ^-π^0e^+e^+$ decay rate.

hep-ex↗

arXiv2021

Search for $K^+$ decays to a muon and invisible particles

The NA62 experiment at CERN reports searches for $K^+\toμ^+N$ and $K^+\toμ^+νX$ decays, where $N$ and $X$ are massive invisible particles, using the 2016-2018 data set. The $N$ particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of ${\cal O}(10^{-8})$ of the neutrino mixing parameter $|U_{\mu4}|^2$ for $N$ masses in the range 200-384 MeV/$c^2$ and lifetime exceeding 50 ns. The $X$ particle is considered a scalar or vector hidden sector mediator decaying to an invisible final state, and upper limits of the decay branching fraction for $X$ masses in the range 10-370 MeV/$c^2$ are reported for the first time, ranging from ${\cal O}(10^{-5})$ to ${\cal O}(10^{-7})$. An improved upper limit of $1.0\times 10^{-6}$ is established at 90% CL on the $K^+\toμ^+νν\barν$ branching fraction.

hep-ex↗

arXiv2020

Search for heavy neutral lepton production in $K^+$ decays to positrons

A search for heavy neutral lepton ($N$) production in $K^+\to e^+N$ decays using the data sample collected by the NA62 experiment at CERN in 2017--2018 is reported. Upper limits of the extended neutrino mixing matrix element $|U_{e4}|^2$ are established at the level of $10^{-9}$ over most of the accessible heavy neutral lepton mass range 144--462 MeV/$c^2$, with the assumption that the lifetime exceeds 50 ns. These limits improve significantly upon those of previous production and decay searches. The $|U_{e4}|^2$ range favoured by Big Bang Nucleosynthesis is excluded up to a mass of about 340 MeV/$c^2$.

hep-ex↗

arXiv2019

Searches for lepton number violating $K^+$ decays

The NA62 experiment at CERN reports a search for the lepton number violating decays $K^+\toπ^-e^+e^+$ and $K^+\toπ^-μ^+μ^+$ using a data sample collected in 2017. No signals are observed, and upper limits on the branching fractions of these decays of $2.2\times 10^{-10}$ and $4.2\times 10^{-11}$ are obtained, respectively, at 90% confidence level. These upper limits improve on previously reported measurements by factors of 3 and 2, respectively.

hep-ex↗

arXiv2019

Search for production of an invisible dark photon in $π^0$ decays

The results of a search for $π^0$ decays to a photon and an invisible massive dark photon at the NA62 experiment at the CERN SPS are reported. From a total of $4.12\times10^8$ tagged $π^0$ mesons, no signal is observed. Assuming a kinetic-mixing interaction, limits are set on the dark photon coupling to the ordinary photon as a function of the dark photon mass, improving on previous searches in the mass range 60--110 MeV/$c^2$. The present results are interpreted in terms of an upper limit of the branching ratio of the electro-weak decay $π^0 \to γν\overlineν$, improving the current limit by more than three orders of magnitude.

hep-ex↗

arXiv2019

First search for $K^+\rightarrowπ^+ν\barν$ using the decay-in-flight technique

The NA62 experiment at the CERN SPS reports the first search for $K^+ \rightarrow π^+ ν\barν$ using the decay-in-flight technique, based on a sample of $1.21\times10^{11}$ $K^+$ decays collected in 2016. The single event sensitivity is $3.15\times 10^{-10}$, 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 $14 \times 10^{-10}$ on the $K^+ \rightarrow π^+ ν\barν$ branching ratio at 95\% CL.

hep-ex↗

arXiv2018

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 $|U_{\ell 4}|^2$ ($\ell=e,μ$) 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.

hep-ex↗

arXiv2017

The Beam and detector of the NA62 experiment at CERN

NA62 is a fixed-target experiment at the CERN SPS dedicated to measurements of rare kaon decays. Such measurements, like the branching fraction of the $K^{+} \rightarrow π^{+} ν\barν$ decay, have the potential to bring significant insights into new physics processes when comparison is made with precise theoretical predictions. For this purpose, innovative techniques have been developed, in particular, in the domain of low-mass tracking devices. Detector construction spanned several years from 2009 to 2014. The collaboration started detector commissioning in 2014 and will collect data until the end of 2018. The beam line and detector components are described together with their early performance obtained from 2014 and 2015 data.

physics.ins-det↗

arXiv2014

Study of the $K^\pm\toπ^\pmγγ$ decay by the NA62 experiment

A study of the dynamics of the rare decay $K^\pm\toπ^\pmγγ$ has been performed on a sample of 232 decay candidates, with an estimated background of $17.4\pm1.1$ events, collected by the NA62 experiment at CERN in 2007. The results are combined with those from a measurement conducted by the NA48/2 collaboration at CERN. The combined model-independent branching ratio in the kinematic range $z=(m_{γγ}/m_K)^2>0.2$ is ${\cal B}_{\rm MI}(z>0.2) = (0.965 \pm 0.063) \times 10^{-6}$, and the combined branching ratio in the full kinematic range assuming a Chiral Perturbation Theory description is ${\cal B}(K_{πγγ}) = (1.003 \pm 0.056) \times 10^{-6}$. A detailed comparison of the results with the previous measurements is performed.

hep-ex↗