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1.
First search for $K^+ \to \pi^0 \pi \mu e$ decays / NA62 Collaboration
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..
arXiv:2409.12981; CERN-EP-2024-224.- Geneva : CERN, 2024-11-12 - 9 p. - Published in : Phys. Lett. B 859 (2024) 139122 Draft (restricted): PDF; Fulltext: CERN-EP-2024-224 - PDF; 2409.12981 - PDF; Publication - PDF;
2.
Measurement of the $K^+ \to \pi^+ \gamma \gamma$ decay / NA62 Collaboration
A sample of 3984 candidates of the $K^+ \to \pi^+ \gamma \gamma$ decay, with an estimated background of $291 \pm 14$ events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. [...]
arXiv:2311.01837; CERN-EP-2023-247.- Geneva : CERN, 2024-02-07 - 11 p. - Published in : Phys. Lett. B 850 (2024) 138513 Draft (restricted): PDF; Fulltext: CERN-EP-2023-247 - PDF; 2311.01837 - PDF; Publication - PDF;
3.
Measurement of the very rare $K^+ \to \pi^+ \nu \bar\nu$ decay / NA62 Collaboration
The decay $K^+\to\pi^+\nu\bar{\nu}$, 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 $K^+\to\pi^+\nu\bar{\nu}$ 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 $K^+\to\pi^+\nu\bar{\nu}$ 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($K^+\to\pi^+X$), where $X$ is a scalar or pseudo-scalar particle. The final result of the BR($K^+\to\pi^+\nu\bar{\nu}$) measurement and its interpretation in terms of the $K^+\to\pi^+ X$ decay from the analysis of the full 2016-2018 data set is presented, and future plans and prospects are reviewed..
2022 - 6 p. - Published in : PoS DISCRETE2020-2021 (2022) 070 Fulltext: PDF;
In : 7th Symposium on Prospects in the Physics of Discrete Symmetries (DISCRETE 2020-2021), Bergen, Norway, 29 Nov - 3 Dec 2021, pp.070
4.
New measurement of radiative decays at the NA62 Experiment at CERN: $K_{e3\gamma}$ / NA62 Collaboration
The NA62 experiment at CERN reports new results from studies of radiative kaon decays ($Ke3\gamma$) $K^+ \rightarrow \pi^0 e^+ \nu \gamma$, using a data sample %recorded collected in 2017-2018. The sample comprises O(100k) Ke3g candidates with sub-percent background contaminations. [...]
2022 - 6 p. - Published in : PoS DISCRETE2020-2021 (2022) 055 Fulltext: PDF;
In : 7th Symposium on Prospects in the Physics of Discrete Symmetries (DISCRETE 2020-2021), Bergen, Norway, 29 Nov - 3 Dec 2021, pp.055
5.
Search for $K^+$ decays to a lepton and invisible particles / NA62 Collaboration
The NA62 experiment at CERN reports searches for $K^+ \to e^+ N$, $K^+ \to \mu^+ N$ and $K^+ \to \mu^+ X$ 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 $O(10^{-9})$ and $O(10^{-8})$ on the neutrino mixing parameter $|U_{e4}|^2$ and $|U_{\mu 4}|^2$, improving on the earlier searches for heavy neutral lepton production and decays in the kinematically accessible mass range. 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 $O(10^{-5})$ to $O(10^{-7})$. An upper limit of $1.0 \cdot 10^{-6}$ is established at 90\% CL on the $K^+\to \mu^+ \nu \nu \bar{\nu}$ branching fraction..
2022 - 6 p. - Published in : PoS DISCRETE2020-2021 (2022) 056 Fulltext: PDF;
In : 7th Symposium on Prospects in the Physics of Discrete Symmetries (DISCRETE 2020-2021), Bergen, Norway, 29 Nov - 3 Dec 2021, pp.056
6.
Search for $K^+$ decays into the $\pi^+e^+e^-e^+e^-$ final state / NA62 Collaboration
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 $(7.2 \pm0 .7)\times 10^{-11}$. [...]
arXiv:2307.04579; CERN-EP-2023-133.- Geneva : CERN, 2023-09-22 - 9 p. - Published in : Phys. Lett. B 846 (2023) 138193 Draft (restricted): PDF; Fulltext: CERN-EP-2023-133 - PDF; Publication - PDF; 2307.04579 - PDF;
7.
A study of the $K^+ \to \pi^0 e^+ \nu \gamma$ decay / NA62 Collaboration
A sample of $1.3 \times 10^5 K^+ \to \pi^0 e^+ \nu \gamma$ candidates with less than 1% background was collected by the NA62 experiment at the CERN SPS in 2017-2018. Branching fraction measurements are obtained at percent relative precision in three restricted kinematic regions, improving on existing results by a factor larger than two. [...]
arXiv:2304.12271; CERN-EP-2023-069.- Geneva : CERN, 2023-09-07 - 16 p. - Published in : JHEP 2309 (2023) 040 Draft (restricted): PDF; Fulltext: CERN-EP-2023-069 - PDF; 2304.12271 - PDF; document - PDF;
8.
A search for the $K^+ \to \mu^- \nu e^+ e^+$ decay / NA62 Collaboration
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..
arXiv:2211.04818; CERN-EP-2022-243.- Geneva : CERN, 2023-03-10 - 12 p. - Published in : Phys. Lett. B 838 (2023) 137679 Draft (restricted): PDF; Fulltext: 2211.04818 - PDF; Publication - PDF; CERN-EP-2022-243 - PDF;
9.
Measurement of the very rare $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ decay at the NA62 experiment at CERN / NA62 Collaboration
The NA62 experiment reports the branching ratio measurement $BR(K^+\to\pi^+\nu\bar\nu)$ 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 $K^+\to\pi^+\nu\bar\nu$ decay, observed with a significance of $3.4\sigma$. [...]
Trieste : SISSA, 2022 - 5 p. - Published in : PoS NuFact2021 (2022) 176 Fulltext: PDF;
In : 22nd International Workshop on Neutrinos from Accelerators, Cagliari, Italy, 6 - 11 Sep 2021, pp.176
10.
Search for $K^+$ decays to a lepton and invisible particles / NA62 Collaboration
Searches for heavy neutral leptons $N$ in the $K^+\to e^+N$ and $K^+\to \mu^+N$ decay channels using the dataset collected by the NA62 experiment at CERN between 2016-2018 are presented. Upper limits on the corresponding mixing matrix elements are reported at the level of $\mathcal{O}(10^{-9})$ and $\mathcal{O}(10^{-8})$, respectively. [...]
Trieste : SISSA, 2022 - 6 p. - Published in : PoS NuFact2021 (2022) 157 Fulltext: PDF;
In : 22nd International Workshop on Neutrinos from Accelerators, Cagliari, Italy, 6 - 11 Sep 2021, pp.157

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1 Hahn, F Ekkehardt
68 Hahn, F.
253 Hahn, Ferdinand
1 Hahn, Fritz
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