37 research outputs found
Measurement of the very rare 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
First observation and study of the decay
International audienceThe NA48/2 experiment at CERN reports the first observation of the K → ππμν decay based on a sample of 2437 candidates with 15% background contamination collected in 2003–2004. The decay branching ratio in the kinematic region of the squared dilepton mass above 0.03 GeV/c is measured to be (0.65 ± 0.03) × 10. The extrapolation to the full kinematic space, using a specific model, is found to be (3.45 ± 0.16) × 10, in agreement with chiral perturbation theory predictions
First observation and study of the decay
The NA48/2 experiment at CERN reports the first observation of the decay based on a sample of 2437 candidates with 15% background contamination collected in 2003-2004. The decay branching ratio in the kinematic region of the squared dilepton mass above ~GeV is measured to be . The extrapolation to the full kinematic space, using a specific model, is found to be , in agreement with chiral perturbation theory predictions
Search for heavy neutrinos in decays
International audienceThe NA62 experiment recorded a large sample of K+→μ+νμ decays in 2007. A peak search has been performed in the reconstructed missing mass spectrum. In the absence of a signal, limits in the range 2×10−6 to 10−5 have been set on the squared mixing matrix element |Uμ4|2 between muon and heavy neutrino states, for heavy neutrino masses in the range 300–375 MeV/ c2 . The result extends the range of masses for which upper limits have been set on the value of |Uμ4|2 in previous production search experiments
Search for dark photon decays to at NA62
International audienceThe NA62 experiment at CERN, designed to study the ultra-rare decay , 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 pairs is reported, based on a sample of 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
Search for lepton number and flavour violation in and decays
Searches for the lepton number violating decay and the lepton flavour violating and decays are reported using data collected by the NA62 experiment at CERN in 20172018. No evidence for these decays is found and upper limits of the branching ratios are obtained at 90% confidence level: B() K^{+} \rightarrow \pi^{-} \mu^{+} e^{+}K^{+} \rightarrow \pi^{+} \mu^{-} e^{+}\pi^{0} \rightarrow \mu^{-} e^{+}20172018\mathcal{B}(K^{+}\rightarrow\pi^{-}\mu^{+}e^{+})<4.2\times 10^{-11}\mathcal{B}(K^{+}\rightarrow\pi^{+}\mu^{-}e^{+})<6.6\times10^{-11}\mathcal{B}(\pi^{0}\rightarrow\mu^{-}e^{+})<3.2\times 10^{-10}$. These results improve by one order of magnitude over previous results for these decay modes
Measurement of the form factors of charged kaon semileptonic decays
International audienceA measurement of the form factors of charged kaon semileptonic decays is presented, based on 4.4 × 10K → πeν (K ) and 2.3 × 10K → πμ±ν (K ) decays collected in 2004 by the NA48/2 experiment. The results are obtained with improved precision as compared to earlier measurements. The combination of measurements in the K and K modes is also presented
Performance of the NA62 trigger system
International audienceThe NA62 experiment at CERN targets the measurement of the ultra-rare decay, and carries out a broad physics programme that includes probes for symmetry violations and searches for exotic particles. Data were collected in 2016–2018 using a multi-level trigger system, which is described highlighting performance studies based on 2018 data
A measurement of the decay
International audienceA sample of 2.8 × 10K → πμμ candidates with negligible background was collected by the NA62 experiment at the CERN SPS in 2017–2018. The model-independent branching fraction is measured to be (9.15 ± 0.08) × 10, a factor three more precise than previous measurements. The decay form factor is presented as a function of the squared dimuon mass. A measurement of the form factor parameters and their uncertainties is performed using a description based on Chiral Perturbation Theory at (p)