39 research outputs found
Search for heavy neutral lepton production in decays
A search for heavy neutral lepton production in 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 to level are established on the elements of the extended neutrino mixing matrix () for heavy neutral lepton mass in the range . This improves on the results from previous production searches in decays, setting more stringent limits and extending the mass range.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
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 leptonic decays of the dark photon at NA62
International audienceThe NA62 experiment at CERN, configured in beam-dump mode, has searched for dark photon decays in flight to electron-positron pairs using a sample of protons on dump collected in 2021. No evidence for a dark photon signal is observed. The combined result for dark photon searches in lepton-antilepton final states is presented and a region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon mass values between 50 and 600 MeV and coupling values in the range to . An interpretation of the search result in terms of the emission and decay of an axion-like particle is also presented
Search for leptonic decays of the dark photon at NA62
International audienceThe NA62 experiment at CERN, configured in beam-dump mode, has searched for dark photon decays in flight to electron-positron pairs using a sample of protons on dump collected in 2021. No evidence for a dark photon signal is observed. The combined result for dark photon searches in lepton-antilepton final states is presented and a region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon mass values between 50 and 600 MeV and coupling values in the range to . An interpretation of the search result in terms of the emission and decay of an axion-like particle is also presented
First search for using the decay-in-flight technique
International audienceThe NA62 experiment at the CERN SPS reports the first search for K+→π+νν¯ using the decay-in-flight technique, based on a sample of 1.21×1011 K+ decays collected in 2016. The single event sensitivity is 3.15×10−10 , 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 14×10−10 on the K+→π+νν¯ branching ratio at 95% CL
Searches for lepton number violating decays
Searches for lepton number violating and decays have been performed using the complete dataset collected by the NA62 experiment at CERN in 2016-2018. Upper limits of and are obtained on the decay branching fractions at 90% confidence level. The former result improves the limit by a factor of four over the previous best limit, while the latter result represents the first limit on the decay rate.Searches for lepton number violating K+→π−e+e+ and K+→π−π0e+e+ decays have been performed using the complete dataset collected by the NA62 experiment at CERN in 2016–2018. Upper limits of 5.3×10−11 and 8.5×10−10 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+→π−π0e+e+ decay rate.Searches for lepton number violating and decays have been performed using the complete dataset collected by the NA62 experiment at CERN in 2016-2018. Upper limits of and 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 decay rate
A search for the decay
A search for the 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 is obtained for the decay branching fraction at 90% CL, improving by a factor of 250 over the previous search
Measurement of the very rare decay
The NA62 experiment reports the branching ratio measurement BR 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 decay, observed with a significance of 3.4. The experiment achieves a single event sensitivity of , corresponding to 10.0 events assuming the Standard Model branching ratio of . This measurement is also used to set limits on BR(), where is a scalar or pseudo-scalar particle. Details are given of the analysis of the 2018 data sample, which corresponds to about 80% of the total data sample
Search for decays to invisible particles
The NA62 experiment at the CERN SPS reports a study of a sample of tagged mesons from , searching for the decay of the to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model-independent upper limit on the branching ratio for the decay where is a particle escaping detection with mass in the range GeV/ and rest lifetime greater than 100 ps. Model- dependent upper limits are obtained assuming to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs.The NA62 experiment at the CERN SPS reports a study of a sample of tagged mesons from , searching for the decay of the to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model-independent upper limit on the branching ratio for the decay , where is a particle escaping detection with mass in the range 0.110-0.155 GeV and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson
Search for decays to a muon and invisible particles
The NA62 experiment at CERN reports searches for and decays, where and are massive invisible particles, using the 2016-2018 data set. The particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of of the neutrino mixing parameter for masses in the range 200-384 MeV/ and lifetime exceeding 50 ns. The 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 masses in the range 10-370 MeV/ are reported for the first time, ranging from to . An improved upper limit of is established at 90% CL on the branching fraction.The NA62 experiment at CERN reports searches for K+→μ+N and K+→μ+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 O(10−8) of the neutrino mixing parameter |Uμ4|2 for N masses in the range 200–384 MeV/ c2 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/ c2 are reported for the first time, ranging from O(10−5) to O(10−7) . An improved upper limit of 1.0×10−6 is established at 90% CL on the K+→μ+ννν¯ branching fraction.The NA62 experiment at CERN reports searches for and decays, where and are massive invisible particles, using the 2016-2018 data set. The particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of of the neutrino mixing parameter for masses in the range 200-384 MeV/ and lifetime exceeding 50 ns. The 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 masses in the range 10-370 MeV/ are reported for the first time, ranging from to . An improved upper limit of is established at 90% CL on the branching fraction