The anomaly in the low-energy distribution of quasielastic neutrino events reported by the MiniBooNE Collaboration is discussed. We show that the observed excess of electronlike events could ...originate from the production and decay of a heavy neutrino (nu(h)) in the MiniBooNE detector. The nu(h) with the mass around 500 MeV is created by mixing in nu(mu) neutral-current interactions and decays radiatively into nu gamma with the lifetime tau(nu(h)) approximately < 10(-9) s due to a transition magnetic moment between the nu(h) and a light neutrino nu. Existing experimental data are found to be consistent with a mixing strength between the nu(h) and the nu_{mu} of |U(mu h)|2 approximately = (1-4)x10(-3) and a nu(h) transition magnetic moment of mu(tr) approximately (1-6)x10(-9) mu(B). Finally, we discuss the reason why no significant excess of low-energy events has been observed in the recent antineutrino data.
In this paper we estimate the sensitivity of the NA64 experiment to millicharged particles (χ). That experimental facility is dedicated to the searching for dark sector particles in missing energy ...events at the CERN SPS. We consider missing momentum signatures in the ≃100 GeV electron and muon beams and show that the later one allows to obtain more stringent bounds on the millicharge Qχ, which for the χ masses 100 MeV≤mχ≤500 MeV at the level Qχ/e≲O(10−3)−O(10−2).
The dark photon (A′) production through the mixing with the bremsstrahlung photon from the electron scattering off nuclei can be accompanied by the dominant invisible A′ decay into dark-sector ...particles. In this work we discuss the missing energy signature of this process in the experiment NA64 aiming at the search for A′→invisible decays with a high-energy electron beam at the CERN SPS (The Super Proton Synchrotron). We show the distinctive distributions of variables that can be used to distinguish the A′→invisible signal from background. The results of the detailed simulation of the detector response for the events with and without A′ emission are presented. The efficiency of the signal event selection is estimated. It is used to evaluate the sensitivity of the experiment and show that it allows us to probe the still unexplored area of the mixing strength 10−6≲ε≲10−2 and masses up to MA′≲1 GeV. The results obtained are compared with the results from other calculations. In the case of the signal observation, a possibility of extraction of the parameters MA′ and ε by using the shape of the missing energy spectrum is discussed.
The Physics Beyond Colliders initiative is an exploratory study aimed at exploiting the full scientific potential of the CERN's accelerator complex and scientific infrastructures through projects ...complementary to the LHC and other possible future colliders. These projects will target fundamental physics questions in modern particle physics. This document presents the status of the proposals presented in the framework of the Beyond Standard Model physics working group, and explore their physics reach and the impact that CERN could have in the next 10-20 years on the international landscape.
It has been recently shown that excess events observed by the LSND and MiniBooNE neutrino experiments could be interpreted as a signal from the radiative decay of a heavy sterile neutrino νh produced ...in νμ neutral-current-like neutrino interactions. If the νh exist, it would be also produced by the νμ beam from the CERN SPS in the neutrino beam line shielding. The νhʼs would penetrate the shielding and be observed through the νh→γν decay followed by the photon conversion into e+e− pair in the active target of the NOMAD detector. The νhʼs could be also produced in the iron of the magnetic spectrometer of the CHORUS detector, located just in front of NOMAD. Considering these two sources of νhʼs we set new constraints on νh properties and exclude part of the LSND/MiniBooNE νh parameter space using bounds on single photons production in neutrino reactions recently reported by the NOMAD Collaboration. We find that broad bands in the parameter space are still open for more sensitive searches for the νh in future neutrino experiments.
We report the first results on a direct search for a new 16.7 MeV boson (X) which could explain the anomalous excess of e^{+}e^{-} pairs observed in the excited ^{8}Be^{*} nucleus decays. Because of ...its coupling to electrons, the X could be produced in the bremsstrahlung reaction e^{-}Z→e^{-}ZX by a 100 GeV e^{-} beam incident on an active target in the NA64 experiment at the CERN Super Proton Synchrotron and observed through the subsequent decay into a e^{+}e^{-} pair. With 5.4×10^{10} electrons on target, no evidence for such decays was found, allowing us to set first limits on the X-e^{-} coupling in the range 1.3×10^{-4}≲ε_{e}≲4.2×10^{-4} excluding part of the allowed parameter space. We also set new bounds on the mixing strength of photons with dark photons (A^{'}) from nonobservation of the decay A^{'}→e^{+}e^{-} of the bremsstrahlung A^{'} with a mass ≲23 MeV.
Abstract
We review the most important models of light dark matter and discuss the NA64 experiment aimed at searching for hypothetical particles, including dark matter, in the mass range ⩽
O
(1) GeV ...with the use of electron and muon beams at the Super Proton Synchrotron (SPS) accelerator at CERN. We consider the methods and results of searches in the NA64 and other accelerator experiments and also discuss their further prospects.
We report on a direct search for sub-GeV dark photons (A^{'}), which might be produced in the reaction e^{-}Z→e^{-}ZA^{'} via kinetic mixing with photons by 100 GeV electrons incident on an active ...target in the NA64 experiment at the CERN SPS. The dark photons would decay invisibly into dark matter particles resulting in events with large missing energy. No evidence for such decays was found with 2.75×10^{9} electrons on target. We set new limits on the γ-A^{'} mixing strength and exclude the invisible A^{'} with a mass ≲100 MeV as an explanation of the muon g_{μ}-2 anomaly.
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