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تسجيل مستخدم جديدDark matter search in missing energy events with NA64
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A search for sub-GeV dark matter production mediated by a new vector boson $A$, called dark photon, is performed by the NA64 experiment in missing energy events from 100 GeV electron interactions in an active beam dump at the CERN SPS. From the analysis of the data collected in the years 2016, 2017, and 2018 with $2.84times10^{11}$ electrons on target no evidence of such a process has been found. The most stringent constraints on the $A$ mixing strength with photons and the parameter space for the scalar and fermionic dark matter in the mass range $lesssim 0.2$ GeV are derived, thus demonstrating the power of the active beam dump approach for the dark matter search.
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We report on a direct search for sub-GeV dark photons (A) which might be produced in the reaction e^- Z to e^- Z A via kinetic mixing with photons by 100 GeV electrons incident on an active target in the NA64 experiment at the CERN SPS. The As would
decay invisibly into dark matter particles resulting in events with large missing energy. No evidence for such decays was found with 2.75cdot 10^{9} electrons on target. We set new limits on the gamma-A mixing strength and exclude the invisible A with a mass < 100 MeV as an explanation of the muon g_mu-2 anomaly.
The current most stringent constraints for the existence of sub-GeV dark matter coupling to Standard Model via a massive vector boson $A^prime$ were set by the NA64 experiment for the mass region $m_{A^prime}lesssim 250$ MeV, by analyzing data from t
he interaction of $2.84cdot10^{11}$ 100-GeV electrons with an active thick target and searching for missing-energy events. In this work, by including $A^prime$ production via secondary positron annihilation with atomic electrons, we extend these limits in the $200$-$300$ MeV region by almost an order of magnitude, touching for the first time the dark matter relic density constrained parameter combinations. Our new results demonstrate the power of the resonant annihilation process in missing energy dark-matter searches, paving the road to future dedicated $e^+$ beam efforts.
We searched for evidence of a Higgsstrahlung process in a secluded sector, leading to a final state with a dark photon U and a dark Higgs boson h, with the KLOE detector at DAFNE. We investigated the case of h lighter than U, with U decaying into a m
uon pair and h producing a missing energy signature. We found no evidence of the process and set upper limits to its parameters in the range 2m_mu<m_U<1000 MeV, m_h<m_U.
We present the results of a search for dark matter production in the monojet signature. We analyze a sample of Tevatron pp-bar collisions at sqrt(s)=1.96 TeV corresponding to an integrated luminosity of 6.7/fb recorded by the CDF II detector. In even
ts with large missing transverse energy and one energetic jet, we find good agreement between the standard model prediction and the observed data. We set 90% confidence level upper limits on the dark matter production rate. The limits are translated into bounds on nucleon-dark matter scattering rates which are competitive with current direct detection bounds on spin-independent interaction below a dark matter candidate mass of 5 GeV/c^2, and on spin-dependent interactions up to masses of 200 GeV/c^2.
We carried out a model-independent search for light scalar (s) and pseudoscalar axionlike (a) particles that couple to two photons by using the high-energy CERN SPS H4 electron beam. The new particles, if they exist, could be produced through the Pri
makoff effect in interactions of hard bremsstrahlung photons generated by 100 GeV electrons in the NA64 active dump with virtual photons provided by the nuclei of the dump. The a(s) would penetrate the downstream HCAL module, serving as shielding, and would be observed either through their $a(s)togamma gamma$ decay in the rest of the HCAL detector or as events with large missing energy if the a(s) decays downstream of the HCAL. This method allows for the probing the a(s) parameter space, including those from generic axion models, inaccessible to previous experiments. No evidence of such processes has been found from the analysis of the data corresponding to $2.84times10^{11}$ electrons on target allowing to set new limits on the $a(s)gammagamma$-coupling strength for a(s) masses below 55 MeV.
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