Probing the explanation of the muon (g-2) anomaly and thermal light dark matter with the semi-visible dark photon channel

Abstract

We report the results of a search for a new vector boson ($A^{\prime }$) decaying into two dark matter particles ${\chi }_1{\chi }_2$ of different mass. The heavier ${\chi }_2$ particle subsequently decays to ${\chi }_1$ and $A^{\prime }\to e^{-}{e}^{+}$. For a sufficiently large mass splitting, this model can explain in terms of new physics the recently confirmed discrepancy observed in the muon anomalous magnetic moment at Fermilab. Remarkably, it also predicts the observed yield of thermal dark matter relic abundance. A detailed Monte-Carlo simulation was used to determine the signal yield and detection efficiency for this channel in the NA64 setup. The results were obtained re-analyzing the previous NA64 searches for an invisible decay $A^{\prime }\to \chi \overline{\chi }$ and axion-like or pseudo-scalar particles $a\to \gamma \gamma$. With this method, we exclude a significant portion of the parameter space justifying the muon g-2 anomaly and being compatible with the observed dark matter relic density for $A^{\prime }$ masses from 2$m_e$ up to 390 MeV and mixing parameter $\epsilon$ between $3\times 10^{-5}$ and $2\times 10^{-2}$.

References in corpus (13)

• Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm
• The anomalous magnetic moment of the muon in the Standard Model
• Leading hadronic contribution to the muon magnetic moment from lattice QCD
• Secluded U(1) below the weak scale
• New Fixed-Target Experiments to Search for Dark Gauge Forces
• Constraints on sub-GeV hidden sector gauge bosons from a search for heavy neutrino decays
• Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays
• Search for Axionlike and Scalar Particles with the NA64 Experiment
• Improved limits on a hypothetical X(16.7) boson and a dark photon decaying into $e^{+}{e}^{-}$ pairs
• Revisiting the Dark Photon Explanation of the Muon Anomalous Magnetic Moment
• Combined search for light dark matter with electron and muon beams at NA64
• Photoproduction of axion-like particles in the NA64 experiment
• Implication of the hidden sub-GeV bosons for the $(g-2{)}_{\mu }$, ${}^8$Be-${}^4$He anomaly, proton charge radius, EDM of fermions and dark axion portal