Search for a new X(16.7) boson and dark photons in the NA64 experiment at CERN
- Banerjee, D. et al
- arXiv:1803.07748CERN-EP-2018-043
 | Schematic illustration of the NA64 setup to search for the $A',X\to \ee$ decays. |
 | Distribution of selected e-m neutral (presumably photon) and signal events in the $(E_{WCAL};E_{ECAL})$ plane from the combined 30 $X_0$ and 40 $X_0$ runs. Neutral e-m events are shown as blue squares. The only signal-like event is shown as a red square. The dashed band represents the signal box. |
 | The 90\% C.L.\ exclusion areas in the ($m_{X}; \epsilon$) plane from the NA64 experiment (blue area). For the mass of 16.7~MeV, the $X-e^-$ coupling region excluded by NA64 is $1.3\times 10^{-4}< \epsilon_e < 4.2~\times~10^{-4}$. The full allowed range of $\epsilon_e$ explaining the $^8$Be* anomaly, $2.0\times 10^{-4} \lesssim \epsilon_e \lesssim 1.4 \times 10^{-3}$ \cite{feng1, feng2}, is also shown (red area). The constraints on the mixing $\epsilon$ from the experiments E774~\cite{bross}, E141~\cite{rio}, BaBar ~\cite{babar1}, KLOE~\cite{kloe2}, HADES~\cite{hades}, PHENIX~\cite{phenix}, NA48~\cite{na48}, and bounds from the electron anomalous magnetic moment $(g-2)_e$ \cite{hd} are also shown. |
 | The 90\% C.L.\ exclusion areas in the ($m_{X}; \epsilon$) plane from the NA64 experiment (blue area). For the mass of 16.7~MeV, the $X-e^-$ coupling region excluded by NA64 is $1.3\times 10^{-4}< \epsilon_e < 4.2~\times~10^{-4}$. The allowed range of $\epsilon_e$ explaining the $^8$Be* anomaly (red area) \cite{feng1, feng2}, constraints on the mixing $\epsilon$ from the experiments E141~\cite{rio}, E774~\cite{bross}, BaBar ~\cite{babar1}, KLOE~\cite{kloe2}, HADES~\cite{hades}, PHENIX~\cite{phenix}, NA48~\cite{na48}, and bounds from the electron anomalous magnetic moment $(g-2)_e$ \cite{hd} are also shown. |