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Search for the dark photon in $\pi^0$ decays

The collaboration
Phys.Lett.B 746 (2015) 178-185, 2015.

Abstract (data abstract)
CERN-NA-048. A sample of $1.69\times 10^7$ fully reconstructed $\pi^0\to\gamma e^+e^-$ decay candidates collected by the NA48/2 experiment at CERN in 2003--2004 is analysed to search for the dark photon ($A'$) production in the $\pi^0\to\gamma A'$ decay followed by the prompt $A'\to e^+e^-$ decay. No signal is observed, and an exclusion region in the plane of the dark photon mass $m_{A'}$ and mixing parameter $\varepsilon^2$ is established. The obtained upper limits on $\varepsilon^2$ are more stringent than the previous limits in the mass range $9~{\rm MeV}/c^2<m_{A'}<70~{\rm MeV}/c^2$. The NA48/2 sensitivity to the dark photon production in the $K^\pm\to\pi^\pm A'$ decay is also evaluated.

• #### Table 1

Data from Figure 4

10.17182/hepdata.67658.v1/t1

The obtained 90% CL upper limits (ULs) on the mixing parameter $\epsilon^2$ for each dark photon (DP) mass hypothesis tested.