Search for the dark photon in π0\pi^0 decays


A sample of 1.69×1071.69\times 10^7 fully reconstructed π0γe+e\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 (AA') production in the π0γA\pi^0\to\gamma A' decay followed by the prompt Ae+eA'\to e^+e^- decay. No signal is observed, and an exclusion region in the plane of the dark photon mass mAm_{A'} and mixing parameter ε2\varepsilon^2 is established. The obtained upper limits on ε2\varepsilon^2 are more stringent than the previous limits in the mass range 9 MeV/c2<mA<70 MeV/c29~{\rm MeV}/c^2<m_{A'}<70~{\rm MeV}/c^2. The prospects of the dark photon search in the K±π±AK^\pm\to\pi^\pm A' decay are also discussed.Comment: Contribution to the proceedings of the PLANCK 2015 conference, Ioannina, Greece, 25-29 May 201

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