NA48/2 studies of rare decays

Abstract

The first observation of about 2000 candidates, with a background contamination below 3%, of the rare decay $K^{\pm }\to {\pi }^{\pm }{\pi }^0{e}^{+}{e}^{-}$ is reported by the NA48/2 experiment. The preliminary branching ratio in the full kinematic region is obtained to be: $\mathcal{B}(K^{\pm }\to {\pi }^{\pm }{\pi }^0{e}^{+}{e}^{-})=(4.06\pm 0.17)\cdot 10^{-6}$ by analyzing the data collected in 2003. A sample of $4.687\times 10^6$ $K^{\pm }\to {\pi }^{\pm }{\pi }_D^0$, decay candidates with a negligible background contamination collected in 2003-04 is analyzed to search for the dark photon ($A^{\prime }$) via the decay chain $K^{\pm }\to {\pi }^{\pm }{\pi }^0$, ${\pi }^0\to \gamma A^{\prime }$, $A^{\prime }\to e^{+}{e}^{-}$. No signal is observed, and preliminary limits in the plane dark photon mixing parameter ${\epsilon }^2$ versus its mass $m_{A^{\prime }}$ are reported.

To be published in La Thuile 2015 proceedings. arXiv admin note: text overlap with arXiv:1412.8053

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