A New Measurement of the Rare Decay $K^+\to π^+ μ^+ μ^-$

Ma, H.; Appel, R.; Atoyan, G. S.; Bassalleck, B.; Bergman, D.; Cheung, N.; Dhawan, S.; Do, H.; Egger, J.; Eilerts, S.; Fischer, H.; Herold, W.; Issakov, V. V.; Kaspar, H.; Kraus, D. E.; Lazarus, D. M.; Lichard, P.; Lowe, J.; Lozano, J.; Majid, W.; Menzel, W.; Pislak, S.; Poblaguev, A. A.; Rehak, P.; Sher, A.; Thompson, J. A.; Truoel, P.; Zeller, M. E.

A New Measurement of the Rare Decay $K^+\to π^+ μ^+ μ^-$

Authors

Description

More than 400 $K^{+}\toπ^{+}μ^+μ^-$ events were observed in a rare $K^+$ decay experiment at the AGS. Normalized to the $K^{+}\toπ^{+}π^+π^-$ decay, the branching ratio is determined to be $(9.22 \pm 0.60 (stat) \pm 0.49 (syst))\times 10^{-8}$. This branching ratio and the $μμ$ mass spectrum is in very good agreement with the measurement of the $K^{+}\toπ^{+}e^+e^-$ decay, but deviates significantly from the previous measurement.
4 pages, 6 figures in 7 eps files. Paper to be submitted to Phys Rev Lett