A New Measurement of the Rare Decay $K^+\to \pi^+ \mu^+ \mu^-$
/ Authors
Hong Ma, R. Appel, G. Atoyan, B. Bassalleck, D. Bergman, N. Cheung, S. Dhawan, H. Do, J. Egger, S. Eilerts
and 18 more authors
H. Fischer, W. Herold, V. Issakov, H. Kaspar, D. Kraus, D. Lazarus, P. Lichard, J. Lowe, J. Lozano, W. Majid, W. Menzel, S. Pislak, A. Poblaguev, P. Řehák, A. Sher, J. Thompson, Peter Truoel, M. Zeller
/ Abstract
More than 400 $K^{+}\to\pi^{+}\mu^+\mu^-$ events were observed in a rare $K^+$ decay experiment at the AGS. Normalized to the $K^{+}\to\pi^{+}\pi^+\pi^-$ 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 $\mu\mu$ mass spectrum is in very good agreement with the measurement of the $K^{+}\to\pi^{+}e^+e^-$ decay, but deviates significantly from the previous measurement.
Journal: Physical Review Letters