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A New Measurement of the Rare Decay K+ π+ μ+ μ-

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

hep-exarXiv:hep-ex/9910047

Abstract

More than 400 K+π+μ+μ- events were observed in a rare K+ decay experiment at the AGS. Normalized to the K+π+π+π- decay, the branching ratio is determined to be (9.22 0.60 (stat) 0.49 (syst))× 10-8. This branching ratio and the μμ mass spectrum is in very good agreement with the measurement of the K+π+e+e- decay, but deviates significantly from the previous measurement.

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