First evidence for the decay KL→e+eμ+μ

P. Gu, P. Haas, W. P. Hogan, S. K. Kim, J. N. Matthews, S. S. Myung, S. Schnetzer, G. B. Thomson, Y. Zou, K. Arisaka, D. Roberts, W. Slater, M. B. Spencer, M. Weaver, R. A. Briere, E. Cheu, D. A. Harris, P. Krolak, K. S. McFarland, A. RoodmanB. Schwingenheuer, S. V. Somalwar, Y. W. Wah, B. Winstein, R. Winston, A. R. Barker, E. C. Swallow, G. J. Bock, R. Coleman, M. Crisler, J. Enagonio, R. Ford, Y. B. Hsiung, D. A. Jensen, V. R. O’Dell, E. Ramberg, R. Tschirhart, E. M. Collins, G. D. Gollin, T. Nakaya, T. Yamanaka

Research output: Contribution to journalArticle


We present the first evidence for the decay KL→e+eμ+μ based on the observation of one event with an estimated background of 0.067-0.025+0.057 event. We determine the branching ratio to be B(KL→e+eμ+μ)=(2.9-2.4+6.7)×10-9. In addition, we set a 90% confidence upper limit on the combined branching ratio for the lepton flavor violating decays KL→e∓e∓μ±μ± to be B(KL→e∓e∓μ±μ±<)<6.1×10-9 assuming a uniform phase space distribution.

Original languageEnglish (US)
Pages (from-to)4312-4315
Number of pages4
JournalPhysical review letters
Issue number23
StatePublished - 1996

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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    Gu, P., Haas, P., Hogan, W. P., Kim, S. K., Matthews, J. N., Myung, S. S., Schnetzer, S., Thomson, G. B., Zou, Y., Arisaka, K., Roberts, D., Slater, W., Spencer, M. B., Weaver, M., Briere, R. A., Cheu, E., Harris, D. A., Krolak, P., McFarland, K. S., ... Yamanaka, T. (1996). First evidence for the decay KL→e+eμ+μ. Physical review letters, 76(23), 4312-4315.