Branching Ratio Measurement of the Decay KL ! e1e2m1m2

A. Alavi-Harati,12 T. Alexopoulos,12 M. Arenton,11 K. Arisaka,2 S. Averitte,10 R. F. Barbosa,7,* A. R. Barker,5 M. Barrio,4 L. Bellantoni,7 A. Bellavance,9 J. Belz,10 R. Ben-David,7 D. R. Bergman,10 E. Blucher,4 G. J. Bock,7 C. Bown,4 S. Bright,4 E. Cheu,1 S. Childress,7 R. Coleman,7 M. D. Corcoran,9 G. Corti,11 B. Cox,11 M. B. Crisler,7 A. R. Erwin,12 R. Ford,7 A. Glazov,4 A. Golossanov,11 G. Graham,4 J. Graham,4 K. Hagan,11 E. Halkiadakis,10 J. Hamm,1 K. Hanagaki,8 S. Hidaka,8 Y. B. Hsiung,7 V. Jejer,11 D. A. Jensen,7 R. Kessler,4 H. G. E. Kobrak,3 J. LaDue,5 A. Lath,10, A. Ledovskoy,11 P. L. McBride,7 P. Mikelsons,5 E. Monnier,4, T. Nakaya,7 K. S. Nelson,11 H. Nguyen,7 V. O’Dell,7 M. Pang,7 R. Pordes,7 V. Prasad,4 B. Quinn,4 X. R. Qi,7 E. J. Ramberg,7 R. E. Ray,7 A. Roodman,4 M. Sadamoto,8 S. Schnetzer,10 K. Senyo,8 P. Shanahan,7 P. S. Shawhan,4 J. Shields,11 W. Slater,2 N. Solomey,4 S. V. Somalwar,10 R. L. Stone,10 E. C. Swallow,4,6 S. A. Taegar,1 R. J. Tesarek,10 G. B. Thomson,10 P. A. Toale,5 A. Tripathi,2 R. Tschirhart,7 S. E. Turner,2 Y. W. Wah,4 J. Wang,1 H. B. White,7 J. Whitmore,7 B. Winstein,4 R. Winston,4 T. Yamanaka,8 and E. D. Zimmerman4 (KTev Collaboration) 1University of Arizona, Tucson, Arizona 85721 2University of California at Los Angeles, Los Angeles, California 90095 3University of California at San Diego, La Jolla, California 92093 4The Enrico Fermi Institute, The University of Chicago, Chicago, Illinois 60637 5University of Colorado, Boulder, Colorado 80309 6Elmhurst College, Elmhurst, Illinois 60126 7Fermi National Accelerator Laboratory, Batavia, Illinois 60510 8Osaka University, Toyonaka, Osaka 560-0043, Japan 9Rice University, Houston, Texas 77005 10Rutgers University, Piscataway, New Jersey 08854 11The Department of Physics and Institute of Nuclear and Particle Physics, University of Virginia, Charlottesville, Virginia 22901 12University of Wisconsin, Madison, Wisconsin 53706 (Received 14 March 2001; published 22 August 2001) We have collected a 43 event sample of the decay KL ! eemm with negligible backgrounds and measured its branching ratio to be 2.62 6 0.40 6 0.17 3 1029. We see no evidence for CP violation in this decay. In addition, we set the 90% confidence upper limit on the combined branching ratios for the lepton flavor violating decays KL ! eemm at B KL ! eemm # 1.23 3 10210, assuming a uniform phase space distribution.