Measurement Of The Branching Ratio Of Pi(0) -> E(+)E(-) Using K-L -> 3 Pi(0) Decays In Flight

A. Alavi-Harati,I. F. Albuquerque,T. Alexopoulos,M. Arenton,K. Arisaka,S. Averitte,A. R. Barker, L. Bellantoni,A. Bellavance,J. Belz,R. Ben-David,D. R. Bergman,E. Blucher,G. J. Bock,C. Bown,S. Bright,E. Cheu,S. Childress,R. Coleman,M. D. Corcoran,G. Corti,B. Cox,M. B. Crisler,A. R. Erwin,R. Ford,A. Golossanov,G. Graham,J. Graham,K. Hagan, E. Halkiadakis,K. Hanagaki,S. Hidaka,Y. B. Hsiung,V. Jejer,J. Jennings,D. A. Jensen, R. Kessler, H. G. E. Kobrak,J. LaDue, A. Lath, A. Ledovskoy,P. L. McBride,A. P. McManus,P. Mikelsons,E. Monnier,T. Nakaya, U. Nauenberg,K. S. Nelson,H. Nguyen,V. O'Dell,M. Pang,R. Pordes,V. Prasad,C. Qiao,B. Quinn,E. J. Ramberg,R. E. Ray,A. Roodman,M. Sadamoto, S. Schnetzer,K. Senyo,P. Shanahan,P. S. Shawhan,W. Slater,N. Solomey,S. V. Somalwar,R. L. Stone,I. Suzuki,E. C. Swallow,R. A. Swanson,S. A. Taegar,R. J. Tesarek,G. B. Thomson,P. A. Toale,A. Tripathi,R. Tschirhart,Y. W. Wah,J. Wang,H. B. White,J. Whitmore,B. Winstein, R. Winston,J.-Y. Wu, T. Yamanaka,E. D. Zimmerman

PHYSICAL REVIEW LETTERS（1999）

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摘要

The branching ratio of the rare decay pi(0) --> e(+)e(-) has been measured in E799-II, a rare kaon decay experiment using the KTeV detector at Fermilab. We observed 275 candidate pi(0) --> e(+)e(-) events, with an expected background of 21.4 +/- 6.2 events which includes the contribution from Dalitz decays. We measured B[pi(0) --> e(+)e(-), (m(e+e-)/m(pi 0))(2) > 0.95] = (6.09 +/- 0.40 +/- 0.24) X 10(-8), where the first error is statistical and the second systematic. This result is the first significant observation of the excess rate for this decay above the unitarity lower bound.

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lower bound

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