Phys. Rev. Lett. 83, 922 - 925 (1999)
Measurement of the Branching Ratio of π0 → e+e- Using KL → 3π0 Decays in Flight
A. Alavi-Harati et al.
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A. Alavi-Harati12, I. F. Albuquerque10, T. Alexopoulos12, M. Arenton11, K. Arisaka2, S. Averitte10, A. R. Barker5, L. Bellantoni7, A. Bellavance9, J. Belz10, R. Ben-David7, D. R. Bergman10, E. Blucher4, G. J. Bock7, C. Bown4, S. Bright4, E. Cheu1, S. Childress7, R. Coleman7, M. D. Corcoran9, G. Corti11, B. Cox11, M. B. Crisler7, A. R. Erwin12, R. Ford7, A. Golossanov11, G. Graham4, J. Graham4, K. Hagan11, E. Halkiadakis10, K. Hanagaki8, S. Hidaka8, Y. B. Hsiung7, V. Jejer11, J. Jennings2, D. A. Jensen7, R. Kessler4, H. G. E. Kobrak3, J. LaDue5, A. Lath10, A. Ledovskoy11, P. L. McBride7, A. P. McManus11, P. Mikelsons5, E. Monnier4, T. Nakaya7, U. Nauenberg5, K. S. Nelson11, H. Nguyen7, V. O'Dell7, M. Pang7, R. Pordes7, V. Prasad4, C. Qiao4, B. Quinn4, E. J. Ramberg7, R. E. Ray7, A. Roodman4, M. Sadamoto8, S. Schnetzer10, K. Senyo8, P. Shanahan7, P. S. Shawhan4, W. Slater2, N. Solomey4, S. V. Somalwar10, R. L. Stone10, I. Suzuki8, E. C. Swallow4,6, R. A. Swanson3, S. A. Taegar1, R. J. Tesarek10, G. B. Thomson10, P. A. Toale5, A. Tripathi2, R. Tschirhart7, Y. W. Wah4, J. Wang1, H. B. White7, J. Whitmore7, B. Winstein4, R. Winston4, J.-Y. Wu5, T. Yamanaka8, and E. D. Zimmerman4 *,†
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 Japan
9Rice University, Houston, Texas 77005
10Rutgers University, Piscataway, New Jersey 08855
11The Department of Physics and Institute of Nuclear and Particle Physics, University of Virginia, Charlottesville, Virginia 22901
12University of Wisconsin, Madison, Wisconsin 53706
Received 10 March 1999
The branching ratio of the rare decay π0→e+e- has been measured in E799-II, a rare kaon decay experiment using the KTeV detector at Fermilab. We observed 275 candidate π0→e+e- events, with an expected background of 21.4±6.2 events which includes the contribution from Dalitz decays. We measured B[π0→e+e-,(me+e-/mπ0)2>0.95] = (6.09±0.40±0.24)×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.
©1999 The American Physical Society
URL: http://link.aps.org/abstract/PRL/v83/p922
DOI: 10.1103/PhysRevLett.83.922
PACS: 13.20.Cz, 13.40.Gp, 13.40.Hq
* To whom correspondence should be addressed.Electronic address: edz@fnal.gov
† Current address: Columbia University, New York, NY 10027.
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