Phys. Rev. Lett. 87, 071801 (2001) [4 pages]Measurement of the Branching Ratio and Form Factor of KL→μ+μ-γReceived 30 January 2001; published 26 July 2001 We report on the analysis of the rare decay KL→μ+μ-γ the 1997 data from the KTeV experiment at Fermilab. A total of 9327 candidate events are observed with 2.4% background, representing a factor of 40 increase in statistics over the current world sample. We find that B(KL→μ+μ-γ) = (3.62±0.04stat±0.08syst)×10-7. The form factor parameter αK* is measured to be αK* = -0.160-0.028+0.026. In addition, we make the first measurement of the parameter α from the D’Ambrosio-Isidori-Portolés form factor, finding α = -1.54±0.10. In that model, this α measurement limits the Cabibbo-Kobayashi-Maskawa parameter ρ>-0.2. © 2001 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.87.071801
DOI:
10.1103/PhysRevLett.87.071801
PACS:
13.20.Eb, 12.15.Hh, 14.40.Aq
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