Observation of Large CP Violation and Evidence for Direct CP Violation in B0-->pi+pi- Decays

Preprint

21 April 2004

preprint
Published by arXiv in arXiv

Abstract

We report the first observation of CP-violating asymmetries in B0 --> pi+pi- decays based on a 140 fb-1 data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We reconstruct one neutral B meson as a B0 --> pi+pi- CP eigenstate and identify the flavor of the accompanying B meson from its decay products. We apply an unbinned maximum likelihood fit to the distribution of the time intervals between the two B meson decay points. The fit yields the CP-violating asymmetry amplitudes Apipi = +0.58+/-0.15(stat)+/-0.07(syst) and Spipi = -1.00+/-0.21(stat)+/-0.07(syst). We rule out the CP-conserving case, Apipi=Spipi=0, at a level of 5.2 standard deviations. We also find evidence for direct CP violation with a significance at or greater than 3.2 standard deviations for any Spipi value.

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All Related Versions

Version 1, 2004-01-18, ArXiv
Version 2, 2004-04-21, ArXiv
Version 3, 2004-05-26, ArXiv
Published version: Physical Review Letters, 93 (2), 021601.

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