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Observation of large CPCP violation and evidence for direct CPCP violation in B0→π+π−B^0 \to \pi^+\pi^- decays

Collaboration
Jan, 2004
11 pages
Published in:
  • Phys.Rev.Lett. 93 (2004) 021601
e-Print:
DOI:
Report number:
  • KEK-PREPRINT-2003-110,
  • BELLE-PREPRINT-2004-1
Experiments:
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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.
  • 11.30.Er
  • 13.25.Hw
  • 12.15.Hh
  • electron positron: colliding beams
  • electron positron: annihilation
  • Upsilon(10570): electroproduction
  • B: pair production
  • B0: hadronic decay
  • pi+: pair production
  • CP: violation