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Difference in direct charge-parity violation between charged and neutral B meson decays


Equal amounts of matter and antimatter are predicted to have been produced in the Big Bang, but our observable Universe is clearly matter-dominated. One of the prerequisites1 for understanding this elimination of antimatter is the nonconservation of charge-parity (CP) symmetry. So far, two types of CP violation have been observed in the neutral K meson (K0) and B meson (B0) systems: CP violation involving the mixing2 between K0 and its antiparticle (and likewise3,4 for B0 and ), and direct CP violation in the decay of each meson5,6,7,8. The observed effects for both types of CP violation are substantially larger for the B0 meson system. However, they are still consistent with the standard model of particle physics, which has a unique source9 of CP violation that is known to be too small10 to account for the matter-dominated Universe. Here we report that the direct CP violation in charged B±K±π0 decay is different from that in the neutral B0 counterpart. The direct CP-violating decay rate asymmetry, (that is, the difference between the number of observed B-K-π0 event versus B+K+ π0 events, normalized to the sum of these events) is measured to be about +7%, with an uncertainty that is reduced by a factor of 1.7 from a previous measurement7. However, the asymmetry for versus B0K+π- is at the -10% level7,8. Although it is susceptible to strong interaction effects that need further clarification, this large deviation in direct CP violation between charged and neutral B meson decays could be an indication of new sources of CP violation—which would help to explain the dominance of matter in the Universe.

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Figure 1: Feynman diagrams for B , ππ.
Figure 2: Mbc projections for K-π+ (a), K+π- (b), K-π0 (c) and K+π0 (d).


  1. Sakharov, A. D. Violation of CP invariance, C asymmetry, and baryon asymmetry of the Universe. Pis'ma Zh. Eksp. Teor. Fiz. 5, 32–35 (1967); JETP Lett. 5, 24–27 (1967)

    CAS  Google Scholar 

  2. Christenson, J. H., Cronin, J. W., Fitch, V. L. & Turlay, R. Evidence for the 2π decay of the meson. Phys. Rev. Lett. 13, 138–140 (1964)

    Google Scholar 

  3. Aubert, B. et al. (BaBar Collaboration). Observation of CP violation in the B0 meson system. Phys. Rev. Lett. 87, 091801 (2001)

    Article  CAS  ADS  Google Scholar 

  4. Abe, K. et al. (Belle Collaboration). Observation of large CP violation in the neutral B meson system. Phys. Rev. Lett. 87, 091802 (2001)

    Article  CAS  ADS  Google Scholar 

  5. Alavi-Harati, A. et al. (KTeV Collaboration). Observation of direct CP violation in K S,Lππ decays. Phys. Rev. Lett. 83, 22–27 (1999)

    Article  CAS  ADS  Google Scholar 

  6. Fanti, V. et al. (NA48 Collaboration). A new measurement of direct CP violation in two pion decays of the neutral kaon. Phys. Lett. B 465, 335–348 (1999)

    Article  CAS  ADS  Google Scholar 

  7. Chao, Y. et al. (Belle Collaboration). Evidence for direct CP violation in B0K+π- decays. Phys. Rev. Lett. 93, 191802 (2004)

    Article  CAS  ADS  Google Scholar 

  8. Aubert, B. et al. (BaBar Collaboration). Direct CP violating asymmetry in B0K+π- decays. Phys. Rev. Lett. 93, 131801 (2004)

    Article  CAS  ADS  Google Scholar 

  9. Kobayashi, M. & Maskawa, T. CP violation in the renormalizable theory of weak interaction. Prog. Theor. Phys. 49, 652–657 (1973)

    Article  CAS  ADS  Google Scholar 

  10. Cohen, A. G., Kaplan, D. B. & Nelson, A. E. Progress in electroweak baryogenesis. Annu. Rev. Nucl. Part. Sci. 43, 27–70 (1993)

    Article  CAS  ADS  Google Scholar 

  11. Kurokawa, S. & Kikutani, E. Overview of the KEKB accelerators. Nucl. Instrum. Meth. A 499, 1–7 (2003)

    Article  CAS  ADS  Google Scholar 

  12. Abashian, K. et al. (Belle Collaboration). The Belle detector. Nucl. Instrum. Meth. A 479, 117–232 (2002)

    Article  CAS  ADS  Google Scholar 

  13. Aubert, B. et al. (BaBar Collaboration). Observation of CP violation in B0K+π- and B0π+π-. Phys. Rev. Lett. 99, 021603 (2007)

    Article  ADS  Google Scholar 

  14. Abulencia, A. et al. (CDF Collaboration). Observation of and measurements of branching fractions of charmless two-body decays of B0 and mesons in collisions at TeV. Phys. Rev. Lett. 97, 211802 (2006)

    CAS  Google Scholar 

  15. Keum, Y. Y. & Sanda, A. I. Possible large direct CP violations in charmless B decays: Summary report of the PQCD method. Phys. Rev. D 67, 054009 (2003)

    Article  ADS  Google Scholar 

  16. Beneke, M. & Neubert, M. QCD factorization for BPP and BPV decays. Nucl. Phys. B 675, 333–415 (2003)

    Article  ADS  Google Scholar 

  17. Aubert, B. et al. (BaBar Collaboration). Study of B0π0π0, B±π±π0, and B±K±π0 decays, and isospin analysis of Bππ decays. Phys. Rev. D 76, 091102(R) (2007)

    Article  ADS  Google Scholar 

  18. Chiang, C.-W., Gronau, M., Rosner, J. L. & Suprun, D. A. Charmless BPP decays using flavor SU(3) symmetry. Phys. Rev. D 70, 034020 (2004)

    Article  ADS  Google Scholar 

  19. Charng, Y.-Y. & Li, H-n. Weak phases from Bππ, decays. Phys. Rev. D 71, 014036 (2005)

    Article  ADS  Google Scholar 

  20. Hou, W.-S., Nagashima, M. & Soddu, A. Difference in B+ and B0 direct CP asymmetry as an effect of a fourth generation. Phys. Rev. Lett. 95, 141601 (2005)

    Article  ADS  Google Scholar 

  21. Baek, S., Hamel, P., London, D., Datta, A. & Suprun, D. A. The B puzzle and new physics. Phys. Rev. D 71, 057502 (2005)

    Article  ADS  Google Scholar 

  22. Baek, S. & London, D. Is there still a BπK puzzle? Phys. Lett. B 653, 249–253 (2007)

    Article  CAS  ADS  Google Scholar 

  23. Li, H.-n., Mishima, S. & Sanda, A. I. Resolution to the BπK puzzle. Phys. Rev. D 72, 114005 (2005)

    Article  ADS  Google Scholar 

  24. Barberio, E. et al. (Heavy Flavor Averaging Group). Averages of b-hadron properties at the end of 2006. Preprint at 〈〉 (2007)

  25. Beneke, B. Corrections to sin(2β) from CP asymmetries in B0→(π0, ρ0, η, η′, ω, φ)K S decays. Phys. Lett. B 620, 143–150 (2005)

    Article  CAS  ADS  Google Scholar 

  26. Cheng, H.-Y., Chua, C.-K. & Soni, A. Effects of final-state interactions on mixing-induced CP violation in penguin-dominated B decays. Phys. Rev. D 72, 014006 (2005)

    Article  ADS  Google Scholar 

  27. Hou, W.-S., Li, H-n., Mishima, S. & Nagashima, M. Fourth generation CP violation effect on B, φK and ρK in next-to-leading-order perturbative QCD. Phys. Rev. Lett. 98, 131801 (2007)

    Article  ADS  Google Scholar 

  28. Atwood, D. & Soni, A. The possibility of large direct CP violation in B-like modes because of long distance rescattering effects and implications for the angle γ.. Phys. Rev. D 58, 036005 (1998)

    Article  ADS  Google Scholar 

  29. Gronau, M. A precise sum rule among four B CP asymmetries. Phys. Lett. B 627, 82–88 (2005)

    Article  CAS  ADS  Google Scholar 

  30. Kakuno, H. et al. Neutral B flavor tagging for measurement of mixing-induced CP violation at Belle. Nucl. Instrum. Meth. A 533, 516–531 (2004)

    CAS  ADS  Google Scholar 

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We thank the KEKB group for the operation of the accelerator, the KEK Cryogenics group for the operation of the solenoid, and the KEK computer group and the NII for computing and Super-SINET network support. We acknowledge support from MEXT and JSPS (Japan); ARC and DEST (Australia); NSFC and KIP of CAS (China); DST (India); MOEHRD, KOSEF and KRF (Korea); KBN (Poland); MES and RFAAE (Russia); ARRS (Slovenia); SNSF (Switzerland); NSC and MOE (Taiwan); and the DOE (USA).

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Correspondence to P. Chang.

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Supplementary Information

The file contains Supplementary Notes with Supplementary Figures 1-2 and Supplementary Table 1. The text describes the Belle detector, explains how signals are extracted and lists the systematic uncertainties of the measurements. (PDF 722 kb)

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The Belle Collaboration. Difference in direct charge-parity violation between charged and neutral B meson decays. Nature 452, 332–335 (2008).

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