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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).


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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.

Supplementary information

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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