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

摘要

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 prerequisites 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 (K~0) and B meson (B~0) systems: CP violation involving the mixing between K~0 and its antiparticle K~0 (and likewise for B~0 and B~0), and direct CP violation in the decay of each meson5""8. The observed effects for both types of CP violation are substantially larger for the B~0 meson system. However, they are still consistent with the standard model of particle physics, which has a unique source of CP violation that is known to be too small to account for the matter-dominated Universe. Here we report that the direct CP violation in charged B~±→K~±π~0 decay is different from that in the neutral B~0 counterpart. The direct CP-violating decay rate asymmetry, A_(k+π~0) (that is, the difference between the number of observed B~-→K~-π~0 event versus B~+→K~+ π~0 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 A_(K~±π~+) for B~0 → K~-π~+ versus B~0→K~+π~- is at the -10% level. 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.