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

Abstract

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(1) 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(2) between K-0 and its antiparticle (K) over bar (0) ( and likewise(3,4) for B-0 and (B) over bar (0)), and direct CP violation in the decay of each meson(5-8). 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(9) of CP violation that is known to be too small(10) to account for the matter-dominated Universe. Here we report that the direct CP violation in charged B-+/- --> K-+/- pi(0) decay is different from that in the neutral B-0 counterpart. The direct CP- violating decay rate asymmetry, A(K)+/- (pi 0) ( that is, the difference between the number of observed B- --> K- pi(0) event versus B+ --> K+ pi(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 measurement(7). However, the asymmetry A(K+/-) p(-/+) for B-0 --> K- pi(+) versus B-0 --> K+ pi(-) is at the -10% level(7,8). 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.