Measurement of branching fractions and CP-violating asymmetries in neutral B meson to neutral kaon-antineutral kaon and B+ meson going to antineutral kaon-kaon+ decays at the BABAR experiment .

摘要

Over the last few years, the B factories have established the Cabbibo-Kobayashi-Maskawa mechanism of CP violation in the Standard Model through the study of the decays of B mesons. The focus of Belle and BABAR has now expanded to the search for signatures of new physics beyond the Standard Model, particularly through examination of flavor-changing neutral-current transitions, which proceed through diagrams involving virtual loops. These decays are suppressed in the Standard Model, increasing sensitivity to new-physics effects but decreasing branching fractions. Exploiting large and growing datasets, BABAR and Belle have made many measurements in loop decays where a b quark transitions to an s quark, observing hints of possible deviations from Standard Model expectations in CP-violating measurements.; This dissertation describes the first observation at BABAR of the B0 → K 0K¯0 and B+ → K0K¯+ decays using about 350 million Upsilon(4S) → BB¯ events. These processes are dominated by the gluonic b → d virtual-loop transition, which is further suppressed in the Standard Model and could have different effects from new physical contributions. The observed branching fractions are B (B0 → K 0K¯0) = (1.08+/-0.28+/-0.11)x10 -6 and B (B+ → K0K¯ +) = (1.61+/-0.44+/-0.09)x10-6. The first measurement of time-dependent CP asymmetries in B0 → K0 K¯0 is also presented, obtaining S = -1.28+0.80+0.11-0.73-0.16 and C = -0.40+/-0.41+/-0.06, while for B+ → K¯0 K+ the measured direct CP asymmetry is A (K¯0K +) = 0.10+/-0.26+/-0.03. These measurements open a new sector of inquiry for the B factories. The dissertation also describes the related measurements of the branching fraction B (B+ → K 0pi+) = (23.9+/-1.1+/-1.0) x10 -6 and direct CP asymmetry A (K0pi+) = -0.029+/-0.039+/-0.010.