Search for Penguin Decays of $B$ Mesons at CDF
Kostas Kordas · 2000
Using a data sample of integrated luminosity ∫ Ldt = 28.9 +/- 1.2 pb-1 of proton-antiproton collisions at a center-of-mass energy s = 1.8 TeV collected with the CDF detector at the Fermilab Tevatron collider, we searched for "penguin" radiative decays of B0d and B0s mesons which involve the flavor-changing neutral-current transition of a b quark into an s quark with the emission of a photon, b→sg . Specifically, we searched for the decays B0d→K*0g, K*0→K+p- and B0s→fg, f→K+K- , as well as for the charge conjugate chains. In order to collect such decays, we designed a specialized trigger which required information on all the decay products of the B meson decay chain, the first such trigger in a hadron collider environment. This "penguin" trigger collected data during the last quarter of the 1994--1996 data taking period. After all selection criteria, we are left with one candidate B0d→K*0g decay and no B0s→fg candidates in the entire data sample. We then proceed to set upper limits on the branching fractions of the penguin channels. We exploit the topological similarity between the B¯→e-D0 X,D0→K-p + and the penguin decays, by forming ratios of branching fractions between the penguin and the B¯→e-D0 X channels. Uncertainties associated with the B meson production cross section, common efficiency corrections and other systematic effects are minimal in the ratio of branching fractions. The uncertainty on the B¯→e-D0 X yield is the biggest contribution to the total uncertainty on the penguin branching fraction. We assume equal production rates for B+u and B0d mesons, while the probability of producing B0s mesons relative to B0d mesons, fs/fd, is taken to be 1/3. The inferred upper limits on the ratios of branching fractions are B(B0 s→fg)B( B¯→e-D0 X)<3.5x10-3 at90% C.L. B(B 0d→K*0g) B(B¯→e- D0X)<1.9x10-3 at90%C.L. Relative branching fraction measurements were combined with the branching fraction measurement of the B¯→e-D0 X,D0→K-p + decay chain, B(B¯→e- D0X)xB(D0→ K-p+) = (294 +/- 40) x 10-5, to extract the following absolute branching fraction limits B(B0s→ fg)<2.8x10-4 at90%C.L. B(B0d →K*0g)<1.5x10-4 at90% C.L. The upper limit for the B0d→K*0g decay is consistent with the branching fraction measurement reported by the CLEO collaboration, B(B0d→K*0 g) = (4.0 +/- 1.9) x 10-5, while the upper limit for the as yet unobserved B0s→fg decay is the most constraining one set to date.