LHCb

Abstract:

We present a search for the decay of a B0 or B̄0 meson to a K̄*0K0 or K*0K̄0 final state, using a sample of approximately 232×106 BB̄ events collected with the BABAR detector at the PEP-II asymmetric energy e+e- collider at SLAC. The measured branching fraction is B(B0→K̄*0K0)+B(B0→K*0K̄0)=(0.2-0.8- 0.3+0.9+0.1)×10-6. We obtain the following upper limit for the branching fraction at 90% confidence level: B(B0→K̄*0K0) +B(B0→K*0K̄0)<1.9×10-6. We use our result to constrain the standard model prediction for the deviation of the CP asymmetry in B0→K0 from sin2β. © 2006 The American Physical Society.

Abstract:

We present the first search for the decay B0→KS0KS0KL0 using a data sample of 232×106 BB̄ pairs. We find no statistically significant evidence for the nonresonant component of this decay. Our central value for the branching fraction, assuming the true Dalitz distribution is uniform and excluding the resonance, is B(B0→KS0KS0KL0)=(2.4-2.5+2.7±0.6) ×10-6 where the errors are statistical and systematic, respectively. We set a single-sided Bayesian upper limit of B(B0→KS0KS0KL0)<7.4×10- 6 at 90% confidence level using a uniform prior probability for physical values. Assuming the worst-case true Dalitz distribution, where the signal is entirely in the region of lowest efficiency, the 90% confidence level upper limit is B(B0→KS0KS0KL0)<16×10-6. © 2006 The American Physical Society.

Abstract:

A search for the decay of the τ lepton to five charged and two neutral pions is performed using data collected by the BABAR detector at the PEP-II asymmetric-energy e+e- collider. The analysis uses 232fb-1 of data at center-of-mass energies on or near the Υ(4S) resonance. We observe 10 events with an expected background of 6.5-1.4+2.0 events. In the absence of a signal, we set the limit on the branching ratio B(τ-→3π- 2π+2π0ντ)<3.4×10-6 at the 90% confidence level. This is a significant improvement over the previously established limit. In addition, we search for the decay mode τ-→2ωπ-ντ. We observe 1 event with an expected background of 0.4+1.0-0.4 events and calculate the upper limit B(τ-→2ωπ-ντ)<5.4×10-7 at the 90% confidence level. This is the first upper limit for this mode. © 2006 The American Physical Society.

Abstract:

We search for the rare leptonic decay B+→τ+ντ in a sample of 232×106 BB̄ pairs collected with the BABAR detector at the SLAC PEP-II B-Factory. Signal events are selected by examining the properties of the B meson recoiling against the semileptonic decay B-→D*0-ν̄. We find no evidence for a signal and set an upper limit on the branching fraction of B(B+→τ+ντ)<2.8×10-4 at the 90% confidence level. We combine this result with a previous, statistically independent BABAR search for B+→τ+ντ to give an upper limit of B(B+→τ+ντ)<2.6×10-4 at the 90% confidence level. © 2006 The American Physical Society.

Abstract:

We present the results of a search for the decay B0→τ+τ- in a data sample of (232±3)×106 Υ(4S)→BB̄ decays using the BABAR detector. Certain extensions of the standard model predict measurable levels of this otherwise rare decay. We reconstruct fully one neutral B meson and seek evidence for the signal decay in the rest of the event. We find no evidence for signal events and obtain B(B0→τ+τ-)<4.1×10-3 at the 90% confidence level. © 2006 The American Physical Society.