We present a search for lepton-flavor-violating τ decays into three leptons (electrons or muons) using 782 fb−1 of data collected with the Belle detector at the KEKB asymmetric-energy e+e− collider. ...No evidence for these decays is observed and we set 90% confidence level upper limits on the branching fractions between 1.5×10−8 and 2.7×10−8.
We present results from a study of X(3872)→ππJ/ψ decays produced via exclusive B→KX(3872) decays. We determine the mass to be MX(3872)=(3871.85±0.27(stat)±0.19(syst)) MeV, a 90% confidence level ...upper limit on the natural width of ΓX(3872)<1.2 MeV, the product branching fraction B(B+→K+X(3872))×B(X(3872)→π+π-J/ψ)=(8.63±0.82(stat)±0.52(syst))×10-6, and a ratio of branching fractions B(B0→K0X(3872))/B(B+→K+X(3872))=0.50±0.14(stat)±0.04(syst). The difference in mass between the X(3872)→π+π-J/ψ signals in B+ and B0 decays is ΔMX(3872)=(-0.71±0.96(stat)±0.19(syst)) MeV. A search for a charged partner of the X(3872) in the decays B0→K-X+ or B+→K0X+, X+→π+π0J/ψ resulted in upper limits on the product branching fractions for these processes that are well below expectations for the case that the X(3872) is the neutral member of an isospin triplet. In addition, we examine possible JPC quantum number assignments for the X(3872) based on comparisons of angular correlations between final state particles in X(3872)→π+π-J/ψ decays with simulated data for JPC values of 1++ and 2-+. We examine the influence of ρ-ω interference in the M(π+π-) spectrum. The analysis is based on a 711 fb-1 data sample that contains 772×106 BB meson pairs collected at the Υ(4S) resonance in the Belle detector at the KEKB e+e- collider.
We search for lepton-flavor-violating τ→ℓV0 decays, where ℓ is an electron or muon and V0 is one of the vector mesons ρ0, ϕ, ω, K⁎0 and K¯⁎0. We use 854 fb−1 of data collected with the Belle detector ...at the KEKB asymmetric-energy e+e− collider. No evidence for a signal is found in any decay mode, and we obtain 90% confidence level upper limits on the individual branching fractions in the range (1.2–8.4)×10−8.
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