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Studies of the Decay B+- -> D_CP K+-

We report studies of the decay B+- -> D_CP K+-, where D_CP denotes neutral D mesons that decay to CP eigenstates. The analysis is based on a 29.1/fb data sample of collected at the \Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric e+ e- storage ring. Ratios of branching fractions of Cabibbo-suppressed to Cabibbo-favored processes involving D_CP are determined to be B(B- -> D_1 K-)/B(B- -> D_1 pi-)=0.125 +- 0.036 +- 0.010 and B(B- -> D_2 K-)/B(B- -> D_2 pi-)=0.119 +- 0.028 +- 0.006, where indices 1 and 2 represent the CP=+1 and CP=-1 eigenstates of the D0 - anti D0 system, respectively. We also extract the partial rate asymmetries for B+- -> D_CP K+-, finding A_1 = 0.29 +- 0.26 +- 0.05 and A_2 = -0.22 +- 0.24 +- 0.04.Comment: 10 pages, 2 figures, submitted to Physical Review Letter

Observation of Ds+K- and evidence for D-s(+)pi(-) final states in neutral B decays

We report the first observation of a B meson decay that is not accessible by a direct spectator process. The channel (B) over bar (0)-->Ds+K- is found in a sample of 85x10(6) B (B) over bar events, collected with the Belle detector at KEKB, with a branching fraction B((B) over bar (0)-->Ds+K-)=(4.6(-1.1)(+1.2)+/-1.3)x10(-5). We also obtain evidence for the B-0-->D(s)(+)pi(-) decay with branching fraction B(B-0-->D(s)(+)pi(-))=(2.4(-0.8)(+1.0)+/-0.7)x10(-5). This value may be used to extract a model-dependent value of \V-ub\

Upper bound on the decay tau ->mu gamma from the Belle detector

We have performed a search for the lepton-flavor-violating decay tau-->mugamma using a data sample of 86.3 fb(-1) accumulated by the Belle detector at KEK. No evidence for a signal is seen, and we set an upper limit for the branching fraction of B(tau-->mugamma) < 3.1x10(-7) at the 90% confidence level

Measurement of the B-0-(B)over-bar(0) mixing parameter Delta m(d) using semileptonic B-0 decays

We present a measurement of the B-0-(B-0) over bar mixing parameter Deltam(d) using neutral B meson pairs in a 29.1 fb(-1) data sample collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We exclusively reconstruct one neutral B meson in the semileptonic B-0-->D*-.(+)nu decay mode and identify the flavor of the accompanying B meson from its decay products. From the distribution of the time intervals between the two flavor-tagged B meson decay points, we obtain Deltam(d)=(0.494+/-0.012+/-0.015) ps(-1), where the first error is statistical and the second error is systematic

Observation of B -> K(*)l(+)l(-)

We report the observation of the flavor-changing neutral current decay B-->K*l(+l-) and an improved measurement of the decay B-->Kl(+l-), where l represents an electron or a muon, with a data sample of 140 fb(-1) accumulated at the Y(4S) resonance with the Belle detector at KEKB. The results for the branching fractions are B(B-->K*l(+l-))=(11.5(-2.4)(+2.6)+/-0.8+/-0.2)x10(-7) and B(B-->Kl(+l-))=(4.8(-0.9)(+1.0)+/-0.3+/-0.1)x10(-7), where the first error is statistical, the second is systematic and the third is from model dependence