Study of B0 → D*− π+ π− π+ and B0 → D*− K+ π− π+ Decays

Using proton-proton collision data collected by the LHCb experiment at √s = 7 TeV, corresponding to an integrated luminosity of 1.0 fb^−1, the ratio of branching fractions of the B0 → D*− π+ π− π+ decay relative to the B0 → D*− π+ decay is measured to be B(B0 → D*− π+ π− π+)/B(B0 → D*− π+) = 2.64 ± 0.04(stat) ± 0.13(syst). The Cabibbo-suppressed decay B0 → D*− K+ π− π+ is observed for the first time, and the measured ratio of branching fractions is B(B0 → D*− K+ π− π+)/B(B0 → D*− π+ π− π+) = (6.47 ± 0.37(stat) ± 0.35(syst)) x 10^−2. A search for orbital excitations of charm mesons contributing to the B0 → D*− π+ π− π+ final state is also performed, and the first observation of the B0 → antiD1(2420)0 π+ π− decay is reported with the ratio of branching fractions B(B0 → (antiD1(2420)0 → D*− π+) π− π+)/B(B0 → D*− π+ π− π+) = (2.04 ± 0.42(stat) ± 0.22(syst)) x 10^−2, where the numerator represents a product of the branching fractions B(B0 → anti-D1(2420)0 π− π+) and B(anti-D1(2420)0 → D*− π+).