Study of B-0 -> D*(-) pi(+)pi(-)pi(+) and B-0 -> D*K--(+)pi(-)pi(+) 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))×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→Dbar1(2420)0π+π− decay is reported with the ratio of branching fractions ℬ(B0→(Dbar1(2420)0→D*−π+)π−π+)/ℬ(B0→D*−π+π−π+)=(2.04±0.42(stat)±0.22(syst))×10−2, where the numerator represents a product of the branching fractions ℬ(B0→Dbar1(2420)0π−π+) and ℬ(Dbar1(2420)0→D*−π+).