Study of B^{0}→D^{*-}π^{+}π^{-}π^{+} and B^{0}→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))×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→D¯1(2420)0π+π- decay is reported with the ratio of branching fractions B(B0→(D¯1(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→D¯1(2420)0π-π+) and B(D¯1(2420)0→D*-π+).