Observation of the suppressed ADS modes B±→[π±K∓π+π−]DK± and B±→[π±K∓π+π−]Dπ±

Abstract An analysis of B ± → D K ± and B ± → D π ± decays is presented where the D meson is reconstructed in the four-body final state K ± π ∓ π + π − . Using LHCb data corresponding to an integrated luminosity of 1.0 fb − 1 , first observations are made of the suppressed ADS modes B ± → [ π ± K ∓ π + π − ] D K ± and B ± → [ π ± K ∓ π + π − ] D π ± with a significance of 5.1 σ and greater than 10 σ , respectively. Measurements of CP asymmetries and CP -conserving ratios of partial widths from this family of decays are also performed. The magnitude of the ratio between the suppressed and favoured B ± → D K ± amplitudes is determined to be r B K = 0.097 ± 0.011 .