Zurich Open Repository and Archive University of Zurich Main Library Strickhofstrasse 39 CH-8057 Zurich www.zora.uzh.ch Year: 2015 First observation and measurement of the branching fraction for the decay B 0 s → D ∗∓ s K ± LHCb Collaboration ; Aaij, R ; Adeva, B ; Adinolf, M ; Anderson, J ; Bernet, R ; Bowen, E ; Bursche, A ; Chiapolini, N ; Chrzaszcz, M ; Dey, B ; Elsasser, C ; Graverini, E ; Lionetto, F ; Lowdon, P ; Mauri, A ; Müller, K ; Serra, N ; Steinkamp, O ; Storaci, B ; Straumann, U ; Tresch, M ; Vollhardt, A ; et al Abstract: The frst observation of the B 0 s → D ∗∓ s K ± decay is reported using 3.0fb −1 of proton-proton collision data collected by the LHCb experiment. The D ∗∓ s mesons are reconstructed through the decay chain D ∗∓ s → γD ∓ s (K ∓ K ± π ∓ ). The branching fraction relative to that for B 0 s → D ∗− s π + is measured to be 0.068 ± 0.005 +0.003 −0.002 , where the frst uncertainty is statistical and the second is systematic. Using a recent measurement of BR(B 0 s → D ∗− s π + ) the absolute branching fraction of B 0 s → D ∗∓ s K ± is measured as ( 16.3 ± 1.2 (stat) +0.7 −0.5 (syst) ± 4.8 (norm) ) × 10 −5 , where the third uncertainty is due to the uncertainty on the branching fraction of the normalisation channel. DOI: https://doi.org/10.1007/JHEP06(2015)130 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-122710 Journal Article Published Version The following work is licensed under a Creative Commons: Attribution 4.0 International (CC BY 4.0) License. Originally published at: LHCb Collaboration; Aaij, R; Adeva, B; Adinolf, M; Anderson, J; Bernet, R; Bowen, E; Bursche, A; Chiapolini, N; Chrzaszcz, M; Dey, B; Elsasser, C; Graverini, E; Lionetto, F; Lowdon, P; Mauri, A; Müller, K; Serra, N; Steinkamp, O; Storaci, B; Straumann, U; Tresch, M; Vollhardt, A; et al (2015). First observation and measurement of the branching fraction for the decay B 0 s → D ∗∓ s K ± . Journal of High Energy Physics, 2015(6):130. DOI: https://doi.org/10.1007/JHEP06(2015)130