The first observation of the decays (B) over bar (0)(s) -> Ds+K-pi(+)pi(-) and (B) over bar (0)(s) -> Ds+K-pi(+)pi(-) are reported using an integrated luminosity of 1.0 fb(-1) recorded by the LHCb experiment. The branching fractions, normalized with respect to (B) over bar (0)(s) -> D-s(+)pi(-)pi(+)pi(-) and (B) over bar (0)(s) -> Ds+K-pi(+)pi(-), respectively, are measured to be B((B) over bar (0)(s)-> DsK-pi(+)pi(-))/B((B) over bar (0)(s)-> D-s pi(-)pi(+)pi(-)) = (5.2 +/- 0.5 +/- 0.3) x 10(-2) and B((B) over bar (0)(s)-> DsK-pi(+)pi(-))/B((B) over bar (0)(s)-> DsK-pi(+)pi(-)) = 0.54 +/- 0.07 +/- 0.07, where the first uncertainty is statistical and the second is systematic. The (B) over bar (0)(s) -> D-s(+) K-pi(+)pi(-) decay is of particular interest as it can be used to measure the weak phase gamma. First observation of the (B) over bar (0)(s) -> D-s1(2536)(+)pi(-), D-s1(+) -> D-s(+) pi(-)pi(+) decay is also presented, and its branching fraction relative to (B) over bar (0)(s) -> D-s(+) pi(-)pi(+)pi(-) is found to be B((B) over bar (0)(s) -> D-s1(2536)(+)pi(-),D-s1(+)-> D-s(+)pi(-)pi(+)/B((B) over bar (0)(s) -> D-s(+)pi(-)pi(+)pi(-))) = (4.0 +/- 1.0 +/- 0.4) x 10(-3). DOI: 10.1103/PhysRevD.86.112005
Jian Wang, Matthias Finger, Qian Wang, Yiming Li, João Miguel das Neves Duarte, Matthias Wolf, Varun Sharma, Yi Zhang, Tian Cheng, Yixing Chen, Alexis Kalogeropoulos, Ioannis Papadopoulos, Hua Zhang, Siyuan Wang, Xin Chen, Michele Bianco, Sebastiana Gianì, Sun Hee Kim, Rakesh Chawla, Jan Steggemann, Konstantin Androsov, Anna Mascellani, Federica Legger, Matteo Galli, Gabriele Grosso