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Abstract

The measurement of time-dependent CP violation in Bs->DsKpipi decays and the determination of the CKM angle gamma is performed using a dataset collected by the LHCb experiment in proton-proton collisions during Run I (2011-2012) and Run II (2015-2017) of the LHC operation, corresponding to an integrated luminosity of 6.7 fb^-1. The results are presented in terms of the CP-violating parameters C, D_f ans S_f, which are found to be

C = 0.68 +/- 0.12 +/- 0.02, D_f = 0.01 +/- 0.32 +/- 0.08, D_fbar = 0.38 +/- 0.30 +/- 0.08, S_f = -0.14 +/- 0.17 +/- 0.04, S_fbar = -0.54 +/- 0.17 +/- 0.04,

where the uncertainties are statistical and systematic, respectively. The measured parameters correspond to 3.4 sigma evidence for CP violation in the interference between decay and decay after mixing. These parameters are used together with the value of the Bs mixing phase beta_s to determine the CKM angle gamma using Bs->DsKpipi decays, yielding

gamma = (65^+27_-20)°,

where statistical and systematic uncertainties are combined. The obtained value of gamma agrees with the world average within its uncertainties. This analysis represents the first determination of CP violation in this decay channel and the second result on the CKM phase gamma from a time-dependent measurement. In addition, an amplitude analysis of Bs->DsKpipi decays is presented and the sensitivity of a time-dependent amplitude model to gamma in this decay channel is discussed.