Selection Study for B+- -> (K-+ pi+- pi-+ pi+-)D K+- and B+- -> (K+ K- pi+ pi-)D K+-".

In this document, a selection of the decay mode B->D(Kpipipi)K is presented. It had been designed to minimise background in this channel, whilst retaining as much signal as possible. This analysis will be used as part of the effort to measure the CKM angle " with the LHCb dataset, the acquisition of which is due to start in the autumn of 2009. The expected signal yield in one nominal year of LHC running has been estimated as 529+212,−151 events, with a total background pollution of 1742+1306,−1045. The selection has also been applied to the similar channel B->D(KKpipi)K for which the signal and background yields have been estimated to be 1280±98 and 856+972,−570 respectively.