Michigan’s most senior state senator was charged with possession and delivery of cocaine and marijuana after a search of his Lansing apartment reportedly turned up small amounts of the two substances. State police said the arrest of Sen. Basil Brown, 58, culminated a monthlong undercover investigation. A search warrant was obtained with the help of a prostitute who knew Brown, a spokeswoman for the state attorney general said. Brown, a Democrat from Highland Park, was free on bond pending a Nov. 18 preliminary hearing of his case.