State Police said they arrested a Hyde Park man carrying more than 6 pounds of heroin in the Jeep Grand Cherokee he was driving Thursday afternoon. Sergeant Michael Richards stopped Ronnie L. Searcy, 51, of Hyde Park, for speeding on the eastbound Massachusetts Turnpike in Grafton, State Police said. Searcy and his passenger, whose name police did not release, had different answers when Richards asked them where they were going. After a drug-sniffing dog was called, police found a black bag with three large plastic-wrapped cylinders containing what field tests determined to be more than 6½ pounds of heroin. Searcy was arrested on charges of heroin possession, speeding, and failing to keep to the right of the road. He was being held on $340,000 bail, State Police said.