NEW YORK: The stock market soared to a new high Thursday amid surging investor confidence that the U.S. economic boom could continue apace without disintegrating into a bust. By the time the short trading day ended at 1 PM EDT, the Dow Jones industrial average had surged an additional 100.43 points to close at a record 7,883.59 -- a staggering 22 percent gain since the beginning of the year. Advancers outpaced decliners by a 5 to 2 margin on the New York Stock Exchange. The main trigger for the buying frenzy was a Labor Department report indicating the country's unemployment rate jumped to five percent in June from a 24-year low of 4.8 percent in May. Adding to the optimism was Wednesday's decision by the Federal Reserve board to leave interest rates alone for now. Today's announcement of a defense merger that will combine Lockheed Martin and Northrop Grumman in a new military manufacturing powerhouse accelerated the rise in prices as stockbrokers wrapped up early for the Independence Day weekend.