US stocks slumped Tuesday as crude tumbled past $48 a barrel after Saudi Arabia disclosed an increase in production, while the dollar advanced as investors gear up for Wednesday’s Federal Reserve decision. Oil slid more than 1.4 percent, while the S&P 500 Index headed for its worst loss in two weeks after OPEC data showed Saudi Arabia reversed one third of the production cuts. Energy, industrial, and materials shares led losses. The dollar was in demand before an anticipated Fed rate hike, and the pound slid as the British prime m inister won permission to trigger the country’s departure from the EU. The yield on 10-year Treasuries fell below 2.60 percent. The CBOE Volatility Index rose 8.4 percent, the most in a month. Oil’s drop interrupted the calm that’s gripped markets ahead of central bank decisions, European political drama and a raft of economic data that could set the tone on financial markets for weeks to come. With the Fed all but certain to raise rates, investors have been weighing how oil’s precarious level and looming inflation readings could impact the central bank’s path for future moves. Tomorrow’s election in the Netherlands will deliver a reading on the state of populism in Europe as races in France and Germany heat up.