Stocks plunged in the United States and worldwide Friday after Britain voted to leave the European Union. The result stunned investors, who reacted by rushing to the safety of gold and US government bonds as they wondered what will come next. Banks took the largest losses by far. Citigroup plummeted $4.16, or 9.4 percent, to $40.30 and JPMorgan Chase fell $4.45, or 6.9 percent, to $59.60. They have the most to lose in Britain’s departure from the EU because they do a lot of cross-border business in Europe based from their offices in London. Oil prices sank. In addition to bonds, other safety assets also soared. Gold jumped $59.30, or 4.7 percent, to $1,322.40. That’s its highest price since July 2014. Silver rose 44 cents, or 2.5 percent, to $17.79 an ounce, its highest in more than a year.