The Special Town Meeting decided Wednesday not to overturn a controversial seasonal ban on gas-powered leaf blowers and voted instead to establish a committee to study changes to the ban. The meeting voted 110 to 95 against a proposal to reverse a bylaw approved by Town Meeting in May that would ban the use of gas-powered leaf blowers on private property between May 15 and Oct. 15 each year. At the urging of selectmen, Town Meeting members voted to establish a committee that will report back in the spring with recommendations.