Maricopa County officials took significant steps Wednesday to sell the downtown Phoenix ballpark that has been the only home of the Arizona Diamondbacks. The county’s Stadium District Board of Directors unanimously voted to sign a letter of intent, opening the door for Integral Group, LLC, to negotiate to buy Chase Field for a minimum price of $60 million. “We are here today to protect the taxpayer,” board chairman Clint Hickman said during the public meeting. “This is the best of what private business can offer.”