The Broad, a contemporary art museum in downtown Los Angeles that will be free to visitors, said Thursday it will open its doors on Sept. 20.The $140 million museum next to Walt Disney Concert Hall will showcase the collection of billionaire philanthropist Eli Broad, who has been instrumental in transforming the once-rundown neighborhood just south of City Hall.Among the artists whose work will be displayed are Andy Warhol, Jasper Johns, Ed Ruscha, Cindy Sherman, and Roy Lichtenstein.Broad said the museum, with its free admission, is his gift to the people of Los Angeles. It will open for a one-day sneak preview on Feb. 15. Tickets for that event will cost $10.The block-long, three-story building designed by architect Elizabeth Diller features a porous, concrete veil sheathed in glass that will provide natural light and a view of some of the works from the street. Through portals, visitors also will get a glimpse of works housed in a vault.Broad, whose wealth is estimated by Forbes at $6.9 billion, made a fortune in real estate as co-founder of homebuilder Kaufman & Broad and later as founder of the investment firm SunAmerica.After selling SunAmerica for $18 billion in 1998, he turned his interests to philanthropy, focusing largely on art and education.