Boston Celtics co-owner Stephen Pagliuca will announce today his plan to run in the Democratic primary for the U.S. Senate seat vacated by the late Edward Kennedy, reports said. Pagliuca, a private-equity investor, will officially announce his candidacy at 3 p.m. at TD Banknorth Garden, the Celtics’ home court, according to The Boston Globe. Pagliuca, who has put in a bid to buy the financially-troubled Globe, enters the senatorial race with vast personal wealth estimated at $400 million, according to The Globe. While his fortune will help build a campaign, some are concerned about his political inexperience and past campaign contributions to Republican politicians such as former Mass. governor Mitt Romney and former president George W. Bush. Pagliuca’s confirmed Democratic opponents are attorney general Martha Coakley and U.S. Rep. Michael Capuano of Somerville, who delivered Boston University’s 2009 commencement address and will formally announce his candidacy Friday. Also likely to run us Alan Khazei, co-founder of City Year, a nonprofit AmeriCorps organization that works to build democracy through service. U.S. Rep. Stephen Lynch announced yesterday that contrary to expectations, he will not run for Kennedy’s senate seat, according to The Globe.