It’s a busy day on the Lower East Side. This morning, there’s a ribbon cutting ceremony at Sara D. Roosevelt Park, where the brand new Hester Street Playground will be formally unveiled. Meanwhile, there will be a lot of activity at Cooper Union, where the Rent Guidelines Board is meeting — and activists and elected officials protesting outside. And “Lush Life,” an inventive new exhibition gets underway at the Sue Scott Gallery. Party cloudy and windy today with a high of 76.