The Belcea Quartet has received acclaim around the world for its performances of repertoire classics, including the string quartets of Beethoven and Bartók, which the ensemble has released in complete recordings as well. But the four musicians—closely associated with the Pierre Boulez Saal since its opening more than six years ago—have also championed contemporary music and commissioned several new works. In a program bookended by Bartók’s First and Beethoven’s Twelfth String Quartet, they now perform a new piece by British composer Julian Anderson.