“They once called me their ‘father.’ But when I work with them, I feel 50 years younger and admire them like brothers,” Helmut Lachenmann said about the JACK Quartet, which released a landmark recording of the composer’s complete string quartets in 2014. The ensemble concludes its three-part concert series this season with Lachenmann’s Reigen seliger Geister. The otherworldly is also explored by the four musicians in works by John Zorn and Caleb Burhans as well as their own arrangement of a 14th-century ars nova hymn.