The avant-jazz guitarist Mary Halvorson has been making a stir in downtown New Music circles for a while now. She is noted for her collaborations with the violist Jessica Pavone, among many others. Halvorson's strong 2008 debut, DRAGON'S HEAD features her new trio, comprised of the extraordinarily fluent bassist John Hebert and drummer Ches Smith (of indie-rockers Xiu-Xiu). Together, they make a far-ranging, expansive, and even accessible sound. Hebert's more-or-less continual dialogue with Halvorson's spidery