Juventas New Music Ensemble, led by Medford composer and conductor Oliver Caplan, opens its 2020-21 virtual concert season with "American Mirror," music that reflects the social fabric of America. Featuring works by Allison Loggins-Hull, Mari Kotskyy, Jessica Meyer, Miguel de Aguila, Derrick Spiva Jr. and Oliver Caplan. With performances by Nick Southwick, flute; Wolcott Humphrey, clarinet; Olga Patramanska-Bell and Ryan Shannon, violin; Lu Yu, viola; Minjin Chung, cello; and Julia Scott Carey, piano. The concert will be live streamed on YouTube:…