This man composed the Kaddish Symphony, which was premiered shortly after JFK's assassination.
This composer wrote the music to a song that contains three G eighth notes followed by three higher C eighth notes followed by descending A F C quarter notes. A so-called "Theatre Piece for Singers, Players, and Dancers" by this composer that centers on a Celebrant is MASS, whose title is all capitalized. This man, who succeeded Dimitri Mitropoulous as music director of the New York Philharmonic, hosted many Young People's Concerts, which were notably televised. This man composed the Kaddish Symphony, which was premiered shortly after JFK's assassination. For 10 points, name this conductor who also composed the music to West Side Story. 
This composer wrote the music to a song that contains three G eighth notes followed by three higher C eighth notes followed by descending A F C quarter notes.
Leonard Bernstein 