Exploring the Beatles’ songbook, the musicians in Classical Mystery Tour performed recently with the Pasadena Pops in a nostalgia-soaked show at the Los Angeles County Arboretum. An appreciative audience heard timeless hits from the Fab Four’s early years through “Sgt. Pepper’s Lonely Hearts Club Band” and the lads’ solo careers, with a special tribute to the 50th anniversary of the White Album — all with the backing of a capable symphony orchestra.