8.已知直四棱柱ABCD−A1B1C1D1ABCD-A_{1}B_{1}C_{1}D_{1}ABCD−A1B1C1D1的棱长均为2,∠BAD=60∘\angle BAD=60\circ∠BAD=60∘.以D1D_{1}D1为球心,5\sqrt{5}5为半径的球面与侧面BCC1B1BCC_{1}B_{1}BCC1B1的交线长为((( )))