Let the cross section formed by the plane be $PQRST$ and it looks like this(orthographic projection on plane $ABCD$): [asy][asy]unitsize(50);dot('$C,S$',(0,0),S); fill((.5,1.5)--(-.5,1.5)--(-1,1)--(0,0)--(1,1)--cycle,gray); dot('$D,T$',(-1,1),W); dot('$A$',(0,2),N); dot('$B,R$',(1,1),E); draw((0,0)--(1,1)--(0,2)--(-1,1)--cycle); dot("$Q$",(.5,1.5),NE); dot("$P$",(-.5,1.5),NW); draw((0,0)--(0,1.5),Arrows); label("$\sqrt{\frac{11}8}$",(0,.75),E); [/asy][/asy]