Circle C_{1} has its center O lying on circle C_{2}. The two circles meet at X and Y. Point Z in the exterior of C_{1} lies on circle C_{2} and X Z=13, O Z=11, and Y Z=7. What is the radius of circle C_{1} ?
Answer Choices
A. 5
B. \sqrt{26}
C. 3 \sqrt{3}
D. 2 \sqrt{7}
E. \sqrt{30}