If the length of the latus rectum of a parabola, whose focus is \( (a,a) \) and the tangent at its vertex is \( x+y=a \), is \( 16 \), then \( |a| \) is equal to:
\( 2\sqrt{2} \)
\( 2\sqrt{3} \)
\( 4\sqrt{2} \)
\( 4 \)