4.
已知过抛物线\(E\):\(y^{2}=2px(p > 0)\)的焦点\(F\),斜率为\( \sqrt {2}\)的直线交抛物线于\(A(x_{1},y_{1})\),\(B(x_{2},y_{2})(x_{1} < x_{2})\)两点,且\(|AB|=6\).
\((1)\)求该抛物线\(E\)的方程;
\((2)\)过点\(F\)任意作互相垂直的两条直线\(l_{1}\),\(l_{2}\),分别交曲线\(E\)于点\(C\),\(D\)和\(M\),\(N.\)设线段\(CD\),\(MN\)的中点分别为\(P\),\(Q\),求证:直线\(PQ\)恒过一个定点.