Consider pp collisions. The reduced center of mass energy assuming the colliding quarks carry a fraction a and $b$ of the proton energy is

$2E\sqrt[\phantom{2}]{?}(a*b)$

$4E\sqrt[\phantom{2}]{?}(a^{{?}^{{?}^{?}}}2)$

$3E\sqrt[\phantom{2}]{?}(a*b)$

$E\sqrt[\phantom{2}]{?}(b^{{?}^{{?}^{?}}}2)$

none of the above