Conn. Gen. Stat. § 53a-16b

In any prosecution for an offense under section 53a-55a , 53a-56a , 53a-60a , 53a-92a , 53a-94a , 53a-102a or 53a-103a in which the defendant was not the only participant, it shall be an affirmative defense that the defendant: (1) Was not armed with a pistol, revolver, machine gun, shotgun, rifle or other firearm, and (2) had no reasonable ground to believe that any other participant was armed with such a weapon.