I don't think I would cap the flop, it looks like BB has a six. You cannot fold for 2 reasons though 1)When BB it comes back to you there are 27SB in the pot so you are getting way more than enough just to try to spike an ace (you also cannot fold the turn as well for this reason alone). 2) The pot is enormous and there is always the chance that BB is overplaying a hand like JJ or A7. Either way I go into call down mode on the turn like you did, I would probably bet when checked to here, too bad that BB is a huge donk and goes for the donk-tacular checkraise here.