FTA, "passengers cannot refuse screening once they have proceeded beyond the screening checkpoint entrance."

More likely, you can refuse, but you'll be escorted out of the terminal (and refused reentry).

I doubt you'll "go to jail" unless you assault the TSA agent, become disorderly, etc.

TSA can't arrest or detain, but they can call the police. I'm quite sure you'd be detained. I don't know on what grounds an arrest could be made, so you're probably right that you'd be removed from the premises after some holding period.