Hide search for logged out users on twenty fourteen child theme

Hello,

Just want to hide the search box for logged out users. Just the box, not the entire bar.
I don't want guests or logged out users to be allowed to search the site at all.
I have searched this fab site for stuff and found many similar questions but not quite it.
Preferably I want to add this to our child theme of twenty fourteen for future-proofness..
I don't have a header.php in the childtheme yet, so ideally the code for such a new file?

thanx
j