Check the question linked in my comment; it's not specifically there, but you can get it with \usepackage{mathrsfs} and \mathscr{U}.
– egregApr 10 '12 at 21:02
2
I hope you don't mind that the question has been closed: we try our best not to scatter information. Be welcome and don't fear to ask.
– egregApr 10 '12 at 21:12
\usepackage{mathrsfs}and\mathscr{U}. – egreg Apr 10 '12 at 21:02