Trim with regular expression based on delimiter?

Hi, trying to tim a collection of song titles that have duplicate different information after a front slash as seen below:

Breaking Ties [A&b Analogue Haven Mix]/A&b Analogue Haven Mix

Want to trim the '/A&b Analogue Haven Mix' off, anything including and after the front slash.

Can't quite get the regular expression to use from the FAQ thread on this and trailing spaces, any help? Thanks -

Action: Format value Field : TITLE_NEW Formatstring: $regexp(%TITLE%,'^(.+?)\[(.+?)\]/\2$','$1[$2]') From : Breaking Ties [A&b Analogue Haven Mix]/A&b Analogue Haven Mix To : Breaking Ties [A&b Analogue Haven Mix]

DD.20150216.1338.CET

Action Type: Guess Values
Source format: %title%
Guessing Pattern: %title%/%dummy%