V$ROLLSTAT XACTS Field

One unknown transaction kill our rollback segment everyday. (make it max # of extent reached ).

I know XACTS Field in V$ROLLSTAT show if there is any active TRansaction in that RB or not right??

Let's say I have one active Transaction in my Rollback R01-03, how can I find what the heck is this TRANS?
what is the content of this Transaction and fire by which user? Please advice

-- Active Rollback segment

select A.xidusn RBS_NO, A.ADDR, B.USERNAME, B.SADDR
from V$TRANSACTION A, v$session B
where A.ADDR = B.TADDR AND username = 'SCOTT' ;