TSQL to detect long running queries against the database

When I'm performing a performance analysis on a 24/7 application and dealing with PSS I had been given the following TSQL to identify the long running queries against a database.

select r.session_id, s.host_name, s.program_name, s.host_process_id,

r.status, r.wait_time,wait_type,r.wait_resource,

substring(qt.text,(r.statement_start_offset/2) +1,

(case when r.statement_end_offset = -1

then len(convert(nvarchar(max), qt.text)) * 2

else r.statement_end_offset end -r.statement_start_offset)/2)

as stmt_executing,r.blocking_session_id, r.cpu_time,r.total_elapsed_time,r.reads,r.writes,

r.logical_reads, r.plan_handle

from sys.dm_exec_requests r

cross apply sys.dm_exec_sql_text(sql_handle) as qt, sys.dm_exec_sessions s

where r.session_id > 50 and r.session_id=s.session_id

order by r.session_id, s.host_name, s.program_name, r.status