Large Transport
Air Traffic Control Fully Certified
Distraction; Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Chart Or Publication; Procedure; Human Factors
Shortly prior to incident I split Sector 14 off from the combined configuration of Sectors 14 and 34. The controller on Sector 34 was the relieving controller during the same time the sectors were being decombined. Aircraft X; an overflight; en route to Sector 14 level at 32000 feet. Aircraft Y was a flash-through from sector 34 landing DEN using local ZDV Standard Operating procedures. Aircraft Y was in communication with Sector 34 controller; given a descent clearance for DEN. I thought he was issued descend and maintain 27000 feet; accepted the handoff and with a descent and flashed the aircraft on to the low arrival sector. Assuming Aircraft Y was descending I didn't re-evaluate the traffic. The aircraft conflict alert started flashing without enough to time to achieve required separation. Aircraft Y was already below 33000 feet. Do not issue pilot discretion descents to DEN arrivals. If in Pilots Discretion descent annotate in 4th line of the data block. Switch all arrivals to Sector 14.
ZFW Center Controller reported receiving a handoff of an aircraft believed to be descending. The pilots had been issued discretion descent which delayed the descent; causing a confliction with opposite direction traffic.