ZDV controller missed an incorrect altitude readback from an aircraft due to distractions in the wor...

Narrative:

It was near the end of my shift; I was being told by the controller in charge (controller in charge) that the sector would be going red for about 20 minutes and was being asked if I wanted to keep a d-side (assist controller) or split out the upper portion of my airspace. About the same time; aircraft X was checking on climbing out of denver. I issued aircraft X a clearance to 37000 feet after doing a quick scan. I then responded to the controller in charge that I would rather just keep a d-side. My d-side then brought my attention to the fact that aircraft X was in conflict with aircraft Y level at 34000 feet but had several minutes to fix the conflict.I issued an amended clearance to aircraft X to maintain 33000 feet. About the same time I was being asked if I wanted a break. I told the controller in charge that I would rather stay on position until I was no longer needed in the area. Several more people were coming in and there was a lot of distractions with my d-side being relieved and also general discussion in the area about the new break board and how to work it. Aircraft X was observed climbing through his assigned altitude and creating a ca with aircraft Y. I issued a 20 degree left turn to aircraft X; told him to maintain 33000 feet and issued a traffic call. Aircraft X read back the clearance but reported they were at 34000 feet and would descend back down to 33000 feet. I then told aircraft Y to turn 20 degrees left. About 5 seconds later; aircraft X reported they were responding to an RA and they were in a climb. I asked aircraft X to report when they were done with the RA. Aircraft X reported level at FL350 right at 5 miles from aircraft Y and I then issued both aircraft clearances back on route.I believe that I was being asked to make several decisions at once while also trying to work traffic and with the line change with a new crew coming in; there were too many distractions that caused me to miss a readback from aircraft X.

Original NASA ASRS Text

Title: ZDV Controller missed an incorrect altitude readback from an aircraft due to distractions in the work area. The aircraft climbed into a conflict with opposite direction traffic.

Narrative: It was near the end of my shift; I was being told by the Controller In Charge (CIC) that the sector would be going red for about 20 minutes and was being asked if I wanted to keep a D-side (Assist Controller) or split out the upper portion of my airspace. About the same time; Aircraft X was checking on climbing out of Denver. I issued Aircraft X a clearance to 37000 feet after doing a quick scan. I then responded to the CIC that I would rather just keep a D-side. My D-side then brought my attention to the fact that Aircraft X was in conflict with Aircraft Y level at 34000 feet but had several minutes to fix the conflict.I issued an amended clearance to Aircraft X to maintain 33000 feet. About the same time I was being asked if I wanted a break. I told the CIC that I would rather stay on position until I was no longer needed in the area. Several more people were coming in and there was a lot of distractions with my D-side being relieved and also general discussion in the area about the new break board and how to work it. Aircraft X was observed climbing through his assigned altitude and creating a CA with Aircraft Y. I issued a 20 degree left turn to Aircraft X; told him to maintain 33000 feet and issued a traffic call. Aircraft X read back the clearance but reported they were at 34000 feet and would descend back down to 33000 feet. I then told Aircraft Y to turn 20 degrees left. About 5 seconds later; Aircraft X reported they were responding to an RA and they were in a climb. I asked Aircraft X to report when they were done with the RA. Aircraft X reported level at FL350 right at 5 miles from Aircraft Y and I then issued both aircraft clearances back on route.I believe that I was being asked to make several decisions at once while also trying to work traffic and with the line change with a new crew coming in; there were too many distractions that caused me to miss a readback from Aircraft X.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1366384
Time
Date	201606
Local Time Of Day	1201-1800
Place
Locale Reference	ZDV.ARTCC
State Reference	CO
Environment
Light	Daylight
Aircraft 1
Make Model Name	Large Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Climb
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Large Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 8
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance

ZDV controller missed an incorrect altitude readback from an aircraft due to distractions in the work area. The aircraft climbed into a conflict with opposite direction traffic.