Pixel Offline Study Jianchun Wang Syracuse University 11/05/04, Pixel testbeam meeting

2 Ghost Track Issue  By requiring that nplane_hit=7, cl_t>0.01, there are ~300 multiple track events out of ~10K events.  Each pair of tracks in the same event is checked to see if there are shared hits.  About ¾ are with 6 shared hits, only a small fraction are real multiple tracks.  It is difficult to separate ghost track from good one most of time. A safe way is to reject events with more than 1 good tracks ( ntrk_good = 1 ).

3 Example of Ghost Tracks event dump>tracks Number of tracks formed: 2 Trk chi2 ndof chi2_t Hits pl hit pl hit col = 9 row=66 col = 9 row=68 Include a nearby Y hit event dump>tracks Number of tracks formed: 8 Trk chi2 ndof chi2_t Hits pl hit pl hit Y hit exchange between two very close tracks. Most ghost tracks are due to that there is no strong constrain between Y planes and X planes.

4 Dead Cell Issue  When a track passes through or near a dead cell/edge, the hit position reconstructed may be wrong as the dead cell might have charge deposition.  Dead cells may result from bump bonding and thus can not be identified by pulse calibration.  10 runs ( ) are used to have a more uniform beam.  Dead cell (shown in magenta) is defined as less than 20% of average number of hits.

5 Effect of Dead Cell and Edge  If a track hit includes one pixel adjacent in row to a dead cell or edge of detector, both the track and the hit are tagged (dead_cell=1, survivor(iz)=1).  In run 1981, about 26% “good” tracks are tagged. The resolution of these tagged tracks are bad as expected.  For serious resolution study these tracks should be removed. Tagged tracks Non-tagged tracks All tracks

6 Unknown Hits For single column track hits I look for extra hits in the same column Track row ID for left side extra hits Row ID of Track Row ID of Extra Hit Plane 5, FPIX1

7 Column ID of Unknown Hits Extra hits tend to happen in the same column as the track hit. (only 1 good track allowed) Column ID of Track Column ID of Extra Hit Plane 5, FPIX1

8 Extra Hits on Different Planes Row ID of Extra hits – Row ID of track Plane 3 FPIX1 Plane 10 FPIX1 Plane 9 FPIX1 Plane 4 FPIX1 Plane 5 FPIX1 Plane 7 FPIX2 Plane 11 FPIX1

9 More Information on Plane 5 N row of Extra Cluster in the Same Column Number of Extra Clusters Whole Plane Same column

10 Possible Sources of These Hits 1)High threshold results in gap in one cluster, especially if there is delta ray. It appears on all planes regardless of threshold. The ADC value of these extra hits are not low, similar to others. 2)Secondary particles from interaction (where?) 3)Power or ground problem when there is a hit: less likely. 4)Readout generates hits that was not seen by the amplifiers: very unlikely. 5)Cross talk has been measured and is negligible. 6)???