Pixel Offline StudyJianchun 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 Tracksevent 480 1367 dump>tracksNumber of tracks formed: 2 Trk chi2 ndof chi2_t Hits pl hit pl hit ... 1 7.2 3 4.4 7 4 1 10 1 3 1 11 1 5 1 7 1 9 1 2 7.3 3 4.4 7 4 1 10 1 3 1 11 2 5 1 7 1 9 1

col = 9row=66

col = 9 row=68

Include a nearby Y hit

event 20424 212352 dump>tracksNumber of tracks formed: 8 Trk chi2 ndof chi2_t Hits pl hit pl hit ... 1 78.7 3 4.8 7 4 1 10 1 3 1 11 1 5 1 7 2 9 2 2 78.2 3 4.9 7 4 1 10 1 3 1 11 2 5 1 7 2 9 2 3 1.7 3 1.5 7 4 1 10 2 3 1 11 1 5 1 7 1 9 1 4 1.7 3 1.5 7 4 1 10 2 3 1 11 2 5 1 7 1 9 1 5 6.3 3 1.8 7 4 2 10 1 3 1 11 1 5 2 7 2 9 2 6 6.1 3 1.8 7 4 2 10 1 3 1 11 2 5 2 7 2 9 2 7 41.2 2 4.7 6 4 2 10 2 3 1 11 1 5 2 7 1 8 41.6 2 4.7 6 4 2 10 2 3 1 11 2 5 2 7 1

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 (1981-2538) are used to have a more uniform beam.

Dead cell (shown in magenta) is defined as less than 20% of average number of hits.

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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 tracksNon-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

Track row ID for left side extra hits Row ID of Track

Row

ID

of

Ext

ra H

it

Plane 5, FPIX1

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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

Col

umn

ID o

f E

xtra

Hit

Plane 5, FPIX1

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Extra Hits on Different Planes

Row ID of Extra hits – Row ID of track

Plane 3FPIX1

Plane 10FPIX1

Plane 9FPIX1

Plane 4FPIX1

Plane 5FPIX1

Plane 7FPIX2

Plane 11FPIX1

9

More Information on Plane 5

Nrow of Extra Cluster

in the Same ColumnNumber 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) ???