# Presentation: 817770

## Noise Studies in EndcapA for Run 1129

- Kevin Lung
- Ana Ovcharova, Boyan Tabakov, Wei-ming Yao, Jim Siegrist, Hemma Mistry

## Noise Occupancy

- The noise occupancy is defined as the number of pixel hits per event readout for a pixel. These pixel hits are outside the range of typical cosmic rays (|BCID-5|≥2).
- Pixels with a noise occupancy above ~8×10-6 are characterized as hot pixels, which demonstrate the presence of noise i.e. pixels hit regularly through the run with a signal outside the typical BCID range.

## Noise Occupancy

- Note: The threshold can be redefined later after initial studies.

## Module Occupancy

- The module occupancy is defined as the number of hot pixel hits per module per event readout.
- The goal of this study is to measure and minimize the  module occupancy for pixel hits outside the cosmic BCID range of 4,5,6 to achieve the most noise suppression.
- Compare the module occupancy to simulated data of the MC as well.

## Module Occupancy

- There is a large fluctuation of module occupancy among the BCID hits outside the cosmic range.

## Hot Pixels per Module

- Modules 34 and 128 show a much larger concentration of hot pixels.

## Hot Pixels

- Of the approximately six million pixels of the endcap, 1547 were characterized as being hot pixels (~.023%).
- Several modules stand out as having a large number of hot pixels – module 34 of layer 0 and module 32 of layer 2.  Of the 1547, these two modules have 1113 of the total hot pixels.

## Location of Hot Pixels

- The random distribution of these pixels within individual modules is characteristic of noise.

- Layer 2 Module 32

- Layer 0 Module 34

## Hot Pixel Proximity

- Most hot pixels occur in close proximity to other hot pixels showing a tendency towards clusterization.
- After removal of the two modules with a larger number of hot pixels, the clusterization trend is still observable.

- Without modules 34 and 128

## Consistency across Runs

- Run 1125 has 1510 hot pixels.  Out of these 1510, only 68 are not characterized as hot in the 1547 of Run 1129.
- Run 1121 has 1482 hot pixels while only 60 are not characterized as hot in Run 1129.
- There is only about a ~4% difference in hot pixels per run, which validates the idea that these pixels are indicative of noise.

## BCID Study

- Once the hot pixels have been quantified, the BCID of all pixel hits of the hot pixels shows a relative noise spectrum across all BCIDs.
- On the other hand, pixels not defined as hot show a clear peak around BCID=5.  The relative noise level has been removed, but there are still random noise hits not yet characterized.

## BCID Study

**Hot Pixels**

**Cold Pixels**

- Shows the relative noise level across all BCIDs

- Shows the peak at BCID = 5 of a cosmic muon signal

## Removal of Hot Pixels

- Once hot pixels are removed, the resulting module occupancies for pixel hits outside the BCID = 4,5,6 range is measured to be ~ 10-10 .
- The remaining pixel hits are also consistent across modules for each BCID range presented.

## Module Occupancy After Removal

- Removing hot pixels improves consistency across all BCID ranges

## Comparison to MC

- For Run 1129, the module occupancy for pixel hits outside the cosmic data range was ~ 10-10.
- For the MC simulation, the module occupancy is on the order of 10-7 as shown below.

## Cause for Concern?

- The very small percentage of hot pixels suggests that only a small portion of the relevant data will be lost if these pixels are removed from the data set.
- It is also important to determine if these pixels are contained within any of the track clusters to see if their removal impacts the track reconstruction.

## Special Pixel Map

- Of the 1547 hot pixels, 319 pixels are present on “good” modules i.e. ones that are not disabled or characterized as noise modules.
- Comparing the 319 pixels to the special pixel map, 295 are found to be contained in the special pixel map.

## Special Pixel Map

- Most of the special pixels are in the 11-14 range with some in the 25-28 range.

- Each bit relates to the user a different piece of information about how the pixel is operating.

- 11- Dead with particles
- 12- Low efficiency with particles
- 13- Threshold not tunable (analog dead)
- 14- ToT not tunable
- 25-28 relate special pixels to each other in order to see if there is a clustering trend among these types of pixels

## Track Studies

- After removal of noisy modules and disabled modules, there are a total of 15369 tracks.
- Removing the tracks with hot pixels and those with clusters completely made of BCID hits outside 4,5,6 range results in 15307 tracks.
- The percentage of tracks removed is ~.01%.
- Tracks with clusters having a BCID hit outside 4,5,6, but also with a pixel hit in range were not removed because the ToT of the clusters in these tracks showed the characteristic ToT curve in general.

## Track Studies - ToT

- Shows ToT of the bad clusters

- Shows ToT of clusters with a combination of bad and good hits

- Shows ToT of all pixel hits on tracksThe combination of bad and good hits has a trend similar to this graph, suggesting that the combination clusters are reconstructed poorly

- On the other hand, the ToT of the bad clusters appears to be random, suggestive of noise

## Overlap Efficiency 

- Previously, the overlap efficiency was quoted to be 98.83% for disk 1, 99.40% for disk 2, 99.69%.
- After the 62 bad tracks are removed, the efficiency increases by about 0.15% for each disk to 99.10% for disk 1, 99.54% for disk 2, and 99.84% for disk 3.
- This is a large increase in efficiency for removing only 0.01% of the tracks.

## Conclusion

- Removal of hot pixels reduces the module occupancy to ~10-10 causing only minimal information loss through bad tracks.
- A relative noise level across all BCID’s is present as shown on slide 12, but other modifications must be made to rid cold pixels of random noise hits.
- Most of the hot pixels have already been characterized through the special pixel map and should be analyzed further.
- The special pixel map serves as a guide for distinguishing hot pixels, but should not be used exclusively because the map will need to be redefined occasionally to account for additional hardware errors when the machine becomes operational.
- The module occupancy for Run 1129 compared to MC is lower, which is expected because of the larger number of event readouts.
- Other definitions of noisy pixels should be tested extensively to see if they provide improved results.