GE1/1-III GEM Cluster S ize and Resolution S tudies with the FNAL Beam T est D ata

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GE1/1-III GEM Cluster S ize and Resolution S tudies with the FNAL Beam T est D ata

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GE1/1-III GEM Cluster S ize and Resolution S tudies with the FNAL Beam T est D ata

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GE1/1-III GEM Cluster Size and ResolutionStudies with the FNAL Beam Test Data

Aiwu Zhang, Vallary Bhopatkar, Marcus Hohlmann

Florida Institute of Technology

CMS GEM workshop IX

14-18/07/2014

- Current data analysis status from the FNAL beam test
- Cluster size (number of strips in a cluster) studies
- Resolution results
- Summary and next plans

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

- Finished basic characteristics: cluster charge distributions, gain curve, detection efficiency, etc.
- Implemented spatial resolution study method in polar coordinates.
- This talk presents the cluster size studies and resolution results, with HV scan data in middle-sector 5 and position scan data in middle position of each sector. Note analog pulse information are decoded from APV chips.

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

HV scan in middle sector 5

Position scan in middle sectors at 3250V

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

4σ threshold

3σ threshold

5σ threshold

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

N=1

N=2

N=3

N=4

N>=5

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

4σ threshold

3σ threshold

5σ threshold

- Majority of the events have cluster size 2 and 3.

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

N=1

N=2

N=3

N=4

N>=5

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

- We study resolution in polar coordinates (φ) due to the trapezoidal shape and radial strips. We use the vertex as origin and align the trackers by finding the X, Y offsets. (rotation of the GEM is also taken into account, not shown here.)

vertex

9.94°

Y offset

tracker

Eta5

X offset

Step 2. Fix a Y offset, loop over X offset with a step 1mm; we find another pair of (X,Y) from the minimal of the parabola of residual sigma.

Step 1. Fix an X offset, loop over Y offset with a step 0.2mm; we get a pair of (X,Y) by requiring residual mean equals to 0.

We assume that any misalignment will shift peak of residual distribution away from zero and give larger residual width (or make distribution wider)

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

σ=138μrad

σ=110μrad

Exclusive residual

Inclusive residual

Exclusive (inclusive) residuals at 3250V in sector 5 (from HV scan data)

Cluster size in GEM and trackers all >0.

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

Resolution vs. HV in middle-sector 5

Resolution vs. sector at 3250V

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

- Centroid position distribution from COG method (in middle-sector 5).

N=2

N=3

- From the centroid position distributions of fixed cluster sizes N=2 and 3, we observe that they have apparent bumps around each strip. For N=2, the positions in the middle of two neighboring strips; for N=3 the positions in the strip. (note we define the position of a strip in its center.)
- This brings us to study the non-linear strip response of charge distribution on position reconstruction, and hence to flat these distributions.

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

h(η2) distribution

h(η3)

distribution

Correction function

for 3-strip events

Correction function

for 2-strip events

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

HV scan data @ 3250V

N=2

Before correction

After correction

N=3

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

HV scan on middle sector 5

N=3

N=4

N=2

Position scan

at 3250V

N=3

N=4

N=2

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

All valid events with cluster sizes 2,3,4

N=2

N=3

N=4

Resolution is not improved after position correction with HV scan data!

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

N=2

All valid events with cluster sizes 2,3 and 4

N=3

N=4

Resolution is not improved after position correction with position scan data!

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX

- Most of the clusters have sizes no more than 5.
- Spatial resolution is on the order of 120μrad.
- We don’t observe improvement on resolution after applying cluster position correction.
- What else can be done with these data (HV scan, position scan in middle sectors):
- Study details of cluster size distributions using VFAT-like strip hits.
- Apply position correction a second time to flatten position distributions even more and to see if resolution could be improved.
- Study resolution with different thresholds.
- What needs to be done with other data:
- We also performed two position scans with the detector tilted by 7degrees from normal incidence. The effect of the inclination needs to be studied.

THANKS!

A. Zhang et al., GE1/1-III GEM Studies with FNAL Beam Test Data, GEM workshop IX