Fermilab Test Beam analysis for CMS GE1/1-III GEM detector

1. Fermilab Test Beam analysisfor CMS GE1/1-III GEM detector Aiwu Zhang, V. Bhopatkar, M. Hohlmann, M. Phipps, J. Twigger Florida Institute of Technology 25/03/2014

2. Outline • Motivation • Setup at Fermilab beam line • Data Analysis • Performances (gain, cluster size, etc.) • Detection efficiency • Tracking methods and resolution results • Summary Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

3. Motivation of beam test • Performance study for large-area GEM detectors: • Study a 1-m long trapezoidal GEM prototype (GE1/1-III) assembled at Florida Tech • Study zigzag-strip readout designed by Fl. Tech (not the topic of this talk). • We conducted a beam test at Fermilab in Oct 2013 and collected more than 3 million raw events. CMS GE1/1-III GEM detector: 1-m long, 22-45 cm trapezoidal detector. CMS muon upgrade with GEM detector Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

4. Fermilab beam test configuration CMS Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

5. Data taking & analysis • Data were collected with AmoreSRS package through SRU system, 60 apv25 chips (7680 channels) were read out simultaneously. • Data are also analyzed using AmoreSRS; cluster information was output into text files for further tracking analysis. • The entire CMS GE1/1 GEM detector needs 24 APVs, but we mounted 8 APVs (one APV on one eta sector) at one time and measured three different groups. Upper APV Middle APV position Lower APV Sector 8 Sector 1 Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

6. Beam profiles • We have measurements with pure 120GeV proton beam, and mixed hadron beam (energy points 20GeV, 25GeV, 32GeV). • Mixed hadron beam had an elliptical spot, ~6cm by 2cm size; pure proton beam spot was much narrower – a 1-2cm diameter circle. • Most of our raw data were taken with 32GeV mixed hadron beam. Mixed hadron beam (32GeV) 120GeV proton beam Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

7. Basic Characteristics of the GE1/1-III GEM detector 2. Cluster size (number of strips) 1. Cluster charge (in ADC counts) HV 3250V, APV in Middle sector 5 @32GeV beam Distribution fits well to a Landau function, MPV is 305 Mean cluster size vs. HV “gain” curve on sector 5: MPV value of above distribution vs. high voltage Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

8. Basic characteristics of the GE1/1-III GEM detector (cont’d) 3. Gain uniformity: variation of mpv. cluster charge vs. eta sector Time bin of max. signal amplitude. (3250V, Eta5) 4. Time bin characteristic: The DAQ was configured to record pulses over 9 time bins (25ns/bin) Mean Time bin vs. HV (Eta5) Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

9. Detector efficiency Efficiencies at 3,4,5,6 sigma (ped. width) cuts on strip charge Efficiencies with the same cut as applied to VFAT (Note: 10 VFAT units ~ 5 sigma) • Detector efficiency was measured in middle eta-sector 5 in 32GeV beam. • Different hit thresholds were applied to strip charges (N-sigma cut on pedestal width, N=3,4,5,6). • Efficiency vs. HV fits well to a sigmoid function. • Plateau efficiency ~ 97.8% (with 5 sigma cut). • With the same threshold as for VFAT(10,12,15), plateau efficiency is 97% Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

10. Tracking: Alignment of trackers • Tracking was done first for reference detectors to make sure that trackers were working properly. Also we found resolutions of the trackers in the process. • Only single-cluster events for each tracker were selected for tracking. • Our alignment method (two steps): • Firstshift the center of the detectors to the beam center • Then perform rotations in (X,Y) plane for the back three trackers, in order to put them in the same orientation as the first tracker. Shift was performed by iterating: (1) Look at residual distributions for straight-line fits on each X and Y plane, fit them with a double-Gaussian function and take the mean values (2) Shift positions by 20% of the mean values of the residuals (3) Repeat these steps until all mean residuals for the 4 trackers are less than 10μm Example: Shift in X for the first tracker Shift par. unit: mm Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

11. Tracking:Alignment of trackers – rotations Rotation of other three detectors relative to the first tracker. • Consider only rotation in XY plane (around Z axis). If detectors are fully aligned, the two coordinate systems have the same origin in XY plane. • An initial approximate rotation angle α could be calculated as most tracks are close to normal onto the detectors. • In the formula on the right, (x,y) are measured by 1st ref detector, (x’,y’) by the other detector (e.g. REF3). • Rotated angles after shift (these are the starting points for final optimization): • Once the angles are known, the positions in each detector can be corrected. In REF3 system In 1st ref. system sin(α) = (x’y – xy’)/(x^2 + y^2) Dist. of angle between 2nd and 1st ref. det. Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

12. Tracking:Alignment of trackers – rotation results Example: Avg. rotation angle for 2nd–1st: 3.9 mrad Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

13. Tracking:Alignment of trackers – rotation results Rotation angle for 3rd-1st: -17.35mrad (avg.) Rotation angle for 4th-1st: -48.5mrad (avg.) Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

14. Inclusive residuals in X for trackers 1st ref. 2nd ref. σ=36μm σ=54μm Double Gaussian Fits 3rd ref. 4th ref. σ=42μm σ=41μm Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

15. Inclusive residualsin Y for trackers σ=27μm σ=43μm σ=44μm σ=40μm Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

16. Exclusive residualsin X for trackers σ=134μm σ=77μm σ=88μm σ=91μm Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

17. Exclusive residualsin Y for trackers σ=99μm σ=62μm σ=73μm σ=92μm Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

18. Final resolutions for trackers Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

19. Transfer to polar coordinates Origin / vertex ~9.94° Y offset CMS Eta5 • CMS GEM detector has a trapezoidal shape with radial strips and measures ϕ. • We have measured its opening angle to be 9.94° directly from the pcb; the angle pitch between neighboring strips is a constant (0.453mrad). This angle is not exactly 10°; need to review r/o board design for the number (also need to be known and verified for next prototypes and final design). • It is most natural to study the CMS spatial resolution in azimuthal direction (ϕ) instead of in Cartesian coordinates (x, y). What we need to do is to choose the vertex (of CMS GEM) as the origin of the tracker system. • We did not measure the distance between vertex and beam center (it is also hard to measure), so we need to figure out the X and Y offsets for trackers from data in order to make the tracker origin match the CMS GEM detector vertex. REF Det. X X offset Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

20. Tracker - Inclusive residuals in “r” σ=69μm σ=46μm σ=55μm σ=59μm Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

21. Tracker - Inclusive residuals in “ϕ” σ=21μrad σ=31μrad σ=23μrad σ=25μrad Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

22. Resolutions in polar coordinates Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

23. Comparison of tracker resolutionsin Cartesian and polar coordinates • Resolutions in (x,y) are also calculated at this origin. • Resolutions in r are very close to resolutions in X. • The last column shows the calculated resolutions in y from resolutions in ϕ, they match with the measured resolutions in y. • Also, <x>≈<r> and <y>≈<ϕ>*L • Tracking in polar coordinates works well and gives high resolutions. σy σϕ L Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

24. Resolution studyfor CMS GE1/1-III GEM detector vertex ~9.94° Y offset CMS Eta5 REF Det. X X offset Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

25. X and Y offsets optimization Track  2 in ϕ versus X @ Y=-28mm Track 2 in ϕ versus X @ Y=-30mm Look at track χ2in ϕ in versus X offset, only between Y at -28mm and -30mm, it shows a parabolic curve. (Y beyond that range gives bad curves) Y=-29mm is taken as the optimized offset; we fit this curve, then we get optimized X offset at -1864mm. Track  2 in ϕ versus X @ Y=-29mm Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

26. Double check Y offsetand global rotation parameter Track Χ2 in ϕ versus Y @ X=-1864mm Minimum point gives Y=-29.1mm Double check Y offset, -29.1mm Consistent with -29mm on last slide. Rotation angle is near zero (28 μrad) Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

27. Resolutions for CMS GEM detectorat eta sector 5 Inclusive residual Exclusive residual σ= 86μrad σ= 111μrad • Inclusive (exclusive) residual widths are 86 (111) μrad or 160 (207) μm • Again form the geometric mean: • Resolution is 98 μrad or 182 μm. • This resolution is considerably better than the VFAT resolution (276μm) as expected for electronicsthat measures charge-sharing well Excl. residual from VFAT test beam in 2012 P. Barria Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

28. Resolution versus HV • Repeat same analysis for data sets taken with different HV applied to CMS GE1/1-III during HV scan. Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

29. Comparison of resolution and detection efficiency • Compare the resolution and efficiency vs. HV • The best spatial resolution is obtained when the detector is operated on the efficiency plateau (as expected) resolution efficiency Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014

30. Summary and outlook • The beam test at Fermilab was successful; the CMS GE1/1-III GEM detector and the tracking detectors performed very well. • GE1/1 GEM was stable with high detection efficiency (97.8%). • The response uniformity for eta sectors 7 and 8 were somewhat worse. This could be due to uneven gaps when stretching the foils. • Spatial resolution analysis in Cartesian and polar coordinates is working properly. • Current best measurement for spatial resolution for eta sector 5 is 98μrad or 182μm (at 3250V). Spatial resolution improves with increasing HV until plateau is reached. Future work: • Measure resolutions for other sectors of the GEM detector and position dependence (as fct. of r and ) • Do tracking with simulated VFAT clusters. • Study and correct for non-linear response of strips. Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014