1. Fermilab Test Beam analysis for CMS GE1/1-III GEM detector Aiwu Zhang, V. Bhopatkar, M. Hohlmann, A.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 2

3. Motivation of beam test Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 3 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 muon upgrade with GEM detector CMS GE1/1-III GEM detector: 1-m long, 22-45 cm trapezoidal detector.

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

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. Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 5 Sector 1Sector 8 Middle APV position Upper APV Lower APV

6. Beam profiles Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 6 Mixed hadron beam (32GeV)  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. 120GeV proton beam

7. Basic Characteristics of the GE1/1-III GEM detector Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 7 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 2. Cluster size (number of strips) Mean cluster size vs. HV “gain” curve on sector 5: MPV value of above distribution vs. high voltage

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

9. Detector efficiency Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 9  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% 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)

10. Tracking: Alignment of trackers Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 10  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):  First shift 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. Example: Shift in X for 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 beamFirst_XFirst_YSecond_XSecond_YThird_XThird_YFourth_XFourth_Y 120GeV3.68761.852-1.77-2.43-8.4115.76-17.53-0.87 32GeV10.721.0186.289-3.296-1.41814.95-10.46-1.443 Shift par. unit: mm

11. Tracking: Alignment of trackers – rotations Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 11 In 1 st ref. system In REF3 system sin(α) = (x’y – xy’)/(x^2 + y^2) 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 1 st 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. Dist. of angle between 2 nd and 1 st ref. det. 2 nd ref.3 rd ref.4 th ref. 9.5mrad-4.7mrad-24.7mrad Rotation of other three detectors relative to the first tracker.

12. 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 2 nd –1 st : 3.9 mrad

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

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

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

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

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

18. Final resolutions for trackers Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 18 Residual width (ex.) error Residual width (in) error Resolution (μm) error 1 st _X1341.9360.5691.4 2 nd _X771.1540.7641.2 3 rd _X881.1420.9611.5 4 th _X911.5410.7611.4 1 st _Y991.5270.4521.1 2 nd _Y621430.7521.2 3 rd _Y731.1440.7571.2 4 th _Y921.2400.5611.1

19. Transfer to polar coordinates Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 19 REF Det. X X offset CMS Eta5 Origin / vertex ~9.94°  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. Y offset

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

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

22. Resolutions in polar coordinates Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 22 exclu. width Error inclu. width Error Resolution (geom. mean) ErrorUnit REF2_r1660.9460.2 80 0.4 μmμm REF3_r980.4690.3820.5 UVA3_r890.4550.2 70 0.4 REF1_r1370.5590.2 90 0.5 REF2_ ϕ 750.3210.1390.2 μrad REF3_ ϕ 440.2310.2370.2 UVA3_ ϕ 380.1230.1 30 0.2 REF1_ ϕ 560.2250.1380.2

23. Comparison of tracker resolutions in Cartesian and polar coordinates Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 23 [μm]σ r [μm] [μrad] σ ϕ [μrad] [μm]σ x [μm] [μm] σ y [μm] REF23.6 46 4.2 21 3.7469 45 REF3-3.6 69 -5.7 31 -3.669-12 69 66 UVA3-11.6 55 -3.6 23 -11.655-8 50 49 REF110595 25 105910 55 53 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, ≈ and ≈ *L Tracking in polar coordinates works well and gives high resolutions. σϕσϕ σyσy L

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

25. X and Y offsets optimization Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 25 Track  2 in ϕ versus X @ Y=-30mm Track  2 in ϕ versus X @ Y=-28mm Track  2 in ϕ versus X @ Y=-29mm Look at track χ 2 in 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.

26. Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 26 Track Χ 2 in ϕ versus Y @ X=-1864mm Minimum point gives Y=-29.1mm Rotation angle is near zero (28 μrad) Double check Y offset and global rotation parameter Double check Y offset, -29.1mm Consistent with -29mm on last slide.

27. Resolutions for CMS GEM detector at eta sector 5 Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 27 Inclusive residual Exclusive residual σ= 86μrad σ= 111μrad Excl. residual from VFAT test beam in 2012 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 electronics that measures charge-sharing well P. Barria

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

29. Comparison of resolution and detection efficiency Aiwu Zhang et al., FNAL Test Beam Analysis / CMS GEM Workshop VIII, March 2014 29 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

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 30