Fermilab Test Beam analysisFermilab Test Beam analysisfor CMS GE1/1-III GEM detectorfor CMS GE1/1-III GEM detector

Aiwu Zhang, V. Bhopatkar, M. Hohlmann,

A.M. Phipps, J. Twigger

Florida Institute of Technology

25/03/2014

OutlineOutline

• Motivation

• Setup at Fermilab beam line

• Data AnalysisPerformances (gain, cluster size, etc.) Detection efficiencyTracking methods and resolution results

• Summary

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Motivation of beam testMotivation of beam test

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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.

Fermilab beam test configurationFermilab beam test configuration

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CMS

Data taking & analysisData 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.

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Sector 1Sector 8

Middle APV position

Upper APV

Lower APV

Beam profilesBeam profiles

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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

Basic Characteristics of Basic Characteristics of the GE1/1-III GEM detectorthe GE1/1-III GEM detector

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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 distributionvs. high voltage

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3. Gain uniformity: variation of mpv. cluster charge vs. eta sector

Basic characteristics of Basic characteristics of the GE1/1-III GEM detector (cont’d)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)

Detector efficiencyDetector efficiency

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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)

Tracking: Tracking: Alignment of trackersAlignment of trackers

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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 trackerShift 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

beam First_X First_Y Second_X Second_Y Third_X Third_Y Fourth_X Fourth_Y

120GeV

3.6876 1.852 -1.77 -2.43 -8.41 15.76 -17.53 -0.87

32GeV 10.72 1.018 6.289 -3.296 -1.418 14.95 -10.46 -1.443

Shift par.unit: mm

Tracking:Tracking:Alignment of trackers – rotationsAlignment of trackers – rotations

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In 1st 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 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.

Dist. of angle between 2nd and 1st ref. det.

2nd ref. 3rd ref. 4th ref.

9.5mrad -4.7mrad -24.7mrad

Rotation of other three detectors relative to the first tracker.

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Tracking:Tracking:Alignment of trackers – rotation resultsAlignment of trackers – rotation results

Example: Avg. rotation angle for 2nd–1st: 3.9 mrad

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Tracking:Tracking:Alignment of trackers – rotation resultsAlignment of trackers – rotation results

Rotation angle for 3rd-1st: -17.35mrad (avg.)

Rotation angle for 4th-1st: -48.5mrad (avg.)

σ=36μm σ=54μm

σ=42μm σ=41μm

InInclusive residuals clusive residuals in in X X for trackersfor trackers

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1st ref. 2nd ref.

3rd ref. 4th ref.

DoubleGaussian

Fits

InInclusive residualsclusive residualsin in Y Y for trackersfor trackers

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σ=27μm σ=43μm

σ=44μm σ=40μm

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σ=134μm σ=77μm

σ=88μm σ=91μm

ExExclusive residualsclusive residualsin in X X for trackersfor trackers

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σ=99μm σ=62μm

σ=73μm σ=92μm

ExExclusive residualsclusive residualsin in Y Y for trackersfor trackers

Final resolutions for trackersFinal resolutions for trackers

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Residual width (ex.) error Residual width (in) error Resolution (μm) error1st_X 134 1.9 36 0.5 69 1.42nd_X 77 1.1 54 0.7 64 1.23rd_X 88 1.1 42 0.9 61 1.54th_X 91 1.5 41 0.7 61 1.41st_Y 99 1.5 27 0.4 52 1.12nd_Y 62 1 43 0.7 52 1.23rd_Y 73 1.1 44 0.7 57 1.24th_Y 92 1.2 40 0.5 61 1.1

Transfer to polar coordinatesTransfer to polar coordinates

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REFDet. X

X offset

CMSEta5

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.

Tracker - Inclusive residuals in “r”Tracker - Inclusive residuals in “r”

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σ=46μm

σ=55μm σ=59μm

σ=69μm

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σ=21μrad σ=31μrad

σ=23μrad σ=25μrad

Tracker - Inclusive residuals in “Tracker - Inclusive residuals in “ϕϕ””

Resolutions in polar coordinatesResolutions in polar coordinates

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exclu. width Error inclu. width ErrorResolution

(geom. mean) Error UnitREF2_r 166 0.9 46 0.2 80 0.4

μmREF3_r 98 0.4 69 0.3 82 0.5UVA3_r 89 0.4 55 0.2 70 0.4REF1_r 137 0.5 59 0.2 90 0.5REF2_ϕ 75 0.3 21 0.1 39 0.2

μradREF3_ϕ 44 0.2 31 0.2 37 0.2UVA3_ϕ 38 0.1 23 0.1 30 0.2REF1_ϕ 56 0.2 25 0.1 38 0.2

Comparison of tracker resolutionsComparison of tracker resolutionsin Cartesian and polar coordinatesin Cartesian and polar coordinates

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<r>[μm] σr [μm] <ϕ>[μrad] σϕ[μrad] <x>[μm] σx[μm] <y>[μm] σy[μm] σy[μm]

REF2 3.6 46 4.2 21 3.7 46 9 45 45

REF3 -3.6 69 -5.7 31 -3.6 69 -12 69 66UVA

3 -11.6 55 -3.6 23 -11.6 55 -8 50 49

REF1 10 59 5 25 10 59 10 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, <x>≈<r> and <y>≈<ϕ>*L• Tracking in polar coordinates works well and gives high resolutions.

σϕ

σy

L

Resolution studyResolution studyfor CMS GE1/1-III GEM detectorfor CMS GE1/1-III GEM detector

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REFDet. X

X offset

CMSEta5

vertex~9.94°

X and Y offsets optimizationX and Y offsets optimization

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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 χ2 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.

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Track Χ2 in ϕ versus Y @ X=-1864mm

Minimum point gives Y=-29.1mm

Rotation angle is near zero (28 μrad)

Double check Y offsetDouble check Y offsetand global rotation parameterand global rotation parameter

Double check Y offset, -29.1mmConsistent with -29mm on last slide.

Resolutions for CMS GEM detectorResolutions for CMS GEM detectorat eta sector 5at eta sector 5

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Inclusiveresidual

Exclusive residual

σ= 86μradσ= 111μrad

Excl. residual from VFAT test beamin 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 wellP. Barria

Resolution versus HVResolution versus HV

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Repeat same analysis for data sets taken with different HV applied to CMS GE1/1-III during HV scan.

Comparison of resolution and Comparison of resolution and detection efficiencydetection efficiency

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• 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

Summary and outlookSummary 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.

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