Transcript PPT - Florida Institute of Technology

Beam Test Results for
a Large-area GEM Detector
Read Out with Radial Zigzag Strips
Aiwu Zhang,
V. Bhopatkar, M. Hohlmann, M. Phipps, J. Twigger
Dept. of Physics and Space Sciences,
Florida Institute of Technology
APS April meeting, Savannah, Georgia
08/04/2014
Outline
Motivation for the beam test
Large-area GEM detector & zigzag readout
Beam test setup at Fermilab
Basic characteristics of the GEM detector
Tracking & Resolution results
Summary
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Motivation
• The next QCD frontier can be explored at a new Electron-Ion Collider (EIC).
The proposed EIC candidates are eRHIC at BNL and MEIC at J-Lab.
• The FLYSUB consortium is performing R&D on tracking and particle ID with
GEM detectors at a future EIC detector.
• FLYSUB: FLorida Tech (FIT), Yale U., Stony Brook U., U. of Virginia and
Brookhaven National Lab. New members are joining into this consortium.
• The consortium conducted a joint beam test at Fermilab in October 2013.
• A 1-m long trapezoidal GEM detector with zigzag readout strips
designed by FIT was studied as an option for EIC forward tracking during
this beam test.
Conceptual design of
EIC detector
eRHIC
EIC at Brookhaven National Lab.
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Forward/backward
GEM trackers
EIC at Jefferson Lab. (MEIC/ELIC)
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Large GEM detector with zigzag readout
• CMS GE1/1-III GEM foils with trapezoidal
shape (1m long, 22-45cm wide) are used
8
7
6 5 4 3
-sectors
• Readout boards
Left: Zigzag strips designed by FIT
Right: Straight strips (for CMS upgrade).
2 1
Zigzag
strips
Zigzag strips (1.37mrad pitch)
•
1.37 mrad
•
0.1mm
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Straight
strips
Both zigzag and straight strips are radial:
strips develop in a fan-shape, full
opening angle for zigzag strips is 10°.
Eight sectors with 8 APVs (128 channels
each) fully read out; need only 1/3
electronic channels of std. CMS GE1/1-III
GEM detector (see Vallary Bhopatkar’s
talk at beginning of this session).
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Beam test setup at Fermilab
• 4 reference GEM detectors (trackers)
• Gas: Ar/CO2 (70:30)
• Beam: 25GeV, 32GeV mixed hadrons
(π, K etc.) and 120GeV protons
• Zigzag 3-GEM det. gaps: 3/1/2/1mm
Trackers
Trackers
1-m GEM w/ zigzag readout
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Basic performances of the zigzag GEM
Mean cluster size vs. HV on sector 5
(number of hits in a cluster)
Stat. errors smaller than marker size
Total cluster charge distribution
• Cluster size: number of strips in a
cluster. Mean cluster size value
increases exponentially with HV
(approximately).
• Cluster charge distribution fits well
to a Landau function.
• We find the typical increase of
“gain” with HV for the middlesector 5.
MPV value of charge distribution vs. HV
peak pos.
in sector 5 at 3200V
Stat. errors smaller than marker size
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Basic performances (cont.)
Charge in different sectors (uniformity)
Detection efficiency
• We scanned two positions on each sector from sector 1 to 7. From sector to sector
the response varies by 20%, which is probably caused by uneven foil gaps.
• Detector efficiency on sector 5 vs. HV can be fitted with a Sigmoid function.
• Different thresholds were compared: N sigma, N=3,4,5,6, where sigma is width of
pedestal distribution.
• Plateau efficiency with 5 sigma cut is (98.4 ± 0.2)%
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Tracking method for the zigzag GEM
Inclusive residual for 1st tracker
Resolution in ϕ for trackers
σ=21μrad
Aligning trackers to zigzag GEM det.
10°
X offset
Eta
5
REF
Det.
X
Y offset
vertex
Errors smaller than marker size
• After aligning the trackers to each other with shifts and rotations, they are giving
resolutions of 70μm or better (≈ typical spatial resolution for std. GEM detectors) in
both X and Y.
• The radial zigzag strips measure the azimuthal coordinate ϕ and have a pitch of
1.37mrad, so we study the resolution in natural polar coordinates (r, ϕ).
• Tracking in polar system was demonstrated to be working as well as in the Cartesian
system. The trackers have azimuthal resolutions around 30μrad.
• The ϕ resolution of the zigzag GEM detector can be studied if its vertex is taken as
the origin of the tracking system. (X,Y) offsets need to be found to align the tracker
origin to the vertex of the zigzag GEM detector.
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Three alignment checks for (X,Y) offsets
Track χ2 in ϕ vs. tracker X offset
for Y = -36.5mm
Residual mean should
be centered at 0
Minimal point gives
X = -1866.4mm
Inclusive residual width
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Residuals after the alignment
Inclusive residual
(zigzag GEM is
included in
track fit)
Exclusive residual
(zigzag GEM is
excluded from
track fit)
σ = 215μrad
σ = 270μrad
• After (X,Y) offsets are optimized, both inclusive and exclusive residuals are calculated for the
zigzag GEM detector.
• The residuals shown above are for sector 5 @3300V.
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Spatial resolution for the zigzag GEM
Resolution vs. HV in middle-sector 5
Resolution as a function of -sectors
• Left: Higher voltage, i.e. higher gas gain, gives better resolution as expected.
• Right: Resolutions in different sectors at 3200V. We observe similar azimuthal
resolutions (variation about 10%) in the first six sectors. Resolution in sector 7 is a
little worse; the reason is likely to be lower gas gain in that sector.
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Summary and Conclusion
• The zigzag strip readout method reduces the number of strips and
readout channels by a factor of 3 which reduces system cost.
• The FNAL beam test was successful. We operated 10 GEM detectors
including a large trapezoidal Triple-GEM with zigzag readout strips.
• The large-area zigzag GEM detector was working quite well. It had
high and stable gain, plateau detection efficiency of 98% and
spatial resolution of 241μrad (449μm) at 3300V.
• The resolution is expected to be improved further by also correcting
for the non-linearity of charge sharing between strips (response fct.)
• The structure of zigzag strips can be optimized to get even better
resolution. For example, the interleaving between zigs and zags can
be improved by industrial PCB factories to yield better charge sharing.
• We conclude that a zigzag GEM detector can be an option for the
cost-conscious construction of a forward tracker in an EIC detector.
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The FLYSUB consortium
We would like to acknowledge BNL
for the support of this work through the EIC RD-6 collaboration
and the staff of the FNAL test beam facility for all their help.
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Backup - EIC physics
• (inclusive or semi-inclusive) DIS is a powerful way to probe the internal
structure of nucleons
• Transverse Momentum Dependent parton distributions (TMDs) open a new
window to understand some of the most fundamental aspects of QCD
• Address the spin problem of the nucleon; illuminate the role played by
angular momentum of partons
• Two golden measurements on an EIC:
 3-d imaging of gluons and quarks, and their spins
 Di-jet measurements
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Backup- how to transfer resolution from μrad to μm
<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
66
UVA3
-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 almost the same as 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
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L
σy
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Backup – electronics, SRU
• The test beam took data for 60 APVs (128ch/ea.) simultaneously through
the Scalable Readout Unit (SRU).
• Data were taken with DATE and amoreSRS under Linux system.
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Backup -- Rotation
• The detector might be rotated a small angle
relative to the first tracker. The angle should
be close to 0 if alignment is correct.
Rotation of the Zigzag
detector should be
minimal at 0 if the
alignment is correct
rotation
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