of Largearea GEM Detectors for a Forward Tracker at a Future ElectronIon Collider Experiment Aiwu Zhang Vallary Bhopatkar Marcus Hohlmann Florida Institute of Technology FIT Kondo Gnanvo Nilanga Liyanage ID: 293950
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Study of Large-area GEM Detectorsfor a Forward Tracker at a Future Electron-Ion Collider Experiment
Aiwu Zhang, Vallary Bhopatkar, Marcus HohlmannFlorida Institute of Technology (FIT)Kondo Gnanvo, Nilanga LiyanageUniversity of Virginia (U.Va)for the EIC RD6-FLYSUB Consortium
Electron Ion Collider Users Meeting
June 24-27, 2014 at Stony Brook University, NYSlide2
ContentsMotivations (will skip)FIT 1-m size zigzag GEM detectorU.Va 1-m size u-v strip GEM detectorBeam test configuration at FermilabBeam test results of the zigzag GEM detectorBeam test results of U.Va’s GEM detector
SummaryA. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC6/27/20142Slide3
Zigzag-strip GEM @ FIT
Zigzag strips, 1.37mrad pitch
0.1mm
1
2
3
4
5
6
7
8
-sectors
1.37
mrad
The zigzag strips run in radial direction and can measure the azimuthal direction. Opening angle is 10 degrees,
angle pitch 1.37mrad
.
The readout board is designed to fit a 1-m long trapezoidal GEM
prototype (originally for CMS
muon
upgrade).
It is divided to 8
η
-sectors with radial length of each sector ~12cm, and
128 strips/sector
.
For the same GEM prototype with straight strips, 24 APV chips are needed to fully read out the chamber. In the zigzag case, only 8 APV chips can fully read out the entire chamber. This means 2/3 electronic channels can be saved.We use self-stretch technique so that GEM foils can be changed easily.
0.5mm
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/2014
3Slide4
Pitch
= 550 mm,
T
op
strips = 140
m
m,
Bottom strips = 490
m
m
12°
2D u/v readout strips
Entrance window
Drift region
Transfer region
Transfer region
Induction region
spacers
Gas inlet
Gas
outlet
2D readout board on Honeycomb support
Cross section of low mass triple GEM
6/27/2014
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
4
2D u/v strip GEM @
U.Va
100 cm
22 cm
44 cm
Key characteristics:
Largest GEM detector with 2D readout ever build
Low mass (narrow edge and honey comb support) and small dead area
Fine strips 2-dimensional flexible small stereo angle u/v
readout so that good spatial resolution can be achieved, and with low capacitance noise
Gluing technique is used so that GEM foils can not be changedSlide5
Beam test setup @ FNAL
zigzag GEM and
U.Va
GEM
Trackers
Trackers
The RD6-FLYSUB consortium conducted a three-week beam test at
Fermilab
(Meson Test area 6, MT6) in Oct 2013,
operated
20
GEM detectors
.
The FIT group and
U.Va
group tested
10 GEMs as a tracking system
.
4 reference detectors (3/2/2/2mm gaps); the
zigzag GEM gaps: 3/1/2/1
mm;
Ar
/CO
2
(70:30) was used to operate all the detectors.
DAQ: RD51 SRS with SRU to read out 4FECs/64APVs simultaneously.
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/2014
5Slide6
Beam test results of the zigzag GEM– basic performances
Cluster charge distribution in sector 5 at 3200V
MPV value of charge distribution vs. HV
Stat.
e
rrors smaller than marker size
peak pos.
Cluster
charge distribution
fits well to a Landau function.
Mean
cluster size
(number of fired strips in one event) from each cluster size distribution shows approximately exponential dependence on HV.
Mean cluster size vs. HV on sector 5
(number of hits in a cluster)
Stat.
e
rrors smaller than marker size
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/2014
6Slide7
Beam test results of the zigzag GEM– basic performances (cont.)Detection efficiency in middle-sector 5. Fitted with a sigmoid function, plateau efficiency ~98.4%.Different thresholds (N=3,4,5,6 times of pedestal
width σ) were tested, the efficiency plateau is not affected by thresholds.
On each sector, two points were measured. The response from sector to sector varies by ~20%.
The
non-uniformity
could be caused by bending of the drift board. The CMS-GEM group is
investigating this aspect to avoid bending after chambers are assembled.
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/2014
7Slide8
Beam test results of the zigzag GEM – spatial resolution studiesThe zigzag strips measure the azimuthal coordinate φ.
Angle pitch between two strips is 1.73mrad. So we study its spatial resolution in polar coordinates.Spatial resolution is calculated from the geometric mean of exclusive and inclusive residual widths:
. Exclusive (Inclusive) means the probed detector is excluded (included) when fitting the tracks.
The trackers are aligned first and their spatial resolutions in (x, y) are found to be around 70
μ
m, which is the typical resolution of a standard triple-GEM. Their resolutions in
φ
coordinate are then calculated to be 30-40
μ
rad.
X offset
Eta5
vertex
10°
Y offset
Aligning trackers to zigzag GEM det.
σ
=21
μ
rad
Inclusive residual for 1
st
tracker
Resolution in
φ
for trackers
Errors smaller than marker size
tracker
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/2014
8Slide9
Beam test results of the zigzag GEM– spatial resolution studies (cont.)A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC6/27/20149
Exclusive residual
σ
=281
μ
rad
Inclusive residual
σ
=223
μ
rad
Residual distributions of the zigzag GEM in middle-sector 5 at 3350V
Hit positions are calculated with
Center of Gravity (COG)
method, and all
cluster size >0 events
are used.
Resolution is
for this case.
Note that the resolution in number of strips is about ~18%
Slide10
Beam test results of the zigzag GEM– spatial resolution studies (cont.)
Resolution of the zigzag-GEM vs. HV in middle-sector 5.At highest tested voltage, resolution is ~240μrad.If only use 2-strip events, resolution is smaller (especially at lower voltages).
Resolution of the zigzag-GEM on different sectors at 3200V
(without cluster size cut).
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/2014
10Slide11
Beam test results of the zigzag GEM– cluster position correctionBy further checking the centroid position distributions of fixed cluster size events, we observe that these distributions have apparent bumps around each strip.
This brings us to study the non-linear strip response of charge distribution on position reconstruction, and hence make these distributions flat.A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC6/27/2014
11
Centroid position distribution from COG method (in middle-sector 5).
2-strip events
3-strip eventsSlide12
Beam test results of the zigzag GEM– cluster position correction (cont)
The idea is to build strip response functions for different cluster sizes (
η
-algorithm
).
, is defined as the centroid position (in strip units) minus the center of strip with maximum charge.
The
position correction functions
can be calculated:
.
h(
η
2
)
distribution
h(
η
3
)
distribution
Correction function
for 2-strip events
Correction function
for 3-strip events
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/2014
12Slide13
Beam test results of the zigzag GEM– cluster position correction (cont.)
After correction functions are figured out, the centroid position of an event can be corrected. Only clusters with 2,3 and 4 strips are because of better statistics (they make up ~90% of all clusters on the efficiency plateau).
2-strip before correction
2-strip after
correction
3
-strip before correction
3
-strip after correction
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/2014
13Slide14
Beam test results of the zigzag GEM– spatial resolution after correction
After position correction, we observe that resolution gets improved at higher voltages (to ~170μrad).Resolution vs. HV in middle-sector 5 after positions are corrected (with 2, 3, 4-strip events)
The results give us a clue that strip response correction is affected by
gas gain
and
incident angle of particles
.
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/2014
14Slide15
ADC Charges distribution
Efficiency vs. HV
Nb
of strips /cluster vs. HV
P1
P3
P2
P4
P5
Position scan with 32 GeV hadron
beam
Spatial resolution in (r,
) at different location in the chamber
6/27/2014
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
15
Performances of the
U.Va
GEMSlide16
Gas input
Gas out
Top Entrance window
Bottom gas window
6/27/2014
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
16
4 new ideas from
U.Va
towards a lighter, better resolution GEM detector
Ultra low mass chamber to minimize multiple scattering and background
“Re-
openable
” chamber – without gluing GEM foils
“mini-drift” GEM tracker to improve spatial resolution at large angle tracks
All readout electronics arranged at the outer edge of the chamber, to further reduce dead area and get better radiation hardness.Slide17
Summary on the zigzag GEMThe zigzag-GEM detector worked well in the beam test at FNAL.The 98% detection efficiency is good. The gain uniformity needs to be further investigated.Corrections for non-linear strip responses bring the resolution from ~240
μrad down to ~ 170μrad on the eff. Plateau, which could be transferred to 170μm at R=1m. The zigzag
structures
can probably still be optimized by interleaving
zigs
and
zags
more to improve resolution performance even further.
We conclude that a readout with zigzag strips is a viable option for
cost efficient
construction for a forward tracker
with GEMs
.
The
U.Va
u/v strip GEM detector also performance well in the beam test.
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/2014
17Slide18
Summary on the dedicated EIC forward tracker with GEMsBoth FIT and U.Va groups have experience on building and operating large-area GEM detectors.
U.Va group has experience on low-materials for drift and readout; FIT group constructs GEMs without gluing foils, and are pursuing a optimized cost effective zigzag readout structure.We are joining forces with Temple U.
in
designing and constructing
a
dedicated GEM
prototype for the EIC forward
tracker
, which goes to even higher eta regions in the forward region.
We plane to work
out e
ntirely
domestically sourced
GEM
foils
(see
the next talk from Temple U. group
).6/27/2014
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC18Slide19
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.
Thanks!
The FLYSUB consortium
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/2014
19Slide20
Back up – align the zigzag detector
X offset
Eta5
vertex
10°
Y offset
Aligning trackers to zigzag GEM det.
tracker
At a fixed Y offset, check residual sigma and chi-2
Residual sigma vs. X offset
Chi2 vs. X offset
At a fixed X offset, check residual mean and chi-2
Residual mean
vs. Y offset
Chi2 vs. Y offset
After checked (X,Y) groups in reasonable ranges, an intersecting point can be found from the scattering plot.
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
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20Slide21
Back up - referencesReferences on the strip response correction:CERN-Thesis-2013-284 by Marco Villa.G. Landi, NIMA 485 (2002) 698; NIMA 497 (2003) 511Reference about inclusive and exclusive residual studyR. K. Carnegie, NIMA 538 (2005) 327
6/27/2014A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC21Slide22
Motivation
Conceptual design of EIC detectorForward/backward GEM trackers
The
RD6-FLYSUB consortium
is jointly working on
tracking and particle ID
,
based on the
Gaseous Electron Multiplier (GEM)
technique,
for a future EIC.
The
zigzag-strip readout
structure is proposed and under study by Florida Tech to make the forward tracker much
less costly
.
Each zigzag strip occupies more space than a straight strip so that the total readout channels can be reduced and hence reduce the cost significantly, while
good spatial resolution can be conserved because of charge sharing on these
zigs and zags.
A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC
6/27/201422
Example of zigzag strips
2.5mm