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J Stewart Vertex 2002 1
The Hermes Recoil Silicon Detector
ââ Introduction Introductionââ Detector design considerations
Detector design considerationsââ Silicon detector overview Silicon
detector overviewââ TIGRE TIGRE microstrip microstrip sensors
sensorsââ Readout electronics Readout electronicsââ Test beam
resultsTest beam results
J. StewartDESY Zeuthen
DESY, Erlangen, and U. Glasgow
Vertex 2002
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J Stewart Vertex 2002 2
The HERMES Spectrometer
â Forward Spectrometer and the 27 GeV polarized e+/e- Hera
beam.â Large solid angle acceptance: |θx| < 170 mrad, 40 <
|θy| < 140 mrad.â Momentum resolution for charged particles ~1%
from 1 to 27 GeV.â Calorimeter resolution on the order of 5%.
Position ofRecoil Detector
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The Development of the Theory of GPDsHas Created a Great Deal of
Interest in the
Study of Exclusive Processes.
ââ GPDs go beyond the probability ofGPDs go beyond the
probability offinding a parton with momentumfinding a parton with
momentumfraction x.fraction x.
ââ Provide a unified description of awide variety of physics
processes.
ââ Measurements of exclusive photonMeasurements of exclusive
photonproduction is the best way to studyproduction is the best way
to studythe GPDs.the GPDs.
Deeply virtual Compton scatteringDVCS
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Limitations of the Existing Hermes Data
ââ missing mass resolution formissing mass resolution forDVCS
candidate events atDVCS candidate events atHERMES: notHERMES:
notsufficient to identifysufficient to identifyexclusive
eventsexclusive eventsindividuallyindividually
ââ at present: limited energyat present: limited energyand
position resolution atand position resolution atHERMESHERMES
ââ exclusivity only for a dataexclusivity only for a datasample
and not forsample and not forindividual eventsindividual eventsMx
resolution leads to negative values
2
e + p Y e + γ + p
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A Major Improvement in the HermesSpectrometer Is Needed!
The recoil protons need to bedetected!
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The Recoil Protons
â Lower momentum cutoff determined bymaterial between target and
detectorÈ Place detector in vacuum!È Silicon detectors
â 0.135 < p < 1.4 GeV/c RealisticÈ Energy deposited in 300
µm silicon:
4.5 MeV to 86 keVÈ Dynamic range of 50+!
â Cover as much of 2π in phi as possible
50 < p < 1400 MeV/c0.1 < θ < 1.35 rad(10 to 80
degrees!)2π in φ
Want good t resolution Y Low t behavior is important!
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Background Suppression
â The transverse momenta of all particles are of comparable
size.• Cuts based on the transverse momentum.• Transverse momentum
resolution needs to be better than 10%.• Angular resolution needs
to be better than 0.1 rad.
â Also cut on coplanarity.
Can achieve factor 5 in background suppression!
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J Stewart Vertex 2002 8
â Use an existing silicon microstrip detector design.• Financial
and time considerations preclude a custom design.
â Use the largest available double sided detector with less
than1 mm pitch.• Adjust the target length to match the size of the
silicon sensor.
â Minimize the material between the target gas and the
siliconsensor.
â Measure the particle momentum using the relation between
theenergy deposited in the silicon and the momentum.
â Cover as much of the 2π as possible.• HERMES has no coverage
below 40 mrad in θy.
Recoil Detector Sensor Design Criteria
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â 16 double sided sensors• each 99 mm × 99 mm
â 2 layer square tube orientation
â 76% Φ acceptanceâ 150 mm long target cellâ θ Coverage
• 0.4 < θ < 1.35 rad
Silicon Detector
Choose the TIGRE detector from MICRON semiconductor.
Readout Hybrid
TIGRESensor
Cooling
Target
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The Detector Coverageâ Deeply virtual Compton Scattering
(DVCS)â Combined Bethe Heitler and DVCSâ Protons from exclusive
ρ
productionâ Protons from delta excitation
â 135 < P[MeV/c] < 400â 400 MeV/c proton Y3 MIPâ Minimum
momentumâ Target + Flexfoil + 1st Siâ 135 < p < 250 MeV/c
PID
Silicon Coverage
Need additional detectorsfor full coverage!
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3D Model of the Recoil Detector
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TIGRE Silicon Sensors
Parameter ValueSensor Size 99 mm x 99 mmActive Area 97.3 mm x
97.3 mmSilicon Thickness 300 mmStrip Pitch 758 mmStrip Separation
56 mmCoupling Capacitance 1 nFTotal Strip Capacitance 25
pFPolysilicon bias resistor 50 MWDepletion voltage 50 V MaxP-Stop
TechnologySingle Guard Ring
Micron has produced detectors with7 MΩ polysilicon for
HERMES
Manufacturer: Micron SemiconductorManufacturer: Micron
Semiconductor
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Measurements of Sample TIGREs
Parameter Value
Single strip leakage current 40 nADepletion voltage 40 VCoupling
capacitor 1.2 nF
Total strip capacitance 30 pFInterstrip capacitance 8 pF
Polysilicon bias resistor >60 MΩ
New sensor 7 MΩ
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Readout Electronics
â Used for the HERMES VC.â Can select between high and
low gain.â Neither pattern generator
nor ADC available.
â Used for the HERMESLambda Wheels
â Dynamic range a problem.â Both the pattern generator
and ADC are available.
â A pipeline chip is needed to accommodate the HERMES trigger.â
A dynamic range of 70 ( 280 fC).â 10 MHz readout to match the HERA
frequency.â Prefer a chip already used in HERMES.
Chip Selection Criteria:
APC HELIX
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Helix 128 - 3.0
â 0.8 µm CMOS process.â 10 MHz sampling frequency.â128 input
channels.âAnalog pipeline 141 cells deep.
âPreamp-Shaper good noise char. âRadiation tolerant 220 krad.
âDynamic range
+/- 40 fC or +/- 10 MIP
Designed by the ASIC lab. at the University of Heidelberg.
Preamp Shaper Buffer
Pipeline Pipeamp MUX
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First Tests Using Charge Injection
â Use an old Zeus MVD Hybridâ Connect the Helix via Zeus
pitch
adapter to a general purpose pitchadapter.
â Capacitively couple an input pulse.â Readout with the Zeus
laser test
stand.
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Helix Response
1 “MIP” =24,000 e-/h+/- “MIP”=Pos/Neg charge
on preamp
Conclusions:
âLinear response over+/-10 “MIP”
âSaturated at ~15 “MIP”
As Expected
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J Stewart Vertex 2002 18
Readout Conceptual Design
âCapacitive coupling readout.âDoubles number of channels.
•32 Y64 Helix 3.0.âCan adjust dynamic range.
70 MIP Possible!
Proposed by W. Lange
Charge Division!
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First Prototype Constructed
ZEUS MVD hybrid Sensor
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DESY2 Test Beam
high gainchannel
low gainchannel
â First silicon prototype module has been tested in 1 GeV
electron beam.• 50% charge collection efficiency due to large
sensor capacitance (30 pF).• Signal to noise ratio of > 6.5 for
a 1 MIP particle.• Indicates we can measure particles depositing
energy up to 140 MIP.
Landau Fit Landau + Gaussian Fit
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Results of Charge Division Studies
ââ CCeffeff can be calculated from the difference in slopes for
high and low gain can be calculated from the difference in slopes
for high and low gainusing charge injection. Cusing charge
injection. Ceffeff = 25 pF = 25 pF•• (agrees fairly well with
published numbers C(agrees fairly well with published numbers
Ceffeff = 31 pF) = 31 pF)
Charge Injection Test BeamCc (pF) Qhigh Qlow Qhigh Qlow22 67%
33% 72% 28%10 78% 22% 82% 18%4.7 86% 14% - -
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Present Status of Mechanical Design
SciFi Connector Holding Structure
Scattering Chamber
TargetCell
HERABeamline
TIGRESensors
Hybrid
CoolingCollimator
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Next Steps
â Set up a test stand using the HERMES pattern generatorand
ADC.
â Test the components to be used for the first
readouthybrid.
â Test the needed Helix 3.0 chips.â Design the layout and
manufacture the first hybrid.â Assemble the first real module.â
Vacuum Testing.â TEST BEAM
â ⋅ ⋅ ⋅⋅ ⋅ ⋅Hope to be ready for installation in spring
2004!
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J Stewart Vertex 2002 24
SummaryâResponse of both the HELIX 3.0 and APC readout chips
to large pulses has been measured.â First prototypes have been
constructed and tested in test
beam.âReadout using charge division has been shown to work.
• 50% charge collection due to large sensor capacitance.• S/N
for 1 MIP is 6.5.• With a 5 pF coupling capacitor, it may be
possible to measure
particles depositing 140 times the energy of a 1 MIP.
âHELIX 3.0 chosen for readout.â Work has started on our first
readout hybrid.âA test stand is under construction at DESY
Zeuthen.