the hermes recoil silicon detectorvertex2002/vprivate/stewart.pdf · 2002. 11. 8. · âuse an...

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


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


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


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


A Major Improvement in the HermesSpectrometer Is Needed!

The recoil protons need to bedetected!


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!


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!


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

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


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!


3D Model of the Recoil Detector


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


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


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


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


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.


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


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!


First Prototype Constructed

ZEUS MVD hybrid Sensor


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


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% - -


Present Status of Mechanical Design

SciFi Connector Holding Structure

Scattering Chamber

TargetCell

HERABeamline

TIGRESensors

Hybrid

CoolingCollimator


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!


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.

the hermes recoil silicon detectorvertex2002/vprivate/stewart.pdf · 2002. 11. 8. · âuse an...

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