The Hermes Recoil Silicon Detector

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1 The Hermes Recoil Silicon Detector Introduction Detector design considerations Silicon detector overview TIGRE microstrip sensors Readout electronics Test beam results Vertex 2002 J. Stewart DESY Zeuthen DESY, Erlangen, and U. Glasgow J Stewart Vertex

2 The HERMES Spectrometer Position of Recoil Detector Forward Spectrometer and the 27 GeV polarized e + /e - Hera beam. Large solid angle acceptance: θ x < 170 mrad, 40 < θ y < 140 mrad. Momentum resolution for charged particles ~1% from 1 to 27 GeV. Calorimeter resolution on the order of 5%. J Stewart Vertex

3 The Development of the Theory of GPDs Has Created a Great Deal of Interest in the Study of Exclusive Processes. GPDs go beyond the probability of finding a parton with momentum fraction x. Provide a unified description of a wide variety of physics processes. Measurements of exclusive photon production is the best way to study the GPDs. Deeply virtual Compton scattering DVCS J Stewart Vertex

4 Limitations of the Existing Hermes Data 2 M x resolution leads to negative values e + p Y e + γ + p missing mass resolution for DVCS candidate events at HERMES: not sufficient to identify exclusive events individually at present: limited energy and position resolution at HERMES exclusivity only for a data sample and not for individual events J Stewart Vertex

5 A Major Improvement in the Hermes Spectrometer Is Needed! The recoil protons need to be detected! J Stewart Vertex

6 The Recoil Protons 50 < p < 1400 MeV/c 0.1 < θ < 1.35 rad (10 to 80 degrees!) 2π in φ Lower momentum cutoff determined by material between target and detector È Place detector in vacuum! È Silicon detectors < p < 1.4 GeV/c Realistic È Energy deposited in 300 µm silicon: 4.5 MeV to 86 kev È Dynamic range of 50+! Cover as much of 2π in phi as possible Want good t resolution Y Low t behavior is important! J Stewart Vertex

7 Background Suppression 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. Also cut on coplanarity. Can achieve factor 5 in background suppression! J Stewart Vertex

8 Recoil Detector Sensor Design Criteria Use an existing silicon microstrip detector design. Financial and time considerations preclude a custom design. Use the largest available double sided detector with less than 1 mm pitch. Adjust the target length to match the size of the silicon sensor. Minimize the material between the target gas and the silicon sensor. Measure the particle momentum using the relation between the energy deposited in the silicon and the momentum. Cover as much of the 2π as possible. HERMES has no coverage below 40 mrad in θ y. J Stewart Vertex

9 Silicon Detector Cooling Readout Hybrid Choose the TIGRE detector from MICRON semiconductor. TIGRE Sensor Target 16 double sided sensors each 99 mm 99 mm 2 layer square tube orientation 76% Φ acceptance 150 mm long target cell θ Coverage 0.4 < θ < 1.35 rad

10 The Detector Coverage Deeply virtual Compton Scattering (DVCS) Combined Bethe Heitler and DVCS Protons from exclusive ρ production Protons from delta excitation Silicon Coverage 135 < P[MeV/c] < MeV/c proton Y3 MIP Minimum momentum Target + Flexfoil + 1 st Si 135 < p < 250 MeV/c PID Need additional detectors for full coverage! J Stewart Vertex

11 3D Model of the Recoil Detector J Stewart Vertex

12 TIGRE Silicon Sensors Manufacturer: Micron Semiconductor Parameter Sensor Size Active Area Silicon Thickness Strip Pitch Strip Separation Coupling Capacitance Total Strip Capacitance Polysilicon bias resistor Depletion voltage P-Stop Technology Single Guard Ring Value 99 mm x 99 mm 97.3 mm x 97.3 mm 300 mm 758 mm 56 mm 1 nf 25 pf 50 MW 50 V Max Micron has produced detectors with 7 MW polysilicon for HERMES J Stewart Vertex

13 Measurements of Sample TIGREs Parameter Single strip leakage current Depletion voltage Coupling capacitor Total strip capacitance Interstrip capacitance Polysilicon bias resistor Value 40 na 40 V 1.2 nf 30 pf 8 pf >60 MΩ New sensor 7 MΩ J Stewart Vertex

14 Readout Electronics Chip Selection Criteria: A pipeline chip is needed to accommodate the HERMES trigger. A dynamic range of 70 ( 280 fc). 10 MHz readout to match the HERA frequency. Prefer a chip already used in HERMES. APC Used for the HERMES VC. Can select between high and low gain. Neither pattern generator nor ADC available. HELIX Used for the HERMES Lambda Wheels Dynamic range a problem. Both the pattern generator and ADC are available. J Stewart Vertex

15 Helix Pipeline Pipeamp MUX Preamp Shaper Buffer Designed by the ASIC lab. at the University of Heidelberg. 0.8 µm CMOS process. 10 MHz sampling frequency. 128 input channels. Analog pipeline 141 cells deep. Preamp-Shaper good noise char. Radiation tolerant 220 krad. Dynamic range +/- 40 fc or +/- 10 MIP J Stewart Vertex

16 First Tests Using Charge Injection Use an old Zeus MVD Hybrid Connect the Helix via Zeus pitch adapter to a general purpose pitch adapter. Capacitively couple an input pulse. Readout with the Zeus laser test stand. J Stewart Vertex

17 Helix Response 1 MIP =24,000 e - /h +/- MIP =Pos/Neg charge on preamp Conclusions: Linear response over +/-10 MIP Saturated at ~15 MIP As Expected J Stewart Vertex

18 Readout Conceptual Design Charge Division! Capacitive coupling readout. Doubles number of channels. 32 Y64 Helix 3.0. Can adjust dynamic range. 70 MIP Possible! Proposed by W. Lange J Stewart Vertex

19 First Prototype Constructed ZEUS MVD hybrid Sensor J Stewart Vertex

20 DESY2 Test Beam 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. high gain channel low gain channel Landau Fit Landau + Gaussian Fit J Stewart Vertex

21 Results of Charge Division Studies C eff can be calculated from the difference in slopes for high and low gain using charge injection. C eff = 25 pf (agrees fairly well with published numbers C eff = 31 pf) Charge Injection Test Beam Cc (pf) Q high Q low Q high Q low 22 67% 33% 72% 28% 10 78% 22% 82% 18% % 14% - - J Stewart Vertex

22 Present Status of Mechanical Design SciFi Connector Holding Structure Target Cell Scattering Chamber Collimator Cooling Hybrid TIGRE Sensors HERA Beamline J Stewart Vertex

23 Next Steps Set up a test stand using the HERMES pattern generator and ADC. Test the components to be used for the first readout hybrid. Test the needed Helix 3.0 chips. Design the layout and manufacture the first hybrid. Assemble the first real module. Vacuum Testing. TEST BEAM Hope to be ready for installation in spring 2004! J Stewart Vertex

24 Summary Response of both the HELIX 3.0 and APC readout chips to large pulses has been measured. First prototypes have been constructed and tested in test beam. Readout 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. HELIX 3.0 chosen for readout. Work has started on our first readout hybrid. A test stand is under construction at DESY Zeuthen. J Stewart Vertex