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Update on UCSC/SCIPP FCAL Activities 32 nd FCAL Workshop May 10-11, 2018 Bruce Schumm

Update on UCSC/SCIPP FCAL Activities 32 nd FCAL Workshop May 10-11, 2018 Bruce Schumm UC Santa Cruz Institute for Particle Physics. Overview Current results in the areas of: T506 Test Beam Results High-dose GaAs charge collection and current draw

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Update on UCSC/SCIPP FCAL Activities 32 nd FCAL Workshop May 10-11, 2018 Bruce Schumm

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  1. Update on UCSC/SCIPP FCAL Activities 32nd FCAL Workshop May 10-11, 2018 Bruce Schumm UC Santa Cruz Institute for Particle Physics

  2. Overview • Current results in the areas of: • T506 Test Beam Results • High-dose GaAs charge collection and current draw • Charge collection vs. shaping time (heavily irradiate Si diode sensor) • Simulation • Radiation dose and power draw for Si diode sensors • SUSY/two-photon event separation

  3. TEST BEAM RESULTS

  4. Recall Experiment T506: Radiation damage studies in the SLAC End Station A Test Beam 2 X0 pre-radiator; introduces a little divergence in shower Sensor sample Not shown: 4 X0 “post radiator” and 8 X0 “backstop” immediately surrounding the sensor

  5. Gallium Arsenide Sensor provided by Georgy Shelkov, JINR Sn-doped Liquid-Encapsulated Czochralski fabrication 300 m thick 0.16 cm2 area 5

  6. GaAs Charge Collection after 100 Mrad Exposure (new) After ~1 day annealing at room temperature (due to required repair) Sean Hyslop Area density of leakage current vs. T at VB= 600 V

  7. kGy Compare to Direct Electron Radiation Results (no EM Shower) Georgy Shelkov, JINR Pre-anneal GaAs Sensor Post-anneal at room temp (1 hr) Post-anneal at room temp (24 hr) Ionizing dose only; 1000 kGy = 100 Mrad 7

  8. GaAs Dark Current Consistent with observation for 21 Mrad exposure • Results consistent with neutron “NIEL” damage coefficient (via FLUKA; see below) Sean Hyslop

  9. GaAs Dark Current (log scale) Measurements done on two separate days (“M”,“F”) General trend preserved; some differences in detail Area density of leakage current vs. T at VB= 600 V

  10. NF Si Diode Area 0.09 cm2 PF Si Diode Area 0.025 cm2 SI DIODE SENSORS Sensors produced by the Micron Corporation Thickness: PF: ~300 m NF: ~400 m 10

  11. PF Type Charge Collection for 570 Mrad 570 Mrad Exposure PF Si Diode Sensor 11

  12. PF Type570 Mrad Charge Collection v. Collection Time (new!) Collection time is the time separation between two arriving charges that produces 1.5 times the single-charge pulse height PF Si Diode Sensor (fC) 570 Mrad Exposure Jane Gunnell (ns) 12

  13. Si Diode Dark Current • Detailed I-V studies done for 270 Mradexposure • Results consistent with neutron “NIEL” damage coefficient (via FLUKA; see below) At -120 C, 300 ns shaping, 3x3mm2 pixel, I estimate S/N of 5 for minimum-ionizing; changes by x2 for every 140 C Area density of leakage current vs. T at VB= 600

  14. Comparison of Si and GaAs Leakage Current • Scale Si Diode currents to GaAs dose of 100 Mrad with linear model (quite robust for Si) • GaAs at VB = 1000 (~1 fC charge collection) • Si Diode at VB = 600 (>3 fC charge collection) Note that S/N scales linearly with collected charge, but as square root of dark current  comparable performance

  15. SIMULATION STUDIES

  16. Recently approved by Speakers/Publications Committee (thank you Veta for leading review) To be submitted to Nuclear Instr & Meth

  17. BeamCal Simulation in FLUKA Ben Smithers • BeamCal absorbs about 10 TeV per crossing, resulting in electromagnetic doses as high as 100 Mrad/year • Associated neutrons can damage sensors and generate backgrounds in the central detector • GEANT not adequate for simulation of neutron field  implement FLUKA simulation • Design parameters from detailed baseline description (DBD) • Primaries sourced from single Guinea Pig simulation of e+- pairs associated with one bunch crossing

  18. Layer 2 Detector - Fluence E+&E- Neutrons

  19. Layer 4 Detector - Fluence E+&E- Neutrons

  20. Layer 6 Detector - Fluence E+&E- Neutrons

  21. Layer 8 Detector - Fluence E+&E- Neutrons

  22. Layer 10 Detector - Fluence E+&E- Neutrons

  23. Layer 12 Detector - Fluence Neutrons

  24. Layer 14 Detector - Fluence Neutrons

  25. Layer 16 Detector - Fluence Neutrons

  26. Idea: Use FLUKA to extrapolate from UCSC radiation-damage studies (T506) Standard working assumption: bulk damage dominated by non-ionizing energy loss (NIEL) • For silicon diode sensors, supported by T506 results • Dominated by neutron component of EM shower (conservative assumption since neutrons are more widely distributed)

  27. Define “fluence” Where l = total path length through sensor of area A and thickness dz. FLUKA provides double-differential fluence distribution, from which we calculate the NIEL density , per bin in neutron energy and angle in MeV/cm3.  is the density of silicon, and Nn(E) is the silicon NIEL function, in MeV/(g/cm2) of material traversed per through-going neutron (next page).

  28. N.B.: Energy distribution of neutrons for T506 and for BeamCal very similar, so damage estimates not particularly dependent upon details of NIEL scaling specific to silicon

  29. T506 simulation 51 C of 13.3 GeV electrons Sensor e- Total neutron NIEL dose of T506 = 2.7 x 1011 MeV/cm3

  30. Simulated BeamCal NIEL Dose – Layer 12 • Per year (107 seconds) of ILC operation • In T506 dose unit T506

  31. Simulated BeamCal NIEL Dose – Layer 30 • Per year (107 seconds) of ILC operation • In T506 dose unit T506

  32. Estimated Power Draw per Layer • Based on average neutron NIEL L in given layer • One year (107 seconds) of ILC operation • Operation at VB = 600 V • Leakage current density (T) from T506 results TS = 9.2o C a = 220 µA/cm2

  33. Layer-by-Layer Power Draw vs Temperature • Accumulation per year (107 s) of ILC operation • Maximum power-draw density is ~25 mW/cm2 at VB = 600 V and T = -10o C (< 5 mW/cm2 at -30oC)

  34. Overall Power Draw vs Temperature Per year of ILC operation • Can limit accumulation to less than 100W per year by operating below -10o C • At -30o C (standard for LHC sensor operation), accumulation would be of order 15 W per year

  35. Peripheral Fluence Estimates • Front-end electronics will likely be mounted just outside BeamCal instrument • Electromagnetic fluence less than 1011/cm2 (less than 2.5 krad) per year at any position • These levels far below conventional levels of concern

  36. SUSY Signal Selection At SCIPP, have simulated e+e-~+~- ; ~0 over a range of ~ mass and ~/0 degeneracy m~= 100, 150, 250 GeV m = m~-m = 20.0, 12.7, 8.0, 5.0, 3.2, 2.0 GeV Must discriminate against two-photon processes that occur with every crossing “Hadronic system” 37 Summer Zuber

  37. Event Observables Basic observables formed for the hadronic system: 38

  38. Fair discrimination for “V” observable 39

  39. Razor Observables • Force two-jet topology: (E1,p1) and (E2,p2) • Boost into frame defined by • Form “razor variables” MR and MTR Explore two-dimensional space of MR, MTR 40

  40. R2 vs. MR for 20 GeV Splitting 41

  41. R2 vs .MR for 8 GeV Splitting 42

  42. R2 vs. MR for 2 GeV Splitting 43

  43. R2 vs. MR for  Background 44

  44. Realistic ILC Beam Crossing Samples • An ILC beam crossing is not a single  of Bhabha event: Events rates from cross sections for •  down to di-pion mass threshold • Bhabhas down to virtuality of Q2 > 1 45

  45. Nominal Event Number Distributions These are input to event generation Two Photons Events (all types) Bhabha Events (all types) 46

  46. Realistic Beam Crossing Simulation Total energy (visible & invisible) for 100,000 nominal ILC beam crossings 47

  47. Summary and Outlook • FLUKA simulation in place • Used for radiation-field calculations and power-draw estimates for a Si-diode based BeamCal • Planning to use for exploring potential problems with BeamCal albedo • “Prediction algorithm” developed • False positive rate of 0.3% could be problematic; need to do “offline” study with SUSY signal • Preparing to explore effects of limiting hadronic coverage • Other studies underway, (no recent progress) • Offline SUSY analysis; razor variables under exploration • BeamCal reconstruction fast simulation algorithm 48

  48. BackUp BackUp…

  49. Comparison of Si and GaAs Leakage Current • Scale Si Diode currents to GaAs dose of 100 Mrad with linear model (quite robust for Si) • GaAs at VB = 1000 (~1 fC charge collection) • Si Diode at VB = 600 (>3 fC charge collection) -12: 6x10-5 /cm^2 7x10-6 /pixel for 270 Mrad 4.4x10^13 e/s per pixel 1.3x10^7 at 300 ns shaping 3620 electrons = 0.6 fC S/N = 5:1 300 ns shaping time -12: GaAs just about 1 uA/cm^2 Si just about 20 uA/cm^2

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