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LHCb Test Beam Report

Discover the advantages of a high-energy test beam facility for studying resolution, efficiency, irradiation effects, alignment, and sensor design in the VELO detector.

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LHCb Test Beam Report

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  1. Andrey Golutvin ITEP/Moscow LHCb Test Beam Report • VELO • Silicon Tracker • Outer Tracker • RICH • Calorimeters • Muon

  2. VELO test beam: the keywords! What studies could we not do so easily without a high-energy test beam facility ? • Resolution and Efficiency • Irradiated vs non-irradiated • p-on-n vs n-on-n Needs low multiple scattering ( < few um) Needs high rates of high energy particles Alignment studies • Internal/external alignment • VELO will move between LHC fills • Level-1 trigger sensitive to position accuracy Great advantages with multi-track vertices (from interactions) Again, needs low multiple scattering (< few um) • Single- vs double-metal layer • Perpendicular vs inclined tracks • VELO will be cold and in vacuum • Approaches LHC beams to a few mm

  3. VELO test-beam: what we learned (1) • Allowed us to discover charge loss due to double-metal design (unique for these radiation levels) • Included in simulation since then • This changed the sensor design • TB was decisive in studying irradiated detectors • Technology choice: n-on-n shows resolution more robust to radiation compared to p-on-n • Led us to the choice of n-on-n sensors Region with single metal layer Region with double metal layer

  4. VELO test beam: what we learned (2) • Used to calibrate the resolution and spill-over in the MC simulation. • Furthermore: • Studied various FE chips with MIPs and realistic environment • Discovered various unwanted features in the FE chip, which had escaped the lab tests with pulses, sources, etc.. • Tested hardware in a more realistic environment than in typical lab tests • Produced wealth of data that could be used for studies of trigger algorithms

  5. VELO test beam: what we are learning • Just finished a very fruitful test beam run ! • Studied 3 pre-series sensors: • 200 um thick R-sensor • 300 um thick R-sensor • 200 um thick Phi-sensor All equipped with 16 Beetle chips of 4 flavours (4x4). • Performed a system test of the whole chain: • sensor + 16 Beetles + hybrid + 60m cable + analogue receiver These data will lead to the final sensor thickness decision very soon, opening the way to mass production

  6. VELO test beam: what we will learn • Check out fully equipped VELO halves in 2006 test beam: • get alignment parameters • TB’06 is only way to check that sensors are positioned within 20 um of nominal after cooling and in vacuum • VELO is least accessible detector in LHCb  check (and correct) before installing • VELO will approach LHC beams to 5 mm, based on its own measurement of the beam positions  full check of vertexing software before installing in the LHCb pit • Continue irradiated sensor studies • VELO sensors must be replaced after ~3 years (aging) • Follow up on R&D for radiation hard sensors, which requires detailed resolution and efficiency measurements A permanent (LHCb) test beam facility, from 2006 onwards, is really essential for the VELO project

  7. Silicon Tracker Test Beam Goals: • test various prototype ladders, all read out with Beetle chip • measure S/N for various detector geometries and as function ofbias voltage, particle position, signal-shaping parameters ... • PS Beam telescope from HERA-B VDS ( track position with ~ 14µm) Played absolutely crucial role in R&D program: • proof that full particle detection efficiency can be ensured for long readout strips and sufficiently fast shaping times • optimisation of sensor thickness and readout strip geometry • proof of principle for long Kapton interconnect cables • test of irradiated Inner-Tracker sensor

  8. Silicon Tracker Fit to test beam results: ENC = 770 e- + 47.9 e-/pF 3 x CMS-OB2 Beetle lab measurements: ENC = 580 e- + 48.8 e-/pF Main findings (1): • sufficiently fast signal shaping reached for all strip lengths • detector noise increases linearly with measured strip capacitance and is compatible with lab measurements on Beetle chips

  9. Silicon Tracker 3 x LHCb-IT 2 x LHCb-IT S/N ≥ 10 required for full efficiency 3 x CMS-OB2 Vbias = 450 V 1 x LHCb-IT left strip right strip Main findings (2): • S/N performance constant over full length of readout strips • significant cross-talk from capacitive coupling between readout strips • significant signal loss in central region between two readout strips • sufficiently high S/N for full particle detection efficiency

  10. Silicon Tracker Interest in 2006 test-beam: • would permit commissioning of fully assembled Inner Tracker detector boxes before their installation in the pit • would (possibly) permit to measure internal alignment of IT boxes • would permit to exercise LHCb DAQ in a realistic environment => expect significant speed-up of detector start-up in LHC

  11. Outer Tracker(TDR Test-Beam Results) Measured t-r relation, coordinate resolution (0.2mm), efficiency (97%) Drift time (ns) Distance from Wire (mm) Ar(75)/CO2 (10)/CF4 (15) selected as baseline

  12. Outer Tracker(Plans for the Test beam at DESY) • Motivation: • 20% modules produced • baseline gas now Ar(70)/CO2 (30) • beam characteristics: • electrons • 1-6 GeV/c • 100-500 Hz. • Requested two periods: • Jan. 17 - : - Jan. 31, 2005 • Mar 28 - : - Apr. 11, 2005

  13. How testbeam results impact on the final RICH detector design • Verified proof of principle of HPDs • Verified HPDs as a viable photon detector • Optimized photon yield/ verified HPD efficiency • Demonstrated resolution – especially pixel/ chromatic • Comparison with detailed simulation • Evaluated and verified proof-of-principle of MAPMTs as an alternative photodetector choice • Optimized properties of aerogel • Optimized thickness • Measured Rayleigh scattering • Verified photon yield/ aerogel clarity • RICH geometry • Understood alignment issues – mirrors/photodetector plane • Learned *many* practical issues/ light-tightness/ calibration etc • Verified final design specifications • Excellent testbed for a full system test • HPD mounting • Electronics evaluation/ electronics noise • The advantages of gaining experience of general operation and training people in realistic environment should not be underestimated

  14. How the testbeam results have helped the understanding of the RICH detector Three Examples 1. Full system tests (2004) 2. Aerogel studies (1998-2004) 3. MAPMT evaluation (2001-2003)

  15. from: to: in : One single HPD One HPD column RICH-2 detector 1. Full system test (2004) • Pre-production HPDs • Complete readout electronics chain • Final mechanical arrangement • Power • Cooling, insulation System test essential in putting these elements together

  16. Test beam Set-up (T9) Full system test HPD column Detector Housing with 3-column HPD Radiator vessel Mirror Thin Al foil - entrance window for beam BeamPipe

  17. L0 Board HPD Column mechanics Test of preproduction electronics HPD Pixel chip, encapsulated in HPD • Binary data shifted out at 40 MHz Level-0 Board • Drives the pixel chip • Distributes clocks, triggers via TTC • Controls DC power levels for pixel chip • Gbit optical links (in LHCb 100 m to counting room) • Controlled using JTAG interface Aluminum spacer Kapton • During the first phase of the test beam pixel chip and L0 board were able to drive out the data at the full LHCb speed of 40 MHz • 1.6Gbit optical link also used successfully

  18. Electrons First results : ~1m N2 radiator 10 GeV/c Pions Electrons : observe4.01±0.59 mm expect 4.17± 0.05 mm Ring radii Pions : observe3.32±0.52 mm expect 3.47± 0.05 mm

  19. Silica Aerogel 2. Silica Aerogel studies (ongoing) • Silica aerogel: Used in RICH-1 (p/K separation from ~1-10 GeV/c) • Tunable density (r~0.15 g/cm3) → tunable refractive index n • Tested tiles with dimensions 100×100×40 mm3 (200×200×50 mm3 now available) • Verify transmittance A~0.95, clarity C~0.0050 µm4/cm; refractive index n~1.03 • Measure Rayleigh scattering Testbeam essential in understanding the aerogel properties

  20. HPDs Aerogel Mirror Aerogel testbeam • Aerogel photons observed by three HPD • Beam tested: pure p- and mixed p+/p • Results • Good p+/p separation, up to ~20s (10GeV/c) • Photoelectron yield ~10 p.e./particle (full circle) in agreement with expectations

  21. 3. MAPMT evaluation (2002/3) • CF4 800 mbar, 8-stage MAPMT, Beetle1.2; with lenses, • HV -900V Beam 10 GeV/c mostly pions raw data cross-talk corrected 10.3 hits/evt 6.5 hits/evt

  22. Requirements for testbeam in 2006 • To further study and understand the angular resolution in the aerogel. This will require a matrix of production HPDs over large acceptance. • To undertake a complete system test with full readout chain and final components (including Level-1 and possibly final readout units) - this would be most useful with a 25ns beam bunch structure. The two requests would be classed as “very useful”, especially with a 25ns bunch structure, but probably not “absolutely essential”.

  23. Beam Tests of Calorimeters The HCAL module at beam on the movable and rotating platform.

  24. Test beam Goals • Pre-calibration and QC of selected modules • Systematic studies of module intrinsic properties • light yield • energy resolution • spatial resolution • light collection efficiency • Studies of electronics components (FE boards, CW, clipping) • R&D of monitoring system

  25. Verification of quality control(outer ECAL modules) TDR goal: pre-calibrate ECAL modules at 10% Good correlation between Cosmic and Beam test measurements Pre-calibrate all modules at CERN cosmic stand Y11 fibers BCF fibers Module-to-module spread for outer modules has an RMS of 5.7%

  26. Light yield 100 GeV Muons Outer modules: ~ 2500 p.e./GeV Middle modules: ~ 4200 p.e./GeV Inner modules: ~ 3000 p.e./GeV 5 GeV Electrons

  27. Light collection efficiency Scan of outer ECAL module with 100 GeV muons Slice (2 mm) covering the row of fibers Slice (2 mm) between fiber rows

  28. Local non-uniformities are smeared out for electrons Steel tape 200 µ Scan with 50 GeV electrons e-beam parallel to the module axis e-beam at ~200 mrad to the module axis Aglobal = 0.46 ± 0.03% Alocal = 0.39 ± 0.01% mm mm X mm X Spread across the module < ± 1.3% Spread across the module < ± 0.6%

  29. E E Energy Resolution of ECAL ECAL module energy resolution: e- beam (9.40.2)%  (0.83  0.02)%   ((145  13) MeV)/E E GeV E 10% Required energy resolution:  1% E

  30. Performance of HCAL modules Pre-calibration Light Yield • 10 HCAL modules were calibrated • at the beam. • Good correlation with radioactive • source measurements Beam-test result on 40 channel HCAL module: Sensitivity ~100 ph.e./GeV Average = 4.7% Tile to tile RMS for 44 HCAL modules

  31. LY in outer cells: 25 phel/mip Preshower setup in X7 beam Outer Preshower module with 4x4 cells Preshower/SPD beam tests Year 2003: Light yield in outer, middle and inner modules was 25 and 30 ph.el./MIP. Cell-to-cell non-uniformity <15%. Year 2004: 56 outer PRS modules were calibrated with 100 GeV muons in X7 beam. The obtained data will be compared with radiation source results.

  32. Signal timing A pulse shape study on 30 GeV electron beam for 6 different layers in depth of the HCAL: 25 ns pulse shaping

  33. Test beam : Calorimeter Electronics • Test conditions : • PM signal sent both to • Front-End board prototype • Lecroy ADC (100ns gate) • Particles in phase with the 40MHz clock • HCAL and ECAL(in 2000) detector cells in beam • Results : • Automatic pedestal subtraction algorithm tested • Cross-talk < 0.4 % • Noise in [1.1, 1.4] ADC count • Linearity < 1% in the full dynamic range (12 bits)

  34. Monitoring system Correction of time- and temperature- instability with the monitoring system prototype ● LED seen by PIN diode ●LED seen by PMT ●electron signal ●electron signal corrected Initial effect of ~4.5% is corrected to better than 0.5%

  35. Muon Beam Tests • Test Beam goals: • Test chamber prototypes and decide on chamber parameters, • such as wire pitch (1.5 vs 2 mm), single vs double cathode readout, • cathode PCB structure with readout traces, gas mixture • Test and validate FE-chip CARIOCA • Check chamber performance in term of efficiency (time resolution), • cluster size, high rate performance, uniformity • Full system test

  36. Photos M2R1 prototype (mixed readout) M2R4 – wire readout ~ 15 prototypes built and tested with (almost) final front-end electronics at T11 test beam area at CERN. M3R3 – cathode readout

  37. Chamber Performance: Time resolution 20ns • Optimum amplifier peaking time ~10ns • Intrinsic time resolution is about 3ns

  38. Chamber Performance: Efficiency Cathode Efficiency: Anode Efficiency: WP WP -> Plateau length is about 350 – 450 V

  39. Time resolution: Double Gap Efficiency in 20 ns: 5 ns 95 % Pad number Pad number Time Resolution and Efficiency Uniformity Example of uniformity measurements on a M3R3 prototype with cathode pad readout: Time rms = (4.30.2) ns ε (HV=2.6 kV) = (96.7 ±0.1) % > 99% pads are inside the specifications

  40. Comparison with Simulation Double gap chamber: • 95% efficiency if the threshold • is set to 30% of the average signal. • 99% efficiency if the threshold is • set to 20% of the average signal. • In order to have a double gap • chamber well within the plateau we • want to be able to use a threshold of • ~15% of the average signal. • Full simulation: • - Primary ionization (HEED) • - Drift, Diffusion (MAGBOLTZ) • - Induced Signals (GARFIELD) -> Good agreement, we understand our detector

  41. Chamber Performance High rate performance: Test @ X7 up to 500 kHz/FEE channel Time resolution stable (no space charge effects) 2.5% Small Efficiency drop due to pile up

  42. 9.7 ns 5.3 ns 4.5 ns 4.5 ns Detector Time Resolution Measurement (triple GEM chamber) Considerableimprovement with respect to the Ar/CO2=70/30 gas mixture, which exhibits a poor time resolution of about 10 ns RMS, is obtained with the new CF4 and iso-C4H10 based gas mixtures, which allow to reach time resolutions better than 5 ns RMS Our Choice: Ar/CO2/CF4 45/15/40 Fast & Non-flammable Single Chamber Time Spectra

  43. Working region, upper limited by Cluster Size = 1.2, is found to be 70 V wide, a large plateau for a micro-pattern gaseous detector! OR Efficiency in 20 ns Working region 2.0 fC Cluster Size 3.0 fC G~20000 G~4000

  44. Conclusion • Test beams were extremely useful in the past • Continue providing important input at present • Request: • Test beam at SPS energy in 2006 in order to • check out fully equipped VELO halves before installation • Essential for the long term future: • Dedicated test beam area in the north area • Facilities for irradiation and high rate tests

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