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Performances of large Pixelized Micromegas detectors in the COMPASS environment

Performances of large Pixelized Micromegas detectors in the COMPASS environment. Florian Thibaud CEA Saclay – Irfu / SPhN. MPGD 2013 Conference July 1 st 2013 Zaragoza. Outline. The COMPASS Experiment at CERN The Pixel Micromegas Detector Motivations

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Performances of large Pixelized Micromegas detectors in the COMPASS environment

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  1. Performances of large PixelizedMicromegas detectors in the COMPASS environment Florian Thibaud CEA Saclay – Irfu/SPhN MPGD 2013 Conference July1st 2013Zaragoza

  2. Outline • The COMPASS Experimentat CERN • The Pixel Micromegas Detector • Motivations • Dischargereduction technologies • Large size detectors readout • Front-end electronics • Performance of Pixel Micromegas in the COMPASS spectrometer • Discharge rate • Efficiency • Spatial resolution • Time resolution • Pixel Micromegas and track reconstruction • Conclusion • Outlook

  3. Dipole SM2 Dipole SM1 ~50 m 2nd spectrometer Target 1st spectrometer µ/h 160-200 GeV Φ = 105-107/s The COMPASS experiment at CERN • COmmonMuonProton Apparatus for Structure and Spectroscopy • High resolution spectrometer • Very good spatial resolution (<100µm) required at small angle for kinematics and particle identification • One of the first experiments to use GEM and Micromegas detectors LHC SPS • Micromegas Detectors • Veryhigh flux • Magneticfield(s)

  4. The Pixel Micromegas Project : motivations • Present COMPASS Micromegas detectors : good performances but room for improvements : • Blind center (5 cm diameter disk, beam area) • Discharges in hadron beam (0.1 discharge/s) • COMPASS II plans for 2015 : • Hadron beam up to 107 hadrons/s • Need for a spark protected detector • Better tracking in the beam area • Need for a detector with active center 40 cm 1024 channels • Pixel Micromegas Project • 10 to 100 times fewer discharges compared to present Micromegas • Read-out with pixels in the beam area

  5. 140 µm 70 µm Dischargereduction technologies • Preamplification stage with a GEM foil • Gain sharedbetween amplification gap and GEM foil • Diffusion of the primaryelectroncloud • Detector withresistive pads and buriedresistors • Quick rise of the resistive pads’ potential • Limitation of the discharge amplitude • Compatible with a pixelizedreadout • 2 solutions investigated : Design by Rui de Oliveira et al.

  6. 2.5x0.4 mm² 6.25x0.4 mm² 25 mm 50 mm Large size detectors : readout Active area • Nominal design after 3 years of development • 40 x 40 cm2 active area • 2560 readoutchannels • 1280 strips • 768 of 400 μm x 20 cm (center) • 512 of 480 μm x 40 cm (edges) • 1280 rectangular pixels • 640 of 400 μm x 2.5 mm • 640 of 400 μm x 6.25 mm

  7. Large size detectors : front-end electronics APV chip • APV card • Preamplification / shaping • ADC board • Analog to digital conversion • HGeSiCAboard • Data concentrator • Trigger distribution • Chain designed for • COMPASS GEM and Silicon detectors by TUM

  8. Large size detectors • 2012 : Pixel Micromegasare included in COMPASS • 2 detectors with GEM foil (+1 spare) replace 2 standard Micromegas detectors • 1 prototype with Buried Resistors is tested in hadron beam • All detectors participate to the physics data taking • Spark resistant Micromegasdetectors used as trackers at a flux up to 650kHz/cm2for the 1st time in a physics experiment Dipole Target PMM_2012.1 - GEM PMM_2011.2 - GEM PMM_2011.3 - BR

  9. Discharges • No dischargeobserved in nominal flux hadron beam on all PMM detectors Standard MM withreduced gain PMM_2011.3 -BuriedResistors Discharges 300 Imesh(nA) Imesh(nA) Time (min) 0 20 40 Time (min) 0 20 40 PMM_2011.2 - GEM PMM_2012.1 - GEM Imesh(nA) Imesh(nA) 0 20 40 Time (min) 0 20 40 Time (min)

  10. Large size detectors : data reconstruction • APV : 3 amplitudes samplesspaced by 75 ns ateach trigger a2 • Samplea2used for position reconstruction Amp. [ADC units] a1 TCS phase latency a2 a0 0 100 200 300 400 500 600 700 800 synchronized trigger Time [ns] trigger • Ratio a1/a2used for time reconstruction xhit x1 x2 x3 x4 x5 a1/a2 TCS phase [ns] Hit time [ns]

  11. Efficiency (Φ=9x105 s-1) PMM_2011.3 - BR PMM_2012.1 - GEM PMM_2011.1 - GEM PMM_2011.2 - GEM Long stripsdisconnected 40 cm ε = 98.2 % ε = 97.8 % ε = 97.8 % ε = 98.0 % 40 cm 2.5 cm 5 cm

  12. Efficiency • Efficiency > 95% for all detectors in all conditions • Slightdecreaseathighest flux : • Pixels : ~ 1.5% • Strips : < 1% *missing front-end card

  13. Spatial Resolution • Residual plots withlow flux and field off • Dectectorresolution : MM02X (standard Micromegas) PMM_2011.3 - BR PMM_2011.2 - GEM Strips σres = 72 µm σdet= 57 µm Strips σres = 85 µm σdet = 78 µm Strips σres = 79 µm σdet = 71 µm Pixels σres = 76 µm σdet= 69 µm Pixels σres = 61 µm σdet= 56 µm • σPMM+GEM<σstandard MM • σPMM+BR >~ σstandardMM

  14. Spatial Resolution : influence of the dipolefield • Dipolefringefield up to 0.2 Tat the prototype position • Far fromdipole • No effect • Close to dipole • Degradation (~ +50%) similar for standard MM and PMM_2011.BR

  15. Spatial Resolution : influence of the beamflux • PMM + GEM • Strips : • Degradation comparable to standard MM (~10-15%) • Pixels : • Degradation (~50%) at the highest flux but still < 90µm (preliminaryresult*) • PMM w/ BR • Degradationworsethan standard MM in the sameregion (25% compared to 3%) PRELIMINARY* PRELIMINARY* Close to dipole *Lack of redundancyatsmall angle Poor trackingresolution

  16. Time Resolution : Gas Mixture PMM_2011.2 - GEM Muon run: 80% Ne + 10% C2H6+ 10% CF4 Hadron run: 85% Ne + 10% C2H6 + 5% CF4 Strips Strips σ = 13.3 ns σ = 8.7 ns Cluster time [ns] Cluster time [ns] Pixels Pixels σ1 = 13.2 ns σ = 9.1 ns Cluster time [ns] Cluster time [ns]

  17. Time Resolution : GEM vs BR Hadron run: 85% Ne + 10% C2H6+ 5% CF4 PMM_2011.2 - GEM PMM_2011.3 - BR Strips Strips RMS = 29.9 ns σ = 13.3 ns Cluster time [ns] Cluster time [ns] Pixels Pixels σ = 13.2 ns RMS = 32.1 ns Cluster time [ns] Cluster time [ns]

  18. Time Resolution • Summary of time resolutionmeasurements (in ns) • σPMM+GEM~ σMM • σPMM+BR ~ 2.5 x σPMM+GEM *due to PCB curvature

  19. Pixel Micromegas and track reconstruction • High flux muon run(5x107 s-1): • 2 PMM+GEM integrated in the tracking (BR off beam) • Difficult conditions for track reconstruction in the beam area : • Beam flux up to 650 kHz/cm2 • Only 5 planes betweentarget and dipole -> PMMs= 40% of the trackers • Necessity for precise time cuts on PMM to reducecombinatorialbackground All clusters (Pixelized area) Clusters close to a track (Pixelized area) Non flat background due to time reconstruction from amplitudes (Not physical) Reconstructed time [ns] Reconstructed time [ns]

  20. Time Cuts Amount of clusters on the pixelizedarea in the highestbeam flux (650 kHz/cm2) -30 40 • Clusters : -70% • Small loss in efficiency (<2%) • Important decrease of background probability -30 40

  21. Impact of Time Cuts on the track reconstruction Observable : Amount of eventswithtoomanytracks or combinationsgenerated by the COMPASS reconstruction software in the zone between the target and the first dipole • Rejectedevents : -90% • Reduction of the combinatorial background

  22. Conclusion • Micromegasdetectors used as trackers in a flux up to 650kHz/cm2for the 1st time in a physics experiment • 2 spark-protection technologies used, no spark observed in nominal intensity hadron beam. • Efficiency : low flux >98%; high flux > 95% • Spatial resolution : • PMM+GEM : • Better than standard COMPASS MM (55-60µmvs 65-70µm) • Flux : degradation at 600 kHz/cm2comparable to standard COMPASS Micromegas • PMM w/ BR : • Comparable to standard COMPASS MM (~70-80µm) • Flux : degradation more important than standard MM • Time resolution : • PMM+GEM : ~9-10 ns (10% CF4), ~13 ns (5% CF4) • PMM w/ BR : ~30 ns (5% CF4) • Tracking : cut on cluster time (-30ns to 40ns) : -90% rejected events

  23. Outlook • Choice GEM/BR : a priori GEM due to better performance, but studies on BR still ongoing. • Production : final detectors will be produced by the CIREA-ELVIA company (see talk by Damien NEYRET during RD51 meeting). • Complete installation : replacement of the 12 standard Micromegas by Pixel Micromegasforeseen for the COMPASS II run in early 2015.

  24. Backup Slides

  25. PMM + GEM : gain & efficiency

  26. PMM BR : gain

  27. Efficiency : hadron beam

  28. Time Resolutionvs position PMM_2011.2 (PixelMM w/ GEM) Mean cluster time vs position Strips Pixels Y [cm] σ = 9.1 ns σ = 8.7 ns X [cm] Cluster time [ns] Cluster time [ns] PMM_2012.1(PixelMM w/ GEM) Mean cluster time vs position Pixels Strips Y [cm] σ = 10.3 ns σ = 12.4ns Largerσ due to detector curvature X [cm] Cluster time [ns] Cluster time [ns]

  29. Pixel Micromegas and track reconstruction All clusters (Pixelized area) All clusters (Pixelized area) a1/a2 Reconstructed time [ns] TCS phase [ns]

  30. Impact of Time Cuts on the track reconstruction + 5% + 4%

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