1. Micromegas detectors for the CLAS12 central tracker Brahim Moreno (for the Saclay group) CLAS12 central detector meeting : 2 december 2009 Cea Saclay CERN experiment: results 1

2. Micromegas detectors for the CLAS12 central tracker CERN experiment: results Introduction Experiment at CERN Results Conclusions and outlook 2

3. Micromegas and CLAS12 What is a spark? Introduction

4. 4 Micromegas and CLAS12 Several points to be adressed before micromegas implementation in CLAS12 AdressedOngoingNot adressedValue (if applicable) bMM feasibility  cbMM feasibility  MM behaviour in magnetic field  Sparks rate (with/ without magnetic field)  Spatial resolution (with beam)  Efficiency (with beam)  bMM: bulk micromegas cbMM: curved bluk micromegas * bMM and cbMM showed the same behaviour Experiment at CERN

5. 5 What is a spark? (1) Drift electrode Mesh PCB 600V 400V Ionizing particle (MIP) conversion amplification e- Signal amplified Charge collected on the strips

6. 6 What is a spark? (2) Drift electrode Mesh PCB 600V 400V Ionizing particle (hadron) conversion amplification High charge density Spark = discharge in amplification gap 0V Discharge blinds MM detector because it sets mesh HV to ground Recovery time depends on Protection circuit (~1 ms) Discharge

7. Experimental set-up Data acquisition Running conditions and data Experiment at CERN Description

8. 8 Experimental set up (1) Main goal: evaluating sparks rate in presence of or without magnetic field x y z Pitch: region a → 400μm region b → 1000μm Distance between strips: 100μm 12345 magnet Goliath Beam Scintillator paddles coupled to PMTs Gaz: 5% Isobutane/Ar x y z Region a Region b 10 cm

9. 9 Experimental set up (2) MM TypeDrift gapDrift materialAmplification gap Mesh material Orientation 1Classic5 mmAluminized mylar128 μmCopperX 2Bulk5 mmAluminized mylar128 μmStainless steel Y 3Bulk2 mmAluminized mylar128 μmStainless steel X 4Bulk5 mmStainless steel128 μmStainless steel X 5Bulk5 mmAluminized mylar128 μmStainless steel X Main detectors characteristics

10. 10 Experimental set up (3) Magnet 1.77 m Upper coil Beam

11. 11 Experimental set up (4) Beam Detectors Electronics

12. 12 Data acquisition (1) Spark monitoring Amplifier Mesh Discriminator HV filter Scaler VME Computer Data file MM Detector Same principle for all detectors All detectors monitored simultaneously Labview based monitoring

13. 13 Data acquisition (2) Spark monitoring: user interface Goes red if one detector is sparking Spark list display Goes red if detector 4 is sparking Clock: +1 every 5s Display updated at the clock frequency Total number of spark VS time Associated derivative Total number of spark Total number of coincidences

14. 14 Data acquisition (3) Spark monitoring: data format Text file Timestamp Clock Total number of spark: a column for each detector Total number of coincidences

15. 15 Running conditions and data Experiment: Oct the 23rd – Nov the 3rd Beam Characteristics: Nature: pion or muon Energy: 150 GeV Spill duration: 9s Time between spill: 1mn Particle/spill: ~10 6 part/spill Measurements at: 0, 0.28, 0.56, 0.7, 0.84, 1.12 and 1.4 T ~210 runs

16. Spark probability Magnetic field effect Results Sparks

17. 17 Spark probability (1): as a function of gain No sizeable different behaviours between classic and bulk micromegas

18. 18 Spark probability (2): transparency effect Transparency : probability for a primary electron to get through the mesh Transparency decreases (at fixed mesh HV) as drift HV increases Lower spark probability Less electron getting through mesh at 1500V than at 600V Increasing drift HV requires to increase the gain in order to compensate the loss in transparency HV mesh (V) Drift HV: 1500V Drift HV: 600V Stainless steel drift electrode

19. 19 Spark probability (3): magnetic field effect Classic MM: HV 380/1500 Y Bulk : HV 380/1200 X Bulk : HV 380/1500 No sizeable (transverse) magnetic field effectHigh HV drift lowers Lorentz angle

20. Conclusions and outlook Conclusions: -Bulk micromegas behaves the same as classic micromegas -No strong magnetic field effect observed Outlook: -Analysis still ongoing: new results expected -New experiment next year to perform gaz mixture optimization -CERN experiment: 150 GeV beam 1.5T magnet extrapolation to CLAS12 experimental conditions not straightforward (hadron ~1 GeV, 5T)

21. Back up slides

22. 22 Micromegas and CLAS12 (2) Use: alternative/complement to silicon vertex tracker 4 x 2MM 4 x 2SI 2 x 2SI + 3 x 2MM Specs.  pT /p T (%) 2.92.11.65   (mrad) 1.315.11.4<10-20   (mrad) 10.92.92.6<10  z (μm) 2121522267tbd. (for  @ 0.6 GeV/c,  = 90°) A mixed solution combines advantages of both the silicon (SI) and micromegas (MM) detectors Curved bulk micromegas Flat bulk micromegas

23. Basic principles of a micromegas detector ~100  m thin gap

24. 24 Basic principles of a micromegas detector: bulk- micromegas Same principle as « classic » micromegas Difference lies in construction process: mesh embedded on the PCB Advantages: Detector built in nearly one process Geometry (flexible PCB) Drift electrode Strips Micromesh Amplification Conversion

25. 25 Description (2) Beam Electronics Oct the 23rd – Nov the 3rd Detectors

26. 26 Description (4): measurements Measurements at: 0, 0.28, 0.56, 0.7, 0.84, 1.12 and 1.5 T -Mesh high voltage variation with fixed drift HV -Drift HV variation at fixed mesh HV Hadron beam 150 GeV

27. 27 Preliminary results: Gain Estimated with Fe source

28. 28 Preliminary results: sparks rate Classic MM (5 mm drift gap) bMM (2 mm drift gap, alumized mylar) bMM with Y strips (5 mm drift gap) bMM (5 mm drift gap, inox) bMM (5 mm drift gap) Total number of sparks Time (s) Detector was off

29. 29 Preliminary results: sparks (2) 2 mm drift gap5 mm drift gap Y-strips 5 mm drift gap X-strips Spill number Number of sparks Sparks rates stable over time ~10 -5 sparks/particle Number of sparks normalized to PMs coincidences (~10 6 c/spill) Hadron beam 150 GeV HT mesh: 370V HT drift: 600V

30. Preliminary results: beam profile (1) Beam profile (classic MM) Beam profile (bMM 5mm drift gap) X strips Y strips Beam profiles Run with beam spread in Y Muon beam (~150 GeV) Online monitoring X (mm) Y (mm) Beam profile (bMM 2mm drift gap)

31. 31 Preliminary results: beam profile (2) Correlation 1-3 (XX) X3 (mm) Correlation 1-2 (XY) X1 (mm) Y2 (mm) Online monitoring 2D beam profiles Run with beam spread in Y Muon beam (~150 GeV) 1 = classic MM (X-strips) 2 = bMM (Y-strips) 3 = bMM (X-strips)

32. Preliminary results: tracking ΔX (strip) = difference between expected and measured hit position Residual ΔX (strip) Before alignment correction Only the small pitch region (400 μm) is taken into account σ < pitch/(12) 1/2