1. Micromegas for the Central Tracker Sébastien Procureur CEA-Saclay

2. Micromegas and CLAS12 MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur - 3 double layers of cylindrical MM (Barrel) - 3 double layers of flat MM (Forward) ~ 4 m²

3. The MM challenges (Cerchi dell'Inferno) MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur “Abandon all hope, you who enter here”

4. Cylindrical Micromegas Make use of the « bulk » technology (2006) MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur 2 to 4 mm 128  m Mini: 4 mm Mesh Photoresist border Photoresist amplification spacer (~300 µm) PCB with strips → more robust → PCB can be thin

5. Cylindrical Micromegas Performance compared to thick flat MM using cosmics MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur → similar performance as thick detectors Thick detector Thin detector

6. Spatial resolution in 5 T X tiles of Barrel Micromegas are sensitive to the Lorentz angle of drifting electrons MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur  x = h tanθ = h v B / E xx h → minimize h (but less signal) → use heavier gas (but more sparks) → increase E field (but lower transparency) Garfield simulation →  ~ 220 µm if  can be lowered down to 20°

7. Spatial resolution in 5 T Test to validate Garfield simulation with a Micromegas in dvcs magnet (Hall B) MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur Garfield validated,  can be as low as 20° → use of a focused UV laser to extract electrons from the drift electrode from the drift electrode P. Konczykowski et al., NIM A612 (2010), 274

8. Large area detectors Full size Y prototypes have been built at CERN MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur → doubled area compared to COMPASS 50x60 cm² 1400 channels → C det ~ 25 nF, C strip from 90 to 120 pF (can be reduced) Scan with Fe 55 source → 90% of strips OK (1st proto!) → ready to build them at Saclay

9. Electronics The limited space requires an off-detector electronics → long cables MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur → Irakli found 70 pF/m (Hitachi) → initial cables were 160 pF/m (FLEX) → C cab = 105 pF ~ C strip → Significant effect on S/B (~50%) → Needs 10 V more to be compensated

10. Electronics - recent developments Dream: reworked input stage adapted to high detector capacitances up to 200 pF → ENC of 2200e for 150 ns peaking time → Expected S/N : 30 – 40 depending on gain Test bench: Dream carrier board in place & route → Up to 7 Dreams → One Dream on a remote board Firmware: in progress → Test bench and front-end unit firmware → Goal: estimate FPGA resources needed Detector cables: Hitachi 50 pF/m cables expected on March 15 th → check ability to withstand sparks → Goal: 40 pF/m cables MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur

11. DREAM and test bench schedule February: Dream carrier board place & route started End of March –Submission of Dream Backup date: end of April –Production of the Dream carrier board April: Dream carrier board in test May: Dream test bench ready –Final adjustments for firmware and software June: packaged Dream ready for tests –T2-T3 – Dream tests MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur

12. Spark rate studies Activity started in 2009 → simulation: try to relate sparks with large energy deposits with Geant4 (Gemc) energy deposits with Geant4 (Gemc) → spark condition: N el ~ 10 7 (Raether) → Quantitatively reproduces (few) existing data MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur → Explains gas effect & give predictions (bulk) S. Procureur et al., NIM A621 (2010), 177

13. Spark rate studies → 6 different detectors in 150 GeV pion beams → bulk ~ non-bulk MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur S. Procureur et al., submitted to NIM (Feb. 1st 2011) Tests at CERN/SPS, October 2009 → Effect of a 1.5 T  magnetic field → 1 st test of a MM+GEM detector (D. Neyret) → No strong effect of B field → 1 week of data

14. Spark rate studies → 1 MM & 1 MM+GEM in FROST setup → simulation ~ OK MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur B. Moreno et al., submitted to NIM (Mar. 8th 2011) Tests at JLab/Hall B, July 2010 → Effect of a 5 T // magnetic field →  100 with GEM foil → x10 with 5 T field → 2.5 days of data

15. Spark rate studies → 12 detectors in π + or π - beam → peaks in spark rates with π + MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur G. Charles et al., submitted to NIM (Feb. 25th 2011) Tests at CERN/PS, August 2010 → beam momentum tunable between 0.2 and 3 GeV/c → confirms GEM effects → 2 MM+GEM to understand spark rate suppression → 2 weeks of data

16. Spark rate – last mysteries → effect of the longitudinal 5 T field → strong hint for significant effect of transverse diffusion MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur 2 observations cannot be reproduced by the naive simulation → spark suppression with the MM-GEM detectors → explains all effects seen with MM-GEM: → large suppression with moderate GEM gains → effect of trans. diff. only at high GEM gains → change of slope at high GEM gain  new spark condition: critical surface charge density

17. Integration MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur

18. Forward Tagger with Micromegas? Project to equip the FMT with central pixels for small angle e- detection - add ~ 6k channels to the FMT (electronics?) - add 2-4 MM layers in front of calo Track finding eff > 95% in pFMT Very large background due to Moeller z φ p  All hits Selected hits MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur

19. Schedule

20. Conclusion MicromegasCLAS collaboration meeting, 09/03/2011 S.Procureur

21. Additional slides

22. Working point ParameterBarrel (Z&Y)ForwardRemarks Drift space2-3 mm5 mm GasAr+10%iC 4 H 10 Ne+iC 4 H 10 Fields ratio5.5-650 Mesh Transparency40% Electron Transparency 40-45%~100%Measured @ B=0 Gain (effective)50003000 Detection Efficiency>90%>95%Measured @ B=0(X) Tracking Efficiency>93%>90%Simulation (tracking) Detectors / layer31-2 Background noise/ Detector 2 MHz12 MHzGeant4 estimate Sparking rate1/s0.4/sGeant4 estimate Space resolution220&100 µm80 µmGarfield estimate Lorentz angle20°0°Garfield estimate, validated