1. Micromegas studies using cosmic rays Franck Sabatié May 7th 2009 Saclay cosmic ray bench Data acquisition system and analysis tools MIP detection Position resolution studies Efficiency studies Noise studies Conclusions

2. AFTER electronics 80cm flex cables Lead Scintillator paddle with PMT Scintillator paddle with PMT Trigger Unit out Trigger in Saclay cosmic ray bench

3. Flex cables Reference detector Curved detector (demonstrator) Scintillator Paddle Lead

4. Detectors used for the cosmic ray tests Small detectors: 144 strips, 21.5 x 53 mm² active area, 400µm pitch, 2mm drift gap Large detector: 288 strips, about 4 times bigger area

5. DAQ and analysis tools More or less the same as for the magnetic tests at JLab : - AFTER electronics, C++ DAQ program, C++/ROOT analyzer - Difference was : up to 2 FECs (8 ASICs) were read out - AFTER sparcification mode was used to reduce data output - Data runs were about 10-hour long to yield enough statistics

6. MIP signal on strip 92 vs. time Det. 1 Det. 2 Det. 3 Det. 4 Quadruple coincidence event Det. 1 Det. 4 Det. 2Det. 3 Thin-flat Thick Minimum Ionizing Particles with Micromegas Typical results

7. Minimum Ionizing Particles with Micromegas Strip multiplicity for MIP events Typical range

8. Position resolution for thick and thin bulk Micromegas This is the residual, it’s a convolution of misalignment between our detector and the reference detectors, and the detector resolution, therefore an overestimate (we expect about 70µm resolution) but … Similar resolutions for thick and thin detectors ! Thick detectorThin detector Ref. 1 Ref. 2

9. Efficiency measurements: Thick, thin, flat, curved Curved detector efficiency setup studied area Curved detector Ref. 2 Ref. 1

10. Efficiency vs. Mesh HV : Thick flat and thin curved detectors Efficiency greater than 98% achieved within a wide HV range Very similar results for thick-flat and thin-curved !

11. Efficiency versus Drift field Gain reduced by about 50% due to transparency issues; Efficiency lowered by only a few % in the worst case : manageable (fairly recent measurement, needs to be examined further and optimized)

12. Flex cable noise studies Coherent noise is obvious After subtraction (averaged over all channel) RMS = 10 RMS = 6.8 ! 220cm flex cable

13. Flex cable noise studies Only ASIC rms=3.1 40cm rms=5.3 160cm rms=6.4 80cm rms=5.8 220cm rms=6.8

14. Conclusions Several important studies were made using the Saclay cosmic bench: -MIP detection in large area, thin Micromegas detectors with long flex cables -Efficiency is high at reasonable mesh high voltage, for all detector types, including the CLAS12 demonstrator -First look at position resolutions yield similar results for thick-flat and thin- curved detectors : specs for CLAS12 should be easily met. More tests soon in an upgraded cosmic bench. -The potential problem of transparency because of high drift HV (needed for the X tiles in the B field) seems manageable (only 50% loss in gain, which does not induce a large effect in efficiency) -One of the key part of the Micromegas setup is the ability to have the FE electronics up to 80cm from the detectors, connected by flex cables. Studies with increasing flex cable length showed only little effect on noise level thanks to modern digitizing electronics. >>>>>>>> No show stoppers, and more upcoming tests (gas, spark rate, noise, etc)