Micromegas for CLAS12 Central Detector - Update Franck Sabatié November 19th 2009 Micromegas option for the Central Detector Why, Where, How ? R&D milestones and illustrations Conclusions and outlook

2 Why Micromegas for the CD : - Complements the silicon vertex tracker (x10 better  resolution, more lever arm at large radius for better p resolution) - Cheap: Detector itself is ~$1000/unit - Geometry : cylindrical shape are now possible, which allows to use the best geometry for physics - Only reasonable available option for forward central tracker 4 x 2MM 4 x 2SI 2 x 2SI + 3 x 2MM Specs.  pT /p T (%)   (mrad) <10-20   (mrad) <10  z (μm) tbd. A mixed solution combines advantages of both the silicon (SI) and micromegas (MM) detectors For the barrel part : Micromegas for CLAS12 Central Detector – Why ?

Curved bulk Micromegas Flat bulk Micromegas Micromegas for CLAS12 Central Detector – Where ? Current concensus is : 3 planes of SVT + 3 planes of MM in the barrel + Full Micromegas forward vertex tracker

4 Several points to be adressed before Micromegas implementation in CLAS12 AdressedOngoing bMM feasibility  cbMM feasibility  Long flex-PCB use  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 Micromegas for CLAS12 Central Detector – How ? 2009 CERN tests !

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 !

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

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

Flex cable noise studies Only ASIC rms=3.1 40cm rms= cm rms=6.4 80cm rms= cm rms=6.8 Noise induced by the detector 80cm flex cable is current max

Just published in NIM A ! Lorentz Angle measurements in Hall B (end of 2008) Low enough Lorentz Angle (~20°) can be achieved at 4.5T field to ensure the required position resolution for the barrel Micromegas

10 Beam Electronics Detectors Spark tests at CERN ( Oct. 23 rd to Nov. 3 rd 2009) 150 GeV Hadron or Muon Beam ~10 6 particles/spill ~3s spills Magnetic field up to 1,5T

11 bMM X (2 mm drift gap, alumized mylar drift) bMM Y (5 mm drift gap, alumized mylar drift) bMM X (5 mm drift gap, stainless steel drift) bMM X (5 mm drift gap, alumized mylar drift) Total number of sparks (scaler readout) Time (s) # Spark versus time

12 2 mm drift gap 5 mm drift gap X-strips Spark probability (per incident hadron) versus spill # Stable spark probability, around 10 -5, lower for the 2mm drift gap detector as expected

Some early findings : -Spark scales as the quantity of heavy material in the detector -The process : nuclear interaction resulting in high-ionizing heavy fragment(s) (  and above) inducing the spark -Simulations seems to confirm this interpretation -Spreading the ionization reduced the spark rate : this was « achieved » by the external magnetic field inducing a Lorentz angle. What can we say for CLAS12 : -Not much ! Conditions are extremely different : 150 GeV hadrons versus ~1 GeV hadrons. It would be extremely valuable (and reassuring) to perform tests at JLab with 6 GeV beam. -However : the 5T field will help us reduce spark rate. Also, the spark probability is about as expected by simulations and previous measurements. -Bulk Micromegas do not spark more than standard Micromegas, this was a common fear among experts and tested for the first time here. Some early and preliminary findings from these tests

Conclusions and Outlook -By the end of the year, our « shopping list » of things to check will be done -Recent spark test at CERN showed bulk Micromegas behave the same as standard Micromegas. As far as we can test without a beam test at 6 GeV JLab (which would be VERY valuable), sparks should not be a problem for us. -Still no show-stoppers, Micromegas seem very promising for CLAS12 CD -Limited work on Forward Vertex Tracker so far, because it’s the « usual » use for Micromegas and only optimization/definition work needs to be done -Some remaining R&D work remains, mostly about the definition of our working point (drift distance, gas, high voltages) as far as the barrel detectors are concerned. -Final technical definition of the barrel and forward Micromegas remain and will be 2010 top priority. Electronics definition are ongoing (potentially used for SVT as well – when would that be decided ?) -Scheduled for the next Saclay SPhN PAC (june ‘10) for final project acceptation and funding. Before that, an official green light from JLab will be necessary so we can start getting/spending money.