1. On behalf of the LCTPC collaboration -Uwe Renz- University of Freiburg renz@physik.uni-freiburg.de Albert-Ludwigs- University Freiburg Physics Department

2. 11/3/2010renz@physik.uni-freiburg.de2 50 µm 70 µm Field in holes >70kV/cm e- e- e - -avalanche from gas amplification I+I+ I+I+ e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- 140 µm Gas amplification confined to region of holes Discharges restricted to GEMs  readout rarely compromised Diffusion in GEM stack: charge spread over several pixels (>50pixels): » high gas gain needed. » cascade several GEMs.

3. 11/3/2010renz@physik.uni-freiburg.de3 Gas amplification in gap between grid and chip Against discharges: deposit thin protection layer (  8 µm) of Si 3 N 4 or a-Si:H Perfect alignment of pixels and grid  electron(s) entering one hole fire one pixel: »spatial resolution not affected by diffusion during gas amplification »single electron counting (e.g. useful for particle identification, dE/dx measurement) 50 µm e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- I+I+ I+I+ >70kV/cm e- e-

4. 11/3/2010renz@physik.uni-freiburg.de4 Dimensions 256 x 256 pixels 2 55 x 55 µm 2 pixel size 14 x 14 mm 2 active area 3 side „buttable“ to combine several chips and increase sensitive area Four recording modes Time Over Threshold (TOT), proportional to input charge TIME, used to measure drift time Hit counting Hit yes/no, not used Only one per pixel TimePix is used as highly segmented charge collecting anode Mixed Mode Alternating pixels are set to TOT and TIME mode. Results in a checkerboard-like fashion. Measure TIME and TOT simultaneously, interpolate missing neighbors.

5. GEMs with TimePix-Quad(s) New board designs for Ingrids »New Nikhef design: gastight multilayer PCB board  no additional mechanical gaskets for detector. »CEA Saclay : “Octopuce: 8 Ingrids on one board  only one readout interface Ingrid Quad and “Octopuce” 11/3/2010renz@physik.uni-freiburg.de5 “Integration” work towards real TPC readout: equip large(r) surfaces with TimePix chips or Ingrids. Existing technology: quad boards developed by NIKHEF » Boards not designed for gas detectors  not gas tight. » For each quad board dedicated readout interface. 2 quads or 1 Octupuce  512k readout channels on 15.68 cm 2.

6. 11/3/2010renz@physik.uni-freiburg.de6 5 GeV electron beam Quad Timepix+Ingrid Gas: He-iC 4 H 10 80/20 A normal track 28 mm Short drift Small diffusion Long drift “large” diffusion 11.5 mm Few tracks from  3-day test at DESY with quad-Ingrid detector Gas: He-iC 4 H 10 80/20 Gas gain  4000 Event Display Pixelman, designed by IAEP Event Display Pixelman, IEAP Prague

7. A cosmic track in the Octopuce with He-iC 4 H 10 (80/20) at a gas gain of  2500 11/3/2010renz@physik.uni-freiburg.de7 Soon: study Octupuce in realistic ILC-TPC model – the Large Prototype. Leakage currents between TimePix and grid. Event Display Pixelman, IEAP Prague 28 mm 56 mm

8. 11/3/2010renz@physik.uni-freiburg.de8 720 mm Endplate: 7 modules with individual readout concepts (e.g. “classic” pads or modern pixels readout) Arrangement of modules resembles design of large TPC at future LC Field cage scalable to real LC-TPC Drift distance up to 60 cm Field cage has 1.2% of radiation length (X 0 ) Field homogeneity between  E/E  10 -3 - 10 -4 Fits into 1 T magnet at DESY Electron beam with up to 5 GeV 56 mm 28 mm Mixed Mode Event from the GEM/TimePix module in the LP at DESY T2K gas: ArCF 4 iC 4 H 10 (95/3/2) B = 1 T Event Display Pixelman, IEAP Prague

9. 11/3/2010renz@physik.uni-freiburg.de9 Conclusion D t and D l agree with simulations to a percent level. Discrepancies can be explained by » gas impurities (e.g. H 2 O, O 2, …). » D t and transverse  0 especially affected by distortions of drift field E Drift and magnetic field B fit parameters no errors given

10. 11/3/2010renz@physik.uni-freiburg.de10 Large diffusion between GEMs » Charge typically spread over > 50 pixels. » High gas gain needed.  Combine several pixels to larger pads collecting more charge. unprocessed pixel cell processing of pixels processed pixel geometries Active pixel area passivated pixel area tested geometries

11. 11/3/2010renz@physik.uni-freiburg.de11 Freiburg setup 5.9 keV g from Fe 55 6mm drift 3 GEMs TimePix Charge per pixel increases for larger pixels. Energy resolution improves with pixel size. Systematics due to charge calibration of TOT and pixel to pixel crosstalk investigated. Pixel to pixel crosstalk through passivation seen (3x3)

12. 11/3/2010renz@physik.uni-freiburg.de12 Transverse resolution slightly deteriorated for large pixels. Systematic effects still investigated. Chip   [µm]D t [µm/  cm] (1x1)(56.4 ± 0.1)(138.264 ± 0.005) (2x2)(55 ± 1)(139.0 ± 2) (4x4)(68 ± 13)(140.0 ± 0.5) (5x5)(75 ± 9)(146.4 ± 0.6) only statistical errors

13. Summary First successful test of large prototypes: »512k readout channels - largest number of readout channels for GEM and Micromegas based TPCs. »Equipped still only an area of 15.68 cm 2. GEMs benefit from large pixels: »Less gas gain needed. »Energy resolution not affected. »Spatial resolution only slightly deteriorated. Successful design of large Ingrid modules: »Unprecedented imaging of primary single electrons in gaseous detectors. »New Quad: gas tight multilayer PCB. Minimizes material budget as additional gaskets are superficial. »Octopuce: Only one readout interface necessary for up to 8 chips. Outlook Continue work to equip still larger surfaces  gain experience with: »Mechanics. »Cooling. »Integration issues with other (sub-)detectors. Development of TimePix2 »Faster readout. »Simultaneous measurement of TOT and Time on each pixel. »Improve energy resolution  reduce electronic noise. Verify results with detailed simulation to improve understanding of measurements. 11/3/2010renz@physik.uni-freiburg.de13

14. 11/3/2010renz@physik.uni-freiburg.de14

15. 11/3/2010renz@physik.uni-freiburg.de15 A TPC at an LC would have: R  2 m L  4-5 m Traditional TPC with MWPC: Needs gating grid between each bunch crossing Limited space resolution: » Wire and pad size » effects ⇒ Suggestion use Micro-Pattern Gas Detectors (MPGD) (“micro” = 50-150 μm) with high granular readout Requirements at a future Linear Collider (LC) Gating only between bunch “trains” Momentum Resolution δ(1/pt) < 10 -4 / GeV Single point resolution in r-φ  100 μm, r-z < 2 mm 2 track resolution in r- φ < 2mm, r-z < 5mm GEM Micromegas

16. 11/3/2010renz@physik.uni-freiburg.de16 Anode plane (GEMs) Readout plane with quad board or Ingrids Head sink and support of anode plane “Red” Frame 100 mm With GEMs Readout plane with 2 TimePix-Quads Readout plane with Octupuce 28 mm 56 mm 28 mm  56 mm Magnet (B max = 1 T) TPC-endplate Module-dummies TimePix module Module with pad readout