Gossip testbeam August 12 – 22 , 2010

1. Gossip testbeam August 12 – 22 , 2010 Maarten van Dijk Martin Fransen Harry van der Graaf Fred Hartjes Wilco Koppert Sjoerd Nauta Rolf Schön

2. Principle of Gossip • High granularity pixel chip • Cell pitch 55 – 60 μm in X and Y • Thinned to 50 – 100 μm (not for this testbeam experiment) • Detection medium: thingas layer instead of bulk semiconductor • Drift gap ~ 1 mm high • Signal (some 6 electrons) enhanced by gas avalanche from a grid • Gain 5000 - 10000 14 mm (256 columns) 14 mm (256 rows) ~1 mm The Gossip project has been recently approved by Atlas collaboration board as an R&D project Scaled up 4x for better visibility

3. Gossip functioning • Pixel chip with integrated Micromegas (InGrid) • Drift gap height 1 mm • Getting > 95% track detection efficiency • Often detecting individual electrons • Track segment characterized by • Crossing point • Direction

4. Reconstructing track segment • Track characterized by , and the crossing point (X, Y) with the reference plane

5. Timepix as a pixel chip • TimePix • Derived from MediPix (X-ray detection) • Matrix of 256 x 256 pixels • 55 µm pitch • => 14.08 x 14.08 mm2 sensitive area • Common clock (100 MHz) to measure drift time for each pixel • Also Time-Over-Threshold (TOT) mode to measure charge signal spectrum • Postprocessing • 7 µm Si doped Si3N4 for spark protection • Amplification grid (InGrid) on TimePix InGrid

6. Chamber gas: DME/CO2 50/50 • DME/CO2 50/50 • Very slow and “cool” gas • High drift field required • Very low diffusion • Suited for TPC • Drift fields used in Gossips • 2 kV/cm (lowest diffusion) • 6 kV/cm (Vd = 50 µm/ns) • LHC tracking

7. Aim of the Gossip testbeam experiment in August 2010 • Gossip parameters • Position resolution • Angular resolution of track segment • Track detection efficiency • Dependence on gas gain • Double track separation • Characterisation of DME/CO2 50/50 mixture • Primary ionisation/cluster density • Drift velocity • Transverse diffusion • Cathode emission • PillarPix detector, NO drift gap • Detecting knock-off electrons from cathode surface • Cathode from three different materials: doped diamond; Cu; Al 19.3 mm ~ 70 µm e-

8. Using Gossip/GridPix telescope as a reference • Measurements done with Gossip 2 • Define track with Gossip 1 and 3 • Reject bad events using the Gridpix detector (19.3 mm drift gap) • Wrong angle (background tracks) • Outside fiducial volume • Multiple tracks (showers) Gossip 3 Gridpix (DICE) Gossip 1 Gossip 2 19.3 mm

9. Angular adjustment Mechanical set-up in testbeam • 1 m optical bench • 4 Gridpix detectors • 3 x Gossip • GridPix • 2 Scintillators 15 x 15 mm • Mass flow controller and meter Remotely adjustable by CERN XSCA table

12. Completely remotely controlled • Communication between barrack and experimental area by 2 Ethernet cables • Using Remote Desktop KATALPA

13. DAQ and services • DAQ of TimePix chips by MUROS • 4 TimePix chips daisy chained • ~ 10 Hz event rate during spill • Complete remote control of • Grid voltages • Field voltages • Gas flow • Logging (every minute) of • All voltages • Gas flow • Temperature • Atmospheric pressure • Advantage • Parameters may be modified during beam on • Experimental conditions of all measurements well known

14. Temperature during testbeam • Logged every minute during the testbeam period • Temperature in hall varying between 20.6 and 25.4 °C

15. Atmospheric pressure during testbeam • Varying between 961 and 968.5 mbar

16. We used a metal tray on the floor, 90 x 130 cm, surrounding the whole gas system

17. Special requirements for flammable gas • Gas mixture from 120 l JSP gas bottle • Prepared at Nikhef • Whole gas system including bottle contained in leak tray • Checking gas leaks by measuring deficit between input flow and exhaust flow • Connected to flammable gas exhaust line

18. LabView controlled gas system • Operation • Flow logged each minute • Alarm at leak rate > 3 ml/min • Shut off at integrated leak volume of 30 ml • Gas flow set between 5 and 50 ml/min • Possible calibration error by factory (flow too low)

19. Gas flow during August testbeam • White: inlet gas steam • Red: exhaust gas stream • Adjusted between 50 ml/min (purge) and 5 ml/min (standby)

20. Data analysis of the August 2010 testbeam • Just started, still most to be done • Only preliminary results are given • Suffering from material of upstream experiment • Several cm of aluminium, copper plates • Showers => many multiple track events • Nuisance, but shower events can be used to study double track separation

21. In total 60 runs containing ~250k events • Almost all done with DME/CO2 50/50 and 150 GeV muons • Last 4 runs with Ar/iC4H10 80/20 • 46k events • ~3k of them were hadrons

22. What has been measured? • 50k events for Gossip under 45° • Grid voltage scan from -510 to -620 V • Mostly at field 2 kV/cm • 2.8 k events at 6 kV/cm • 10k events under 4 other angles • 0; 5.75; 11.5 and 23° • Both at drift field of 2 and 6 kV/cm • 25k events with secondary emission detector • 44k events in GridPix under 90° • 5k events with parallel tracks in Gossip e-

23. Typical event in all 4 detectors (angle 10°)

24. Typical event in GridPix under 45° • Very small diffusion but big time slewing From aside From top

25. Comparing DME/CO2 to Ar/isobutane Tracks under 10° DME/CO2 50/50 Ar/iC4H10 80/20 In Y direction In Y direction

26. DME/CO2 has big advantages wrt diffusion DME/CO2 50/50 Ar/iC4H10 80/20 434run55_3.txt 9.5 um/ns 361run58_0.txt 35 um/ns In X direction In X direction

27. Data analysis • Cuts on each detector individually • Cuts on fitted tracks • Slope • Intercept Z=0 • Fit residue • Cuts on pixel hits • Fiducial area • Maximum drift time

28. Drift time spectrum of a Gossip Vg = -530 V -600 V • TimePix chip suffering from time slewing • Less dominant at high gain -620 V -570 V

29. Number of hits per track in Gossip vs grid voltage Tracks under 45° • Unexpected difference between the three Gossips • If drift gap of Gossip 3 were 1.0 mm, then Gossip 4 =>1.13 mm and Gossip 2 => 0.84 • => not consistent with metrology (differences of 40 µm) • Expected: • 6.4 clusters • 12.5 electrons

30. Jump caused by change in atmospheric pressure? • 961 mbar at -600 V • 964 mbar at -610 V • Would a higher gas density give higher gas gain?? • Analysis of other data needed to confirm this Vgrid = -600V Vgrid = -610V Vgrid = -620V Vgrid = -590V

31. Jump caused by change in temperature? • ~ 23 ° C at -600 V • ~ 22.5 ° C at -610 V • 23.3 ° C at -620 V • Would a higher gas density give higher gas gain?? Vgrid = -600V Vgrid = -610V Vgrid = -620V Vgrid = -590V

32. Track detection efficiency • Tracks selected by GridPix detector • Completely flat plateau from ~ -570 V on • Expected for 1.0 mm DME/CO2: 98.9%

33. Concluding:Detectors operating well, but some results not understood • All Gossips were operating reliably without any HV problem at high gain • The older GridPix (mostly running at -560 V) had less good gain, but probably rather good single electron efficiency • Profited Infrastructure of remote control of HV and gas • Parameters may be modified when beam is on • Values permanently logged • We have collected data to determine position resolution and angular resolution for 5 difference angles of incidence • Gossips have excellent track detection efficiency (~ 99%) from -570 V on • Not yet understood: • Jump in number of hits for Vgrid going from -600 V to -610 V • Difference in number of hits between Gossip 2, 3 and 4 (not consistent with metrology)