Fred Hartjes 1 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Gossip testbeam August 12 – 22, 2010 Maarten van Dijk Martin Fransen Harry van der Graaf Fred Hartjes Wilco Koppert Sjoerd Nauta Rolf Schön

Fred Hartjes 2 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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: thin gas layer instead of bulk semiconductor Drift gap ~ 1 mm high Signal (some 6 electrons) enhanced by gas avalanche from a grid Gain Scaled up 4x for better visibility ~1 mm 14 mm (256 columns) 14 mm (256 rows) The Gossip project has been recently approved by Atlas collaboration board as an R&D project

Fred Hartjes 3 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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

Fred Hartjes 4 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Reconstructing track segment Track characterized by ,  and the crossing point (X, Y) with the reference plane

Fred Hartjes 5 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Timepix as a pixel chip TimePix Derived from MediPix (X-ray detection) Matrix of 256 x 256 pixels 55 µm pitch => x mm 2 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

Fred Hartjes 6 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Chamber gas: DME/CO 2 50/50 DME/CO 2 50/50 o Very slow and “cool” gas o High drift field required o Very low diffusion o Suited for TPC Drift fields used in Gossips o 2 kV/cm (lowest diffusion) o 6 kV/cm (Vd = 50 µm/ns) o LHC tracking

Fred Hartjes 7 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Aim of the Gossip testbeam experiment in August Gossip parameters Position resolution Angular resolution of track segment Track detection efficiency Dependence on gas gain Double track separation 2.Characterisation of DME/CO2 50/50 mixture Primary ionisation/cluster density Drift velocity Transverse diffusion 3.Cathode emission PillarPix detector, NO drift gap Detecting knock-off electrons from cathode surface Cathode from three different materials: doped diamond; Cu; Al ~ 70 µm 19.3 mm e-e-

Fred Hartjes 8 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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 1Gossip 2 Gossip 3Gridpix (DICE) 19.3 mm

Fred Hartjes 9 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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 Angular adjustment Remotely adjustable by CERN XSCA table

Fred Hartjes 10 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010

Fred Hartjes 11 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010

Fred Hartjes 12 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Completely remotely controlled Communication between barrack and experimental area by 2 Ethernet cables Using Remote Desktop KATALPA

Fred Hartjes 13 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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

Fred Hartjes 14 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Temperature during testbeam Logged every minute during the testbeam period Temperature in hall varying between 20.6 and 25.4 °C

Fred Hartjes 15 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Atmospheric pressure during testbeam Varying between 961 and mbar

Fred Hartjes 16 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 We used a metal tray on the floor, 90 x 130 cm, surrounding the whole gas system

Fred Hartjes 17 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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

Fred Hartjes 18 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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)

Fred Hartjes 19 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Gas flow during August testbeam White: inlet gas steam Red: exhaust gas stream Adjusted between 50 ml/min (purge) and 5 ml/min (standby)

Fred Hartjes 20 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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

Fred Hartjes 21 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 In total 60 runs containing ~250k events Almost all done with DME/CO 2 50/50 and 150 GeV muons Last 4 runs with Ar/iC 4 H 10 80/20 46k events ~3k of them were hadrons

Fred Hartjes 22 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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-e-

Fred Hartjes 23 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Typical event in all 4 detectors (angle 10°)

Fred Hartjes 24 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Typical event in GridPix under 45° Very small diffusion but big time slewing From aside From top

Fred Hartjes 25 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Comparing DME/CO 2 to Ar/isobutane DME/CO 2 50/50 Ar/iC 4 H 10 80/20 Tracks under 10° In Y direction

Fred Hartjes 26 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 DME/CO 2 has big advantages wrt diffusion DME/CO 2 50/50 Ar/iC 4 H 10 80/20 361run58_0.txt 35 um/ns434run55_3.txt 9.5 um/ns In X direction

Fred Hartjes 27 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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

Fred Hartjes 28 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Drift time spectrum of a Gossip V g = -530 V -570 V -600 V -620 V TimePix chip suffering from time slewing Less dominant at high gain

Fred Hartjes 29 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Number of hits per track in Gossip vs grid voltage 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 Expected: 6.4 clusters 12.5 electrons Tracks under 45°

Fred Hartjes 30 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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 V grid = -600VV grid = -610VV grid = -620V V grid = -590V

Fred Hartjes 31 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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?? V grid = -600VV grid = -610VV grid = -620V V grid = -590V

Fred Hartjes 32 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 Track detection efficiency Tracks selected by GridPix detector Completely flat plateau from ~ -570 V on Expected for 1.0 mm DME/CO 2 : 98.9%

Fred Hartjes 33 6 th RD51 collaboration workshop, Bari (Italy), October 9, 2010 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 V grid going from -600 V to -610 V Difference in number of hits between Gossip 2, 3 and 4 (not consistent with metrology)