Comparing geometries Kenneth Wraight on behalf of UK ATLAS ITk Pixel Upgrade Cluster based comparison of alternative ITk geometries Alternative geometries Mapping pixels to readout with strong interactions Comparison of geometries Clusters Charge ‘bleeding’ Residuals AC/DC comparison 1

Alternative geometries Cern Pixel 5 (CP5) production involved alternative geometry pixel sensors Possible alternative for improved vertex resolution  b-tagging Charge sharing, capacitance, biasing Pitch (µm2) Ncols:Nrows Channels 250x50 80:336 26880 125x100 160:168 167x125 120:134 16080 (3/5) 500x25 40:672 Data taken over several test beams DESY 2013/14/15 SLAC 2014 CERN 2015 Devices come from Micron, bump-bonded at Advacam FEI4 readout chip: 80x336 channels: 20x16.8mm2 Pixel array may not match readout channel array Problematic for clustering: pixel-readout mapping required AC/DC readout possible (only DC readout devices studied here) 300 μm, 10 kOhms/cm, DC, ~80V depletion voltage Pixel efficiency comparison (Milovanovic et al, JINST): http://iopscience.iop.org/1748-0221/9/11/C11010/

Alternative geometries 500x25µm2 125x100µm2 Each readout pattern specific to sensor Square pixels have long readout strips to accommodate geometry 167x125µm2

Strong scattering at CERN SPS pion beam Pions interact strongly with nucleus (moreso with >Z) Secondary interactions seen in detectors Isotropic decays crossing many pixels See increased pixel occupancy w.r.t. DESY  Larger cluster sizes rate >100 (250x50µm2) pixel clusters: 5 in 10,000 Not enough to upset reconstruction Reference sensors Pixels hit/event 250x50µm2 500x25µm2 167x125µm2

Visual Mapping: 500x25µm2 Check mapping in events with >100 pixels firing unmapt mapt v2 mapt v2 zoom mapt v1

Mapping by Cluster Parameters 500x25µm2 Visual analysis matches mapped clustering results Mapping version1 has correct ordering of cluster sizes and looks reasonable w.r.t. reference  good Version2 has almost equal cluster sizes and doesn’t compare well to reference  bad So can make comparison of AC & DC (THL=3000, -100V) DUT Sig cluX cluY mult 250x50 9.07 1.06 1.41 1.27 500x25 v1 8.75 1.02 1.81 1.25 500x25 v2 6.93 1.38 1.44 1.58 DUT Sig cluX cluY mult 500x25 DC 8.75 1.02 1.81 1.25 500x25 AC 7.93 1.03 1.69 1.16

Mapping by Cluster Parameters 167x125µm2 TB Itinerary Mapping by Cluster Parameters 167x125µm2 From comparing mapped cluster parameters: Versions 2,3&5 have wrong order of cluster size  bad Versions 2,3&4 have parameters which are too low bad Versions 1,6 seem to have correct cluster parameters… DUT Sig cluX cluY mult 250x50 9.07 1.06 1.41 1.27 167x125 v1 9.93 1.31 1.35 1.08 167x125 v2 7.99 1.11 0.888 167x125 v3 7.90 0.915 167x125 v4 6.76 1.03 1.04 0.539 167x125 v5 9.66 1.26 1.14 167x125 v6 1.25 1.33

Visual Mapping: 167x125µm2 Check any events with >100 pixels firing unmapt zoom unmapt mapt v1 zoom mapt v6 zoom

The Imitation Game “Imitate” pixel sizes to get expected response Use smallest pitch available: 25µm Group pixels to similar sizes as other sensors: n*25µm DUT Sig cluX cluY mult 250x50 9.07 1.06 1.41 1.27 500x25 8.75 1.02 1.81 1.25 500x“50” 8.83 1.03 1.33 1.24 500x“100” 8.9 1.17 1.23 500x“125” 8.92 1.18 500x“150” 8.93 1.12 1.22 500x“175” 8.94 1.13 See agreement between simulated and normal pitch parameters 500x“125”, 500x“150”, 500x“175” cases give approximate values expected for 167x125 clusters

167x125µm2 Mapping With expected values one mapping looks most successful From imitation: 167x125 cluster size should be ~1.13 and ~1.18 for X & Y respectively unmapt zoom mapt v5 zoom DUT Sig cluX cluY mult 167x125 v1 9.93 1.31 1.35 1.08 167x125 v5 9.66 1.26 1.14 1.11 167x125 v6 1.25 1.33

Evidence of charge leaking Vertical track suggests reason for X cluster problem mapt v5 167x125µm2 167x125µm2 Unlikely charge made zig-zag track Looks like straight vertical track with alternate adjacent pixels firing due to charge leakage  More trouble for 125x100µm2 device 2/4 pixels have long readout connections 125x100µm2

Cluster Size Map 167x125µm2 (CoG) map of per pixel cluster ave. size Global ave. cluster size X,Y = 1.18, 1.15 See pattern in X absent from Y 1/3 pixels cooler than rest Correspond to pixels without long readout connection and not adjacent to long RO Structure found in profile Average X cluster size per pixel Average X cluster size per pixel X Profile Average Y cluster size per pixel

Cluster Size Map 125x100µm2 (CoG) map of per pixel cluster ave. size Global ave. cluster size X,Y = 1.31, 1.18 No pattern seen in X map as all pixels either have long readout connections or are adjacent to long RO Structure found in profile Average X cluster size per pixel Average Y cluster size per pixel Average X cluster size per pixel X Profile

Cluster Size Map 125x100µm2 no CoG Using cluster midpoint to populate map, see column structure: bias introduced in calculation of cluster coordinate Also seen in using seed pixel coordinate Profile plots show structure from increased entries per pixel In seed position case this matches long RO pixels Average X cluster size per pixel Cluster midpoint Seed postion

Cluster size comparison Comparison based on DESY Nov’13 & CERN Sep’15 @THL=3000e, V=-100V Mapping specific to each device Expected mapping “imitated” using multiples of 25µm pitch Based on 500x25µm2 sensor at DESY Two sets of points for 125µm pitch X & Y dimensions See effect of charge “bleeding” in X dimension square pixel sensors at 125µm & 167µm See CERN cluster size consistently smaller than DESY less scattering? charge deposition? Cluster size Vs pixel pitch Cluster size follows trend at DESY & CERN Cluster size most sensitive at smaller pitch sizes

See Alex’s talk GBL Form triplets on both upstream and downstream arms Triplet: form doublet from first and third planes (with cut), add middle plane (with cut) Triplets meet in middle of telescope with cut on coincidence position and slope Each track is parameterised as straight line. The track is extrapolated or interpolated to form a trajectory Plots available to tune cuts

Initial Residual comparison Residuals calculated from mapped clusters Residuals for all cluster sizes shown Ideal residual pitch/√12 CERN residual consistently smaller than DESY scattering? charge deposition? See effect of charge “bleeding” in X dimension square pixel sensors at 125µm & 167µm Sins in sensors masked by sins in set-up Residual Vs pixel pitch Residuals follows ideal trend at DESY & CERN Some deviation (separation) of trends at (lower)extremes

DESY 250x50µm2 AC/DC comparison 250x50µm2 AC/DC comparison Relative signal drop for AC across biases from testbeam Similar magnitude to lab tests: 10-20% Pixel efficiency comparison shows both perform well Response comparison with SPS desirable 250x50µm2 DC, AC ToT 8ToT@20ke THL=3000 Bias 250x50 AC 250x50DC (Ref) 20V 0.9960+/-0.0002 0.9949+/-0.0002 50V 0.9972+/-0.0003 0.9971+/-0.0003 80V 0.9967+/-0.0002 0.9962+/-0.0002 100V 0.9972+/-0.00001 0.9966+/-0.00001 AC DC Efficiency Analysis from H. Hayward

July SPS AC/DC signal comparison ToT 250x50µm2@100V 500x25µm2 167x125µm2 8ToT@20ke THL=3000 Comparison with Liverpool lab tests Same: 500x25µm2 has lower response than 167x125µm2 Diff: No change in AC/DC order with bias present in lab test Diff: smaller discrepancy seen (same tuning) Need to look into details of ToT calculations: cluster signal vs. pixel source scan

Summary & Next steps Reconstruction comparison of DC devices Residuals vs pitch 2 separate testbeam environments Next complete analysis: single/double pixel cluster comparison Move to Tbmon-II analysis Initial look into charge sharing Possible metric Initial comparison of AC & DC devices suggest differences in response and charge evolution Next testbeams will focus of AC comparison of pitch sizes

Beyond the Standard Slides Back-up Beyond the Standard Slides

EUTelescope mapping recipe Here, used EUTelescope trunk version ~May 2015 In order to read in alternative geometry Define DUTs with correct pixel array edit $EUTELESCOPE/src/FEI4Single.cc as template edit $EUTELESCOPE/src/EUTelescopeGenericPixGeoMgr.cc Add new geometries to gear file Define as plane (appropriate Nrows & Ncols etc.) Use new libraries e.g. FEI4Single_250x50.so Additional reconstruction step to map converter pixels before clustering No changes made to clustering Clustering by $EUTelescope/src/EUTelProcessorGeometricClustering.cc General Broken Lines used patternRecognition and GBLAlign

GBL Form triplets on both upstream and downstream arms Triplet: form doublet from first and third planes (with cut), add middle plane (with cut) Triplets meet in middle of telescope with cut on coincidence position and slope Each track is parameterised as straight line. The track is extrapolated or interpolated to form a trajectory Plots available to tune cuts

GBL steps Usual converter, clustering & hitmaker steps Alignment takes place in a couple of steps between hitmaker & track fitting DAFfitter combines steps in single processor Hitlocal step produces augmented gear file with basic plane orientation and XY offset calculated based on correlations … input to … Pattern recognition creates track candidates and filters based on supplied cuts (viewable in histo file) GBLAlign makes final alignment of telescope. New gear file GBLTrackFit produces residual plots and can produce TBmon readable root file for further APIX analysis

TB Itinerary Seed Fraction Maps of cluster_seed_charge/cluster_charge: only 2 hit clusters considered 167x125 X 167x125 Y Derive global seed fraction maps: fraction of cluster charge found in hottest pixel in cluster For non-leaky devices (250x50, 500x25) see larger pitch leads to smaller seed fraction Leaky devices have reverse trend, i.e. smaller pitch has smaller seed charge DUT Ave. seedFrac X Ave. seedFrac Y 250x50 0.675, 0.676 0.686, 0.690 500x25 0.677, 0.643 0.707, 0.705 167x125 0.788 0.691 125x100 0.823 0.670 "500x125" 0.687 , 0.645 0.712, 0.705

Leak rate Suppose charge falls homogenously across devices Neglect cluSize>2 (~1% or less from measurements) 125x100 example Imitation of 125 pitch estimates cluster size = 1.16 Suppose (Ax+By)=C, where A,B are cluster sizes from different processes C is total cluster size (for one dimension) x,y are fraction of time clusters produced by process  x+y=1  y=(A-C)/(A-B) Solving how often normal clustering occurs (2-1.31)/(2-1.16)=0.8214 So charge leaking occurs ~18% of all hits (far below 50%) 2/4 are do not have long connection to readout So, other 50% is liable for the leakage leakage twice as likely  frequency of pixels leaking: (1-0.8214)*(2/1)=0.3572 i.e. about a third of the time pixels with long connection leak 125x100 500x“125” THL=3ke, -100V 125x100 167x125 estimate 1.16 1.13 measure 1.31 1.18 Leak rate 18% 5% Next pixel leak rate 36% 17%