Dominik Dannheim (CERN-PH-LCD) Beam-induced backgrounds in the CLIC vertex- and tracking-detectors CLIC meeting 26. August 2011 CERN

26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors2 CLIC detectors 2 CLIC detector concepts “inherited” from ILC and adapted to CLIC conditions Status report by Lucie in CLIC meeting on June 24 th 2011 ( CLIC_SiD_CDR Here: concentrate on inner-detector regions and beam-induced backgrounds (Dimensions in mm)

26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors3 Outline CLIC detector requirements and challenges Beam-induced backgrounds Vertex- and tracking detector layouts Occupancies and layout optimization Radiation exposure Vertex-detector technology options Summary/conclusions

e+e- collisions at CLIC 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors4 CLIC will deliver e + e - collision with √s up to 3 TeV Precision measurements of new particles discovered at the LHC (or at CLIC!): Momenta and invariant mass of the decay products  Need tracking system with very good momentum resolution p=1 GeV: σ(p T )/p T = 0.1% (CMS: 0.7%) p=100 GeV: σ(p T )/p T = 0.2% (CMS: 1.5%) Tagging of “rare” particles: heavy quarks and tau leptons  Need high-resolution pixel detector to measure displaced vertices p=1 GeV: σ d0 ~20 μm (CMS: 90 μm) p=100 GeV: σ d0 ~5 μm (CMS: ~10μm) d0d0 b

CLIC challenges for detectors 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors5 Unfortunately not only interesting physics events: ~10 8 background events produced at IP with every physics event Time structure of the collisions poses challenges: 312 BX per train, 0.5 ns spaced  Physics events are buried inside an abundance of overlapping background  Occupancy = #hits / #readout-cells can reach large values  Need time stamping and sophisticated pattern-recognition algorithms to disentangle physics from background 50 Hz train-repetition rate  trigger-less readout of whole train  power pulsing of readout electronics, to minimize material needed for cooling …………..… 312 bunches = 156 ns 0.5 ns …………..… 20 ms

Beam-induced backgrounds e + e - pairs and γγ  hadrons at √s=3 TeV, simulated with GUINEA-PIG + Pythia (D. Schulte): 6 x 10 8 coherent particles / BX Spectrum falls very steeply with θ 7 x 10 6 trident particles / BX Spectrum falls very steeply with θ 3 x 10 5 incoherent particles / BX Larger contribution in detector Backscatters from forward region need particular attention 102 γγ  hadron particles / BX (m γγ >2 GeV) Harder p T spectrum (<~5 GeV) Mostly direct hits Full simulation in Geant4 within detector-simulation frameworks (Mokka/SLIC): Incoherent pairs  Dedicated studies of occupancies, to optimize geometry γγ  hadrons  overlaid to physics events in Monte-Carlo mass production 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors6 Detector starts at θ>10 mrad

26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors7 Backgrounds kinematics Incoherent pairsγγ  hadr. Outside beam pipe (θ>10 mrad): 8 x 10 4 / BX96 (47 charged) / BX In vertex-detector (θ>7.3 o p T >20 MeV): 60 / BX54 (25 charged) / BX

γγ  hadrons simulation γγ luminosity spectrum generated with GUINEA-PIG (D. Schulte) Two different MC generators for γγ  hadrons simulation: Pythia (D. Schulte) SLAC generator (T. Barklow) + Pythia for hadronization Comprehensive comparison of the two generators performed resulting detector effects very similar Pythia sample is default for event overlay in CDR Monte Carlo production 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors8 PYTHIA SLAC γγ luminosity spectrumσ γγ  hadrons

γγ  hadrons comparison of samples 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors9 Observed occupancies and energy releases in detector in agreement within 15% for the two generators Pythia samples were chosen for CDR Monte-Carlo mass production

CLIC_ILD detector model CLIC_ILD Based on ILC-ILD scaled + optimized for 3 TeV CLIC 4 Tesla B-field 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors10 (Dimensions in mm) Tracking region

CLIC_ILD tracking region 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors11 x IP Silicon External Tracker Endcap Tracking Disk Time Projection Chamber Silicon Inner Tracker Forward-Tracking Disks Vertex Detector

CLIC_ILD: beam pipe and inner Si tracking 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors12 VXD 1-6 FTD 1-6 FTD 7 FTD 8 FTD 9 FTD 10 FTD 11 SIT 1 SIT 2

CLIC_SiD detector model Based on ILC-SiD, scaled and optimized for 3 TeV CLIC parameters Similar acceptance and performance as CLIC_ILD_CDR Larger B-field (5 Tesla) 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors13 Tracking region HCAL Coil Yoke ECAL

CLIC_SiD all-silicon tracker 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors14 (Dimensions in mm) Outer tracker Vertex region Vertex-barrel layers beam pipe

Vertex-detector material budgets 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors15 CLIC_ILDCLIC_SiD Integrated amount of material seen by particles originating from the IP: X/X 0 ~ 1% (at 90 o ) LHC pixel detectors (for comparison): X/X 0 ~ 10% (at 90 o )

Vertex-detector parameters 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors16 ParameterCLIC_ILDCLIC_SiDCMS Magnetic field4 T5 T3.8 T Beam pipeBeryllium R i =29.4 mm t=0.6 mm Beryllium R i =24.5 mm t=0.5 mm Beryllium R i =29 mm t=0.8 mm Barrel pixel layers3x2 layers5 layers3 layers Material X/X0 (90 o )~0.9%~1.1%~10% Forward pixel layers (per ½) 3x2 layers7 layers2 layers Pixel size20 x 20 μm x 150 μm 2 # pixels1.84 G2.76 G66 M Time resolution5-10 ns <~25 ns Power/pixel<~0.2 μW 28 μW

Optimization of CLIC_ILD interaction region (I) 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors17 direct hits from incoh. Pairs for 3 TeV direct hits from incoh. pairs for 500 GeV High occupancy in inner-forward region, cut-off ~parabolic shape 500 GeV situation similar, though lower rates  place beam pipe outside high-occupancy region 3 TeV 500 GeV

26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors18 Optimization of CLIC_ILD interaction region (II) Minimal distance of beam pipe to IP constrained by hit rate Varied beam-pipe radius and checked occupancies in critical regions  Reduced rates at 500 GeV allow for smaller radius for a given occupancy

Layout optimization: forward region 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors19 Reduction of back scatters by thick conical beam pipe Chose Fe 4 mm as baseline Pointing to IP  no material in front of forward tracker Side effect: some additional showering inside beam pipe Incoherent pairs hitting LumiCal and BeamCal scatter back towards the interaction region Be Fe

Occupancies in CLIC_ILD vertex region 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors20 Barrel cylinder layersForward disk layers Direct hits from pairs dominate Good agreement between two different detector-simulation setups Up to 3x10 -4 hits/mm^2/BX in barrel region  1.9% train occupancy / pixel Up to 5x10 -4 hits/mm^2/BX in forward region  2.9% train occupancy / pixel (includes factors for simulation uncertainty and clustering)

CLIC_ILD Time Projection Chamber 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors21 Time Projection Chamber (TPC): Charged particles ionize gas Electrons drift in high electric field towards end-plate anodes Readout with micro-pattern gas detectors (MPGD) Integration over bunch train No timing information, z-coordinate from drift time Excellent pattern recognition (224 radial readout layers) Low material budget: field cage + gas (X/X0 ~ 5%)

Occupancies in CLIC_ILD TPC 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors22 Readout unit: voxel = time bucket in pad row Voxel-occupancies are high, dominated by γγ  hadrons Safety factors not yet included: x2 for γγ  hadrons (direct effects) x5 for incoh. pairs (indir. Effects) Occupancies <~40% tolerable (experience from ALICE TPC) Further studies required, to reduce occupancies in inner pad rows: Remove inner layers? Forward-region optimization, to suppress indirect hits? Different gas mixture? Pixelated readout? Combined tracking performance

Radiation exposure in silicon layers 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors23 NIEL: TID: Non-Ionizing Energy Loss (NIEL): Displacement damage in silicon Obtained from hit rates scaled with tabulated damage factors Total Ionizing Dose (TID): Obtained from simulated energy loss in silicon layers CLIC_ILDLHC NIEL VTX barrel [1-MeV-n eq /yr]4x10 10 >~10 14 NIEL FTD [1-MeV-n eq /yr]5x10 10 TID VTX barrel [Gy/yr]200 >~ 10 5 TID FTD [Gy/yr]180 FTD VTX barrel  Small expected radiation exposure, compared to LHC experiments

Pixel-detector technology options 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors24 20x20 μm 2 pixel sizes  need small feature sizes Time-stamping ~5-10 ns  need high-resistivity sensor 0.1%-0.2% material/layer  allows for ~50 μm sensor + ~50 μm electronics Read out full 156 ns bunch train, no trigger Technology Choices: 1) Hybrid Thinned high-resistivity fully depleted sensors Fast, low-power highly integrated readout chip Low mass interconnects 2) Integrated technologies Sensor and readout combined in one chip Charge collection in epitaxial layer

Pixel-detector in hybrid technology 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors25 Thinned depleted high-resistivity sensors, ~50 um active width Example: ALICE pixel upgrade  meet CLIC goals Fast, low-power, highly integrated readout chips Example: Timepix3 (2012) 130 nm IBM CMOS 50x50 μm 2 pixels  needs further reduction (<~90 nm process) 1.5 ns time resolution  exceeds CLIC goals P~350 mW/cm 2  meets CLIC goals (with power pulsing) Low-mass interconnects between sensor+readout cost driver  needs further R&D Advantages: Use industry-standard processes for readout Factorize sensor and readout R&D Drawbacks: Higher material budget than integrated approach Interconnects difficult/expensive Handling/bonding of thinned structures difficult 110 μm 220 μm Timepix3 design X. Llopart 2x4 superpixel

Pixel-detector in integrated technology 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors 26 Integrate sensor and readout in one chip Signal collection through electron drift in epitaxial layer Example: MIMOSA chip family, 0.35 μm CMOS process 50 μm total thickness  meets CLIC goal <<1 μm depleted area  need to increase 100 μs readout time (rolling shutter)  need single-pixel r/o 18.4 μm pitch, σ SP ~4 μm  meets CLIC goal P~250 mW/cm 2  meets CLIC goal (with power pulsing) Advantages: Very low material budgets achievable Very low power consumption possible Drawbacks: Custom-made processes (availability in 10 years?) Difficult to get fast signal collection + good S/N Fast readout not yet demonstrated Mimosa 26 M. Winter High resistivity Low resistivity Epitaxial layer:

Vertex-detector cooling 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors27 P~500 W in vertex detectors Need low-mass cooling solutions Forced air flow no extra material may work in barrel region: Up to 240 liter/s flow, ~40 km/h flow velocity Micro-channel cooling Integrate cooling channels in Si Could be solution for forward disks Connectors are major challenge Water cooling Sub-atmospheric pressure Can use thin PEEK pipes Need simulations to asses impact of material on performance Bot Sensor 200um ASIC150um Glue 50um Connector Top Sensor 200um ASIC150um Nanoport connector A. Mapelli, J. Buytaert B. Cooper NA62 GTK

Summary / Conclusions 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors28 Physics at CLIC requires high-precision vertex- and tracking detectors CLIC environment poses severe challenges: High background rates Narrow bunch spacing however: only moderate radiation-hardness required Ongoing layout optimization studies R&D on CLIC vertex-detector technology has started: Small feature sizes Fast readout with time stamping Power pulsing Low-mass cooling systems More information on LCD studies in the CLIC CDR Volume 2:

Backup slides 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors29

γγ  hadrons comparison of samples 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors30 Detector effects in agreement within 15% for the two generators Pythia samples were chosen for CDR MC mass production

Layout optimization: forward-tracking region 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors31 Background hits will confuse track finding and extrapolation How many layers do we need? Maximal distance between layers? Resolution (strip pitch / stereo angle)?  Simulation to optimize geometry in high-occupancy forward region R/phi R

Layout optimization: forward-tracking region (results) 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors32 Fixed resolution in Rphi: 5 μm Vary resolution in R and distance between layers Outside-in track extrapolation  Look at projected error ellipse and count background hits  Need ~ 50 μm resolution in R  extra layer introduced

Layout optimization: interaction region CLIC_ILD (II) 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors33

Tracking performance in simulation 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors34 Impact parameter d 0 Transv. momentum p T CLIC_SiD CLIC_ILD

Occupancies in CLIC_ILD forward-tracking region 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors35 hits from pairs dominate Innermost FTD up to 15x10 -3 hits/mm^2/BX (incl. safety factors)  long strips not feasible (14 hits/train/strip) Incoherent pairsγγ  hadr.

Radiation damage Estimate radiation damage (in silicon) from non-ionizing energy loss (NIEL): Simulation based on setups used for estimating occupancies Scale hits with displacement-damage factor  1-MeV-neutron equivalent fluence Estimate radiation damage from total ionizing dose (TID): Sum up energy released in corresponding silicon layers, as obtained in Geant4 detector simulation To obtain expected fluence and TID per year, assume: 1 year =100 days effective runtime = 100*24*60*60 seconds; 50*312 bx per second 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors36

NIEL in silicon layers 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors37 Barrel region Barrel region: NIEL dominated by γγ  hadrons Up to ~4x MeV-n-equiv. cm -2 / year in innermost pixel layers (incl. safety fact.) Forward region: γγ  hadr. and incoh. Pairs contribute simil. Up to ~5x MeV-n-equiv. cm -2 / year in forward pixel layers (incl. safety fact.) For comparison: ATLAS pixel layers: >~ MeV-n-equiv. cm -2 / year Forward region hadrons Forward region incoh. pairs

TID in silicon layers 26. Aug. 2011Backgrounds in the CLIC vertex- and tracking detectors38 Barrel region Barrel region: TID dominated by incoherent pairs Up to ~200 Gy / year in innermost pixel layers (incl. safety fact.) Forward region: TID dominated by incoherent pairs Up to 180 Gy / year in forward pixel layers (incl. safety fact.) For comparison: ATLAS inner pixel layers: ~160 kGy / year Forward region hadrons Forward region incoh. pairs