Performance of ATLAS & CMS Silicon Tracker International Europhysics Conference on High Energy Physics EPS 2003, July 17th-23rd 2003, Aachen, Germany Performance of ATLAS & CMS Silicon Tracker Alessia Tricomi University and INFN Catania

What LHC means… H  bb event p-p collision @ √s = 14 TeV bunch spacing of 25 ns Luminosity low-luminosity: 2*1033cm-2s-1 (first years) high-luminosity: 1034cm-2s-1 ~20 minimum bias events per bunch crossing ~1000 charged tracks per event Radius: 2cm 10cm 25cm 60cm NTracks/(cm2*25ns) 10.0 1.0 0.10 0.01 Severe radiation damage to detectors H  bb event @ high luminosity Plus 22 minimum bias events Challenging requirements for the Tracking system Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

Tracker Requirements Efficient & robust Pattern Recognition algorithm Fine granularity to resolve nearby tracks Fast response time to resolve bunch crossings Ability to reconstruct narrow heavy object 1~2% pt resolution at ~ 100 GeV Ability to operate in a crowded environment Nch/(cm2*25ns) = 1.0 at 10 cm from PV Ability to tag b/t through secondary vertex Good impact parameter resolution Reconstruction efficiency 95% for hadronic isolated high pt tracks 90% for high pt tracks inside jets Ability to operate in a very high radiation environment Silicon detectors will operate at -7°C  -10°C to contain reverse annealing and limit leakage current Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

Two different strategies… 46m Long, 22m Diameter, 7’000 Ton Detector 2.3 m x 5.3 m Solenoid ~ 2 Tesla Field ~ 4 Tesla Toroid Field ATLAS ATLAS Inner Detector ID inside 2T solenoid field Tracking based on many points Precision Tracking: Pixel detector (2-3 points) Semiconductor Tracker – SCT (4 points) Continuous Tracking: (for pattern recognition & e id) Transition Radiation Tracker – TRT (36 points) Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

Two different strategies… CMS has chosen an all-silicon configuration 13m x 6m Solenoid: 4 Tesla Field  Tracking up to h ~ 2.4 ECAL & HCAL Inside solenoid Muon system in return yoke First muon chamber just after solenoid  Extended lever arm for pt measurement 5.4 m Outer Barrel –TOB- Inner Barrel –TIB- End cap –TEC- Pixel 2.4 m volume 24.4 m3 running temperature – 10 0C dry atmosphere for YEARS! Inner Disks –TID- CMS CMS Tracker Inside 4T solenoid field Tracking rely on “few” measurement layers, each able to provide robust (clean) and precise coordinate determination Precision Tracking: Pixel detector (2-3 points) Silicon Strip Tracker (220 m2) – SST (10 – 14 points) 22m Long, 15m Diameter, 14’000 Ton Detector Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

The ATLAS Pixel Detector 3 barrel layers* r = 5.05 cm (B-layer), 9.85 cm, 12.25 cm 3 pairs of Forward/Backward disks r= 49.5 cm, 6.0 cm, 65.0 cm ~ 2% of tracks with less than 3 hits Fully insertable detector Pixel size: 50 mm x 300 mm (B layer) & 50 mm x 400 mm ~ 2.0 m2 of sensitive area with 8 x 107 ch Modules are the basic building elements 1456 in the barrel + 288 in the endcaps Active area 16.4 mm x 60.8 mm Sensitive area read out by 16 FE chips each serving a 18 columns x 160 row pixel matrix * Several changes from TDR Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

The ATLAS SCT Detector 1.53 m 1.04 m 5.6 m Endcap: 9 wheel pairs pitch 70 - 80 mm 3 types of modules Inner (400) Middle (640 incl. 80 shorter) Outer (936) Barrel: 4 layers pitch ~ 80 mm radii: 284 – 335 – 427 – 498 mm 2112 modules, with 2 detectors per side, read out in the middle All detectors are double-sided (40 mrad stereo angle) 4088 modules 61 m2 of silicon 6.3 x 106 channels Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

The CMS Pixel Detector 3 barrel layers r = 4.1 – 4.6 cm, 7.0 – 7.6 cm, 9.9 – 10.4 cm ~ 32 x 106 pixels 2 pairs of Forward/Backward disks Radial coverage 6 < r < 15 cm Average z position: 34.5 cm, 46.5 cm Later update to 3 pairs possible (<z> ~ 58.2 cm) Per Disk: ~3 x 106 pixels  3 high resolution space points for h < 2.2 Pixel size: 150 mm x 150 mm driven by FE chip  Hit resolution: r-f s ~ 10 mm (Lorentz angle 28° in 4 T field) r-z s ~ 17 mm Modules are the basic building elements 800 in the barrel + 315 in the endcaps Occupancy is ~ 10-4 Pixel seeding fastest starting point for track reconstruction despite the extremely high track density Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

The CMS Silicon Strip Tracker 12 layers with (pitch/12) spatial resolution and 110 cm radius give a momentum resolution of A typical pitch of order 100mm is required in the f coordinate To achieve the required resolution Outer Barrel (TOB): 6 layers Thick sensors (500 mm) Long strips 9’648’128 strips  channels 75’376 APV chips 6’136 Thin sensors 18’192 Thick sensors 440 m2 of silicon wafers 210 m2 of silicon sensors 3’112 + 2*1’512 Thin modules 5’496 + 2*1’800 Thick modules ss ds=b-to-b (100mrad) ~17’000 modules ~25’000’000 Bonds p+ strips on n-type bulk <100> crystal lattice orientation Polysilicon resistors to bias the strips Strip width over pitch w/p=0.25 Metal overhang and multiguard structure to enhance breakdown performance Endcap (TEC): 9 Disk pairs r < 60 cm thin sensors r > 60 cm thick sensors 6 layers TOB 4 layers TIB 3 disks TID Radius ~ 110cm, Length ~ 270cm h~1.7 h~2.4 9 disks TEC Silicon sensors CF frame Strip length ranges from 10 cm in the inner layers to 20 cm in the outer layers. Pitch ranges from 80mm in the inner layers to near 200mm in the outer layers Inner Disks (TIB): 3 Disk pairs Thin sensors Inner Barrel (TIB): 4 layers Thin sensors (320 mm) Short strips FE hybrid with FE ASICS Pitch adapter Black: total number of hits Green: double-sided hits Red: ds hits - thin detectors Blue: ds hits - thick detectors Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

Track reconstruction efficiency ET = 200 GeV Fake Rate < 8 *10-3 ET = 50 GeV Fake Rate < 10-3 <10-5 99% Single m Efficiency for p is lower compared to m due to secondary interactions in the Tracker Efficiency can be increased by relaxing track selection Dijet events CMS Global efficiency: selected Rec.Tracks / all Sim.Tracks Algorithmic efficiency: selected Rec.Tracks / selected Sim.Tracks (Sim.Track selection: at least 8 hits, at least 2 in pixel) Global efficiency limited by pixel geometrical acceptance Efficiency for particles in a 0.4cone around jet axis No significant degradation compared to single pions Loss of efficiency is dominated by hadronic interactions in Tracker material Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

Track resolutions ATLAS & CMS Good track parameter resolution have similar performance Good track parameter resolution already with 4 or more hits CMS CMS s(pT)/pT s(d0) mm For lower pt tracks multiple scattering becomes significant and the h dependence reflects the amount of material traversed by tracks Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

ATLAS & CMS performances ATLAS and CMS have thick trackers: each pixel layer contributes >2% X0 plus global support and cooling structures and thermal/EMI screens The momentum & impact parameter resolution depends strongly on: radius of innermost pixel layer thickness of pixel layers radius and thickness of beam pipe Example: effect of the new ATLAS layout: now (TDR) s(d0) mm s(1/pT) TeV-1 Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

The dark side: material budget in the Tracker 2 1.5 1 0.5 X/X0 ATLAS Degrades tracking performance, due to multiple scattering, Bremsstrahlung and nuclear interactions (see pt resolution and reconstruction efficiency) CMS Dominates energy resolution for electrons Reduces (somewhat) efficiency for usefully reconstructing H gg Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

ATLAS & CMS Silicon Tracker: vertexing At LHC design luminosity ~ 20 interaction per beam crossing spread out by s(z)=5.6 cm Identification of primary and secondary vertices fundamental Pixel detectors allow fast vertex reconstruction with s(z)<50mm Slower but better resolution (15 mm) achievable using the full Tracker CMS H  4 m ATLAS Primary vertex in A  tt s ~ 40mm “easy” channel “difficult” channel s ~ 16mm uu 100 GeV h<1.4 Pixel Full Tracker Several algorithms available Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

ATLAS & CMS Silicon Tracker: vertexing Secondary Vertex: Exclusive Vertices The basic tool for the vertexing classes is a general purpose fitter. Test on B0s  J/ f, with J/  mm and f  KK Secondary Vertex: Inclusive Vertices Useful for b and t tagging Two methods available and tested (Combinatorial method, d0/F method) The typical resolution using RecTracks is ~55 mm in the transverse plane and ~75 mm in z Typical efficiency ranges from ~35% to ~25% for Track Purity>50% Difference between the simulated Bs decay vertex and the fitted one in transverse and longitudinal directions Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

ATLAS & CMS Silicon Tracker: btagging Several algorithms tried by CMS and ATLAS, based on: impact parameter (track counting and jet probability secondary vertex reconstruction decay length Typical performance for both experiments: average: e(u) ~ 1% for e(b) = 60% for “interesting” jet pT range (50 < pT < 130 GeV) and all h best: e(u) ~ 0.2% for e(b) = 50% for pT ~ 100 GeV and central rapidity CMS: 2-D & 3-D I.P. prob.: e(b) vs e(u) ATLAS: 2-D I.P. prob.: e(u) vs pT (all h) Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen

Conclusions Tracking at LHC is a very challenging task: Very high rates Very harsh radiation environment High accuracy needed Extensive R&D programs carried on to design detectors which fulfil these requirements Design of ATLAS & CMS Trackers almost complete Production and construction of various components/detectors already started Both ATLAS & CMS have robust performances: Pixel detectors allow for fast and efficient track seed generation as well as vertex reconstruction pt resolution of ~ 1% for 100 GeV muons over about 1.7 units of rapidity Robust & efficient track reconstruction algorithms available (see D.Rousseau Talk) Jet flavour tagging under study to improve and extend the Physics reach Extensive use of track information @ HLT (see G. Bagliesi’s Talk) Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen