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

Alessia Tricomi - University & INFN CataniaEPS July, Aachen What LHC means… p-p √s = 14 TeV bunch spacing of 25 ns Luminosity – low-luminosity: 2*10 33 cm -2 s -1 (first years) – high-luminosity: cm -2 s -1 ~20 minimum bias events per bunch crossing ~1000 charged tracks per event Radius: 2cm 10cm 25cm 60cm N Tracks /(cm 2 *25ns) Severe radiation damage to detectors H  bb event Plus 22 minimum bias events H  bb high luminosity Challenging requirements for the Tracking system

Alessia Tricomi - University & INFN CataniaEPS July, Aachen Tracker Requirements Efficient & robust Pattern Recognition algorithmEfficient & robust Pattern Recognition algorithm –Fine granularity to resolve nearby tracks –Fast response time to resolve bunch crossings Ability to reconstruct narrow heavy objectAbility to reconstruct narrow heavy object –1~2% p t resolution at ~ 100 GeV Ability to operate in a crowded environmentAbility to operate in a crowded environment –Nch/(cm 2 *25ns) = 1.0 at 10 cm from PV Ability to tag b/  through secondary vertexAbility to tag b/  through secondary vertex –Good impact parameter resolution Reconstruction efficiencyReconstruction efficiency –95% for hadronic isolated high p t tracks –90% for high p t tracks inside jets Ability to operate in a very high radiation environmentAbility 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 CataniaEPS 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 CataniaEPS July, Aachen CMS 5.4 m Outer Barrel –TOB- Inner Barrel –TIB- End cap –TEC- Pixel 2.4 m volume 24.4 m 3 running temperature – 10 0 C dry atmosphere for YEARS! Inner Disks –TID- Two different strategies… 22m Long, 15m Diameter, 14’000 Ton Detector 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 m 2 ) – SST (10 – 14 points) 13m x 6m Solenoid: 4 Tesla Field  Tracking up to  ~ 2.4 ECAL & HCAL Inside solenoid Muon system in return yoke First muon chamber just after solenoid  Extended lever arm for p t measurement CMS has chosen an all-silicon configuration

Alessia Tricomi - University & INFN CataniaEPS July, Aachen The ATLAS Pixel Detector 3 barrel layers* –r = 5.05 cm (B-layer), 9.85 cm, 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  m x 300  m (B layer) & 50  m x 400  m ~ 2.0 m 2 of sensitive area with 8 x 10 7 ch Modules are the basic building elements –1456 in the barrel 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 CataniaEPS July, Aachen The ATLAS SCT Detector 5.6 m 1.53 m 1.04 m Barrel: 4 layers pitch ~ 80  m radii: 284 – 335 – 427 – 498 mm 2112 modules, with 2 detectors per side, read out in the middle Endcap: 9 wheel pairs pitch  m 3 types of modules Inner (400) Middle (640 incl. 80 shorter) Outer (936) All detectors are double-sided (40 mrad stereo angle) 4088 modules 61 m 2 of silicon 6.3 x 10 6 channels

Alessia Tricomi - University & INFN CataniaEPS July, Aachen 3 barrel layers –r = 4.1 – 4.6 cm, 7.0 – 7.6 cm, 9.9 – 10.4 cm –~ 32 x 10 6 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 ( ~ 58.2 cm) –Per Disk: ~3 x 10 6 pixels  3 high resolution space points for  < 2.2 Pixel size: 150  m x 150  m driven by FE chip  Hit resolution: –r-  ~ 10  m (Lorentz angle 28° in 4 T field) –r-z  ~ 17  m Modules are the basic building elements –800 in the barrel in the endcaps The CMS Pixel Detector Occupancy is ~ Pixel seeding fastest starting point for track reconstruction despite the extremely high track density

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

Alessia Tricomi - University & INFN CataniaEPS July, Aachen 99%99% Single  Track reconstruction efficiency 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 Efficiency for  is lower compared to  due to secondary interactions in the Tracker Efficiency can be increased by relaxing track selection ET = 200 GeV Fake Rate < 8 *10 -3 ET = 50 GeV Fake Rate < <10 -5 Dijet events CMS

Alessia Tricomi - University & INFN CataniaEPS July, Aachen Track resolutions Good track parameter resolution already with 4 or more hits CMS ATLAS & CMS have similar performance For lower pt tracks multiple scattering becomes significant and the  dependence reflects the amount of material traversed by tracks CMS  (p T )/p T  (d 0 )  m

Alessia Tricomi - University & INFN CataniaEPS 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)  (1/p T ) TeV -1  (d 0 )  m

Alessia Tricomi - University & INFN CataniaEPS July, Aachen Degrades tracking performance, due to multiple scattering, Bremsstrahlung and nuclear interactions (see p t resolution and reconstruction efficiency) The dark side: material budget in the Tracker  X/X 0 ATLAS Reduces (somewhat) efficiency for usefully reconstructing H  Dominates energy resolution for electrons CMS

Alessia Tricomi - University & INFN CataniaEPS July, Aachen ATLAS Primary vertex in A   ATLAS & CMS Silicon Tracker: vertexing At LHC design luminosity ~ 20 interaction per beam crossing spread out by  (z)=5.6 cm Identification of primary and secondary vertices fundamental CMS H  4  “easy” channel “difficult” channel Pixel detectors allow fast vertex reconstruction with  (z)<50  m Slower but better resolution (15  m) achievable using the full Tracker Pixel Several algorithms available  ~  m  ~  m Full Tracker uu 100 GeV  <1.4

Alessia Tricomi - University & INFN CataniaEPS 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 B 0 s  J/ , with J/    and   KK Difference between the simulated B s decay vertex and the fitted one in transverse and longitudinal directions Secondary Vertex: Inclusive Vertices Useful for b and  tagging Two methods available and tested (Combinatorial method, d 0 /  method) Typical efficiency ranges from ~35% to ~25% for Track Purity>50% The typical resolution using RecTracks is ~55  m in the transverse plane and ~75  m in z

Alessia Tricomi - University & INFN CataniaEPS 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:  (u) ~ 1% for  (b) = 60% for “interesting” jet p T range (50 < p T < 130 GeV) and all  best:  (u) ~ 0.2% for  (b) = 50% for p T ~ 100 GeV and central rapidity CMS: 2-D & 3-D I.P. prob.:  (b) vs  (u) ATLAS: 2-D I.P. prob.:  (u) vs p T (all  )

Alessia Tricomi - University & INFN CataniaEPS 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 –p t 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 HLT (see G. Bagliesi’s Talk)