performance of atlas & cms silicon tracker alessia tricomi university and infn catania...
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Performance of Performance of ATLAS & CMS Silicon TrackerATLAS & CMS Silicon Tracker
Alessia TricomiUniversity and INFN Catania
International Europhysics Conference on High Energy PhysicsEPS 2003, July 17th-23rd 2003, Aachen, Germany
Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen
What LHC means…
• 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 eventRadius: 2cm 10cm 25cm 60cmNTracks/(cm2*25ns) 10.0 1.0 0.10 0.01
• Severe radiation damage to detectors
H bb event
Plus 22 minimum
bias events
H bb event @ high luminosity
Challenging requirements for the Tracking system
Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen
Tracker Requirements• Efficient & robust Pattern Recognition algorithmEfficient & robust Pattern Recognition algorithm
– Fine granularity to resolve nearby tracksFine granularity to resolve nearby tracks– Fast response time to resolve bunch crossingsFast response time to resolve bunch crossings
• Ability to reconstruct narrow heavy objectAbility to reconstruct narrow heavy object– 1~2% p1~2% ptt resolution at ~ 100 GeV resolution at ~ 100 GeV
• Ability to operate in a crowded environmentAbility to operate in a crowded environment– Nch/(cm2*25ns) = 1.0 at 10 cm from PV
• Ability to tag b/Ability to tag b/ through secondary vertex through secondary vertex– Good impact parameter resolutionGood impact parameter resolution
• Reconstruction efficiencyReconstruction efficiency– 95% for hadronic isolated high p95% for hadronic isolated high ptt tracks tracks– 90% for high p90% for high ptt tracks inside jets tracks inside jets
• Ability to operate in a very high radiation Ability to operate in a very high radiation environmentenvironment– Silicon detectors will operate at -7°C Silicon detectors will operate at -7°C -10°C to contain -10°C to contain
reverse annealing and limit leakage current 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
ATLASATLAS Inner DetectorID inside 2T solenoid fieldTracking based on many pointsPrecision 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
CMS
5.4
m
Outer Barrel –TOB-
Inner Barrel –TIB-
End cap –TEC-Pixel
2.4
m
volume 24.4 m3
running temperature – 10 0Cdry atmosphere for YEARS!
Inner Disks –TID-
Two different strategies…
22m Long, 15m Diameter, 14’000 Ton Detector
CMS Tracker Inside 4T solenoid fieldTracking rely on “few” measurement layers, each ableto provide robust (clean) and precise coordinate determinationPrecision Tracking:• Pixel detector (2-3 points)• Silicon Strip Tracker (220 m2) – SST (10 – 14 points)
13m x 6m Solenoid: 4 Tesla Field Tracking up to ~ 2.4
ECAL & HCALInside solenoid
Muon system in return yoke
First muon chamber just after solenoid Extended lever arm for pt measurement
CMS has chosen an all-silicon configuration
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 m x 300 m (B layer) & 50 m x 400
m • ~ 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
5.6 m
1.53 m
1.0
4 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 70 - 80 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 m2 of silicon• 6.3 x 106 channels
Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen
• 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 < 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 + 315 in the endcaps
The CMS Pixel Detector
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 TrackerOuter 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 layers6 layersTOBTOB
4 layers4 layersTIBTIB
3 disks TID3 disks TID
Radius ~ 110cm, Length ~ 270cmRadius ~ 110cm, Length ~ 270cm ~1.7~1.7
~2.4~2.4
9 disks TEC9 disks TECInner Disks (TIB): 3 Disk pairs• Thin sensors
9’648’128 strips channels
75’376 APV chips
6’136 Thin sensors18’192 Thick sensors
440 m2 of silicon wafers 210 m2 of silicon sensors
3’112 + 2*1’512 Thin modules5’496 + 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 stripsStrip width over pitch w/p=0.25
Metal overhang and multiguard structure to enhance breakdown performance
FE hybrid FE hybrid with FE with FE ASICSASICS
Pitch Pitch adapteradapter
Silicon Silicon sensorssensors
CF frameCF frame
12 layers with (pitch/12 layers with (pitch/12) spatial 12) spatial resolution and 110 cm radius resolution and 110 cm radius give a momentum resolution ofgive a momentum resolution of
Tevp
BT
Lm
mpitch
pp T
141.1
10012.0
121
A typical pitch of order A typical pitch of order mmis required in the is required in the coordinate coordinate
To achieve the required resolutionTo achieve the required resolution
Black: total number of hitsGreen: double-sided hitsRed: ds hits - thin detectorsBlue: ds hits - thick detectors
Strip length ranges fromStrip length ranges from 10 cm10 cm in the in the inner layers toinner layers to 20 cm 20 cm in the outer in the outer layers.layers.
Pitch ranges fromPitch ranges from 80 80mm in the inner in the inner layers to nearlayers to near 200200mm in the outer in the outer layerslayers
Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen
99%99% 99%99%
Single
Track reconstruction efficiency
Global efficiency: selected Rec.Tracks / all Sim.TracksGlobal efficiency: selected Rec.Tracks / all Sim.Tracks
Algorithmic efficiency: selected Rec.Tracks / selected Sim.TracksAlgorithmic efficiency: selected Rec.Tracks / selected Sim.Tracks
(Sim.Track selection: at least 8 hits, at least 2 in pixel)(Sim.Track selection: at least 8 hits, at least 2 in pixel)
Global efficiency limited by pixel geometrical acceptanceGlobal efficiency limited by pixel geometrical acceptance
Efficiency for particles in a Efficiency for particles in a 0.4cone around jet axis0.4cone around jet axis
No significant degradation No significant degradation compared to single pionscompared to single pions
Loss of efficiency is dominated by Loss of efficiency is dominated by hadronic interactions in Tracker hadronic interactions in Tracker materialmaterial
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 < 10-3
<10-
5
Dijet events
CMS
Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen
Track resolutionsGood track parameter resolution
already with 4 or more hits
CMS 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 CMS
(p
T)/
pT
(d
0) m
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)m
t0 p
)106.8(67.611.7(10.5))σ(d
1
TT
TeVp
18.0(14.7)0.6(0.4)
p1
σ
(1/p
T)
TeV
-1(
d0) m
Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen
Degrades tracking performance, due to Degrades tracking performance, due to multiple scattering, Bremsstrahlung and multiple scattering, Bremsstrahlung and
nuclear interactionsnuclear interactions(see p(see ptt resolution and reconstruction efficiency) resolution and reconstruction efficiency)
The dark side: material budget in the Tracker
-4 -2 0 2 4
2
1.5
1
0.5
0
X/X
0
ATLAS
Reduces (somewhat) efficiency forReduces (somewhat) efficiency forusefully reconstructing usefully reconstructing H H
Dominates energy resolutionDominates energy resolutionfor electronsfor electrons
CMS CMS
Alessia Tricomi - University & INFN Catania EPS 2003 17-23 July, Aachen
ATLAS
Primary vertex in A
ATLAS & CMS Silicon Tracker: vertexing
At LHC design luminosity ~ 20 interaction per beam crossingspread 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)<50m
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 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 B0
s J/, with J/and
Difference between the simulated Bs 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, d0/ 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 Catania EPS 2003 17-23 July, Aachen
ATLAS & CMS Silicon Tracker: btaggingSeveral 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 pT range (50 < pT < 130 GeV) and all • best: (u) ~ 0.2% for (b) = 50% for pT ~ 100 GeV and central rapidity
CMS:
2-D & 3-D I.P. prob.:(b) vs (u)
ATLAS:
2-D I.P. prob.: (u) vs pT (all )
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)