26/10/2005prof. dr hab. elżbieta richter-wąs physics program of the experiments at l arge h adron...
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26/10/2005Prof. dr hab. Elżbieta Richter-Wąs
Physics Program of the experiments at
Large HadronCollider
Lecture 2
26/10/20052Prof. dr hab. Elżbieta Richter-Wąs
Outline of this lecture
What is general purpose detector?ATLAS detector: Magnet System Inner Detector Calorimetry Muon Spectrometer Trigger
ATLAS detector test beam 2004
26/10/20053Prof. dr hab. Elżbieta Richter-Wąs
General Purpose Detectors
When it became more and more likely, early in 1980, that an electron–positron collider, energetic enough to produce the as yet undiscovered Z boson, would be constructed at CERN, some of us got together to initiate discussions on a
possible experiment. Some of us who collaborated in the CDHS neutrino experiment were joined by colleagues from Orsay, Pisa, Munich (Max Planck)
and Rutherford Labs.
The first question we asked ourselves was: ‘Can we think of a focused experiment, requiring a specialized rather than general-purpose detector?’
The answer was a clear no, and in fact, no special purpose detector was ever built at LEP. So we started to think of a general-purpose, 4π detector, such as
had been developed at the DESY Petra and the SLAC PEP colliders, but clearly more ambitious in all aspects: tracking resolution, angular coverage,
calorimetry, and particle identification.
Jack Steinberger – Nobel Laureate and first spokesman of the Aleph Jack Steinberger – Nobel Laureate and first spokesman of the Aleph ExperimentExperiment
26/10/20054Prof. dr hab. Elżbieta Richter-Wąs
General Principle
The dimension of the detector are driven by the required resolution . The calorimeter thickness change only with the logarithm of the energy: for this reason the dimension of the detectors change only slightly with the energy.
Collider detectors look all similar since they must perform in sequence the same basic measurements.
26/10/20055Prof. dr hab. Elżbieta Richter-Wąs
General purpose detector
Identification … for event selection
For both, need different stages:Inner trackerCalorimetersMuon system(trigger andprecisionchambers)
… and measurementfor event reconstruction.
26/10/20056Prof. dr hab. Elżbieta Richter-Wąs
Particle identification Muon chambers
Hadronic calorimeter
Electromagnetic calorimeter
Inner tracker
µ
en
p
26/10/20057Prof. dr hab. Elżbieta Richter-Wąs
Particle measurement
Detectors must be capable of
Resolving individual tracks, in-and-outside the calorimeters
Measuring energy depositions of isolated particles and jets
Measuring the vertex position.
Detector size and granularity is dictated by
… the required (physics) accuracy… the particle multiplicity.
Size + granularity determine… the no. of measuring elements
… i.e. the no. of electronics channels.
26/10/20058Prof. dr hab. Elżbieta Richter-Wąs
The ATLAS Detector
Length : 40 m Radius : 10 m Weight : 7000 tonsElectronics channels : 108
26/10/20059Prof. dr hab. Elżbieta Richter-Wąs
Basic design criteria
Very good electromagnetic calorimetry for electron and photon identification and measurements, complemented by full-coverage hadronic calorimetry for accurate jet and missing transverse energy (ET
miss) measurements.
High precision muon momentum measurements, with capability to guarantee accurate measurements at the highest luminosity using the external muon spectrometer alone.
Efficient tracking the high luminosity for high-pT-lepton-momentum measurements, electron and photon identification,-lepton and heavy-flavour identification, and full event reconstruction capability at lower luminosity.
Large acceptance in pseudorapidity () with almost full azimuthal angle () coverage everywhere. The azimuthal angle is measured around the beam axis, whereas pseudorapidity relates to the polar angle () where is the angle from
Triggering and measurements of particles at low-pT thresholds, providing high efficiencies for most physics processes of interest
26/10/200510Prof. dr hab. Elżbieta Richter-Wąs
Basic design criteria
• Lepton measurement: pT GeV 5 TeV ( b lX, W’/Z’)
• Mass resolution (m ~ 100 GeV) : 1 % (H , 4l)
10 % (W jj, H bb)
• Calorimeter coverage : || < 5
(ETmiss, forward jet tag for strongly interacting Higgs)
• Particle identification : b 50 % Rj 100 (H bb, SUSY) 50 % Rj 100 (A/H ) 80 % Rj > 103 (H ) e > 50 % Rj > 105
e/jet ~ 10-3 s = 2 TeV
e/jet ~ 10-5 s = 14 TeV
26/10/200511Prof. dr hab. Elżbieta Richter-Wąs
Basic design criteria
e/jet ~ 10-3 s = 2 TeV
e/jet ~ 10-5 s = 14 TeV
In addition : 3 crucial parameters for precision measurements
• Absolute luminosity : goal < 5% Main tools: machine, optical theorem, rate of known processes (W, Z, QED pp pp ll)
• EM energy scale : goal 1‰ most cases 0.2‰ W mass Main tool: Z ll (1 event / 1 /s at low L) close to mW, mh
N.B.: 1‰ achieved by CDF/D0 (despite small Z sample) • Jet energy scale : goal 1% (mtop, SUSY) (limited by physics) Main tools : Z + 1 jet (Z ll) W jj from top decays (10-1 events/s low L) N.B. 4% at Tevatron
26/10/200512Prof. dr hab. Elżbieta Richter-Wąs
The ATLAS Magnet System
Barrel toroid
End-cap toroid
Central Solenoid
Fe yoke (calorimeter)3 3
superconducting superconducting air core toroidsair core toroids
superconductingsuperconducting
solenoidsolenoid
• 26m long, 20m outer diameter 1350 tons
26/10/200513Prof. dr hab. Elżbieta Richter-Wąs
The ATLAS Magnet System
The magnet configuration is based on an inner thin superconducting solenoid surrounding the inner detector cavity, and large superconducting air-core toroids consisting of independent coils arranged with an eight-fold symmetry outside the calorimeters.The solenoid provides a central magnetic field of 2T (peak at 2.6T). The peak magnetic field of barrel toroid is 3.9T and of end-cap toroid is 4.1T.
length of 5.3length of 5.3 m and diameter of 2.4m and diameter of 2.4 mm
5.7 tons5.7 tons
The solenoid has been inserted into the LAr cryostatat the end of February 2004, and it was tested at full current (8 kA) during July 2004
26/10/200514Prof. dr hab. Elżbieta Richter-Wąs
The ATLAS Magnet System
Toroid system
Barrel Toroid parameters25.3 m length 20.1 m outer diameter 8 coils1.08 GJ stored energy370 tons cold mass830 tons weight4 T on superconductor56 km Al/NbTi/Cu conductor20.5 kA nominal current4.7 K working point
End-Cap Toroid parameters5.0 m axial length 10.7 m outer diameter 2x8 coils2x0.25 GJ stored energy2x160 tons cold mass2x240 tons weight4 T on superconductor2x13 km Al/NbTi/Cu conductor20.5 kA nominal current4.7 K working point
End-Cap Toroid:8 coils in a common cryostat
Barrel Toroid:8 separate coils
26/10/200515Prof. dr hab. Elżbieta Richter-Wąs
The ATLAS Magnet System
Barrel Toroid coil transport and installation
26/10/200516Prof. dr hab. Elżbieta Richter-Wąs
The ATLAS Magnet System
●Magnetic field calculation
–Impact of coils & magnetic material positions
26/10/200517Prof. dr hab. Elżbieta Richter-Wąs
Inner Detector
The Inner Detector (ID) is organized into four sub-systems:
Pixels (0.8 108 channels)
Silicon Tracker (SCT)(6 106 channels)
Transition Radiation Tracker (TRT)(4 105 channels)
Common ID items
26/10/200518Prof. dr hab. Elżbieta Richter-Wąs
Inner Detector
The Inner Detector (ID) is contained within a cylinder of length 7m and a radius of 1.15m, in a solenoidal field of 2T.
Pattern recognition, momentum and vertex measurements, and electron identification are achieved with a combination of discrete high-resolution semiconductor pixel and strip detectors in the inner part of the tracking volume, and continous straw-tube tracking detectors with transition capability in its outer part.
26/10/200519Prof. dr hab. Elżbieta Richter-Wąs
Inner Detector
First complete SCT barrel cylinder
TRT barrel support with all modules
First completed disk (two layers of 24 modules each, with 2’200’000 channelsof electronics
26/10/200520Prof. dr hab. Elżbieta Richter-Wąs
Inner Detector total weights
1.1. PIXEL volumePIXEL volume 78 kg 78 kg RRmeanmean 15cm 15cm
2.2. SCT volumeSCT volume 345 kg 345 kg RRmeanmean
38cm38cm
3.3. TRT volume(no C-wheels)TRT volume(no C-wheels) 1960 kg 1960 kg RRmeanmean
86cm86cm
4.4. Services volumeServices volume 2500 kg2500 kg
Total ID 4880 kgTotal ID 4880 kg
GeoModel services breakdown
TRT services 2150 kgSCT services 292 kgPixel services 68 kg
Required understanding material description to better than 1%
26/10/200521Prof. dr hab. Elżbieta Richter-Wąs
Calorimetry
Tile barrel Tile extended barrel
LAr forward calorimeter (FCAL)
LAr hadronic end-cap (HEC)
LAr EM end-cap (EMEC)
LAr EM barrel
26/10/200522Prof. dr hab. Elżbieta Richter-Wąs
CalorimetryHad Tiles
Had LAr
EM LAr
Forward LArSolenoid
Barrel cryostat
Highly granular liquid-argon (LAr) electromagnetic (EM) sampling calorimetry, with excellent performance in terms of energy and position resolution, covers the pseudorapidity range || < 3.2.
In the end-caps, the LAr technology is also used for the hadronic calorimeters, which share the cryostats with the EM endcaps.
The same cryostats also house the special LAr forward calorimeters which extend the pseudorapidity coverage to || < 4.9.
The bulk of the hadronic calorimetry is provided by a novel scintillator-tile calorimeter, which is separated into large barrel and two smaller extended barrel cylinders, one on each side of the barrel.
The overall calorimeter system provides the very good jet and ET
miss performance of the detector.
26/10/200523Prof. dr hab. Elżbieta Richter-Wąs
Calorimetry
LAr barrel EM calorimeter after insertion into thecryostat
Solenoid just before insertion into the cryostat
26/10/200525Prof. dr hab. Elżbieta Richter-Wąs
Muon Spectrometer System
Precision chambers:- MDTs in the barrel and end-caps- CSCs at large rapidity for the innermost end-cap stationsTrigger chambers:- RPCs in the barrel- TGCs in the end-caps
The Muon Spectrometer is instrumented with precision chambers and fast trigger chambers
A crucial component to reach the required accuracy is the sophisticated alignment measurement and monitoring system
26/10/200526Prof. dr hab. Elżbieta Richter-Wąs
Muon Spectrometer System
The calorimeter is surrounded by the muon spectrometer. The air-core toroid system, with a long barrel and two inserted end-cap magnets, generates a large magnetic field volume with strong bending power within a light and open structure.
Multiple-scattering effect are minimised, and excellent muon momentum resolution is achieved with three stations of high-precision tracking chambers.
The muon instrumentation also included as a key component trigger chambers with fast time response.
26/10/200527Prof. dr hab. Elżbieta Richter-Wąs
The installation of the barrelmuon station has started in the feet region of the detectoras well as within the third BT
26/10/200528Prof. dr hab. Elżbieta Richter-Wąs
ATLAS detector in G4 simulation
Jaka jest skala problemu?
• 25,5 millionów oddzielnych elementów
• 23 000 różnych obiektów geometrycznych
• 4 673 różnych typów geometrycznych
• kontrolowanie nakładających się na siebie przypadków
• 1 000 000 sygnałów w detektorze na przypadek
26/10/200530Prof. dr hab. Elżbieta Richter-Wąs
The ATLAS experiment
Weight: 7000
t44 m
22 m
Interactions every 25 ns …In 25 ns particles travel 7.5 m
Cable length ~100 meters …In 25 ns signals travel 5 m
Trigger
26/10/200531Prof. dr hab. Elżbieta Richter-Wąs
Event ratesN = no. events / secL = luminosity = 1034 cm-2 s-1
inel = inel. cross-section = 70 mbE = no. events / bunch xingt = bunch spacing = 25 ns
N = L x inel = 1034 cm-2 s-1 x 7 10-26 cm2
= 7 108 Hz
E = N / t = 7 108 s-1 x 25 10-9 s = 17.5
(not all bunches are filled) = 17.5 x 3564 / 2835 = 22 events / bunch xing
The LHC produces 22 overlapping p-p interactions every 25 ns
26/10/200532Prof. dr hab. Elżbieta Richter-Wąs
Particle multiplicity
… still much more complex than a LEP event
= rapidity = log(tg/2) (longitudinal dimension) uch = no. charged particles / unit- nch = no. charged particles / interaction Nch = no. chrgd particles / bunch xing Ntot = no. particles / bunch xing
nch = uch x = 6 x 7 = 42
Nch = nch x 22 = ~ 900
Ntot = Nch x 1.5 = ~ 1400
The LHC flushes each detector with ~1400 particles every 25 ns
26/10/200533Prof. dr hab. Elżbieta Richter-Wąs
Cross-section
Orders of magnitude amongst x-sections of various physics channels:
• Inelastic : 109 Hz• W -> l : 102 Hz• t-t production : 101 Hz• Higgs (m=100 GeV/c2) : 10-1 Hz• Higgs (m=600 GeV/c2) : 10-2 Hz
==> selection power : 1010-11
… lepton decay BR : ~ 10-2
==> Selection power for Higgs discovery : 1013
26/10/200535Prof. dr hab. Elżbieta Richter-Wąs
ARCHITECTURE
40 MHz
Trigger DAQ
10’s PB/s(equivalent)
~ 100 Hz ~ 100 MB/sPhysics
Three logical levels
LVL1 - Fastest:Only Calo and
MuHardwired
LVL2 - Local:LVL1
refinement +track
associationLVL3 - Full
event:“Offline” analysis
~3 s
~ ms
~ sec.
Hierarchical data-flow
On-detector electronics:
Pipelines
Event fragments buffered in
parallel
Full event in processor farm
26/10/200536Prof. dr hab. Elżbieta Richter-Wąs
ARCHITECTURE
Event Filter
40 MHz
Trigger DAQ
10s PB/s(equivalent)
Level-1
Level-2
100 kHz
~3 s
~ ms
~ sec.
~ kHz
Pipelines
Buffers
Event Filter Processor
100 GB/s
~ GB/s
Recording
~ 100 Hz ~ 100 MB/sPhysics
26/10/200537Prof. dr hab. Elżbieta Richter-Wąs
Physics and Trigger
p pH
µ +
µ -
µ +
µ -
Z
Zp p
e-
e
q
q
q
q
1
-
g~
~
2
0~
q~
1
0~
Production of heavy objects may be detected via one or more of the following signatures:
One or more isolated, high-pT charged leptons
Large missing ET (from neutrinos, dark matter candidates)
High multiplicity of large pT jets
Isolated high-pT photons
Copious b production relative to QCD
High pT Physics
26/10/200538Prof. dr hab. Elżbieta Richter-Wąs
Physics and Trigger
H(130 GeV) Z0Z0*+-e+e-Minimum Bias
26/10/200539Prof. dr hab. Elżbieta Richter-Wąs
Looking for interesting event
Higgs → ZZ → 2e+2Higgs → ZZ → 2e+2 23 min bias events23 min bias events
26/10/200540Prof. dr hab. Elżbieta Richter-Wąs
Inclusive Selection Signatures
Object Examples of physics coverage Nomenclature
ElectronsHiggs (SM, MSSM), new gauge bosons,
extra dimensions, SUSY, W/Z, top e25i, 2e15i
PhotonsHiggs (SM, MSSM), extra dimensions,
SUSY 60i, 220i
MuonsHiggs (SM, MSSM), new gauge bosons,
extra dimensions, SUSY, W/Z, top 20i, 210
Jets SUSY, compositeness, resonances j360, 3j150, 4j100
Jet+missing ETSUSY, leptoquarks, “large” extra
dimensions j60 + xE60
Tau+missing ETExtended Higgs models (e.g. MSSM),
SUSY 30 + xE40also inclusive missingET, SumET, SumET_jet
• To select an extremely broad spectrum of “expected” and “unexpected” Physics signals (hopefully!).
• The selection of Physics signals requires the identification of objects
that can be distinguished from the high particle density environment.
The list must be non-biasing, flexible, include some redundancy,
extendable, to account for the “unexpected”.
& many prescaled and mixed triggers
Inclusive Selection SignaturesInclusive Selection Signatures
26/10/200541Prof. dr hab. Elżbieta Richter-Wąs
Region of Interest (RoI) Mechanism
LVL2 uses Regions of Interest • local data access, reconstruction &
analysis• sub-detector matching of RoI data• produces LVL2 result• average latency ~10 ms
LVL2 uses Regions of Interest • local data access, reconstruction &
analysis• sub-detector matching of RoI data• produces LVL2 result• average latency ~10 ms
LVL1 triggers on high pT objects• calorimeter cells and muon chambers
to find e/,,jet, candidates above thresholds
• identifies Regions of Interest • fixed latency 2.5 s
LVL1 triggers on high pT objects• calorimeter cells and muon chambers
to find e/,,jet, candidates above thresholds
• identifies Regions of Interest • fixed latency 2.5 s
H →2e + 2H →2e + 2
22
2e2e
Event Filter• can be “seeded” by LVL2 result• potential full event access, • offline-like Algorithms O(1 s)
latency
Event Filter• can be “seeded” by LVL2 result• potential full event access, • offline-like Algorithms O(1 s)
latency
Hardware
Software
Software
26/10/200542Prof. dr hab. Elżbieta Richter-Wąs
ATLAS Event Size
ATLAS event size: 1.5 MbytesATLAS event size: 1.5 Mbytes140 million channels140 million channelsorganized into ~1600 Readout Linksorganized into ~1600 Readout Links
ATLAS event size: 1.5 MbytesATLAS event size: 1.5 Mbytes140 million channels140 million channelsorganized into ~1600 Readout Linksorganized into ~1600 Readout Links
2828~104~104LVL1 (calo)LVL1 (calo)
Fragment size - kB
Fragment size - kBChannelsChannelsTriggerTrigger
3073073.7x1053.7x105TRTTRT
1101106.2x1066.2x106SCTSCT
60601.4x1081.4x108PixelsPixels
Fragment size - kB
Fragment size - kBChannelsChannelsInner DetectorInner Detector
664.4x1054.4x105TGCTGC
12123.5x1053.5x105RPCRPC
2562566.7x1046.7x104CSCCSC
1541543.7x1053.7x105MDTMDT
Fragment size - kB
Fragment size - kBChannelsChannelsMuon
Spectrometer
Muon Spectrometer
4848104104TileTile
5765761.8x1051.8x105LArLAr
Fragment size - kB
Fragment size - kBChannelsChannelsCalorimetryCalorimetry
At 40 MHz: 1 PB/secAt 40 MHz: 1 PB/sec
affordable mass storage affordable mass storage b/w:b/w:
300 MB/sec 300 MB/sec ☛☛ 3 PB/year3 PB/yearfor offline analysisfor offline analysis
☛☛ ~ 200 Hz Trigger Rate~ 200 Hz Trigger Rate
At 40 MHz: 1 PB/secAt 40 MHz: 1 PB/sec
affordable mass storage affordable mass storage b/w:b/w:
300 MB/sec 300 MB/sec ☛☛ 3 PB/year3 PB/yearfor offline analysisfor offline analysis
☛☛ ~ 200 Hz Trigger Rate~ 200 Hz Trigger Rate
26/10/200543Prof. dr hab. Elżbieta Richter-Wąs
ATLAS Three Level Trigger Architecture
2.5 s
~10 ms
~ sec.
• LVL1 decision made
with calorimeter data with relatively coarse granularity
and muon trigger chambers data. •Buffering on detector
• LVL2 uses Region of Interest data (ca. 2%)
with full granularity
combines information from all detectors
performs fast rejection. •Buffering in ROBs
• EventFilter refines the selection
can perform event reconstruction at full granularity
using latest alignment and calibration data.
•Buffering in EB & EFsoft
war
eh
ard
war
e
~200 Hz
~2 kHz
26/10/200544Prof. dr hab. Elżbieta Richter-Wąs
LVL1 - Muons & Calorimetry
Muon Trigger looking for coincidences in muon trigger chambers 3 out of 4 (low-pT; >6 GeV) and 3 out of 4 + 1/2 (Barrel) or 2/3 (Endcap)
(high-pT; > 20 GeV)
Trigger efficiency 91% (low-pT) and 87% (high-pT)
Muon Trigger looking for coincidences in muon trigger chambers 3 out of 4 (low-pT; >6 GeV) and 3 out of 4 + 1/2 (Barrel) or 2/3 (Endcap)
(high-pT; > 20 GeV)
Trigger efficiency 91% (low-pT) and 87% (high-pT)
Calorimetry Trigger looking for e/isolated hadron, jets
• Various combinations of cluster sums and isolation criteria
• ETem,had , ET
miss
Calorimetry Trigger looking for e/isolated hadron, jets
• Various combinations of cluster sums and isolation criteria
• ETem,had , ET
miss
Toroid
e/ trigger
26/10/200545Prof. dr hab. Elżbieta Richter-Wąs
ATLAS LVL1 Trigger Architecture
Concepts:
– Identify basic “physics objects”
• Leptons, photons, quarks/gluons, weakly-interacting particles
– Classify by ET (& isolation)
– Threshold and multiplicity information used by Central Trigger Processor to select events
– Provide “Regions of Interest” to guide LVL2 processing.
26/10/200546Prof. dr hab. Elżbieta Richter-Wąs
LVL1 Trigger Rates
LVL1 rate is dominated by candidate electromagnetic clusters: 78% of physics triggers
ET values imply 95% efficiency w.r.t. to asymptotic value
Illustrative menu
26/10/200547Prof. dr hab. Elżbieta Richter-Wąs
HLT Selection
Isolation
pt>15GeV
Cluster shape
trackfinding
Isolation
pt>15GeV
Cluster shape
trackfinding
EM15i EM15i+
e15i e15i +
e15 e15+
e e +
ecand ecand+
Signature
Signature
Signature
Signature
LVL1 seed
STEP1
STEP 4
STEP 3
STEP2
t i m
e
Basic concept: Seeded and Stepwise
Reconstruction
• RoIs “seed” Trigger reconstruction chains• Reconstruction in steps
(one/more algorithm per step)• Algorithms are seeded by features from
previous algorithms• Validate step-by-step
Check intermediate signatures• Rejects as early as possible
example: Z e+e-
Managed by HLT Steering
• LVL2 accesses only a fraction of the full event
Only few % of event shipped over the network from the ROBs
• Full event building happens only at EF
26/10/200548Prof. dr hab. Elżbieta Richter-Wąs
Data volumes
Average event size (ATLAS & CMS) : 1-2 MB-> design system for ~ 100 GB/s
26/10/200549Prof. dr hab. Elżbieta Richter-Wąs
ATLAS Teast Beam 2004Full “vertical slice” of ATLAS tested on CERN H8 beam line May-November 2004
x
z
y
Geant4 simulated layout of the test-beam set-up
For first time, all ATLAS sub-detectors integrated and run together with common DAQ, “final” electronics, slow-control, etc. Gained lot of global operation experience during ~ 6 month run. Common ATLAS software used to analyze the data
26/10/200550Prof. dr hab. Elżbieta Richter-Wąs
ID + CalorimetersID + Calorimeters
T IL
EC
ALL
A rTRT
TILE EBMDTRPCBOS
PixelSCT
MBPS
Cable holder
TRTLAr
Tilecal
MDT-RPC BOS
Pixel+SCT
26/10/200551Prof. dr hab. Elżbieta Richter-Wąs
2004 Data samples and goals
•6 Months6 Months long data taking period
•3 magnets (1 ID) (2 MS)3 magnets (1 ID) (2 MS) used to measure particles P evt-by-evtP evt-by-evt
•Beam settings:Beam settings:
–e±/± 1 -> 250 GeV
±/±/p up to 350 GeV
– ~20-100 GeV
•Total ~ 90 millions90 millions events ~ 4.64.6 TBTB
Test beam goals
•Performance and stability test of all ATLAS sub-detectors with “final” FE electronics
•Common readout of all sub-detectors with ATLAS DAQ(-1)
•Test and develop of ALTAS:
–Online tools: monitoring, configuration DB, event display
–Calibration and alignment algorithms
–Offline software: reconstruction, simulation, conditions data
•Perform many interesting combined physics analyses with ATLAS offline tools