26/10/2005prof. dr hab. elżbieta richter-wąs physics program of the experiments at l arge h adron...

26/10/2005Prof. dr hab. Elżbieta Richter-Wąs

Physics Program of the experiments at

Large HadronCollider

Lecture 2


Outline of this lecture

What is general purpose detector?ATLAS detector: Magnet System Inner Detector Calorimetry Muon Spectrometer Trigger

ATLAS detector test beam 2004


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


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.


General purpose detector

Identification … for event selection

For both, need different stages:Inner trackerCalorimetersMuon system(trigger andprecisionchambers)

… and measurementfor event reconstruction.


Particle identification Muon chambers

Hadronic calorimeter

Electromagnetic calorimeter

Inner tracker

µ

en

p


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.


The ATLAS Detector

Length : 40 m Radius : 10 m Weight : 7000 tonsElectronics channels : 108


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



• 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



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


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



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



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



Barrel Toroid coil transport and installation



●Magnetic field calculation

–Impact of coils & magnetic material positions


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


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.


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


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%


Calorimetry

Tile barrel Tile extended barrel

LAr forward calorimeter (FCAL)

LAr hadronic end-cap (HEC)

LAr EM end-cap (EMEC)

LAr EM barrel


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.


Calorimetry

LAr barrel EM calorimeter after insertion into thecryostat

Solenoid just before insertion into the cryostat


Calorimetry


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


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.


The installation of the barrelmuon station has started in the feet region of the detectoras well as within the third BT


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


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


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


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


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


Bunch crossing rates


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


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


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


Physics and Trigger

H(130 GeV) Z0Z0*+-e+e-Minimum Bias


Looking for interesting event

Higgs → ZZ → 2e+2Higgs → ZZ → 2e+2 23 min bias events23 min bias events


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


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


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


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


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


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.


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


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


Data volumes

Average event size (ATLAS & CMS) : 1-2 MB-> design system for ~ 100 GB/s


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


ID + CalorimetersID + Calorimeters

T IL

EC

ALL

A rTRT

TILE EBMDTRPCBOS

PixelSCT

MBPS

Cable holder

TRTLAr

Tilecal

MDT-RPC BOS

Pixel+SCT


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

26/10/2005prof. dr hab. elżbieta richter-wąs physics program of the experiments at l arge h adron...

Documents

elbieta richterws outline

detector size

generalpurpose detector

special purpose detector

atlas detector length

aleph experiment slide

accurate measurements

basic measurements