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Physics Program of the experiments at L arge H adron C ollider. Lecture 2. Outline of this lecture. What is general purpose detector? ATLAS detector: Magnet System Inner Detector Calorimetry Muon Spectrometer Trigger

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Physics program of the experiments at l arge h adron c ollider

Physics Program

of the experiments at

Large HadronCollider

Lecture 2


Outline of this lecture

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

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 Experiment


General principle

General Principle

Collider detectors look all similar since they must perform in sequence the same basic measurements.

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.


General purpose detector

General purpose detector

  • Identification …

    • for event selection

  • For both, need different stages:

    • Inner tracker

    • Calorimeters

    • Muon system(trigger andprecisionchambers)

  • … and measurement

    • for event reconstruction.


Particle identification

n

µ

Muon chambers

g

Hadronic calorimeter

e

n

Electromagnetic calorimeter

p

Inner tracker

Particle identification


Particle measurement

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

The ATLAS Detector

Length : 40 m

Radius : 10 m

Weight : 7000 tons

Electronics channels : 108


Basic design criteria

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 (ETmiss) 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, t-lepton and heavy-flavour identification, and full

    event reconstruction capability at lower luminosity.

  • Large acceptance in pseudorapidity (h) with almost full azimuthal angle (f)

    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


Basic design criteria1

Basic design criteria

  • Lepton measurement: pT GeV  5 TeV

  • ( b lX, W’/Z’)

  • Mass resolution (m ~ 100 GeV) :

  •  1 % (H  gg, 4l)

  •  10 % (W  jj, H  bb)

  • Calorimeter coverage : || < 5

  • (ETmiss, forward jet tag for strongly interacting Higgs)

  • Particle identification :

  • eb 50 % Rj  100 (H  bb, SUSY)

  • et 50 % Rj  100 (A/H  tt)

  • eg 80 % Rj > 103 (H  gg)

  • ee> 50 % Rj > 105

e/jet ~ 10-3s = 2 TeV

e/jet ~ 10-5 s = 14 TeV


Basic design criteria2

Basic design criteria

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

e/jet ~ 10-3s = 2 TeV

e/jet ~ 10-5 s = 14 TeV

Requirements: tracker material to 1%, overall

alignment to 0.1 mm, overall B-field to 0.1‰,

muon E-loss in calorimeters to 0.25%, etc.


The atlas magnet system

The ATLAS Magnet System

Fe yoke (calorimeter)

3 superconducting air core toroids

Barrel toroid

Central Solenoid

superconducting

solenoid

End-cap toroid

  • 26m long, 20m outer diameter 1350 tons


The atlas magnet system1

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.

The solenoid has been

inserted into the LAr cryostat

at the end of February 2004,

and it was tested at full current

(8 kA) during July 2004

  • length of 5.3m and diameter of 2.4m

  • 5.7 tons


The atlas magnet system2

Toroid system

Barrel Toroid parameters

25.3 m length

20.1 m outer diameter

8 coils

1.08 GJ stored energy

370 tons cold mass

830 tons weight

4 T on superconductor

56 km Al/NbTi/Cu conductor

20.5 kA nominal current

4.7 K working point

End-Cap Toroid parameters

5.0 m axial length

10.7 m outer diameter

2x8 coils

2x0.25 GJ stored energy

2x160 tons cold mass

2x240 tons weight

4 T on superconductor

2x13 km Al/NbTi/Cu conductor

20.5 kA nominal current

4.7 K working point

Barrel Toroid:

8 separate coils

End-Cap Toroid:

8 coils in a common cryostat

The ATLAS Magnet System


The atlas magnet system3

The ATLAS Magnet System

Barrel Toroid coil transport and installation


The atlas magnet system4

The ATLAS Magnet System

  • Magnetic field calculation

    • Impact of coils & magnetic material positions


Inner detector

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 detector1

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 detector2

Inner Detector

First completed disk (two layers of 24

modules each, with 2’200’000 channels

of electronics

First complete SCT barrel cylinder

TRT barrel support with all modules


Inner detector total weights

Inner Detector total weights

  • PIXEL volume 78 kg Rmean 15cm

  • SCT volume 345 kg Rmean 38cm

  • TRT volume(no C-wheels)1960 kg Rmean 86cm

  • Services volume2500 kg

  • Total ID 4880 kg

GeoModel services breakdown

TRT services2150 kgSCT services 292 kgPixel services 68 kg

Required understanding material description to better than 1%


Calorimetry

Tile barrel

Tile extended barrel

LAr hadronic

end-cap (HEC)

LAr EM end-cap (EMEC)

LAr EM barrel

LAr forward calorimeter (FCAL)

Calorimetry


Calorimetry1

Calorimetry

Had Tiles

Highly granular liquid-argon (LAr) electromagnetic (EM) sampling calorimetry, with excellent performance in terms of energy and position resolution, covers the pseudorapidity range |h| < 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 |h| < 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 ETmiss performance of the detector.

Had LAr

EM LAr

Solenoid

Forward LAr

Barrel cryostat


Calorimetry2

Calorimetry

LAr barrel EM calorimeter after insertion into the

cryostat

Solenoid just before insertion into the

cryostat


Calorimetry3

Calorimetry


Muon spectrometer system

Muon Spectrometer System

Precision chambers:

- MDTs in the barrel and end-caps

- CSCs at large rapidity for the

innermost end-cap stations

Trigger 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 system1

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.


Physics program of the experiments at l arge h adron c ollider

The installation of the barrel

muon station has started in

the feet region of the detector

as well as within the third BT


Atlas detector in g4 simulation

ATLAS detector in G4 simulation

Jaka jest skala problemu?

  • 25,5 millionów oddzielnych elementów

  • 23 000różnych obiektów geometrycznych

  • 4673różnych typów geometrycznych

  • kontrolowanie nakładających się na siebie przypadków

  • 1 000 000sygnałów w detektorze na przypadek


The atlas experiment

22 m

Weight: 7000 t

44 m

  • Interactions every 25 ns …

    • In 25 ns particles travel 7.5 m

Trigger

The ATLAS experiment

  • Cable length ~100 meters …

    • In 25 ns signals travel 5 m


Event rates

Event rates

  • N = no. events / sec

  • L = luminosity = 1034 cm-2 s-1

  • inel= inel. cross-section = 70 mb

  • E = no. events / bunch xing

  • Dt= bunch spacing = 25 ns

  • N =L x inel=1034 cm-2 s-1 x 7 10-26 cm2 = 7 108 Hz

  • E = N / Dt= 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

Particle multiplicity

  • h = rapidity = log(tg/2)

    (longitudinal dimension)

  • uch = no. charged particles / unit-h

  • nch = no. charged particles / interaction

  • Nch = no. chrgd particles / bunch xing

  • Ntot = no. particles / bunch xing

  • nch= uch x h= 6x 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

Cross-section

Orders of magnitude amongst x-sections of various physics channels:

• Inelastic : 109 Hz

• W -> ln : 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

Bunch crossing rates


Architecture

~ 100 Hz

Physics

~ 100 MB/s

ARCHITECTURE

Trigger

DAQ

40 MHz

10’s PB/s(equivalent)

Three logical levels

Hierarchical data-flow

LVL1 - Fastest:Only Calo and MuHardwired

On-detector electronics: Pipelines

~3 ms

LVL2 - Local:LVL1 refinement +track association

Event fragments buffered in parallel

~ ms

LVL3 - Full event:“Offline” analysis

Full event in processor farm

~ sec.


Physics program of the experiments at l arge h adron c ollider

ARCHITECTURE

Trigger

DAQ

40 MHz

10s PB/s(equivalent)

Level-1

Pipelines

~3 ms

100 kHz

100 GB/s

~ ms

Level-2

Buffers

~ kHz

~ GB/s

Event Filter

Processor

Event Filter

~ sec.

Recording

~ 100 Hz

Physics

~ 100 MB/s


Physics and trigger

n

-

e

e

q

µ

+

-

c

1

µ

-

~

q

q

Z

~

p

g

H

p

p

p

~

q

Z

+

m

µ

+

-

q

~

m

c

0

µ

2

-

~

c

0

1

Physics and Trigger

High pT Physics

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


Physics and trigger1

Physics and Trigger

H(130 GeV) Z0Z0*+-e+e-

Minimum Bias


Looking for interesting event

Higgs → ZZ → 2e+2m

Looking for interesting event

23 min bias events


Inclusive selection signatures

Inclusive Selection Signatures

Inclusive Selection Signatures

  • 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 distinguishedfrom the high particle density environment.

also inclusive missingET, SumET, SumET_jet

& many prescaled and mixed triggers

The list must be non-biasing,flexible, include some redundancy,

extendable, to account for the “unexpected”.


Region of interest roi mechanism

2

2e

Region of Interest (RoI) Mechanism

Hardware

  • LVL1 triggers on high pT objects

    • calorimeter cells and muon chambers

    • to find e/g,t,jet,m candidates

    • above thresholds

    • identifies Regions of Interest

    • fixed latency 2.5 ms

Software

  • LVL2 uses Regions of Interest

    • local data access, reconstruction & analysis

    • sub-detector matching of RoI data

    • produces LVL2 result

    • average latency~10 ms

Software

  • Event Filter

    • can be “seeded” by LVL2 result

    • potential full event access,

    • offline-like Algorithms O(1 s) latency

H →2e + 2


Atlas event size

Inner Detector

Channels

Fragment size - kB

Muon Spectrometer

Channels

Fragment size - kB

Pixels

1.4x108

60

MDT

3.7x105

154

SCT

6.2x106

110

CSC

6.7x104

256

TRT

3.7x105

307

RPC

3.5x105

12

TGC

4.4x105

6

Calorimetry

Channels

Fragment size - kB

Trigger

Channels

Fragment size - kB

LAr

1.8x105

576

LVL1 (calo)

~104

28

Tile

104

48

ATLAS Event Size

At 40 MHz: 1 PB/sec

affordable mass storage b/w:

300 MB/sec ☛3 PB/yearfor offline analysis

☛~ 200 Hz Trigger Rate

ATLAS event size: 1.5 Mbytes140 million channelsorganized into ~1600 Readout Links


Atlas three level trigger architecture

ATLAS Three Level Trigger Architecture

  • 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 & EF

hardware

2.5 ms

software

~10 ms

~2 kHz

~200 Hz

~ sec.


Lvl1 muons calorimetry

LVL1 - Muons & Calorimetry

e/ trigger

Toroid

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/g, ,/isolated hadron, jets

  • Various combinations of cluster sums and isolation criteria

  • SETem,had , ETmiss


Atlas lvl1 trigger architecture

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 Trigger Rates

Illustrative menu

ET values imply 95% efficiency w.r.t. to asymptotic value

LVL1 rate is dominated by candidate electromagnetic clusters: 78% of physics triggers


Hlt selection

e15i

e15i

+

+

e15

e15

+

e

e

ecand

ecand

+

+

EM15i

EM15i

HLT Selection

example: Z  e+e-

Signature

  • Basic concept:

  • Seededand 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

  • Iso

    lation

    Iso

    lation

    STEP 4

    Signature

    pt>

    15GeV

    pt>

    15GeV

    STEP 3

    Signature

    t i m e

    track

    finding

    track

    finding

    STEP2

    Managed by HLT Steering

    Signature

    Cluster

    shape

    Cluster

    shape

    • 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

    STEP1

    LVL1 seed


    Data volumes

    Data volumes

    Average event size (ATLAS & CMS) : 1-2 MB

    -> design system for ~ 100 GB/s


    Atlas teast beam 2004

    y

    x

    z

    ATLAS Teast Beam 2004

    Full “vertical slice” of ATLAS tested on CERN H8 beam line May-November 2004

    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


    Physics program of the experiments at l arge h adron c ollider

    MDT-RPC BOS

    T

    I

    L

    E

    C

    A

    L

    Tilecal

    Pixel+SCT

    T

    R

    T

    L

    A

    r

    MBPS

    TILE

    EB

    MDT

    RPC

    BOS

    Pixel

    SCT

    Cable holder

    LAr

    TRT

    ID + Calorimeters


    2004 data samples and goals

    2004 Data samples and goals

    • 6 Months long data taking period

    • 3 magnets (1 ID) (2 MS)used to measure particlesP evt-by-evt

    • Beam settings:

      • e±/p± 1 -> 250 GeV

      • - p±/m±/p up to 350 GeV

      • g ~20-100 GeV

    • Total ~ 90 millions events ~ 4.6TB

    • 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


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