A glance at LHC Detector Systems EIROforum School of Instrumentation LHC Detector Systems 2 B S h...

A glance atLHC Detector Systems

Burkhard Schmidt, CERN PH-DT

Germany and CERN | May 2009

Enter a New Era in Fundamental ScienceStart-up of the Large Hadron Collider (LHC), one of the largest and truly global

scientific projects ever, is the most exciting turning point in particle physics.

Exploration of a new energy frontier Proton-proton collisions at ECM = 7 (14) TeV

LHC ring:27 km circumference

CMS

ALICE

LHCb

ATLAS

The LHC accelerator and the detectors

2nd EIROforum School of Instrumentation 2LHC Detector Systems B S h idt

The LHC Detectors

• ATLAS• 7000 ton• l = 46m• D = 22m

ATLAS and CMS are general purposedetectors for high-luminosity operation.

ALICE detector is optimized for studyof heavy-ion (HI) collisions

LHCb detector is a specialized detector for the study of b-quark physics

ATLAS7000 tonl = 46mD = 22m

CMS12500 tonl = 22md = 15m

2nd EIROforum School of Instrumentation 3LHC Detector Systems B.Schmidt

Outline

• General challenges– Physics, Pile-up, radiation, environment, timing, etc.

• Detector Requirements• General Detector Layout

– ATLAS/CMS and LHCb

• Selected sub-detector systems– Magnet systems– Muon systems– Trackers– Trigger and Data-Acquisition

• Conclusions and acknowledgements


The Physics Challenge

Rates for L = 1034 cm-2 s-1:

New physcis events are rareHigh Luminosity is needed

Inelastic proton-proton reactions: 109 / s

bb pairs 5x106 / s tt pairs 8 / s

W → e ν 150 / s Z → e e 15 / s

Higgs (150 GeV) 0.2 / s Gluino, Squarks (1 TeV) 0.03/ s


The ‘Event-Pile-up’ ChallengeAt high luminosity:• up to 20 additional min

bias events• ~1600 charged particles

in the detector

• Example of goldenHiggs channelH→ZZ →2e2μ

• Large magnetic field and high granularity helps

• Need to understand the detector first before lumican be fully exploited


The Radiation EnvironmentIonizing radiation:• Causes damages through energy deposition of charged particles in the

detector material. The damage is proportional to the dose :– 1 Gy = 1 Joule / kg = 100 rads– 1 Gy = 3 x109 particles per cm2 of material with unit density

• At LHC design luminosity the ionizing dose is ~ 2 x106 Gy / rT2 / year(rT [cm] : transverse distance to beam)

Neutrons:• Neutrons are created in hadron showers

in the calorimeters and in the forward shielding (detectors, beam/collimators.)

– very large fluences: up to 3 x 1013 cm-2/year– They modify directly the crystalline structure

of semiconductors.

Need radiation-hard electronics as well as radiation-hard active detector material (silicon sensors, crystals etc.)


The Timing ChallengeInteractions every 25ns : In 25 ns particles travel 7.5m

Cable length ~100m : In 25 ns signals travel 5 m

22m

46m


• The length of the project:1990-2000

1998-20082008 – 202x

• The collaboration size : 700 - 3000 physicists . . .

Construction Phase

Other challenges

Exploitation Phase

Design Phase


Detector Requirements• Large Magnetic Fields, capable of bending trajectories of a few 100 GeV

charged particles by a mm (sagitta): 1-4 Tesla Fields . . . best not in the calorimeters region• Trackers and Calorimeters capable of 1% momentum/energy resolution: High space granularity for particle identification and position resolution 108 pixels, 105cells in electromagnetic calorimeter• Fast detector response: 20-50 ns response time for electronics• Radiation resistance: In forward calorimeters : up to 1017 n/cm2 over 10 years of LHC operation• Careful choice of material distribution: very low near to the beam pipe (inner detector) enough material to contain EM and HAD showers in the calorimeters• Identification of leptons (e, μ) and γ with large transverse momentum pT

Electromagnetic calorimetry, muon systems


Detector Requirements• Hermetic coverage down to the beam pipe (5-6 cm), in order to measure

all the transverse energy flow to allow transverse missing energy identification

Coverage down to rapidity ~ 5• Good jet reconstruction Good resolution, absolute energy measurement, low fake-rate• Efficient b-tagging and tau identification Silicon strip and pixel detectors Good particle ID capability: different detection techniques• Signal cross section as low as 10-14 of total cross section Detectors must identify extremely rare events, mostly in real time Online rejection to be achieved : 107

• Store huge data volumes to disk/tape : 109 events of ~1 Mbyte /year


Collider Detector Layout

Central detector • Tracking, pT, MIP

• Em. shower position • Topology

• Vertex

Electromagnetic and Hadron calorimeters • Particle identification (e, γ Jets, Missing ET) • Energy measurement

Each layer identifies and enables the measurement of the momentum or energy of the particles produced in a collision

µµnn

pp

γγ

Heavy materials

νν

Heavy materials (Iron or Copper + Active material)

ee

Materials with high number of protons + Active material

Light materials

Muon detector • µ identification

Hermetic calorimetry • Missing Et measurements


Detector Layout: CMS example


Detector Layout: LHCb Example

LHCb acceptance:Forward single arm spectrometer 1.9<η<4.9 • b-hadrons produced at low angle

• Correlated bb-production in same hemisphere

InteractionPoint

Muon System

CalorimetersTracking System

Vertex Locator

RICH Detectors

Fixed target geometry

Advantages of beauty physics at hadron colliders:High value of beauty cross section expected at ~10 TeV


ATLAS and CMS Magnet Systems

Toroid Magnets Solenoid

Solenoid

CMS Solenoid Magnet• Length 13m, radius 3m, • field 4T nominal (3.8T actual)• I= 20kA, stored energy = 2.7 GJ• 64 Atm radial magn. pressure

Barrel toroid• 8 superconducting coils,• each 25 m long and 5m wide, 100 tons• I=20.5 kA, T=4.5 K, typical field 0.5 T

Endcap toroid (x2)• 8 coils in common cryostat, • 11m diameter,240 tons• I=20.5 kA, T=4.5 K, typical field 1T

Solenoid• 5.8m long, 2.5m diameter.• I=7.7 kA, T=4.5 K, field 2 T


ATLAS and CMS Magnet Systems


ATLAS and CMS Magnet SystemsATLAS A Toriodal LHC AppartuS

Air Core Toroid:No iron in muon systemNo multiple scattering, good resolution Bending in r,z, straight track in r,φSolenoid:Bending in transversal plane r,φ

Homogenous B-field

CMS Compact Muon Solenoid

Solenoid:Requires return yoke in Muon systemResolution limited by multiple scatteringBending in transversal plane r,φ, In r,z straight track (extrapolation to

beam, trigger on impact parameter)

Inhomogeneous field at large η


Detectors for Muon Systems• Requirements:

– Very large areas to cover (few hundred m2)

• Main technologies (at LHC):– Gas filled detectors in many different implementations

• Advantages of Gas detectors:– Large volumes / areas possible, – Can be segmented, multiple layers in a station– Low occupancy allows relatively large cell sizes– Relatively inexpensive– Large radiation length X0, multiple scattering proportional

to 1/sqrt(X0)


CMS Muon SystemTechnologies:• Barrel: Drift Tubes 40 x 11 mm2

• 250 Chambers, 200K Channels TDC• 250μm Resolution

• Encaps: Cathode strip chambers– 468 chambers, 240K strips– 150μm resolution

• Triggering: Resistive Plate Chambers– Course position, fine– timing, 172K channels

Performance drivenby inner tracker

Muon system contributesOnly for p>100GeV/c


ATLAS Muon System

End-wall wheels Big wheels

Small wheels

(%)

pT(GeV)

STAC

O(%

)

pT(GeV)

(%)

pT(GeV)

STAC

O

pT (GeV)

10

GEANT simulation

Technologies:• Barrel:

– 700 barrel precision chambers (MDT)– 600 barrel trigger chambers (RPC, |η|<1.05)

• Encaps:Big wheels (and end-wall wheels):

– ~400 MDT precision chambers– ~3600 TGC trigger chambers

Small wheels :– ~80 MDT chambers– ~32 CSC chambers

• Channels: – MDT 341k– CSC 31k– RPC 359k– TGC 318k

2nd EIROforum School of Instrumentation

Muon momentum resolutionMuon systems only (standalone)


ATLAS and CMS TrackersATLAS

Inner Detector (|η|<2.5, B=2T):80 M Si Pixels and 6.3 M strips (SCT) +

400K Transition Radiation strawsPrecise tracking and vertexing,

Momentum resolution:σ/pT ~ 3.4x10-4 pT (GeV) ⊕ 0.015

CMSInner Detector (|η|<2.5, B=4T):

PixelsSilicon Microstrips

210 m2 of silicon sensors9.6M (Str) & 66M (Pix) channels

σ/pT ~ 1.4% @ 100 GeV in central region(2 x better than Atlas)

2nd EIROforum School of Instrumentation LHC Detector Systems B S h idt

22

ATLAS and CMS Trackers


23

Biggest operational problem for both

experiments is the COOLING

ATLAS CMS

Muon Momentum resolution

With inner tracker

Muon Systemstandalone


Trigger / DAQ systems

• DAQ is responsible for collecting data from detector systems and recording them to mass storage for offline analysis.

• Trigger is responsible for real-time selection of the subset of data to be recorded.


Trigger Requirements• Low latency (time until a trigger decision is taken):

– Need to avoid dead-time and expensive buffer– Particularly important for first level trigger

• Large rejection factor– Rejections of 104-105 common

• High efficiency– Any events rejected are lost for ever– Efficiency should also be measurable

• Be affordable and flexible

A part of the LHC sub-detectors are designed for use in triggerExample: LHCb Muon system


LHCb Muon System• Main Purpose:

Triggering on muons produced in the decay of b-hadrons by measuring PT

• 5 Muon stations, M1 in front and M2-M5 behind the calorimeters

• Technologies:- MWPC (4 gas-gaps); - in a small part triple GEMs

- 1380 chambers covering 435m2

- 122k channels


• Main Requirement:A muon trigger requires the coincidence of hits in all 5 stations within a bunch crossing (25ns) in a region of interest that selects the muon PT

Good time resolution (few ns) for reliable bunch-crossing identification

LHCb Trigger System

2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 28

LHCb DAQ System


CalorimeterTrigger

MuonTrigger

CTP

Latency <2.5µs

ROD ROD ROD

Calo & Muontrigger boards Other detectors

1 PB/s

200 Hz

40 MHz

RoI data (~ 2%)

75 kHzL1 Accept

Event Builder

EB

4 GB/s

ROS

ROB ROB ROB

120 GB/s

300 MB/s, 1.5 MB / event

3.5 kHzL2 Accept

RoI’s

EF Accept

RoIrequests

Trigger & Data FlowATLAS

EFN

L2

L2P

L2SV

L2NL2PL2P

ROIB

Latency <10ms

Level-1[hardware]

High-Level

Trigger

[software]

L3EFP

EFPEFP

Latency <1 sEvent data

Storage[CASTOR]

Trigger streams

Tier-0 farmT0-PCs

~48 hours delay

Recon-struction

In cavern

On surface

In cavern

On surface



31

Regions of Interest (RoI)

EM RoI

EM RoI

Jet RoI

Jet RoI

Jet RoIs

Trigger /DAQ comparison

LHC Trigger/DAQs are order of magnitude larger than before


Conclusions• The LHC design parameters created unprecedented detector challenges

because of the high luminosity, high particle multiplicity and energy, andthe short bunch spacing:

– Signal speed– Detector granularity– Radiation tolerance– Detector dimensions– DAQ and data processing

• The detectors are performing very well – beyond expectations• It is just the beginning of a long and exciting data collection period

that will hopefully lead to great discoveries . . .. . . but is will bring to light also new challenges


Acknowledgements and literature

• Some material taken from the following presentations

– G. Dissertori, LHC Detectors, Galileo GaIilei Institute, Firenze, September 2007– A. Clark, The LHC experimental challenge, ICFA instrumentation school,

Bariloche, January 2010– K. Hoepfner, Muon Detection at the LHC, and– B. Petersen, Trigger and Data Acquisition, lectures given in May 2011 at CERN

in the context of Academic Training on Detectors

• Literature – Further Reading:

– The Large Hadron Collider: Accelerator and Experiments, JINST, December 2009


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