A glance at LHC Detector Systems Burkhard Schmidt, CERN PH-DT
The Enter LHC a New accelerator Era in Fundamental and the detectors Science Start-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. CMS LHCb Exploration of a new energy frontier Proton-proton collisions at E CM = 7 (14) TeV ALICE LHC ring: 27 km circumference Germany and CERN May 2009 ATLAS 2nd EIROforum School of Instrumentation LHC Detector Systems 2
The LHC Detectors ATLAS 7000 ton l = 46m D = 22m ATLAS 7000 ton l = 46m D = 22m ATLAS and CMS are general purpose detectors for high-luminosity operation. LHCb detector is a specialized detector for the study of b-quark physics CMS 12500 ton l = 22m d = 15m ALICE detector is optimized for study of heavy-ion (HI) collisions 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 3
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 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 4
The Physics Challenge Rates for L = 10 34 cm -2 s -1 : Inelastic proton-proton reactions: 10 9 / s bb pairs 5x10 6 / s tt pairs 8 / s W e ν Z e e Higgs (150 GeV) Gluino, Squarks (1 TeV) 150 / s 15 / s 0.2 / s 0.03/ s New physcis events are rare High Luminosity is needed 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 5
The Event-Pile-up Challenge At high luminosity: up to 20 additional min bias events ~1600 charged particles in the detector Example of golden Higgs channel H ZZ 2e2μ Large magnetic field and high granularity helps Need to understand the detector first before lumi can be fully exploited 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 6
Ionizing radiation: The Radiation Environment 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 x10 9 particles per cm 2 of material with unit density At LHC design luminosity the ionizing dose is ~ 2 x10 6 Gy / rt 2 / year 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 10 13 cm -2 /year They modify directly the crystalline structure of semiconductors. (rt [cm] : transverse distance to beam) Need radiation-hard electronics as well as radiation-hard active detector material (silicon sensors, crystals etc.) 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 7
The Timing Challenge Interactions every 25ns : In 25 ns particles travel 7.5m 22m 46m Cable length ~100m : In 25 ns signals travel 5 m 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 8
Other challenges The length of the project: 1990-2000 Design Phase 1998-2008 Construction Phase 2008 202x Exploitation Phase The collaboration size : 700-3000 physicists... 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 9
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 10 8 pixels, 10 5 cells in electromagnetic calorimeter Fast detector response: 20-50 ns response time for electronics Radiation resistance: In forward calorimeters : up to 10 17 n/cm 2 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 p T Electromagnetic calorimetry, muon systems 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 10
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 : 10 7 Store huge data volumes to disk/tape : 10 9 events of ~1 Mbyte /year 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 11
Collider Detector Layout Materials with high number of protons + Active material Hermetic calorimetry Missing Et measurements Electromagnetic and Hadron calorimeters Particle identification (e, γ Jets, Missing E T ) Energy measurement µ e γ n p Heavy materials Muon detector µ identification ν Heavy materials (Iron or Copper + Active material) Light materials Central detector Tracking, p T, MIP Em. shower position Topology Vertex Each layer identifies and enables the measurement of the momentum or energy of the particles produced in a collision 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 12
Detector Layout: CMS example 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 13
Detector Layout: LHCb Example Vertex Locator RICH Detectors Muon System Fixed target geometry Advantages of beauty physics at hadron colliders: High value of beauty cross section expected at ~10 TeV Interaction Point Tracking System LHCb acceptance: Forward single arm spectrometer 1.9<η<4.9 b-hadrons produced at low angle Calorimeters Correlated bb-production in same hemisphere 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 14
ATLAS and CMS Magnet Systems Toroid Magnets Solenoid 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 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 Solenoid 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 15
ATLAS and CMS Magnet Systems 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 16
ATLAS and CMS Magnet Systems ATLAS A Toriodal LHC AppartuS CMS Compact Muon Solenoid Air Core Toroid: No iron in muon system No multiple scattering, good resolution Bending in r,z, straight track in r,φ Solenoid: Bending in transversal plane r,φ Solenoid: Requires return yoke in Muon system Resolution limited by multiple scattering Bending in transversal plane r,φ, In r,z straight track (extrapolation to beam, trigger on impact parameter) Homogenous B-field Inhomogeneous field at large η 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 17
Detectors for Muon Systems Requirements: Very large areas to cover (few hundred m 2 ) 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 X 0, multiple scattering proportional to 1/sqrt(X 0 ) 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 18
CMS Muon System Technologies: Barrel: Drift Tubes 40 x 11 mm 2 250 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 driven by inner tracker Muon system contributes Only for p>100gev/c 2nd EIROforum School of Instrumentation LHC Detector Systems 19
ATLAS Muon System End-wall wheels Small wheels Big wheels 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 STACO (%) STACO 10 GEANT simulation 2nd EIROforum School of Instrumentation p T (GeV) p T (GeV)
Muon momentum resolution Muon systems only (standalone) 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 21
ATLAS and CMS Trackers ATLAS Inner Detector ( η <2.5, B=2T): 80 M Si Pixels and 6.3 M strips (SCT) + 400K Transition Radiation straws Precise tracking and vertexing, Momentum resolution: σ/p T ~ 3.4x10-4 p T (GeV) 0.015 CMS Inner Detector ( η <2.5, B=4T): Pixels Silicon Microstrips 210 m2 of silicon sensors 9.6M (Str) & 66M (Pix) channels σ/p T ~ 1.4% @ 100 GeV in central region (2 x better than Atlas) 2nd EIROforum School of Instrumentation LHC Detector Systems 22
ATLAS and CMS Trackers ATLAS CMS Biggest operational problem for both experiments is the COOLING 2nd EIROforum School of Instrumentation LHC Detector Systems 23
Muon Momentum resolution With inner tracker Muon System standalone 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 24
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. 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 25
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 10 4-10 5 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 trigger Example: LHCb Muon system 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 26
LHCb Muon System Main Purpose: Triggering on muons produced in the decay of b-hadrons by measuring P T 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 435m 2-122k 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 P T Good time resolution (few ns) for reliable bunch-crossing identification 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 27
LHCb Trigger System 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 28
LHCb DAQ System 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 29
In cavern On surface Trigger & Data Flow ATLAS Level-1 [hardware] High- Level Trigger [software] Reconstruction Calorimeter Trigger L2 Latency <2.5µs CTP RoI s L2P L2P L2P L3 ROIB Muon Trigger Latency <10ms EFP EFP EFP T0-PCs L2SV L2N Latency <1 s Tier-0 farm 40 MHz L1 Accept 75 khz 200 Hz Calo & Muon trigger boards Other detectors RoI requests RoI data (~ 2%) L2 Accept 3.5 khz Event data EF Accept ~48 hours delay ROD ROD ROD ROB ROB ROB ROS Event Builder Trigger streams EB EFN Storage [CASTOR] 4 GB/s 1 PB/s 120 GB/s In cavern On surface 300 MB/s, 1.5 MB / event 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 30
Regions of Interest (RoI) Jet RoIs Jet RoI EM RoI Jet RoI EM RoI 2nd EIROforum School of Instrumentation LHC Detector Systems 31
Trigger /DAQ comparison LHC Trigger/DAQs are order of magnitude larger than before 2nd EIROforum School of Instrumentation LHC Detector Systems 32
Conclusions The LHC design parameters created unprecedented detector challenges because of the high luminosity, high particle multiplicity and energy, and the 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 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 33
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 2nd EIROforum School of Instrumentation LHC Detector Systems B.Schmidt 34