The ATLAS Experiment at the Large Hadron Collider

1
The ATLAS Experiment at the Large Hadron
Collider

• Hong Ma
• Physics Department, BNL
• RHIC/USATLAS Technology Meeting
• Aug 23, 2004

2
Exploring the Energy Frontier
Overview of Experiments at the Large Hadron
Collider
ATLAS,CMS Large General Purpose Detectors ALICE
Heavy Ion LHC-B B-physics
3
Outline of the presentation

• The Physics Motivations
• The Standard Model of Particle Physics
• Physics Beyond the Standard Model
• The Large Hadron Collider at CERN
• The ATLAS Experiment
• The Detector
• Physics with the ATLAS Detector
• Analysis and Computing at BNL
• Summary

4
Matter and Interactions

• Electromagnetic interactions
• Light, chemistry
• Strong interaction
• Nuclear fission or fusion
• Weak interaction
• Radioactive decays
• Building blocks of ordinary matters up/down
  quarks and electrons
• The first generation of the elementary particles.

5
The Standard Model
Higgs
6
Higgs and particle masses

• Particles in Standard Model would
• have been massless if there is no Higgs.
• But we do have mass
• The particles acquire mass through
• interaction with the Higgs field, a
• Spin 0
• Higgs field has an expectation value even in
  vacuum!
• The theory does not prediction the mass of Higgs
• There have been extensive experimental tests of
  Standard Model, they are all consistent (within
  errors) with the theory if there is a Higgs with
  mass 114GeV lt MHlt 200GeV
• Direct search in ee- collider
  MHgt114 GeV
• Precision electroweak measurements MHlt 200GeV

7
Global fit to precision electroweak data
Constraint to Higgs mass
8
Standard Model Higgs

• Higgs production is well predicted by SM
• Production is dominated by gluon fusion, gg ?
  Higgs
• Decay pattern strongly depends on mass
• This drives the detector design

9
Open questions in Particle Physics

• Why there are three generations, and what
  determines their masses
• Standard Model is not likely to be valid at
  higher energy scale
• Fine tuning problem, naturalness
• Supersymmetry, extra dimensions ?
• Cosmological Connection
• Dark matter in the universe
• Dark energy?
• CP violation, matter vs antimatter.
• Neutrino Oscillation

10
The Large Hadron Collider

• First considered in 1984, approved in 1996.
• Being built in the existing LEP tunnel
• 27 kilometers long
• 7TeV 7TeV proton-proton collision
• 7 times higher than Tevatron at FermiLab
• Two-in-one super-conducting magnets
• One ring in the tunnel
• 1296 15m-long dipoles, B8.36Tesla
• 4000 corrector magnets
• 40,000 tons of cold mass, at T1.9oK
• High luminosity
• gt100 times higher than Tevatron
• stot 100mb, L1034/cm2/sec ? 109
  interactions/sec
• Scheduled to operate in 2007

11
Aerial view of LHC in Geneva
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Dipoles are being installed
Over 260 Dipole magnets are cold-tested
Members of the Installation Coordination group
are seen here in the LHC tunnel with CERNs
Director General, Robert Aymar.
13
BNL Magnet Production
Part of the US/Japan collaboration to provide the
LHC Interaction Regions. BNL provides the
specialty dipoles (based on RHIC style coils)
The last series of dipoles (D3s) are in
production 2-in-1 RHIC style cold masses in a LHC
style cryostat
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Collision at LHC
One interesting event in 100,000,000,000,000
background events
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The ATLAS Detector

• 2T central solenoid
• Tracking
• Silicon Pixel
• Silicon strips
• Transition radiation straw tubes
• Calorimeter
• EM LAr accordion
• Hadronic LAr and Steel-Scintillator
• Air core toroid magnets
• BarrelEndcaps
• Muon detectors
• Monitored Drift Tubes
• Cathode Strip Chambers
• Resistive Plate Chambers
• Thin gap chambers

• Overall dimensions length 46 m,
• diameter 25 m, weight 7000 tons

16
The ATLAS Collaboration
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The Experimental Area

• 100 meters underground
• 50 meters tall experiment hall
• All surface buildings and underground
  engineering are done
• ATLAS installation started in spring 2003

18
The ATLAS Experiment Hall
April, 2002
April, 2003
Sept, 2003
Aug, 2004
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Barrel Toroid Magnets
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US Contributions

• US-ATLAS has a fixed budget of 163.75M from
  DOENSF
• a construction project up to Sept, 2005 for
  most of our deliverables.
• We have major involvement in the following
  subsystems
• Silicon pixels, strips, readout drivers
• Transition Radiation Tracker Barrel and
  electronics
• Liquid Argon Calorimeter cryostat, feedthroughs,
  cryogenics, electronics, forward calorimeter
• Tilecal Extended Barrel modules and electronics
• Muon spectrometer Monitored Drift Tube chambers
  and electronics, Cathode Strip Chambers and
  electronics, alignment
• Trigger/DAQ Technical Design Report just
  completed, ready for baselining
• US has major responsibility in computing and
  software.
• Framework, Database, Detector Software (LAr
  Muon), Analysis, Grid

21
BNL in detector construction

• BNL construction responsibilities matched to our
  physics interest and technical expertise.
• BNL Physics Dept and Instrumentation Division
  were pioneers in RD for both LAr calorimeter and
  Cathode Strip Chambers.
• Liquid Argon Calorimeter
• Cryostat and Cryogenics, LAr electronics readout
• Cathode Strip Chambers for the Muon system
• Focus on overall system, from construction,
  electronics, detector software to physics
  performance
• USATLAS Project Office
• ATLAS Technical Coordination for installation and
  commissioning

22
Liquid Argon Calorimeter
Production of Front End Electronics and
integration tests
Barrel Cryostat construction
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Cathode Strip Chambers

• Precision chamber in high rate environment
• Measure charge with Signal/Noise1501 ,
  position s60mm

32 Chambers are being built and tested at BNL
24
US-ATLAS Computing Tier-1 Center at BNL

• Part of the ATLAS Virtual Offline Computing
  Facility
• Computing for LHC experiments will reply on GRID
  technology Distributed computing resources.
• Co-located and operated with RHIC Computing
  Facility
• Currently operated at 1 of 2008 capacity
• Primary US data repository for ATLAS
• Complete data set on disk at Tier-1
• Software development for data management,
  distributed analysis, and grid integration

25
Installation
Barrel Calorimter Installation in progress
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Physics with the ATLAS Detector

• Search for, or exclude the Standard Model Higgs
  in the full mass range
• Search for physics beyond the Standard Model
• Supersymmetry (SUSY)
• Extra dimensions
• Exotic processes
• Study of Standard Model physics processes
• Top quark, Electroweak physics, B-physics
• Heavy Ion collision (?)

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Reconstructing the Events

• Reconstruct components
• (Isolated) electrons and muons
• High energy photons
• Jets
• tau lepton
• Vertex, secondary vertex
• Missing transverse energy
• Each physics process will have different
  signatures, and interesting events will have
  special combination of these components

Muon chambers
Hadronic calorimeter
Electromagnetic calorimeter
Inner detector
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Higgs? gg

• Requires excellent photon reconstruction
• Energy, position, direction, shower shape
• Reject jet background

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Search for Higgs in ATLAS

• Discovery potential
• Full mass coverage
• 100GeV to 1000GeV
• Determine the mass
• Measure its decay properties
• More than one decay channel at any mass

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Supersymmetry

• A leading candidate for physics beyond the
  Standard Model
• Can be a valid theory to very high energy
  scale(1019 GeV? )
• Each particle has a super-partner, spin differs
  by ½.
• Supersymmetry is broken
• super-partners mass is different from
  particles mass
• General Supersymmetry can have 100 unknown
  parameters
• Specific SUSY breaking model has 5 parameters
• Experimental challenges
• Find SUSY if it exists
• Identify specific SUSY model
• Many models, large parameter space.

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SUSY and Dark Matter

• The stable massive neutral supersymmetric-particle
  is a candidate for cold dark matter.
• Given the recent cosmological result on cold dark
  matter, and a specific SUSY model, the SUSY
  parameters are constrained.
• If LHC can find SUSY in the region consistent
  with cosmology, then we would find the
  explanation for Dark Mattter.

32
SUSY Reach

• The cosmologically interesting region of SUSY
  search will be covered in the first weeks of LHC
  running The mass range up to 2TeV will be
  covered within one year at low luminosity.

• Discovery
• Excess of high mass events
• production of heavy SUSY particles
• The LHC should be able to establish the existence
  of SUSY and open many avenues to study masses and
  decays of SUSY particles

SM
SUSY
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Example Reconstruction Of a SUSY Decay Chain
ATLAS 100 fb-1 LHC Point 5
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Large Extra Dimensions

• There may be 4d dimensions
• A possible extension of SM.
• Planck energy scale MP in TeV range
• Gravity propagates in all dimensions, other
  particlesinteraction in 4-D
• Blackhole production
• If EgtMP , black hole can be created
• Decay by Hawking radiation
• ? excess of high energy events
• Excitation by gravitons
• Excess of high energy particle pair production
• Single jet with missing energy

A Black Hole Event with MBH 8TeV
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ATLAS Computing Timeline
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Computing near term goals

• Support of Combined Testbeam
• Continue through Nov 2004
• Support of Data Challenge 2 and validation of
  Computing Model
• Generation, Simulation, Pile-up, Digitization,
  ByteStream Production, Reconstruction and Physics
  Analysis
• Tier-0 exercise of processing simulated ATLAS raw
  events
• Support of Physics Studies leading up to Spring
  2005 Physics Workshop
• Continuous Production, initial detector
  configuratioin
• Support of High Level Trigger testbed

37
Data Challenge II
Software Components Data Flow

• part I production of simulated data (on-going)
• Geant4, digitization and pile-up in Athena, POOL
  persistency, 10M Event on GRID
• part II test of Tier-0 operation (Oct 2004?)
• reconstruction will run on Tier-0 prototype as if
  data were coming from the online system ( at 10
  of the rate )
• output (ESDAOD) will be distributed to Tier-1s
  in real time for analysis
• part III test of distributed analysis on the
  Grid ( ? )
• access to event and non-event data from anywhere
  in the world both in organized and chaotic ways

38
BNLs Leading Roles in Software Physics

• D. Adams
• K. Assamagan
• H. Ma
• F. Paige
• S. Rajagopalan
• T. Wenaus

Distributed Analysis Coordinator Analysis Tools
Coordinator LAr Database Coordinator SUSY Physics
Co-coordinator LAr Software Coordinator Member of
SPMB LCG Application Area Coordinator ATLAS
Database co-coordinator Member of CMB
Omega Group, PAS and ACF will all expand in the
next a few year to get ready for LHC turn-on.
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US ATLAS Analysis Support Group

• Recently formed to help physicists starting using
  ATLAS software for analysis
• Current members
• D. Costanzo, I. Hinchliffe (LBNL), J. Shank
  (Boston),
• H. Ma (Leader), F. Paige, S. Rajagopalan (BNL),
• P. Loch (Arizona), F. Luehring (Indiana), F.
  Merritt (Chicago)
• Near term goal
• Bring more US ATLAS physicists into physics
  analysis, participate in DC2, and 2005 ATLAS
  Physics Workshop in Rome.

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Scope of the Support Group

• Provide up-to-date information on sub-detector
  and software components. Maintain up-to-date
  analysis web pages.
• Provide analysis software tutorials
• Identify existing (or the lack of) expertise
  within U.S. ATLAS, establish a network of
  support.
• Work with the U.S. physicists to resolve
  software, detector or physics problems
  encountered in their analyses.
• Facilitate communications by holding regular
  meetings and  providing a forum for technical
  discussions
• Hosting visitors and visiting U.S. institutions
  for informal discussions
• Develop and follow-up analysis plans with U.S.
  institutes. Assign an ASG member to follow
  closely with specific analysis activity.
• Provide advisory role for students and post-docs.
  
• ASG also has presence at CERN to provide support
  to U.S. activities.
• ASG communicates effectively to make analysis in
  US a success.

41
Atlas Physics Analysis Center at BNL

• Goal to establish a center for ATLAS physics
  analysis in US
• Physics analysis of an experiment as complex as
  ATLAS requires extensive understanding of the
  detector as well as software tools. We envision a
  BNL ATLAS Physics Analysis Center, aimed to
  provide US-ATLAS physicists with critical mass
  where ATLAS physics analyses will be done.
• Support from BNL
• Remote users, in-house visitors, video
  conferencing, heavy use of the Tier-1 center.
• It is essential that we provide adequate support
  for the analysis activities.

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Summary

• The Large Hadron Collider will be the highest
  energy proton accelerator when it starts to
  operate in 2007. It will open a new era in HEP.
  
• The LHC experiments will put the Standard Model
  to the ultimate test, and explore the physics
  beyond.
• BNL has played an important role in ATLAS, and we
  look forward to doing a lot of interesting
  physics at the ATLAS physics analysis center.