Visualizing Data from the LHC with the Atlantis Event Display Program

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Visualizing Data from the LHC with the Atlantis
Event Display Program

• Joshua Auriemma
• Advisor Andy Haas

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Part I Everything You Always Wanted to Know
About ATLAS, Only Wrong

• A general overview of detector components.

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A Toroidal LHC Apparatus
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Inner Detector

• Is mainly a tracking detector, required in
  order to determine the momentum, position, and
  impact parameter (?INT)
• The inner detector consists of three main
  sections the pixel detector, the semi-conductor
  tracker, and the transition
  radiation tracker.

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The Pixel Detector

• Provides tracking information for pattern
  recognition near the collision point and largely
  determines the Inner Detectors ability to find
  secondary vertices.
• Three measurements over the full acceptance are
  performed in order to find the impact parameter
  resolution, and the detectors ability to find
  short-lived particles such as B hardrons and t
  leptons.

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Semi-Conductor Tracker

• A charged particle passing through this detector
  liberates charge carriers, electrons, and
  "holes". When separated by the E-field, the
  "holes" drift to the back-plane, and the
  electrons to the readout strip. This creates a
  potential difference which can be measured.

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Transition Radiation Detector

• Why Have a TRD? Many high-energy particles look
  very similar to each other due to similar
  momentum. The TRD measures E/m a value which
  differs greatly depending on the particle.
• How Does it Work? As high-energy electrons
  transverse the detector, X-Rays are produced
  which ionize a gasseous Xe and CO2 compound.
• All particles will create a signal!

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Calorimeter Detectors

• The calorimeter detectors are designed to stop
  basically every particle except neurtinos and
  muons.
• The inner-most calorimeter detector is known as
  the electromagnetic detector.
• The outer-most calorimeter detector is the
  hadronic calorimeter detector.

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Electromagnetic Calorimeter

• Responsible for stopping electrons, positrons,
  and photons.
• Detector material causes bremsstrahlung.
• The energy lost is found by
• Insufficient technique for photons
  (photoelectric, Rayleigh, Compton, pair
  production).

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Hadronic Calorimeter

• Hadrons have most likely already interacted with
  the EM Calorimeter.
• Generally in the first interaction jets of
  particles are produced.
• Charged particles will interact with
  scintillator.

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Muon Chambers

• Because muons are so massive, they generally pass
  straight through the inner detector, and both
  calorimeters without losing very much energy.
• Extremely massive muon detectors must therefore
  be constructed in order to detect these
  particles.
• The detection system is based on the deflection
  of muons by the large barrel toroid.
• The muons are measured in three layers of
  chambers around the beam axis using Monitored
  Drift Tubes and a Cathode Strip Chambers.
  Detection will occur inside the Resistive Plate
  Chambers and the Thin Gap Chambers.

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Monitored Drift Tubes

• Aluminum tubes pictured above act as beam pipes
  for the muons.
• Each tube has a wire within it with a potential
  difference.
• Changes in the muons course due to the E-field
  provided by the toroid will cause induction in
  the wire and can be measured.
• Knowledge of the drift-speed allows for tracking.

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Cathode Strip Chambers

• The CSCs are multi-wire proportional chambers
  with cathode strip read-outs.
• The precision coordinate is obtained by measuring
  the charge induced on the segmented cathode by
  the avalanche formed by the anode wire.
• Relatively good special resolutions can be
  obtained through charge interpolations
  (resolution of 60 mm).
• Absence of hydrogen in the gas mixture, combined
  with a small gap width, allows for a low
  sensitivity to neutron background.
• Less sensitive to variations in gas parameters
  than the MDTs

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Resistive Plate Chambers

• The RPS is a gaseous detector (C2H2F4).
• There is a narrow gap formed by two parallel
  plates made from bakelite of 2 mm thickness which
  is separated by insulating spacers.
• Avelanches are generated by high field of 4.5
  kV/mm.
• The signal is measured through a capacitive
  coupling by metal strips on both sides of the
  detector.

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Thin Gap Chambers

• In the TGCs, however, the wire distances are
  small enough to guarantee short drift times, and
  therefore, good timing resolution.
• The anode plane is sandwiched between two cathode
  planes made of 1.6 mm G-10 plates on which the
  graphite cathode is deposited.
• On the backside of the cathode plates facing the
  center plane of the chamber, etched copper strips
  provide the readout of the azimuthal coordinate.
• On the outside, the gas pressure is sustained by
  5 mm thick paper honeycomb panels.

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Part II Neat Physics with Atlantis
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About Atlantis

• The Atlantis project is a java-based event
  display program that represents over 40 years of
  work.
• The Atlantis collaboration currently consists of
  14 members at 8 different institutions.
• Atlantis subscribes to the following 3
  principles
• Atlantis is fast
• Atlantis is used intuitively.
• Atlas is used for complete ATLAS events.

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Reasons for Atlantis

• The Atlantis program has two main objectives.
• To serve as a means of examining and verifying
  pre-flagged interesting physics.
• To obtain a physics understanding of algorithms
  related to the detector.

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Confirming New Physics

• While Atlantis will likely never be the first
  program to find new
• physics, it certainly serves as a useful
  verification of physics. For
• example, one may note an obvious B hadron due to
  the track
• reconstruction near the point of interaction.
  That same person may
• note that two very prominent electrons were
  absorbed in the
• calorimeter detector. Theoretically, it would
  seem logical that the
• missing ET of this event would be low, since it
  is likely that a top
• quark decayed into a W-boson and a b-quark, and
  that b-quark then
• decayed into an electron and an electron neutrino.

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Algorithm Construction

• While algorithm construction is loosely tired to
  the first goal, many
• of Atlantis' contributors actually consider this
  reason the number one
• reason for the existence of a graphical display
  program. One may be
• programming something which uses vertices in
  order to b-tag. While
• out of context, the algorithm may make very
  little sense, applying it in
• the context of an event display such as Atlantis,
  the code can become
• much more intuitive.

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Understanding the Coordinate System

• The ATLAS coordinate system (x,y,z) is defined
  as
• z beam axis cylinder axis
• x horizontal axis
• y vertical axis
• Additionally, the coordinate system (f,h,r) is
  defined as
• r sqrt(x2 y2)
• f arctan(y/x)
• h arctan(r/Z)

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Revisiting the Detector

• The resolution of the detector is fine enough
  such that it is possible to make out the
  structure of the detector through hits.

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The Pixel Detector
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Inner Detector
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Impact Parameter
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Examining Simulated Events

• Having simulated data for specific types of
  events, Atlantis can be used in order to verify
  that these algorithms are working properly.

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Electron (XY)
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Electron (rZ)
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Electron (Lego plot)
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Muon (XY)
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Muon (rZ)
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Jet (XY)
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Jet (rZ)
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Jet (Lego Plot)
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In Conclusion

• Although it is not meant to replace triggering
  systems, Atlantis is a great way of visualizing
  events.
• Extremely complicated events can be very easily
  examined through the use of a graphical display
  program.
• Atlantis is great!