Cosmic Air Shower Array

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Cosmic Air Shower Array

• Diana Fulton, University of Colorado, Colorado
  Springs
• Eric Kalix, Lycoming College
• Ryan Rowekamp, University of St. Thomas
• Dr. Robert C. Webb, Texas A M University
• Dr. James T. White, Texas A M University

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ABSTRACT

• By measuring the differences in time of incoming
  pulses from an array of detectors, we can
  determine the angle from which the shower
  originated.
• We were able to determine the angle of origin for
  35 events. The events favored the direction of
  the interior of the building.

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Cosmic Rays

• Elementary particles e-, e, g, n
• Atomic Nuclei 1H thru U
• Nuclei heavier than Ni are very rare.
• Cosmic rays interact with air nuclei in
  atmosphere (altitude about 20km).
• Most never reach ground.

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Shower Development

• Initial particle primary cosmic ray
• Particles in an air shower secondary cosmic rays
• An area the size of your hand is hit with about
  one particle per second.
• The number of particles that reach the ground
  depends on the energy, type of incident cosmic
  ray, and altitude.
• Higher energy particles lose about ½ of their
  energy in the interactions, and the jet of
  particles created travels in almost the same
  direction as the cosmic rays.

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Air Shower Detection

• Most common detectors are scintillation counters.
• Other types include water Cherenkov counters,
  resistive plate chambers, and a variety of
  position-sensitive devices.
• We do not see the primary cosmic ray, but
  rather the secondary rays, which can be used to
  infer about the primary ray (number of particles,
  timing, energy, direction).
• Extensive air showers are not common
  coincidences of several particle detectors are
  required.
• The size of air shower detector can range from a
  few detectors spaced 10-20 meters apart to
  detectors spaced about a kilometer apart.

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Experimental Methods

• The 8 polystyrene scintillators were wrapped in
  black vinyl, which was clad in aluminized mylar
  on one side.
• A photomultiplier tube (PMT) was adhered to one
  side to detect cosmic rays.
• The set up in figure 1 was used for an overnight
  test run.

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• The data collected in the test was used to
  determine minor light leaks and differences in
  signal cable lengths. The program used was called
  Physics Analysis Workstation (PAW).
• The scintillators were moved to the configuration
  in figure 2 for a second overnight test run.

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• For an official data run, the PMT voltage was
  1800 volts.
• We rearranged the scintillators as shown in
  figure 3.
• Scintillator 4 sat above scintillator 1. This was
  due to another experiment being done on muon
  lifetime by another group.
• The data was collected overnight.

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Description of Alignment

• One set of detectors lies on the x-axis while
  another lies on the y-axis, represented by boxes
• The red arrow points in the direction of the
  showers origin
• The blue arcs represent q0 for the x and y
  detector sets
• The green arc represents f0 for the y detector set

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Calculation of Angles

• Dt The difference in times between the
  detectors (red line)
• t0 The time it takes light to travel between
  detectors (along axis)
• q Blue line
• f Green line
• R Dt / t0 sin(q q0) cos(f f0)
• Rx Dtx / t0x sinq cosf (I)
• Ry Dty / t0y sinq sinf (II)
• Ry / Rx tanf (I) / (II)
• f tan-1(Ry / Rx)
• q cos-1(Rx / cos(f))

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Angular Distribution

• 22 came from the direction of the interior of the
  building (blue)
• 11 came from the direction of the exterior wall
  (green)
• 2 came from directly above (red)
• Many events are originating from the interior of
  the building.

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References

• Konrad Bernlöhr. Shower Detection.
  http//www.mpi-hd.mpg.de/hfm/CosmicRay/ShowerDetec
  tion.html. June 28, 2003.
• Konrad Bernlöhr. Cosmic-ray air showers.
  http//www.mpi-hd.mpg.de/hfm/CosmicRay/Showers.htm
  l. June 28, 2003.
• High Energy Cosmic Ray Group. How do we study
  cosmic rays?. May 13, 1999. http//ast.leeds.ac.uk
  /haverah/dets.shtml. June 28, 2003.

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Special Thanks

• Dr. Robert C. Webb, TAMU
• Dr. James T. White, TAMU
• Jianting Gao, TAMU
• The RUG Program
• All who worked on building the array