Ultra High Energy Cosmic Rays

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Ultra High Energy Cosmic Rays

• Glennys R. Farrar
• Center for Cosmology and Particle Physics,
• Department of Physics, New York University

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A Timeline History of High-Energy Cosmic Rays
1912 Hess discovered cosmic rays hot air
balloon 1927 Cosmic rays seen in cloud
chamber 1932 Anderson discovered antimatter
(positron) Debate over cosmic rays 1937
Discovery of muon 1938 Auger discovered extensive
air showers 1946 First air shower experiments
Discovery of pion and kaons 1949 Fermi's theory
of cosmic rays 1962 First 1020 eV cosmic ray
detected 1966 Proposal of GZK cutoff energy for
cosmic rays 1991 Fly's Eye detected
highest-energy cosmic ray 1994 AGASA high-energy
event 1995 Pierre Auger Project begun to be
completed 2005 2002 HiRes and AGASA Debate the
GZK cutoff
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An Ultrahigh Energy Shower

• First interaction p 14N -gt thousands of
  secondary particles, such as
• p, p-, p0, K-0, L, S, p, n, ...
• Subsequent interactinos
• p- air nucleus -gt few hundred particles OR
• p- -gt m- nm
• p0 -gt g g
• g initiates an electromagnetic cascade,
  producing e- and more gs

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Some Types of Cosmic Particles

• Atomic nuclei protons and neutrons. E.g., 12 C
  is composed of 6 p and 6 n.
• Protons the hydrogen atom is 1 p and 1 e-
• Neutrons decay into a proton via the reaction
  n -gt p e- ne with a lifetime
• t 103 sec.
• Electrons and positrons e- and e .
• Quanta of light photons or gammas (g)

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Cosmic Ray Energies

• A standard unit for elementary particle energies
  is the electron Volt eV.
• 1 eV is the kinetic energy of 1 electron moved
  through a potential of 1 Volt.
• Ultra-high energy cosmic particles have energies
  greater than 1019 eV.
• 1 MeV 1 Mega eV 106 eV
• 1 GeV 1 Giga eV 109 eV
• 1 TeV 1 Tera eV 1012 eV

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Some Terminology

• Flux the amount of something arriving in one
  unit of area (e.g., 1 m2) in one unit of time
  (e.g., 1 sec).
• Spectrum A plot showing the amount of
  something, as a function of energy. In the next
  slide, the something is the number of particles
  in one bin of energy.

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Cosmic Ray Energy Spectrum

• In this spectrum, the Log of the flux in one unit
  of angle (sr) is plotted versus the Log of the
  energy. A sphere has 4 p steradian.
• The CR spectrum falls rapidly as energy
  increases dN/dE E-3

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Problems

1. From the graphed spectrum, find a more exact
   value of the exponent p, in the expression flux
   E-p. (Hint take the Log of this formula).
2. Approximately how many events of energy above
   1019 eV would we expect to see per year of
   full-time data-taking with the NYSCPT if its area
   is 100 km2?

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Hajo Dreschers Shower Simulations

• 1019 eV proton primary
• Horizontal grid units 1 km
• Vertical box 30 km
• Heavy thinning for r lt 30 m
• e, e-, g, m, hadrons

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Vertical shower, 51 aspect ratio
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Inclined Shower, 11 aspect ratio
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Electromagnetic Component
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Muons
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Hadronic component (neutrons)
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Two Types of Cosmic Ray Detectors

• Ground Shower Array (AGASA, Auger, NYSCPT)
• Large area because of low flux (1/ km2 / century
  gt 1020 eV)
• Collects data day and night, any weather
• Measures direction by arrival times across array
• Relies on modeling of shower to infer energy and
  primary type
• Air Fluorescence (HiRes, Auger)
• 10 duty cycle (clear, moonless nights)
• Difficult to calibrate
• Insensitive to atmospheric shower modeling

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AGASA AUGER 2005
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AGASA Photos
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Greisen Zatsepin Kuzmin Cutoff

• Ultra-high energy protons above 1020
  electron Volts (10 Joules!)
• Collide with low energy Cosmic Microwave
  Background photons (400 / cm 3 )
• p g -gt p p
• Pion takes energy from the initial proton
• gt energy of a UHE proton degrades in 100
  Million light years (nearby in cosmic terms!
  visible universe is about 10 billion light years
  across)

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AGASA Doesnt See the Predicted GZK Cutoff!
Dotted line expected spectrum at Earth if
sources are uniformly distributed throughout the
Universe and UHECP Energy is degraded as
predicted by GZK. Will HiRes confirm absence of
GZK cutoff? If so, what is going on????
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Important Science Goals of a UHECP Telescope

• Good energy resolution ( 10 ?)
• AGASA, HiRes, Auger 30
• Structure in energy spectrum will elucidate
  source.
• Good angular resolution (0.1 degree ?)
• Identify sources
• Determine the magnetic field in our galactic halo
  and between (only possible with good energy
  resolution)
• Detailed information on shower structure (e.g.,
  arrival time)
• Validate model of atmospheric shower
• Improve determination of primary energy and type

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Cutting Edge UHE Cosmic Particle Telescope in New
York City

• What design?
• Ground Array (no need for expensive Air
  Fluorescence because Auger will cross calibrate
  techniques).
• For better resolution closer spacing than
  AGASA, much closer than Auger -- being simulated
  now.
• How large an area?
• Best large (1000 km2), for more statistics.
• Useful smaller (100 km2), because of high
  resolution and detailed shower information.
• Can start small and improve.
• Flash ADC and high resolution gt NYSCPT will
  be a premier Air Shower Array, even with just 100
  detectors.

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New York City 10 times the area of AGASA and
350 High Schools
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A Plan

• Deployment staged over three years.
• Stage I Core group of HS teachers and students
  (masters)
• collaborate with physicists to build and use
  prototype detectors and develop curriculum.
  (NYSCPT Summer Institute, Aug. 9-23, 2002).
• Stage II Second group of teachers ( 10 per
  master teacher?) will be engaged including most
  public, private and parochial high schools
• Stage III Include remaining schools deploy
  additional non-school-based detectors (roofs of
  homes, libraries, apartment buildings). Expand
  to middle schools? Beyond city limits?

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Timetable

• Summer 2002
• 10 HS teachers with 18 students
• 2 week Institute build prototype detectors,
  work on initial curriculum ideas
• AY 02-03
• Operate 10 detector systems initial science
  analyses.
• Complete simulations and finalize the design.
• Investigate issues with non-school detectors.
• Refine and extend curriculum materials.
• Summer 2003 AY03-04
• Build, deploy, and operate 100 detectors
• First scientific results
• Summer 2004 AY04-05
• Build, deploy, and operate 1000 detectors
• Major scientific results

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Serious Contributors to the Effort so far

• Scientists
• Faculty Glennys Farrar (NYU), Reshmi Mukherjee
  (Barnard), Stefan Westerhoff (Columbia)
• Expert Consultants M. Teshima (AGASA), P.
  Sokolsky and L. Weincke (HiRes), Brian Fick
  (Auger), D. Hanna (STACEE)
• Postdoc Hajo Drescher (NYU -- simulation)
• Grad students Britt Reichborn-Kjennerud, Doug
  Bramel, Segev Benzi, Andy ONeill
• Undergrad Dietrech Washington
• Educators Wesley Pitts (CUNY Gateway to
  Learning)
• Supported by National Science Foundation, NYU,
  Columbia, Wolfram Research

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Other Projects and Sources

• CROP (Nebraska) low resolution, large area
• http//www.unl.edu/physics/crop.html
• CHICOS (Los Angeles) low resolution, large area
  http//www.chicos.caltech.edu/
• NALTA North American Large Area Time Coincidence
  Array http//csr.phys.ualberta.ca/nalta/
• NYSCPT high resolution large area in Stage III
• http//www.physics.nyu.edu/NYSCPT