COSMIC RAYS

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Introduction to Cosmic Rays and Cosmic Air Shower
Experiments
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• Cosmic Rays in a Nutshell
• High energy particles traveling throughout
• our galaxy at close to the speed of light.
• Consist of elementary particles such as
• electrons (and positrons) and
• nuclei of atoms, mostly single
• protons (a few are much heavier).

Cosmic Rays continually bombard the Earth. In
fact, about 100,000 cosmic rays will pass
through a person every hour!
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Cosmic rays-a long story

• C.T.R Wilson discovered in 1900 the continuous
  atmospheric ionization. It was believed to be
  due to the natural radiation of the Earth. In
  other words, from the ground up.
• Wilson noticed the reappearance of drops of
  condensation in expanded dust free gas, the first
  cloud chamber.
• Wilson suspected the
• tracks might be condensation on nuclei - ions
  that were the cause of the residue conductivity
  of the atmosphere.

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Where did the ions come from?

• At the beginning of the 20th century scientists
  were puzzled by the fact that more radiation
  existed in the environment than could be
  explained by natural background radiation
• The debate was solved on a balloon flight in
  1912 from the University of Vienna.

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Victor Hess

• In 1912 a Victor Hess, a German scientist, took a
  radiation counter (a simple gold leaf
  electroscope) on a balloon flight.
• He rose to 17, 500 feet (without oxygen) and
  measured the amount of radiation increase as the
  balloon climbed.
• Victor discovered that up to about 700 m the
  ionization rate decreased but then increased with
  altitude showing an outer space origin for
  ionization.

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Not from the Sun

• During subsequent flights Hess determined that
  the ionizing radiation was not of solar origin
  since it was similar for day and night.
• It was initially believed that the radiation
  consisted of gamma rays only.
• But there was still a dispute as to whether the
  radiation was coming from above or from below.

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Birth Cries of the Atoms

• In 1925 Robert Millikan of Caltech introduced the
  term cosmic rays after concluding that the
  particles came from above not below a cloud
  chamber.
• He used elaborate electroscopes.

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Cosmic Rays are Charged Particles!

• In 1929 a Russian scientists, D. Skobelzyn,
  discovered ghostly tracks made by cosmic rays in
  a cloud chamber.
• Also in 1929 Bothe and Kolhorster verified that
  the cloud chamber tracks were curved by the
  magnetic field. Thus the cosmic radiation was
  charged particles.

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Carl Anderson discovers antimatter

• Milliken became President of Caltech and was
  instrumental in the building of a high magnetic
  field cloud chamber.
• Carl Anderson and Milliken made numerous
  photographs of both positive and negative
  particles tracks.
• 1933 While watching the tracks of cosmic rays
  passing through his cloud chamber, Carl Anderson
  discovered antimatter in the form of the
  anti-electron, later called the positron.

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Who ordered that? I. Rabi

• 1937
• Seth Neddermeyer and Carl Anderson discovered the
  elementary subatomic particle called the muon in
  cosmic rays.
• The positron and the muon were the first of
  series of subatomic particles discovered using
  cosmic raysdiscovered using cosmic rays,
  discoveries that gave birth to the science of
  elementary particles physics.
• Particle physicists used cosmic rays for their
  research until the advent of particle
  accelerators in the 1950's.

Carl Anderson at LBNL 1937
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Extensive air showers

• 1938
• Pierre Auger, who had positioned particle
  detectors high in the Alps, noticed that two
  detectors located many meters apart both signaled
  the arrival of particles at exactly the same
  time. Auger had discovered "extensive air
  showers," showers of secondary subatomic
  particles caused by the collision of primary
  high-energy particles with air molecules.
• On the basis of his measurements, Auger concluded
  that he had observed showers with energies of
  1015 eVten million times higher than any known
  before.

• Movie

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An Extensive Air Shower

• Cosmic rays enter the earths upper atmosphere
  and interact with nuclei.
• Secondary particles result that also interact.
• The shower grows with time.

• Certain particles never reach the surface.
• Some particles, such as muons, do reach the
  surface and can be detected.
• It is these that we wish to detect.

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composition of primaries

• 90 protons (not anti-protons)
• The remainder mostly follow solar system
  abundances (eg meteorites and solar photosphere)
• Spallation of O and C nuclei, for example, create
  more Li, Be, B than is typical of solar system

cosmic rays
solar system
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Cosmic rays at earths surface (secondaries)

• Primaries interact at z?15 km, producing a shower
  of (mostly) short-lived particles.
• e.g. pion (??) lifetime is 2.6?10-8 s
• The long-lived secondaries are
• e?, photons mostly absorbed
• neutrinos (?) practically invisible
• muons (??) ??lifetime is 2.2?10-6 s
• Without time dilation, muons would travel
  d?c?660 m, with a survival fraction e-0.66/15
  ?10-10
• Instead, for a 10 GeV muon, ?10/0,1100, then
  mean distance is 66 km. (OK)
• Detectable (vertical) flux is ?1/cm2/min
• Simulated event start...end
• Movie
• Sim tool

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Present Cosmic Ray Studies

• Cosmic Ray studies continue in spite of the
  development of high energy particle accelerators.
• The energy of the highest energy cosmic rays
  still cannot be duplicated in accelerators.
• The field is still very active as indicated by
  the presentation of over 300 papers at the most
  recent international conference on cosmic rays.

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Whats been learned from the researchWhat are
cosmic rays?

• Primaries are particles with energies from 109
  eV to 1021 eV.
• An eV is a unit of energy. A 40 W reading light
  uses about 1034 eV of energy in one hour.
• (from James Pinfoli,
• Pinfold_at_phys.ualberta.ca)

• Cosmic rays within the range of 1012 eV to 1015
  eV have been determined to be
• 50 protons
• 25 alpha particles
• 13 C, N, and O nuclei
• lt1 electrons
• lt0.1 gammas

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The Energy Spectrum

• Existing models for the production of cosmic rays
  only work to 1015 eV.
• CR in excess of 1019 eV are believed to come from
  sources relatively close to our Galaxy, but the
  sources are unknown.
• The highest energies!
• (www.phys.washington.edu)

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The Oh My God Particle

• In 1991 at the Flys Eye CR observatory in Utah a
  primary particle of 3 x 1020 eV was recorded.
  This is the equivalent of 51 joules
• At present particle accelerators can reach
  energies of 1012 eV.
• The Fly Eye
• (from www.physics.adelaide.edu)

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The AGASMA EVENT

• In Japan, in 1993, the worlds largest array
  recorded a large air shower believed to be the
  result of a primary particle measured at 1021 eV.
  These particles have energies six times higher
  than present theories allow.
• The mystery is, of course, what is the source of
  the high energy particles including these
  ultrahigh energy particles.

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Where do they come from?

• Low energy rays (less than 10 GeV) come from the
  sun.
• Supernovae may be the source of particles up to
  1015 eV.
• The sources for ultrahigh cosmic rays are
  probably, active galactic nuclei and gamma ray
  bursts.
• (www.phys.washington.edu)

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Supernovas

• 1949
• Enrico Fermi put forth an explanation for the
  acceleration of cosmic rays. In Fermi's cosmic
  ray "shock" accelerator, protons speed up by
  bouncing off moving magnetic clouds in space.
  Exploding stars (supernovae) are believed to act
  as such cosmic accelerators, but they alone
  cannot account for the highest energy cosmic
  rays.
• Nuclei receive energy from the shock wave of the
  supernova explosion.
• The energy spectrum indicates that most of the
  supernova particles have less than 1015 eV
• (image from www.drjoshuadavidstone.com/
  astro/supernova.jpg

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SN1006 Crab Nebula

• The Crab Nebula in visible light

and in cosmic rays (radiation from electrons in
the supernova remnant), showing the shell of the
supernova remnant still expanding into space
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How do we know SNs make galactic cosmic rays?

• One clue the abundances of different nuclei in
  galactic cosmic rays (GCR) is almost the same as
  the abundances in a mature star like the Sun

• Differences between solar and GCR abundances in
  the graph above are almost perfectly explained by
  nuclei fragmenting as they travel through
  interstellar space and strike occasional bits of
  matter
• The average GCR spends several million years
  wandering around our Galaxy before reaching Earth
  (we deduce this from abundances of radioactive
  elements)

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The ultra high particles?

• Without going into great detail the problem with
  the source of the UHECR is that to achieve the
  high energies they must originate in a very large
  extragalactic field or from a process that
  doesnt require such distance.
• Suggestions abound but there is not a agreement
  as to the origin. Maybe there isnt a single
  source.
• One suggestions is that UHE CRs originate from
  the decay of more primary particles resulting
  from the big bang.

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Whats been learned from the research Summary
-Energy Density of CR

• Lower energy, lt 1016 eV
• Direct observation possible, 85 are protons.
• Most likely source are supernova shock wave
  acceleration.
• These are particles below the knee in the energy
  spectrum.

• Ultra High energy, gt 1016 eV.
• Only indirect EAR shower information is
  available.
• Source of the particles with gt 1016 eV is
  unknown.

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High School Based Detectors

• Numerous detector arrays using high schools as
  sites for individual detectors have been built or
  are in the process of development.
• The projects range from arrays using hundreds of
  detectors covering thousands of km2 to small
  arrays involving only a few detectors in an area
  only a few hundred meters square.

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Why put cosmic ray detectors in schools?

• Important open questions about extremely high
  energy (UHE) cosmic rays
• Where do cosmic rays with Egt1020 eV come from?
• How can they be produced and accelerated?
• How can they reach us through intergalactic
  space?
• UHE-CR research requires simple detectors, spread
  over a large area, with accurate time
  synchronization
• High cost for conventional physics experiment
  new equipment, land use, data networks, and site
  support
• Example Auger Project gt US 108
• Solution Physicists provide surplus HEP
  equipment, schools provide sites and Internet
  port

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School-network approach

• Pioneered by U. of Alberta in Canada (ALTA) and
  U. of Nebraska in USA (CROP)
• University joins secondary schools to build a
  very large detector array at low cost, using
  existing resources in the community, and surplus
  equipment
• Use schools existing Internet access to link the
  sites
• Students and teachers participate in forefront
  research
• More than a one-time field trip or term paper
• Doing, not watching
• Research is ongoing, in the school every day
• Students help monitor detectors and analyze data
• Long-term relationship between school and
  University

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CHICOS (California high school cosmic ray
observatory)

• Operated by Caltech, CHICOS is an active research
  array with a goal to study CR is the range of
  1018 to 1021 eV using refurbished detectors from
  a neutrino experiment and 1 m2 scintillators
• Currently 51 sites are setup and working.
• Image from www.chicos.caltech.edu

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ALTA (University of Alberta Large Time
Coincidence Array)

• The stated purpose of the ALTA project is to
  search for time correlations between EASs.
• At present 16 high schools are involved.
• The project is part of the Canadian learning
  standards with students receiving credit.
• (image from www.physics.ubs.ca)

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ALTA MAP
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CROP (Cosmic Ray Observatory Project, University
of Nebraska)

• A project to study EAS from particles gt 1018 eV.
• Thirty operating schools covering 75000 sq miles
  is the goal of the project.
• Detectors are 1 m2 scintillators donated by the
  Chicago Air Shower Array.
• Image from Marion High School. Http//marian.creig
  hton.edu

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SALTA (Snowmass Area Large-scale Time-coincidence
Array)

• A project to set up detectors in Colorado.
• Linking high schools via Internet connecting to
  form a large array.
• A modern hot-air balloon flight in 2001 reenacted
  Hesss 1912 flight. Image from
  http//faculty.washington.edu/wilkes

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WALTA (Washington Large Area Time Array)

• A project of the University of Washington.
• As of late 2006 eighteen high schools around
  Seattle are participating. See image. (from
  www.phys.washington.edu )

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The Pitt/UMSL Projects

• A project of the University of Pitt and
  University of Mo at St. Louis.
• The project involves high school teachers
  building and using scintillator type detectors
  aimed at muon detection.

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The QuarkNet Detector
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Cosmic Ray E-lab
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ExampleStudent Poster
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Example StudentPlot