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COSMIC RAYS

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Introduction to Cosmic Rays and Cosmic Air Shower Experiments Cosmic rays-a long story C.T.R Wilson discovered in 1900 the continuous atmospheric ionization. – PowerPoint PPT presentation

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Title: COSMIC RAYS


1
Introduction to Cosmic Rays and Cosmic Air Shower
Experiments
2
  • 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!
3
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.

4
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.

5
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.

6
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.

7
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.

8
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.

9
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.

10
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
11
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

12
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.

13
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14
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
15
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


16

17

18
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.

19
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

20
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)

21
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)

22
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.

23
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)

24
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

25
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
26
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)

27
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.

28
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.

29
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.

30
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

31
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

32
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

33
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)

34
ALTA MAP
35
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

36
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

37
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 )

38
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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40
The QuarkNet Detector
41
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Cosmic Ray E-lab
43
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45
ExampleStudent Poster
46
Example StudentPlot
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