Title: COSMIC RAYS
1Introduction 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!
3Cosmic 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.
4Where 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.
5Victor 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.
6Not 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.
7Birth 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.
8Cosmic 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.
9Carl 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.
10Who 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
11Extensive 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.
12An 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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14composition 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
15Cosmic 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 18Present 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.
19Whats 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
20The 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)
21The 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)
22The 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.
23Where 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)
24Supernovas
- 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
25SN1006 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
26How 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)
27The 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.
28Whats 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.
29High 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.
30Why 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
31School-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
32CHICOS (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
33ALTA (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)
34ALTA MAP
35CROP (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
36SALTA (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
37WALTA (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 )
38The 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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40The QuarkNet Detector
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42Cosmic Ray E-lab
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45ExampleStudent Poster
46Example StudentPlot