debris of a cosmic ray shower. From inspection of thi

1
An Introduction to Cosmic Rays, Relativity, and
MARIACHI

• M. Marx
• November 16, 2006

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Radioactivity

• Radiactive material is classified according to
  its activity the number of decays per second
• Ndecays Npresent x t x time interval
• t is the lifetime of the material
• t1/2 or half-life t ln 2 0.6931471806 t
• Half-life is the time required for half of the
  radioactive material to decay
• We have identified particles and isotopes with
  half-lives ranging from
• 10-23 seconds (time it takes light to cross a
  nucleus)
• 109 years (comparable to age of universe)

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Puzzles

• Puzzle 1
• There are lots of short lived radioactive
  isotopes that can be found naturally on the
  surface of the earth
• Deep underground (i.e. in mines) one only finds
  isotopes whose half lives are comparable to the
  age of the Earth (109 years)
• Where does the short lived stuff come from?
• ? ? Continuously replenished by radiation from
  Outer Space!!

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Puzzles

• Puzzle 2
• Early researchers on radioactivity had great
  difficulty in shielding their equipment from
  ubiquitous radiation
• Where does it come from?
• ? ? Outer Space!!

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Discovery of cosmic radiation

• Victor Hess in 1914
• Electroscopes always discharge
• Radiation increases with altitude (balloon!)
• Varies with location and direction Earths
  magnetic field!
• Led to discoveries of new particles
• Positron, muon, pion, strange particles.
• Good example of relativity in action!

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Special Relativity (1905)

• Einsteins postulates
• Nothing can move faster than light in vacuum
• Speed of light looks the same to all independent
  of observer velocity

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Special Relativity Consequences

• Consequences
• Moving objects look shorter L
  Lo (1-v2/c2)1/2
• Moving clocks appear to run slower to t
  (1-v2/c2)1/2
• Moving objects get more massive mo
  m (1-v2/c2)1/2
• Mass and energy are interchangeable
• E mc2 m0c2/ (1-v2/c2)1/2
• Velocity of light ( c )
• 186,000 miles per second
• 3 x 108 meters per second
• Effects of relativity are not noticeable in daily
  life

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Consequences

• v v/c (1-v2/c2)1/2
  1/(1-v2/c2)1/2
• 28,000km/h 3 x 10-5 1 1
• (Shuttle in orbit)
• 0.1 .99 1.005
• 0.25 .96 1.03
• .99 .14 7.07
• .9999 .014 70.7
• A particle traveling at 99 of speed of light has
  7 times more mass, is 1/7 of its length, and
  lives 7 times as long!

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Why Study Cosmic Rays?

• Cosmic rays are a tool to study phenomena at the
  extreme ends of sizes
• Very small gt fundamental particles (building
  blocks of all matter)
• Very large gt window on energetic processes in
  the universe (supernovae, black holes, colliding
  galaxies, and the unknown!)
• Early discoveries of fundamental particles before
  the era of accelerators (atom-smashers)
• Studies of ultra-high energy particles beyond the
  reach of man-made accelerators

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Why Study Cosmic Rays?

• Cosmic rays are the prime source of natural
  background radiation
• Short lifetime isotopes continuously replenished
• Cosmic radiation increases with altitude the
  atmosphere shields us from most of it
• Radiation dose doubles every 5000ft!
• Deep rocks contain only long-lived isotopes
• Cosmic ray interactions with DNA of living cells
  may be prime (continuing) agent in evolution

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Fundamental Particles- The Elements
The periodicity strongly suggests an underlying
structure, i.e. all are composed of common
building blocks Now we know that these blocks are
proton, neutron, and electron
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Fundamental Particles The Atom
All atoms are composed of nuclei surrounded by a
cloud of electrons The nuclei are composed of
protons and neutrons We know now that the
protons and neutrons are themselves composed of
quarks and gluons
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Fundamental Particles
Generation 1
Generation 2
Generation 3
ALL ordinary matter is composed solely of first
generation particles atoms have nuclei
composed of protons (uud) and neutrons (udd)
surrounded by clouds of electrons to make the
atom electrically neutral. Second and third
generation particles can be produced if there is
sufficient energy available in a collision ( E
mc2), but all these particles decay
eventually into lower generations.
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Introduction to Cosmic Rays

• What are cosmic rays?
• Nuclei with composition similar to the solar
  system gammas, neutrinos
• Interaction and decay products reach the ground
• Rates at ground level are 1 per second per cm2
• Huge range of energies Mev EeV gt
• Different energies come from various sources
• Low energies from sun (10 gt 100 MeV typical)
• Galactic sources supernovae
• Highest energies ( above 10 EeV) are a mystery

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Cosmic Ray Energy Spectrum
Units 1 electron-Volt 1 eV Energy gain of a
charged Particle ( q 1e) accelerated thru
1V 2 4 eV visible light Kev Xrays Mev
Binding of nucleons Mass electron c2 ½
MeV GeV Massc2 of nucleons EeV (1018 eV)
pitched baseball
Sun
Our Galaxy
1 particle/km2/century Origin Unknown -
A dozen seen!
Extra-galactic
GeV gt
EeV
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Cosmic Rays
Primary Cosmic Ray Nucleus ( H .Fe) strikes
Atmospheric Molecule
Secondary particles nucleons (p,n), pions (p,
p-, p0), Kaons
Secondaries interact with atmospheric molecules
Neutral pions decay p gt g g
Charged pions decay p gt m n
Gamma rays initiate Electromagnetic showers g gt
ee-
Low energy muons decay m gt e n n
http//www.auger.org/observatory/image_gallery_i
ndex.html
Shower debris reaches Earth m, g, e,e-
- very low
energy fragments of original
shower
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Cosmic Rays and Special Relativity

• The primary cosmic ray collides with a molecule
  in the atmosphere transferring much of its energy
  into a shower of secondary particles
• Lifetime of charged pions is 10-8 sec and they
  all decay before reaching Earth (p gt m n)
• Lifetime of muons is 10-6 sec
• At close to speed of light would expect decays (m
  gt e n n)
• S vt 3 x 108 m/s x 2.2 x 10-6 s
  660m
• But most muons reach Earth (10km!!) because their
  clocks are slowed by relativity!
• From the muons perspective they see the distance
  to Earth shrunk to lt 660m they could move by
  their own clocks!
• Einstein was amazed by this practical proof of
  his theory

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Shower Animations 1 Tev Proton Initiated Shower
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Detection of Radiation/Particles

• We have many ways at our disposal to detect the
  passage of ionized (i.e. charged) particles the
  particles themselves are not visible
• Uncharged particles can only be detected
  indirectly, either by their decay into charged
  particles, or by their interactions which produce
  charged particles.
• Charged particles disrupt the clouds of electrons
  surrounding the atoms in their path, exciting the
  electrons to higher energy states, or by knocking
  out an electron and ionizing the atom.
• The paths are marked by these disturbed electrons
  which can be collected and measured by several
  means.

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Simplest Radiation Detector
X-rays are neutral and not detectable however,
they knock out charged electrons ionizing atoms
in the film, creating grains that become visible
once developed. The picture shows the intensity
of X-rays reaching the film (negative!) Film was
the medium for Roentgens discovery of
X-rays and radiation.
Film was originally and still is used for studies
of cosmic rays through stacks of emulsions. Many
of the early discoveries were made with it
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Nuclear Emulsions (Film) Provides a
Complete picture Of an event Excellent
spatial resolution Excellent energy density
gives identification and directions,
speed Provides no time information
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Bubble Chamber
m - muon
e - electron

• This bubble
• chamber picture
• shows the decay
• chain
• p gt n
• m gt e n n
• This decay chain is very
• common in the
• debris of a cosmic ray shower

From inspection of this picture one can tell the
direction of the particles by their ionization
(and the magnetic field confirms this!)
p - pion
Measuring the curvature determines the sign
and momentum of the particles. There is no time
information.

• Why are the neutrinos invisible?
• Why is the muon track so short?

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Pierre Auger Observatory Argentina
Surface Array 1600 detector stations 1.5 km
spacing 3000 km2
Fluorescence Detectors 4 Telescope enclosures 6
Telescopes per enclosure 24 Telescopes total
http//www.auger.org/observatory/animation.html
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Three Key Pieces of Radar detectors to find
reflected TV signals from cosmic rays, meteors,
lightning Scintillator detectors to confirm
cosmic ray signals (and do correlations) The
grid for data acquisition and analysis
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Radar (EM wave) Reflections from an Ionized Plasma

• Radio (electromagnetic waves) are routinely
  reflected by metallic objects radar
• They can also be reflected from areas where the
  ionization densities are high enough exceeding
  the plasma frequency given by

(Hz)
8.98
ne is the ionization density me is the
electron mass e is the electron charge
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Cosmic Ray Coverage

The primitive Mariachi array we are implementing
now on Long Island covers an area of
about 6000 km2 or twice the area of Auger!
http//www-mariachi.physics.sunysb.edu/wiki/index.
php/Ground_Array
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Radar Echo Signals
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Radar Echoes from Meteors
Meteor data acquired from April 16th to April
26th showing the Lyrids meteor shower that
peaked on April 22nd and a secondary minor
shower that peaked on April 25th. The diurnal
variation is due to the Earth's rotation.
Typical echo from a meteor trail, with a weak
echo from a second TV station.
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Why Ground Arrays

• Mariachi hopes to exploit the new technique of
  Radio Cosmic Ray Scatter to detect and then study
  UHECR (and neutrinos!)
• We hope to identify a class of short duration
  radio echoes that are UHECR candidates
• To confirm their identity we need simultaneous
  detection by proven techniques we use
  scintillator ground arrays for their simplicity
  and reliability.
• This also provides the opportunity to include in
  Mariachi the community of high school teachers
  and students, to learn about science and
  cyberinfrastucture, while contributing to the
  scientific goals of the project.

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Scintillation Counters and Phototubes
Charged particle Velocity c Time D/c, 1ns/ft
Raw pulse from PMT
Logic pulse
D

• Photomultiplier Tube
• Photon ejects electron by photo-electric effect
• Electron guided to dynode ejecting
• several electrons
• Process repeated many times
• Electron cloud arrives at anode negative pulse
• Transit time 100ns

Discriminator Provides standard height and width
pulse whenever input pulse is over
preset threshold

• Scintillation Counter
• Doped plastic emits
• light
• Light travels to ends by
• total internal reflection
• Transit time 2.5ns/ft

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Scintillator
See-through PMT assembly
Light-tight student proof lockable case
The final design
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The MARIACHI Grid

• The dream
• A transparent global network of computing
  resources available to all users uniformly. Like
  the World Wide Web via the Internet.
• User defines a job
• An input file.
• A program to run (installed or provided).
• A place to put the output file.
• A set of constraints (CPU speed, memory,etc.).
• Users submit job.
• ...to chosen Grid sites (OSG) or the entire Grid
  (LCG) and await results.

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Mariachi Wiki

• See our wiki based web site at
• http//www-mariachi.physics.sunysb.edu/
• Opportunities to participate in this educational
  research for teachers and students at all levels!

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High Energy Protons see Cosmic Microwave
Background as High Energy Gamma Rays!
WMAP
p?cmb? ? ? p ?0 ? n ?
GZK Cutoff
UHECR are too energetic to originate from known
sources in our galaxy or nearby galaxies. UHECR
are too energetic to propagate through the
microwave background from distant sources
Neighboring Galaxies
Galaxy Clusters
Milky Way