Exploring the Universe with Particles and Rays: a,

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Exploring the Universe with Particles and
Raysa, ß, ?, X, Cosmic, Toby BurnettProf, UW
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So what is a ray ?

• ray
• A thin line or narrow beam of light or other
  radiant energy.
• radiation
• Emission and propagation and emission of energy
  in the form of rays or waves.
• Energy radiated or transmitted as rays, waves, in
  the form of particles.
• A stream of particles or electromagnetic waves
  emitted by the atoms and molecules of a
  radioactive substance as a result of nuclear
  decay.
• Common theme
• A source emits a particle, which
• propagates in space, until it
• interacts with another particle, .
• producing secondary particles that are detected

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Dictionary

• propagation
• The act or process of propagating, especially the
  process by which a disturbance, such as the
  motion of electromagnetic or sound waves, is
  transmitted through a medium such as air or
  water.

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Waves or particles?

• Particle point-like object
• Wave spread-out
• Quantum mechanics in a nutshell
• Light, and all radiation, is discrete.
  (quantized)
• The quanta of light are particles called photons,
  that have zero mass. (Same for all EM waves.)
• Emission and absorption behave like particles.
• Propagation is wave-like. (Famous example
  double-slit)
• Energy and frequency are the same thing! (Ehf)
• Same for momentum and inverse wavelength
  (pmvh/?)
• Special relativity
• No massive particle can travel faster than the
  speed of light c 3x108 m/s 30 cm/ns.
• E2 m2 c4 p2 c2

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Experiments and observations

• Recall the theme source?propagation?interaction?
  secondaries?detector
• Each stage can provide info about the world
  around us.
• Consider a microscope.

Wavelength limits resolving power. Solution use
higher energy (like electrons) Same paradigm as
particle accelerators, one reason for high energy
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The electron Volt

• SI unit of energy joule.
• We use the electron Volt (eV) energy gained by an
  electron passing through a electrical potential
  difference ?V of 1 Volt. (Energy is force x
  distance)
• 1 eV 1.6 x 10-19 J. This is the scale of
  chemical interactions.
• Photons detected from space

3 degree microwave background 3 x 10-4 eV
Visible light 3 eV
Highest energy ever seen 1012 eV 1 TeV
Prefixes Prefixes
MeV 106
GeV 109
TeV 1012
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A rather big microscope

• The Fermilab Tevatron particle accelerator.
• accelerates protons to 1 TeV
• uses some to make anti-protons (in collisions)
• accelerates anti-protons to 1 TeV.
• collides them!
• Why?
• Study nature of matter by analyzing produced
  particles

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The CR spectrum revisited
Flux particles/(m2 sr s GeV)
Kinetic Energy (GeV)
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Solid angle (Greek omega, ?)

• Whats a steradian?
• Ordinary (plane) angles are a measure of the
  opening between 2 lines
• How can we express a field of view on the sky in
  terms of solid angle?
• Recall 1 radian 57 degrees
• (angle subtended by an arc of length R on a
  circle)
• 1 arcsec 4.8x10-6 radian
• By analogy
• solid angle subtended by an area of 1 m2 on a
  sphere of radius 1 m 1 steradian (sr)
• Whole sphere 4p sr
• Recall surface area of sphere 4pR2
• Hemisphere of sky visible 2p sr

W
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A little exercise

• I am interested in the low-energy part of this
  spectrum, which is a background, for me!
• The total, integrated over energy, flux of cosmic
  rays near the Earth is 100 particles/(m2 sr s)
• Suppose we have a horizontal square detector, 1 m
  on a side, exposed to this flux. What is the rate
  of particles passing through it from above?
  Assume it is isotropic.

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Air showers
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What is an air shower?

• Cosmic ray enters the upper atmosphere and
  interacts..
• Secondary particles interact also..
• The cascade grows
• The shower front sweeps through the atmosphere
• Shower develops in space and time
• The shower is axially symmetric

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Particles every cosmic rayer should know and love

• Protons smash nuclei and produce pions
• Pions decay after 10 nanosec (in their own rest
  frame), into a muon and a neutrino
• Muons also decay radioactively, after 2.2
  microsec (in their own rest frame) into an
  electron and 2 neutrinos
• Neutrinos are almost massless, and stable
• (but because they are not precisely massless,
  they can turn into other kinds of neutrinos by a
  quantum process called neutrino oscillation)

Rule of thumb from relativity divide energy of
particle by its rest mass to get the Lorentz
Factor ? E/m then its lifetime in our rest
frame ? t t lifetime in particles rest
frame Example a 1 GeV muon has ? 10, so its
lifetime would be about 22 microsec in our
reference frame
Particle Mass Lifetime
proton (p) 1 GeV Stable
electron (e) 0.5 MeV stable
pion (?) 140 MeV 10 nsec
muon (?) 105 MeV 2.2 microsec
neutrino(?) 0.1 eV (?) 3 kinds, mix
photon (?) 0 stable
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The Greek alphabet
Selected letters from the Greek Alphabet
(alpha-beta) -- and things they are commonly used
for in physics
a alpha a-particle (helium nucleus)
b beta b-particle (electron)
g gamma g-ray (photonparticle of light)
d delta (small difference)
e epsilon (a very small number)
q theta plane angle
s sigma error, cross-section (prob.of interaction)
W Omega solid angle
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Cosmic ray timeline
1911-12 Discovery by Victor Hess from space
1930s East-west and latitude effects discovered by Compton, Millikan and others CRs are charged particles Discovery of air showers by Pierre Auger
1940s Discovery of short-lived elementary particles produced by cosmic rays origin of particle physics First large-scale extensive air shower detector built at Echo Lake, CO
1950s EAS detectors around the world find UHE cosmic rays come from all directions
1960s Supernovae found to be likely source of cosmic rays (below 1016 eV)
1970s Flys Eye built in Utah (J. Wilkes does thesis research at Echo Lake)
1980s AGASA detector built in Japan CASA detector built in USA
1990s Flys Eye, AGASA observe cosmic rays with energy gt 1020 eV
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Victor Hess after his 1912 balloon flight,
during which he discovered cosmic rays come from
space.
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Jeff Wilkes and Heather Zorn re-enact Hesss
flight(Sunday, July 8)
Greg Snow holds a replica of Hesss electroscope
carried on the balloon flight
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Pierre Auger, discoverer of cosmic ray air
showers.
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Neutrinos

• An aside can those neutrinos from interactions
  in the atmosphere be detected?
• A big local angle!

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The Super-Kamiokande Detector
Electronics Huts
50,000 ton water Cherenkov detector (40m
tall!) ID 11,146 50cm (20)PMTs, non-reflective
liner OD 1,885 20cm (8) PMTs wavelength
shifters, reflective liner (Tyvek) Took data
continuously from 5/31/96 to last year Detects
solar neutrinos (5-20 MeV), atmospheric neutrinos
(0.22 GeV), search for proton decay, search for
supernovae (10,000 events!)
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Atmospheric Neutrinos

• Produced by cosmic rays in upper atmosphere
  (altitude Z1520 km)
• pnucleus n other particles
• Flight path L to SK detector depends on zenith
  angle qZ

• Energy 100 MeV ? 100 GeV
• Cant be solar
• ESOLAR20 MeV max
• Cant be astrophysical
• flux ltlt atmospheric n
• below 10 TeV

cosqZ0.8 L25 km
ZENITH
qZ
SK
cosqZ0 L500 km
cosqZ-0.8 L10000 km
NADIR
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20 Photomultiplier Tube

• Hamamatsu R3600 PMT
• Single-photon efficiency 22
• Rise time 1.252.5 nanosec

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The SK Yacht Club at sea (1/96)

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Water Cherenkov Detector

• Arrival times shown in nanosec
• (t0 when n interacts)

21.9 20.4 19.0 17.5 17.0
61 66 71 76 80
Relative light intensities shown in arbitrary
units
water (n1.33)
n m
0 7.3
12.7
vc
PMTs
light rays (v0.75c)
Cherenkov light wavefronts
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Cherenkov ring

Outer Detector
Inner Detector
Electron Neutrino Event
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Solar Neutrinograph
1 on the sky Exposure 500 days
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Another Local Angle detecting cosmic gamma-rays