Transcript , … Exploring the Universe with Particles and Rays:

Exploring the Universe with
Particles and Rays:
α, β, γ, X, Cosmic, …
Toby Burnett
Prof, UW
So what is a ray ?
ray :
A thin line or narrow beam of light or other radiant energy.
ra·di·a·tion :
1.
2.
3.
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
prop·a·ga·tion
 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! (E=hf)
 Same for momentum and inverse wavelength (p=mv=h/)
Special relativity:
 No 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.
photon
detector
detection
system
interaction
Wavelength: limits resolving power.
Solution: use higher energy (like
electrons)
Same paradigm as particle
accelerators, one reason for
high energy
(light) source
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…and a telescope
astrophysical,
or cosmological
process
Interesting things
can happen here!
photons
This is a photon detector
designed to collect as many as
possible from a distant source,
and measure the precise
direction
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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
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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 antiprotons (in collisions)
accelerates anti-protons
to 1 TeV.
collides them!
Why?

Study nature of matter
by analyzing produced
particles
Current run information
http://www-bd.fnal.gov/servlets/d11
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The D0 experiment: running now
a real picture
schematic view
Online pictures
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http://d0.phys.washington.edu/Projects/live_event/
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GLAST: A telescope for gamma rays!
Low Earth orbit: 500 km, 27o
Launch March 2006 from
Cape Canaveral, Delta II
Energies 20 MeV - ~500 GeV
Compared with an
optical telescope:
 No focussing!
 Huge field of view
 Poor (energydependant) angular
resolution
 Integral spectroscopy
(~10%)
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GLAST has 2 instruments
 Large Area
Telescope(LAT)
 GLAST Burst Monitor
(GBM)
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The “Standard Model”
A unifying framework, description of particles and
forces.
Known to not be complete: challenge to find the missing
pieces that will show up at higher energies.
A fancy poster
http://particleadventure.org/particleadventure/frameless/chart_cutouts/particle_chart.pdf
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