Cosmic Ray Workshop May 15, 2010

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May 15, 2010

Rutgers Cosmic RayWorkshop

Cosmic Ray Workshop May 15, 2010

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Cosmic Rays

Earth is continually bombarded by particles from outer space

• What are they?

• Where do they come from?

• How are they created?

• How do we detect them?

Cosmic Ray Workshop May 15, 2010

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Discovery of Cosmic Rays

Cosmic rays discovered in 1912 by Victor Hess

• measured radiation levels aboard a balloon up to 17,500 feet (without oxygen)

• found increasing radiation levels at higher altitudes

Cosmic Ray Workshop May 15, 2010

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Primary Particle Flux

flux falls ~30 orders of magnitude, spanning12 orders of magnitudein energy

Power Law

Intensity ~ E–2.7

look for features

seems monotonous

but

Cosmic Ray Workshop May 15, 2010

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Cosmic Ray Workshop May 15, 2010

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At the Surface of the Earth

~ 2 particles per secondthrough outstretched hand

Rule of Thumb:

irreducible source of natural radioactivity

28 mrem/year at sea level

twice as much if you live in Denver

• mostly muons (and neutrinos)

• primary cosmic rays interact in the atmosphere

Cosmic Ray Workshop May 15, 2010

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What are the cosmic ray particles?

Must be stable in order to get here• protons• electrons• neutrinos• photons• nuclei (He Fe)

Not neutrons neutron lifetime ~ 15 minutes

what about antiparticles• anti protons• positrons• anti nuclei

Not seen we live in matter universe

Cosmic Ray Workshop May 15, 2010

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Cosmic Ray Workshop May 15, 2010

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Cosmic Ray Workshop May 15, 2010

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Composition

• 80% protons

• 15% He

• 0.1% photons

• rest mostly C and Fe

some electrons below 10 GeV

generally

depends on energy

Cosmic Ray Workshop May 15, 2010

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Where do the Cosmic Rays Come From?

Basically we’re not sure!

Cosmic Ray Workshop May 15, 2010

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Primary Cosmic Ray Flux

Cosmic Ray Workshop May 15, 2010

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Cosmic Ray Air Shower

Cosmic Ray Workshop May 15, 2010

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Particles at Surface