Fermilab

You asked:

Hi,

I had just a couple of questions
1) What are cosmic rays made of? If it is not known, what do the early reports say on the compostition of cosmic rays?

2)Will this add/ refine/ or refute the Standard Model?

Thanks Goonjan Shah

Goonjan:

The composition of cosmic rays appears to change with energy. At energies of about 10**18 eV and higher the composition begins to become lighter. That is, the composition changes from heavier nuclei (up to iron) to light nuclei, mostly protons. This has been interpreted as an indication that the origin of particles above 10**18 eV are from beyond the galaxy. Because of their energy and light weight the highest energy cosmic rays are bent only slightly by magnetic fields in the galaxy and in intergalactic space. The Auger Observatory, therefore, stands a good chance of finding their sources.

Studying the origin of high energy cosmic rays using air showers doesn't tell us very much directly about the standard model. Even though the collisions at the top of the atmosphere are much more energetic then those at accelerators such as the Tevatron at Fermilab, interesting effects of these collisions are washed out by the time the air showers reach the surface of the earth. This is a disadvantage and an advantage. We don't learn much about the high energy interactions at the top of the atmosphere but on the other hand we can get a much more reliable measurement of the shower energy since the measurement of the showers at the surface does not depend on the particulars of the first interactions.

I hope this is helpful.

Paul

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