Groping for the (Cosmic Ray) Knee Frank Jones, Robert Streitmatter and Demos Kazanas Physics at the End of the Galactic Cosmic Ray Spectrum Aspen, April 25 – May 1, 2005

If Simon Swordy didn’t exist we would have to invent him.

Two Component CR Spectrum Log E (eV) Flux X E nd Tooth Fairy 1 st Tooth Fairy

One Knee Scenario: There is another proton component that would explain the drop in just below the knee.

He P other P total All Particle Fe CNO Ne-S P SN

Vernov, Zatsepin, Khristiansen, and Chudakov, Report to the All Union Conference on Cosmic Rays, Tbilisi, 1956 Kulikov and Khristiansen, JETP 35, 635, 1958 Why was the knee discovered? – New Physics?

The Idea! A new production channel opens up in the particle collision cross section. Some products are “invisible” resulting in “lost” energy. Produces apparent steepening of the cosmic-ray spectrum. We follow the approach of Kazanas and Nicolaidas

Toy Model

To obtain the bend in the observed spectrum it turns out that we require:

Toy Model: Spectrum at Knee Energy (GeV) Differential Flux X E 2.8 (Arbitrary Units)

To make the mass appear to become heavier we need to make the hadronic cross sections increase at the same energy that the new channel opens up. Typically, the mass of a primary particle is determined by the depth in the atmosphere of the shower maximum. What could make the mass look heavier?

Toy Model: Shower Maximum In an air shower that involves the new process there are two effects that can raise the position of the shower maximum. –If the cross section increases for energies > E c then each leg of the cascade in this energy region will be shorter. –If the multiplicity increases there is an additional raising of the maximum because the energy is diluted quicker.