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
1st Tooth Fairy 2nd Tooth Fairy Two Component CR Spectrum 1 0 Flux X E2.7 -1 10 11 12 13 14 15 16 17 18 19 20 21 Log E (eV)
One Knee Scenario: There is another proton component that would explain the drop in <lnA> just below the knee.
All Particle P total P SN CNO P other Ne-S Fe He
Why was the knee discovered? – New Physics? • Vernov, Zatsepin, Khristiansen, and Chudakov, Report to the All Union Conference on Cosmic Rays, Tbilisi, 1956 • Kulikov and Khristiansen, JETP 35, 635, 1958
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
To obtain the bend in the observed spectrum it turns out that we require:
Toy Model: Spectrum at Knee 100 (Arbitrary Units) Differential Flux X E2.8 10 5 6 7 8 10 10 10 10 Energy (GeV)
What could make the mass look heavier? Typically, the mass of a primary particle is determined by the depth in the atmosphere of the shower maximum. 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.
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 > Ec 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.