(3) Interaction of high energy photons with matter - LUTH
(3) Interaction of high energy photons with matter - LUTH
(3) Interaction of high energy photons with matter - LUTH
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Excitation <strong>of</strong> Resonances - the GZK effect (1)<br />
Resonances are excited hadronic states <strong>of</strong> a very short lifetime.<br />
In astrophysics the + (1232) - resonance, an excited proton state <strong>of</strong> mass 1232 MeV, plays an<br />
important role for the propagation <strong>of</strong> cosmic rays through the CMB. This resonance has a<br />
lifetime <strong>of</strong> the order <strong>of</strong> 10 -23 s.<br />
In the rest frame <strong>of</strong> ultra-<strong>high</strong> <strong>energy</strong> cosmic ray protons, the CMB <strong>photons</strong> can reach<br />
sufficiently <strong>high</strong> energies to excite the resonance:<br />
p CMB <br />
The resonance then decays quickly, following mostly two principal channels:<br />
p 0 p 2<br />
n n p e − e <br />
A. Zech, Instrumentation in High Energy Astrophysics<br />
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