Astroparticle Physics

494 Physics of Particleand Radiation Detection“Every physical effect can be used as a basisfor a detector.”AnonymousThe measurement techniques relevant to astroparticle physicsare rather diverse. The detection of astroparticles is usuallya multistep process. In this field of research, particle detectionis mostly indirect. It is important to identify the natureof the astroparticle in a suitable interaction process. Thetarget for interactions is, in many cases, not identical withthe detector that measures the interaction products. Cosmicraymuon neutrinos, for example, interact via neutrino–nucleon interactions in the antarctic ice or in the ocean,subsequently producing charged muons. These muons sufferenergy losses from electromagnetic interactions with theice (water), which produces, among others, Cherenkov radiation.The Cherenkov light is recorded, via the photoelectriceffect, by photomultipliers. This is then used to reconstructthe energy and the direction of incidence of the muon, whichis approximately identical to the direction of incidence of theprimary neutrino.In this chapter, the primary interaction processes willfirst be described. The processes which are responsible forthe detection of the interaction products in the detector willthen be presented.The cross sections for the various processes depend onthe particle nature, the particle energy, and the target material.A useful relation to determine the interaction probabilityφ and the event rate is obtained from the atomic- (σ A )ornuclear-interaction cross section (σ N ) according toφ {(g/cm 2 ) −1 }= N AA σ A = N A {g −1 } σ N {cm 2 } , (4.1)where N A is Avogadro’s number, A is the atomic mass ofthe target, and σ A is the atomic cross section in cm 2 /atom(σ N in cm 2 /nucleon), see also (3.56) and (3.57). If the targetrepresents an area density d {g/cm 2 } and if the flux ofprimary particles is F {s −1 }, the event rate R is obtained asR = φ {(g/cm 2 ) −1 } d {(g/cm 2 )} F {(s −1 )} . (4.2)indirect particle detectioncross sectionevent rate