1 FK7003 Lecture 17 – Interactions in Matter ● Electromagnetic interactions in material ● Hadronic interactions in material ● Electromagnetic and hadronic showers

2 FK7003 Why we can neglect weak interactions E (TeV) Neutrino interaction lengthi In water/km Probability of interaction ~ / km water at 100 TeV energy 100 billion neutrinos pass through your thumbnail each second but only 1-2 will interact in your body during your lifetime. From lecture 3 Mean distance between interactions of neutrino + water molecule as neutrinos pass through water (interaction length).

3 FK7003 Strategy Energy loss of particles in matter  Electromagnetic energy loss ● Energy loss through collisions (ionisation) ● Radiation loss ● Electromagnetic shower  Hadronic energy loss ● Energy loss through nuclear collisions ● Hadronic shower

4 FK7003 Ionisation energy loss M

5 FK7003 M l Semi-classical derivation (skip)

6 FK7003

7 M

8

9

10 FK7003 Interaction between two particles

11 FK7003 Bethe-Bloch formula (17.23)

12 FK7003 Bethe-Bloch formula

13 FK7003 Measurements of ionisation energy loss e

14 FK7003 Strategy Energy loss of particles in matter  Electromagnetic energy loss ● Energy loss through collisions (ionisation) ● Radiation loss ● Electromagnetic shower  Hadronic energy loss ● Energy loss through nuclear collisions ● Hadronic shower

15 FK7003 Radiation energy loss E0E0 x

16 FK7003 Energy loss of an electron in copper ECEC

17 FK7003 Question

18 FK7003 Strategy Energy loss of particles in matter  Electromagnetic energy loss ● Energy loss through collisions (ionisation) ● Radiation loss ● Electromagnetic shower  Hadronic energy loss ● Energy loss through nuclear collisions ● Hadronic shower

19 FK7003 Photons

20 FK7003 Photon absorption in lead Lead

21 FK

22 FK (i) (ii)

23 FK7003 Electromagnetic shower E0E0 E 0 /2 E 0 /4 t=No. X 0 No. e + No. e - No.  No. particles

24 FK7003 Electromagnetic shower Observed electromagnetic shower (next lecture)

25 FK7003 Strategy Energy loss of particles in matter  Electromagnetic energy loss ● Energy loss through collisions (ionisation) ● Radiation loss ● Electromagnetic shower  Hadronic energy loss ● Energy loss through nuclear collisions ● Hadronic shower

26 FK7003 Hadronic energy loss p xx 

27 FK7003 Nuclear shower EM Cascade Nuclear cascade

28 FK7003 A simple model for hadronic scattering in material p   p L xx

29 FK7003 p   L Interaction Length xx 1 23 p

30 FK7003 Proton-nucleon cross sections p p

31 FK7003 Nuclear interaction length

32 FK7003 Stopping in iron

33 FK7003 Strategy Energy loss of particles in matter  Electromagnetic energy loss ● Energy loss through collisions (ionisation) ● Radiation loss ● Electromagnetic shower  Hadronic energy loss ● Energy loss through nuclear collisions ● Hadronic shower

34 FK7003 Energy loss mechanisms Important energy loss mechanisms for collider experiments (next lecture). ParticleIonisation energy loss Radiation energy loss Hadronic energy loss e + e - pair production e-e- Important only for low energies (<30 MeV) † xx  Important only at high energies (E >several hundred GeV ) † xx Charged hadrons (p,    K  …) Important only at high energies (E > several hundred GeV:    K - ; E> 1 TeV: p ) † x Neutral hadrons (n,K 0 ) xx x Photon xxx † Not important for these lectures

35 FK7003 Summary ● Interactions of particle in material ● Electromagnetic and hadronic energy loss  Ionisation and radiation energy loss (em)  Hadronic energy loss (strong) ● Now ready to design an detector for a collider experiment (next lecture).