1. ParticleZoo

2. The Standard Model The body of currently accepted views of structure and interactions of subatomic particles. Interaction Coupling Charge Field Boson Mass/ GeVc -2 JJ strongcolorgluons (8)01-1- elmgnelectric (e)photon (  )01-1- weak W +, W -, Z 0 1001 Interactions FermionsFamilyQ/eColorSpin Weak Isospin Quarks u c t d s b +2/3 -1/3 r, b, g½½ Leptons e   e  0 none½½ Particles Weak interactions violate certain symmetries (parity, helicity) see later

3. The Standard Model ct’d Combine weak and elm interactions  “electro-weak” Type of isospin-symmetry : same particles carry weak and elm charge. Force range Electromagnetic: ∞ Weak: 10 -3 fm Strong qq force increases with distance 2m q c 2 V qq r 1 fm 0 There are no free quarks. All free physical particles are colorless.

4. Confinement and Strings Why are there no free quarks? Earlier: symmetry arguments. Property of gluon interaction between color charges (“string*-like character). Q: Can one dissociate a qq pair? energy in strings proportional to length 0.9GeV/fm field lines: color strings successive q/q-bar creation, always in pairs!

5. Baryon Production with Strong Interactions Typically: Energetic projectile hits nucleon/nucleus, new particles are produced. Rules for strong interactions: Energy, momentum, s, charge, baryon numbers, etc., conserved q existing in system are rearranged, no flavor is changed q-q-bar pairs can be produced u u u d _d_d u u u s _s_s p    annihilation creation d, d-bar s, s-bar time 

6. Baryon Resonances Typically: Energetic projectile hits nucleon/nucleus, intermediate particle is produced and decays into other particles. u u u  ++ u u d _ d u time  u u d _ d u p ++ p ++  ++ produced as short-lived intermediate state,  = 0.5·10 -23 s corresp. width of state:  = ħ/  = 120 MeV This happens with high probability when a nucleon of 300 MeV/c, or a relative energy of 1232 MeV penetrates into the medium of a nucleus.  Resonance

7. Conservation Laws Quantum numbers are additive. Anti-quarks have all signs of quark quantum numbers reversed, except spin and isospin. Derived quantities: In a reaction/transmutation, decay, the following quantities are conserved (before=after): The total energy, momentum, angular momentum (spin), The total charge, baryon number, lepton number

8. Conservation Laws in Decays Decay A  B + C possible, if m A c 2 ≥ m B c 2 + m C c 2 Otherwise, balance must be supplied as kinetic energy. Example: Conservation of charge, baryon number, lepton number in neutron decay.

9. Weak Interactions 1 0 -5 weaker than strong interaction, small probabilities for reaction/decays. Mediated by heavy (mass ~100GeV) intermediate bosons W ±,Z 0. Weak bosons can change quark flavor u d W+W+ W-W- Z0Z0 u s u u up-downstrange-non-strange no flavor change conversion conversion carries +e carries –e carries no charge

10. Decays of W ± and Z 0 Bosons Hadronic decays to quark pairs are dominant (>90%), leptonic decays are weak. All possible couplings:

11. Examples of Weak Decays Can you predict, which (if any) weak boson effects the change? n ? ? ? p p e-e- _ e p   e-e- e time n-decay? neutrino scattering neutrino-induced off protons? reaction off e - ?

12. Examples of Weak Decays Answer: Yes, all processes are possible. These are the bosons, n W-W- W+W+ Z0Z0 p p e-e- _ e p   e-e- e time n-decay neutrino scattering neutrino-induced off protons reaction off e - Method: Balance conserved quantities at the vortex, where boson originates. Remember W ± carries away charge ±|e|. Balance conserved quantities at lepton vortex.

13. Particle Production  e-e- e+e+ -- ++  e-e- e+e+ fermion e-e- e+e+ -- ++  anti- fermion electromagnetic weak example In electron-positron collisions, particle-anti-particle pairs can be created out of collision energy, either via electromagnetic or weak interaction.  collision energy (GeV) probability

14. The End