ParticleZoo

1. ParticleZoo The Zoo of Subatomic Particles Particle Transmutation

2. The Standard Model Interactions Weak interactions violate certain symmetries (parity, helicity) see later The body of currently accepted views of structure and interactions of subatomic particles. Particles

3. Combine weak and elm interactions “electro-weak” Type of isospin-symmetry: same particles carry weak and elm charge. r 1 fm The Standard Model ct’d Vqq Force range Electromagnetic: ∞ Weak: 10-3fm Strong qq force increases with distance 0 2mqc2 There are no free quarks. All free physical particles are colorless.

4. 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? Confinement and Strings energy in strings proportional to length 0.9GeV/fm field lines: color strings successive q/q-bar creation, always in pairs!

5. u u u d s _d _s u u 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 time  u S+ p K+ p+ annihilation creation d, d-bar s, s-bar

6. p p+ time  _ d u _ d u u u d u u d p p+ Baryon Resonances Typically: Energetic projectile hits nucleon/nucleus, intermediate particle is produced and decays into other particles. D++ produced as short-lived intermediate state, t = 0.5·10-23s corresp. width of state: G = ħ/t = 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 u u u D++

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 mAc2 ≥ mBc2 + mCc2 Otherwise, balance must be supplied as kinetic energy. Example: Conservation of charge, baryon number, lepton number in neutron decay.

9. Weak Interactions 10-5 weaker than strong interaction, small probabilities for reaction/decays. Mediated by heavy (mass ~100GeV) intermediate bosons W± ,Z0. Weak bosons can change quark flavor d u u Z0 W+ W- u u s up-down strange-non-strange no flavor change conversion conversion carries +e carries –e carries no charge

10. Decays of W± and Z0 Bosons Hadronic decays to quark pairs are dominant (>90%), leptonic decays are weak. All possible couplings:

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

12. Answer: Yes, all processes are possible. These are the bosons, Examples of Weak Decays _ne p ne p e- n m- W+ Z0 W- time n n nm p e- 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 In electron-positron collisions, particle-anti-particle pairs can be created out of collision energy, either via electromagnetic or weak interaction. probability  collision energy (GeV) anti-fermion fermion m+ m- m+ m- Z0 g Z0 e- e- e+ e+ e- e+ electromagnetic weak example

14. The End