1. Option 212: UNIT 2 Elementary Particles Department of Physics and Astronomy SCHEDULE 26-Jan-15 13.00pm LRB Intro lecture 28-Jan-15 12.00pm LRBProblem solving (2-Feb-15 10.00amEProblem Workshop) 4-Feb-15 12.00pm LRB Follow-up

2. UNIT 2: OUTLINE SYLLABUS: 1st Lecture Introduction Hadrons and Leptons Spin & Anti-Particles The conservation laws: Lepton Number Baryon number Strangeness 2nd Lecture 3rd Lecture Follow-up Fundamental forces and field particles The standard model Problem solving Check a decay for violation of conservation laws Quarks Properties of a particle given quark combination

3. Answer: a) B = 1+1 on left hand side B = 2 on right hand side too! Allowed reaction! b) B = 2 on left hand side B = -1 on right hand side Forbidden reaction Checking Baryon Numbers a) p + + n b)p + + n 2p + + p + n p + + p + p _ _ _

4. Answer: a) Before decay L e = 0 and L  = +1 After decay L e = 0 and L  = +1 Allowed reaction! b) Before decay L  = 0 and L e = 0 After decay L  = 0 and L e = 1 Forbidden reaction! Checking Lepton Numbers a) µ - b) π + e - + e +  µ + +  + e _

5. Is Strangeness Conserved? a) π + + n b) π - + p K + +    - +   Answer: a) Initial state has S = 0 Final state has S = +1 - 1 = 0 Allowed reaction! b) Initial state has S = 0 Final state has S = -1 Forbidden reaction!

6. Some Fundamental Particles ParticleSymbol Rest energy MeVB LeLe Antiparticle Neutrino Electron Muon Tau Pion Kaon Proton Neutron Lambda Sigma e      0 0.511 105.7 1784 oo 140 135 oo p+nop+no 938.3 939.6 1115.6 1189.4 1192.5 1197.3 e      LL LL S  00  photon 0 000 Leptons Photon       Hadrons Mesons K+KoK+Ko 493.7 497.7     K-KoK-Ko    Baryons p-np-n      Category See also Tipler Table 41-1 Page 1337 For strangeness, examine Figure 41-3 Page 1344 _ _ _ _ _ _ +1

7. Conservation Laws Test the following decays for violation of the conservation of electric charge, baryon number and lepton number. (a) n ->         (b)    e + + e - + 

8. Conservation Laws Solution Method: Use Table 41-1 and the conservation laws for Baryon number and Lepton number (a) n ->         –Total charge on both sides = 0 : conserved –Baryon number changes from +1 to 0: violated –L  = 0 on both sides : conserved –Process not allowed (b)    e + + e - +  –Total charge on both sides = 0 : conserved –Baryon number on both sides = 0 : conserved –L e = 0 on both sides: conserved –Process is allowed

9. Quarks - The Smallest Building Blocks of Matter Gell–Mann & Zweig 1963

10. Three Different Types of QUARKS There are three elementary quarks (flavors) That make up the fundamental particles: Up u Down d Strange s Name Spin Charge Baryon Strangeness Up u 1/2 +2/3 1/3 0 Down d 1/2 -1/3 1/3 0 Strange s 1/2 -1/3 1/3 -1 Anti-quarks maintain spin, but change sign of S and B! u d π+π+ Meson u u d p Baryon

11. Different types of quarks contd. Mesons – quark + anti-quark ( q q ) Baryons – three quarks ( q q q ) Anti-baryons – three anti-quarks ( q q q) By 1967 it was realised that new kinds of quarks were required to explain discrepancies between the model and experiment Charm (c) Bottom (b) – discovered 1977 Top (t) – discovered 1995

12. Quark combinations Find the baryon number, charge & strangeness of the following quark combinations and identify the hadron: (a) uud (b) udd (c) uus (d) dds

13. Quark combinations Solution Method: for each quark combination determine the baryon number B, the charge q and the strangeness S; then use Tipler Table 41-2 to find a match. (a) uud –B = 1/3 + 1/3 + 1/3 = 1 –q = 2/3 + 2/3 – 1/3 = 1 –S = 0 –It is a proton (b) udd –B = 1/3 + 1/3 + 1/3 = 1 –q = 2/3 – 1 /3 – 1/ 3 = 0 –S = 0 –It is a neutron (c) uus –Ditto, B=1, q=1, S= -1 and it is a  + (d) dds –Ditto, B=1, q=-1, S= -1 and it is a  -

14. Some Fundamental Particles ParticleSymbol Rest energy MeVB LeLe Antiparticle Neutrino Electron Muon Tau Pion Kaon Proton Neutron Lambda Sigma e      0 0.511 105.7 1784 oo 140 135 oo p+nop+no 938.3 939.6 1115.6 1189.4 1192.5 1197.3 e      LL LL S  00  photon 0 000 Leptons Photon       Hadrons Mesons K+KoK+Ko 493.7 497.7     K-KoK-Ko    Baryons p-np-n      Category See also Tipler Table 41-1 Page 1337 For strangeness, examine Figure 41-3 Page 1344 _ _ _ _ _ _ +1

15. Quark spin The angular momentum vector of a spin ½ quark can have one of two settings up or down So a meson can have its two quark spins parallel with each other or anti-parallel: Spin 1 Spin 0

16. Quark spin contd. Baryons e.g. uud: Spin 3/2 Spin 1/2 The spin ½ particle is a proton, spin 3/2 particle is a   Note that is also spin ½ (parallel, parallel, anti-parallel)

17. EIGHT FOLD WAY PATTERNS S = 0 S = -1 S = -2 Q = +1 Q = 0 Q = -1   n    p  The Baryon Octet - Eight Spin 1/2 Baryons (uud) (ddu)