1. Lecture 13 – the weak force
When is it weak and when is it strong ?
Weak interactions of quarks
Cabibbo angle
CKM matrix
Handedness in charged current interactions.
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2. When is a force weak or strong ?
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3. gX
X,|Q| gX
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4. When the weak force is weak
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5. When the weak force become strongerne e- e-
g,Z0 W- p p
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6. Electromagnetic and weak force strength
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7. The weak force in detail
Charged currents
Basic processes for quarks and leptons
Lepton-quark symmetry
Cabibbo angle
CKM matrix
V-A theory
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8. Basic charged current processes involving leptons
Weak coupling at a vertex: gW
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9. Quark interactions via the weak force.
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10. Cabibbo mixing
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11. Lepton quark symmetry
c s’ c s c d
gcd
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12. Determination of the Cabibbo angles K- u
gud
gus
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13. Cabibbo–Kobayashi–Maskawa Matrix
gab
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14. More on the CKM Matrix
The CKM matrix is generalisation of Cabibbo’s mixing for the light quarks by Kobayashi and Maskawa
When generalising CP violation was introduced/discovered as a property of weak decays.
Kobayashi and Maskawa won the 2008 Nobel prize for this work.
Many particle physicists (probably Cabibbo included) were surprised at Cabibbo’s exclusion.
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15. Decay of W
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16. Spin dependence of charged current interactions
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17. V-A interactions s s s s s
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18. Top quark non-discovery
1984 CERN
UA1 experiment
pp (630 GeV cm energy)
Something they would
rather forget
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19. Top quark discovery
quark pdf q(x)
Anti-quark pdf q(x)
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20. Top quark lifetime
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21. Selected top quark decays at the Tevatron
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22. A top quark pair production ”event”
Event observed at the D0 experiment.
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23. Top quark discovery
top
background
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24. Summary The weak force was studied
The weak force is of comparable strength with the electromagnetic force for interactions with |Q|>MW
Charged current interactions take place in quark doublets of mixed physical states.
Cabibbo theory and the CKM matrix formalise mixing.
At relativistic energies, the W couples preferentially to left- handed fermions and right-handed antifermions (V-A theory).
Next lecture – neutral currents, electroweak unification and the Higgs.
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