1. Introduction to Particle Physics I Sinéad Farrington 18 th February 2015

2. Sinead Farrington, University of Warwick 2 The Large Hadron Collider ATLAS pp Collisions of proton bunches travelling at high energy Superconducting dipole magnetic field 8.3 Tesla 2808 bunches, 10 11 particles in each 99.9999991% x speed of light, 11000 revolutions per second Interactions between beams every 25 nanoseconds

3. Sinead Farrington, University of Warwick 3 The Large Hadron Collider 27 km LHC Circle line Circumference 27km 22.5km Depth 100m 15m Diameter 3.8m 3.4m

4. Sinead Farrington, University of Warwick 4 Two particles collide at very high energy Particle Collisions ? New particles are produced which we detect and study

5. Sinead Farrington, University of Warwick 5 Why?

6. Sinead Farrington, University of Warwick 6 Understanding the Universe Older ….. larger … colder ….less energetic now Big Bang

7. Sinead Farrington, University of Warwick 7 How do we do it? To probe the conditions of the early universe we smash particles together J. Ellis

8. Sinead Farrington, University of Warwick 8 The Energy Frontier Size of structure we can probe with a collider like LHC = h / p (de Broglie, 1924) h = Planck’s constant = 6.63 x 10 -34 Js p = momentum of protons The larger the momentum (energy), the smaller the size probed

9. Sinead Farrington, University of Warwick 9 Standard Model of Particle Physics Strong, weak and Electromagnetic forces Describes interaction of matter particles by the means of force carrier particles Greeks

10. Sinead Farrington, University of Warwick 10 Matter Particles First generation: these are the only particles needed to make all the matter we see; all chemical elements

11. Sinead Farrington, University of Warwick 11 Matter Particles But we see three generations Undergoing similar interactions Mass hierarchy Each has an antiparticle

12. Sinead Farrington, University of Warwick Forces 12 In the Standard Model, we depict (and calculate) forces as the exchange of a force-carrier boson, between particles

13. Sinead Farrington, University of Warwick Electromagnetic Force 13 Mediated by the photon Acts on particles carrying electric charge

14. Sinead Farrington, University of Warwick Strong Force 14 Mediated by the gluon Acts on particles carrying colour charge

15. Sinead Farrington, University of Warwick Weak Force 15 Mediated by the W, Z bosons Acts on all matter particles

16. Sinead Farrington, University of Warwick Gravitational Force 16 Mediated by the Graviton? Acts on all massive particles

17. Sinead Farrington, University of Warwick Relative Strengths of Forces Each force has an intrinsic strength Electromagnetism: 17

18. Sinead Farrington, University of Warwick Relative Strengths of Forces Each force has an intrinsic strength 18

19. Sinead Farrington, University of Warwick Running Couplings When is a constant not a constant? The forces’ intrinsic strengths change with distance (or momentum) scale Electromagnetic screening process: the bare particle charge is screened by e + e - pairs 19

20. Sinead Farrington, University of Warwick Running Couplings When is a constant not a constant? The forces’ intrinsic strengths change with distance (or momentum) scale Strong force screening process: same as EM but has an additional effect 20

21. Sinead Farrington, University of Warwick Running Couplings When is a constant not a constant? The forces’ intrinsic strengths change with distance (or momentum) scale Strong force screening process: same as EM but has an additional effect 21

22. Sinead Farrington, University of Warwick Unification? 22

23. Sinead Farrington, University of Warwick Compare the Forces 23 Allows quark flavour to change so that matter can change into antimatter

24. Sinead Farrington, University of Warwick Higgs Boson Introduced to give mass to W and Z bosons Requires a new potential to be added to the Standard Model Introduction of “complex doublet” implies 4 new degrees of freedom, 3 of which are the W +, W - Z boson mass Fourth is the Higgs boson itself 24 Massless bosons Spontaneous symmetry breaking

25. Sinead Farrington, University of Warwick Summary The Standard Model describes the fundamental particles and the forces that act among them Forces are mediated by force-carrier bosons While the forces are mediated in a common way, they display different phenomena Tomorrow’s lecture: Experimental measurements How do we know what we know? What does a data analysis look like? (Example: The Higgs Search) Question… Relative merits of pp, pp, e + e - 25 -