The Future of Particle Physics

1. The Future of Particle Physics S F King Southampton, March 22, 2004 universe.exe

5. Cosmic microwave background Our Universe is filled with photons from the time of atom formation (380,000 yrs). They were produced during the BIG BANG. Their temperature distribution gives information about the age and composition of the universe. Microwave Anisotropy Probe

6. Temperature Maps Earth Universe Relic radiation from the big bang fireball began its journey as visible light 13 billion years ago. During its long journey the Universe has expanded and its wavelength has been stretched to microwave wavelengths of a few cm. Picture above shows hot and cold fluctuations which seeded clusters of galaxies. The sound you hear is the (frequency shifted) “sound of the big bang” during the first 700,000 years, based on BOOMERANG data.

7. …means the Universe is flat

8. The Energy Budget of the Universe

10. Answer: only 84 times! A single atom A nucleus with orbiting electrons nanometre What have we learned from High Energy Physics? - Matter is made of particles (“particle physics”) To understand this, take an apple and a knife, and cut the apple in half once. Then cut one half in half again. Then continue the process. After some number of cuts you will arrive at a single atom. Question: how many cuts are required?

11. Matter Antimatter Matter The electrical attraction is caused by photon exchange -

12. The quarks are stuck together by gluons The nucleus of the atom is positively charged It is made of protons (p) and neutrons (n) The protons and neutrons are made of charged quarks The quarks also carry a new “colour charge”

13. I think I finally understand atoms

14. This decay process is very weak (15 minutes is an eternity!) Without such weak interactions the Sun would shut down! Nothing lasts for ever The (free) neutron is radioactive and decays after 15 minutes into proton, electron and “neutrino” (electron-like neutral particle)

15. Photo of Sun taken underground using neutrinos Neutrinos from the Sun Question: How many neutrinos from the Sun are passing through your fingernail in one second? Answer: 40 billion! – day and night since neutrinos can pass right through the Earth without interacting

16. Electroweak theory predicted a heavy version of the photon called the which was discovered in 1983 W particles – the left-handed alchemists Just like rifle bullets, quarks and leptons spin as they whizz along The quarks and leptons can only see W particles if they spin to the left! This shatters mirror symmetry!

17. The four forces of Nature

18. Quarks and Leptons

20. Mass t u d c e s b What is the origin of the particle masses?

21. The Higgs Boson In the“Standard Model”the origin of mass is addressed using a mechanism named after the British physicistPeter Higgs.This predicts a new particle:the Higgs boson. What is the Higgs boson? In 1993, the then UK Science Minister, William Waldegrave, issued a challenge to physicists to answer the questions 'What is the Higgs boson, and why do we want to find it?' on one side of a single sheet of paper. This cartoon is based on David Millar’s winning entry.

22. With such high energy it is hoped to produce the Higgs boson via . 1 TeV The CERN Large Hadron Collider (LHC) will collide protons on protons at energy of 14 trillion electron Volts (14 TeV)

23. The CERN Large Hadron Collider c.2007 Atlas particle_event_full_ns.mov

24. Isn’t all this too expen$ive? The practical benefits of Particle Physics - discovery of electrons gave us electronics - discovery of positron gave us positron emission tomography - discovery of the Internet at a particle physics lab CERN The intellectual benefits of Particle Physics - the greatest adventure of all is the voyage of scientific discovery - like building a cathedral over generations - same reason as Chinese went into space - “(doing particle physics) will do nothing to defend our country except to make our country worth defending” Robert Wilson

26. . . Neutrino Oscillations (only possible if neutrinos have mass)

27. Atmospheric oscillations have been seen

28. Solar oscillations have also been seen

29. In the Standard Model the neutrinos spin only to the left and so travel straight through the Higgs field without acquiring mass Neutrino Mass The discovery of neutrino oscillations and hence mass is the greatest discovery in particle physics in the past 20 years (since W and Z) So neutrino mass implies new physics beyond the Standard Model!

30. 1. Neutrinos must have a very small mass The single right-handed neutrino then couples equally to and causing them to have one small mass, and mix strongly SFK 98- A theoretical interpretation 2. Neutrinos mix strongly with one another These two facts can be explained by introducing one new heavy neutrino into the Standard Model which spins to the right (plus some other less important right-handed neutrinos).

31. This is based on the see-saw mechanism Thanks to David King

32. This is based on the see-saw mechanism Thanks to David King

33. What about Super- symmetry?

34. Quote from Ed Witten in preface of Gordon Kane’s book “Supersymmetry” “Supersymmetry, if it holds in nature, is part of the quantum structure of space and time… Discovery of supersymmetry would be one of the real milestones in physics… Indeed, supersymmetry is one of the basic requirements of string theory… Discovery of supersymmetry would surely give string theory an enormous boost… The search for supersymmetry is one of the great dramas in present day physics.”

35. Fermions have half units of spin, and tend to shy away from each other, like people who always stay in single rooms at the fermion motel. Bosons have zero or integer units of spin, and like to be with each other, like people who stay in shared dormitories at the boson inn. Supersymmetry says that for every fermion in Nature there must be a boson and vice-versa. Supersymmetric particles have not been observed (yet) so they must be heavier - SUSY must be broken by some mechanism What is Supersymmetry ? There are two types of particles in nature: fermions and bosons.

36. SPIN ½ FERMIONS SPIN 0 BOSONS Squarks Quarks Sleptons SUSY Leptons The Generations of Smatter The Generations of Matter

37. BOSONS SUSY Photino FERMIONS Gluino Gravitino

38. Higgs Boson Higgs Boson Higgsino Higgsino SUSY SUSY SUSY What about the Higgs Boson? A further non-interacting “singlet” Higgs and Higgsino can even explain the origin of Higgs mass itself (Elliott, SFK, White 93-95)

39. Desperately seeking SUSY

40. The SUSY Standard Model acts like a Digital radio that eliminates nearly all the fine-tuning – however a few % tuning remains (SFK, Kane 98) The Standard Model requires fine-tuning to one part in a trillion trillion to work! - it is rather like fine-tuning the knobs on an old fashioned radio What has SUSY ever done for us?

41. So what else has SUSY ever done for us? SUSY provides an excellent candidate for dark matter: the spin ½ partner to the photon which is the lightest SUSY particle and is cosmologically stable called the photino!

42. But what else has SUSY ever done for us? SUSY provides the basis for cosmological theories in which the Universe naturally inflates to its present size, and explain how the microwave background radiation appears isotropic For example a SUSY version of the Standard Model with extra Higgs singlets has been constructed that explains inflation, large scale structure, the origin of Higgs mass, and the origin of right-handed neutrino mass (Bastero-Gi,SFK, Di Clemente)

43. Standard Model SUSY Strong Weak Electromagnetic OK, but what else has SUSY ever done for us?

44. t u c d b s GUT e The pattern of quark and lepton masses is explained by assigning each SUSY generation a new charge (SFK, G.Ross 01,03) colour

45. string1.avi Strings live in 11 dimensions

47. Why wouldn’t we notice extra dimensions?

48. Brane New Worlds

49. Both! – nutcracker approach Top-down or bottom-up? Energy 1 trillion trillion Volts 1 trillion Volts

50. The Next Standard Model The Future of Particle Physics: Neutrino Physics SUSY Cosmology Strings