From Electrons to Quarks - 2 l The Standard Model l …And Beyond

Electron – 1897 J.J Thomson Top quark 1995 A Century of Particle Physics

… And The Particle Zoo!  ±,  0, e,  ±, K ±, K 0 S, K 0 L,  0, p, n,  +,  0, , , …

u uu d dde b bb  c cc s ss  gggggggg  ZW+ e   Quarks Leptons +2/3-1/ I II III BosonsFermions The Standard Model H t tt W-

The Standard Model d u d Neutron Proton u d u Delta++ u u u

The Electromagnetic Force q2q2 q1q1 Electron Proton Photon

n Neutron nene Anti-electron neutrino W-W- The Weak Force Radioactive decay of the neutron e Electron Proton p

The Strong Force u u d d g Strong force caused by the exchange of gluons

The Standard Model Summary All known matter is of quarks and leptons that interact via one or more forces: Strength Gravity Weak10 -5 Electromagnetic10 -2 Strong 1

The Mass Puzzle

Imagine a room full of physicists From L. Smith, Scientific American, July 2000

… and someone famous walks in…

… he attracts admirers, which makes it difficult for him to move… …he has acquired inertia, that is, mass!!

Now imagine that it’s only a rumor that he is about to arrive…

… physicists cluster together to discuss the rumor… … just as they did before, but minus the famous person

Mr Higgs Boson Professor Peter Higgs

…And Beyond

Fermilab

The Just-So Puzzle ParticleMass [MeV] electron 0.51 muon tau u 2.25 d 5.00 s c b t 170, Why is the neutron heavier than the proton? NucleonMass [MeV] __________________ N (u d d)939.6 P (d u u)938.3 __________________ 1.3 MeV

The Vacuum Energy Puzzle The Standard Model predicts the energy density of the vacuum is > 10 2 GeV/fm 3 According to observation, the energy density of the vacuum is < GeV/fm 3 Oops!

The Gravity Puzzle Why is gravity so weak?

Nature’s Big Clue The Fundamental Parameters of Nature hPlanck’s constant cSpeed of light in vacuum GNewton’s gravitational constant l p ~ 4 x m l p ~ 4 x m The Planck Length

Brane Worlds Our 3-dimensional world could be embedded within a higher dimensional space Perhaps ours is but one of numerous brane worlds

The Era of the LHC The Era of the LHC Graviton Our world