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Transcript

New Frontiers in Particle Physics Jeff Forshaw University of Manchester 1 What we know • There are a few elementary particles that interact with each other. • The interactions come in four types: Gravity Electromagnetism Weak Strong 2 Standard Model • Crowning glory of 20th Century physics. • A single theoretical framework that describes the weak, strong and electromagnetic interactions of (nearly) everything! ne W d eu 4 Foundations Input • Particle content of world • Gauge symmetry of forces Then impose the following Rules • Quantum mechanics • Relativity 1979 Nobel Prize for Glashow, Weinberg & Salam 5 What is Gauge Symmetry? Y Ye ij(x) • Multiply quantum wavefunction by a space-time dependent complex phase. • Insist that this is a symmetry. • Photons and the electric charge emerge as new physical concepts! 6 Beyond electric charge • Colour charge • Weak charge • Electric charge QCD Electroweak The Standard Model is not a GUT! But it does partially unify three of Nature’s four forces. 7 The Higgs Boson That’s almost the whole story…. But the gauge symmetries of the Standard Model do not permit particles to carry mass! Q. How is mass generated? A. By the non-trivial action of the vacuum! It grabs hold of things! 8 The Standard Model Works! • Experiments around the world, especially at CERN, have tested the Standard Model to remarkable accuracy. (1 part in a thousand) 1999 Nobel Prize to ‘t Hooft & Veltman • A “light” Higgs is predicted. We await the LHC (2005) for a detailed study of the Higgs. 9 Mass of Higgs is less than 300 GeV (95% confidence). (from data collected at LEP, SLC and the Tevatron.) 10 A simulated Higgs event at LHC 11 Beyond the Standard Model Despite all its successes the Standard Model can never hope to explain some things. There must be NEW physics! 12 There are lots (more than 20) free parameters whose values are not explained. What is the origin of gauge symmetry? Why are there 3 generations? Are the particles fundamental? How does confinement work? 13 A 5th force? Is the Higgs particle there? Maybe it’s not! In any case, something must show up when we start to collide particles with energies bigger than of order 1 TeV. 14 Do the neutrinos carry mass? Why are they so light? 15 Neutrinos In the Standard Model, the neutrinos do not carry mass. But data say otherwise! Sub eV scale masses. Could this be the first evidence of a Grand Unified Theory? Next decade will see extensive study of the “neutrino sector”. 16 How we’ll study the neutrinos: 17 18 Why is the world nearly 100% matter when the Big Bang would have spewed out initially equal amounts of matter and anti-matter? 19 CP Violation Sakharov: If Big Bang is to produce unequal amounts of matter & anti-matter CP must be violated. “Physics is not the same when all particles are replaced by their corresponding anti-particles and then everything is viewed in a mirror.” New frontier experiments: SLAC (BaBar) in USA KEK (Belle) in Japan (1999). 20 What is the “dark matter”? 21 Dark Matter There is a lot more matter in the Universe than is visible to us! What is it? UK physicists actively searching for the dark matter at the Boulby salt and potash mine in Yorkshire. 22 Candidates for Dark Matter 23 The Boulby Mine 24 What about gravity!? 25 Beyond particles: String Theory & Quantum Gravity Since Einstein, a dream of particle physicists has been to find a single theory that explains all natural phenomena, including gravity. Over the years string theory has emerged as the undisputed leader in the pursuit for a Theory of Everything. 26 Strings Rather than particles, the basic building blocks of all things are postulated to be tiny pieces of “string” that vibrate. Typical distance: 10 -33 cm So they look like point particles when viewed in experiments. The different modes of vibration lead to the spectrum of particles we see in experiment. 27 Gravity and gauge symmetry emerge “for free”! No evidence yet though. Astonishingly, the theories also only make sense if the Universe has extra curled up dimensions! Superstrings are 1-dimensional objects vibrating in a space-time of 10 dimensions. 28 Supersymmetry For string theories to make sense, the world must be supersymmetric. SUSY particles could well be produced at the LHC. 29 30 Duality Around 1995, string theorists led by Ed Witten at Princeton discovered that all their seemingly different theories are in fact different aspects of the same theory! To date, nobody has managed to write down the underlying theory. Although it has been given a name: M-Theory. 31 11-dimensional supergravity Type IIA Type IIB M-Theory E8xE8 heterotic SO(32) heterotic Type I 32 The future We are poised at the edge of a new era of physics beyond the Standard Model. Supersymmetry & ToE Higgs and the origin of mass Neutrino physics CP violation Dark Matter 33 Experiment will lead the way Today: BaBar, HERA, LEP, Tevatron, Boulby Near term: MINOS Large Hadron Collider Long term: New linear collider Muon collider & neutrino beam ??????? 34