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The beginning of physics IoP Physics Update 2008 Forces and fields Particles and symmetries Cosmology The Large Hadron Collider Particle detectors A Ring-Imaging.

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Presentation on theme: "The beginning of physics IoP Physics Update 2008 Forces and fields Particles and symmetries Cosmology The Large Hadron Collider Particle detectors A Ring-Imaging."— Presentation transcript:

1 The beginning of physics IoP Physics Update 2008 Forces and fields Particles and symmetries Cosmology The Large Hadron Collider Particle detectors A Ring-Imaging Cherenkov detector A Cosmic Ray detector

2 14-15th December 2008 Steve Wotton 2 Forces – A particle physicist’s view ŸFamiliar electric, magnetic and gravitational forces are described by separate theories ŸClassical picture ŸAction at a distance – two bodies feel a mutually attractive or repulsive force even though separated by large distances ŸIntroduce abstract concept of a field – the strength and direction of the force felt by a test body is uniquely defined at every point in space ŸStrength of force from an idealised point body decreases according to an inverse square law. ŸWe draw pictures of the fields as if they had a physical existence (a prejudice reinforced by e.g. iron-filings aligning along magnetic field lines) ŸQuantum field theory view ŸForces are due to the exchange of (virtual) particles that carry momentum ŸStrength of the force is determined by the coupling to the force carrying particle. The strength is (very) different for the known forces. ŸA consistent mathematical description is formulated by combining quantum mechanics and relativity.

3 14-15th December 2008 Steve Wotton 3 Unification of forces ŸElectricity and magnetism once considered separate phenomena. ŸNow unified and enshrined in Maxwell’s equations. ŸElectric and magnetic forces are merely different manifestations of the same underlying mechanism. ŸBy changing our viewpoint, an electric field can become a magnetic field (and vice versa). Relativity at work. ŸAdd an extra ingredient – Quantum Mechanics – we get Quantum Electrodynamics. The photon (quantum of light) is the force carrying particle. ŸA very, very, very, very, very, very, very, very, well-tested theory. ŸFeynman expressed the calculations in pictures (Feynman diagrams) ŸEach diagram represents a mathematical term in the solution to a problem

4 14-15th December 2008 Steve Wotton 4 Force unification – the next step ŸCan we include gravity? ŸWe’d like to but it is HARD. ŸIs there anything else? ŸYes. ŸThe weak nuclear force (beta decay). ŸThe strong nuclear force (binds protons and neutrons in nuclei). ŸBuild on the success of QED ŸNew ingredients ŸNew interactions ŸNew particles ŸNew diagrams n p e-e- e W-W- e-e- e-e- Z 0, 

5 14-15th December 2008 Steve Wotton 5 Particle zoo ŸThe quest for the elements ŸA search for order ŸEarth, air, fire and water ŸThe chemical elements ŸPeriodic table ŸPatterns are due to a set of quantisation rules that must be followed when adding more electrons to an atom. ŸA complicated picture (many elements with different properties) simplified by applying a set of rules to build elements from a small number of more fundamental objects. ŸThe chart of the nucleides ŸA periodic table for nuclei ŸPatterns also due to quantisation rules ŸA complicated picture simplified…

6 14-15th December 2008 Steve Wotton 6 Particle zoo 2 ŸMany different particles can be created in the lab. ŸA complicated picture but we can discern patterns. ŸMust be due to an underlying theory that combines a smaller number of more fundamental particles using a set of rules. ŸThe fundamental particles ŸAll ordinary matter made of up quark, down quark, electrons and electron neutrinos. ŸAll forces (except gravity) mediated by photon, Z boson, W boson and gluon. ŸBut there are problems ŸDuplication – why? ŸMass hierarchy – how? ŸAnti-matter – where? ŸGravity – still mysterious.

7 14-15th December 2008 Steve Wotton 7 Where we are ŸThe Standard Model. ŸDescribes all known particles and their electroweak and strong interactions. ŸNo significant deviations from SM observed to date. ŸObserved differences between forces due to non-exact symmetry. ŸPossibly the best physical theory in the history of physics. ŸBut… ŸWe are still waiting for the Higgs boson ŸWe don’t understand the origin of mass ŸWe don’t know how to solve the hierarchy problem ŸSupersymmetry ŸExtra dimensions ŸWe don’t know how to include gravity ŸWe don’t know the origin of symmetry breaking ŸWe do know that The Standard Model must break down at TeV energies

8 14-15th December 2008 Steve Wotton 8 Higgs – the solution or the problem? LHC – the kill or cure? ŸIf the Higgs particle is not found in the mass range accessible to the LHC… ŸBreakdown of Standard Model. ŸViolation of unitarity in WW scattering for large m H (sum of probabilities cannot exceed 1). ŸIf the Higgs particle is found at the LHC… ŸLow mass (compared to Planck mass) implies a convenient cancellation of large terms. ŸOr there must be new physics. ŸSupersymmetry is a favourite candidate for new physics (symmetry is good, more is better) but... ŸRequires new particles to exist (Who ordered that?, Rabi). ŸProperties must explain why they haven’t been observed already (heavy, or weakly interacting).

9 14-15th December 2008 Steve Wotton 9 Cosmology 1 ŸLooking back in time ŸUniverse contains fixed amount of energy (mass and radiation) ŸSpace is expanding, universe is cooling. ŸkT = hc/λ = eV relates temperature (T), length (λ), accelerating potential (V) through fundamental constants k, h, c, e. ŸE.g 14TeV = m = K (Note: size of proton = m) LHC analogies: A time machine that recreates conditions of early universe. A microscope that sees objects smaller than can be seen with light.

10 14-15th December 2008 Steve Wotton 10 Cosmology 2 ŸThe LHC will recreate the conditions of the early Universe. ŸProvides evidence of the processes that are assumed to operate. ŸMay explain: ŸDark matter. ŸMatter-antimatter asymmetry. ŸMechanisms driving evolution of early universe. ŸThe origin of mass. ŸThe unification of all known forces.

11 14-15th December 2008 Steve Wotton 11 Detection techniques ŸA discussion of techniques used in particle detectors…

12 14-15th December 2008 Steve Wotton 12 Ring-Imaging Cherenkov Detectors ŸIdentifying particles using Cherenkov radiation… ŸCerenkov worksheet ŸRICH animator

13 14-15th December 2008 Steve Wotton 13 Cosmic Ray detection ŸA practical demonstration of detection of high energy particles in the classroom…

14 14-15th December 2008 Steve Wotton 14 Other connections ŸMedical imaging ŸPhotomultiplier tubes ŸMRI ŸRadio-isotopes production in accelerators ŸProton cancer therapy ŸSecurity scanning ŸImage Intensifiers ŸX-ray ŸGamma-ray ŸCosmic-ray ŸNon-destructive testing ŸCosmic rays or neutrinos (“X-raying” the Pyramids) ŸFragile/valuable objects ŸPaintings ŸSculptures ŸWine ŸArchaeological remains ŸEngineering


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