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The beginning of physics

The beginning of physics. Forces and fields Particles and symmetries Cosmology The Large Hadron Collider Particle detectors A Ring-Imaging Cherenkov detector A Cosmic Ray detector. IoP Physics Update 2008. Forces – A particle physicist’s view.

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The beginning of physics

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

  2. Forces – A particle physicist’s view Steve Wotton • Familiar electric, magnetic and gravitational forces are described by separate theories • Classical picture • Action at a distance – two bodies feel a mutually attractive or repulsive force even though separated by large distances • Introduce 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 • Strength of force from an idealised point body decreases according to an inverse square law. • We 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) • Quantum field theory view • Forces are due to the exchange of (virtual) particles that carry momentum • Strength of the force is determined by the coupling to the force carrying particle. The strength is (very) different for the known forces. • A consistent mathematical description is formulated by combining quantum mechanics and relativity.

  3. Unification of forces Steve Wotton • Electricity and magnetism once considered separate phenomena. • Now unified and enshrined in Maxwell’s equations. • Electric and magnetic forces are merely different manifestations of the same underlying mechanism. • By changing our viewpoint, an electric field can become a magnetic field (and vice versa). Relativity at work. • Add an extra ingredient – Quantum Mechanics – we get Quantum Electrodynamics. The photon (quantum of light) is the force carrying particle. • A very, very, very, very, very, very, very, very, well-tested theory. • Feynman expressed the calculations in pictures (Feynman diagrams) • Each diagram represents a mathematical term in the solution to a problem

  4. Force unification – the next step Steve Wotton • Can we include gravity? • We’d like to but it is HARD. • Is there anything else? • Yes. • The weak nuclear force (beta decay). • The strong nuclear force (binds protons and neutrons in nuclei). • Build on the success of QED • New ingredients • New interactions • New particles • New diagrams p n e- W- ne e- Z0 , g e-

  5. Particle zoo Steve Wotton • The quest for the elements • A search for order • Earth, air, fire and water • The chemical elements • Periodic table • Patterns are due to a set of quantisation rules that must be followed when adding more electrons to an atom. • A 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. • The chart of the nucleides • A periodic table for nuclei • Patterns also due to quantisation rules • A complicated picture simplified…

  6. Particle zoo 2 Steve Wotton • Many different particles can be created in the lab. • A complicated picture but we can discern patterns. • Must be due to an underlying theory that combines a smaller number of more fundamental particles using a set of rules. • The fundamental particles • All ordinary matter made of up quark, down quark, electrons and electron neutrinos. • All forces (except gravity) mediated by photon, Z boson, W boson and gluon. • But there are problems • Duplication – why? • Mass hierarchy – how? • Anti-matter – where? • Gravity – still mysterious.

  7. Where we are Steve Wotton • The Standard Model. • Describes all known particles and their electroweak and strong interactions. • No significant deviations from SM observed to date. • Observed differences between forces due to non-exact symmetry. • Possibly the best physical theory in the history of physics. • But… • We are still waiting for the Higgs boson • We don’t understand the origin of mass • We don’t know how to solve the hierarchy problem • Supersymmetry • Extra dimensions • We don’t know how to include gravity • We don’t know the origin of symmetry breaking • We do know that The Standard Model must break down at TeV energies

  8. Higgs – the solution or the problem? LHC – the kill or cure? Steve Wotton • If the Higgs particle is not found in the mass range accessible to the LHC… • Breakdown of Standard Model. • Violation of unitarity in WW scattering for large mH (sum of probabilities cannot exceed 1). • If the Higgs particle is found at the LHC… • Low mass (compared to Planck mass) implies a convenient cancellation of large terms. • Or there must be new physics. • Supersymmetry is a favourite candidate for new physics (symmetry is good, more is better) but... • Requires new particles to exist (Who ordered that?, Rabi). • Properties must explain why they haven’t been observed already (heavy, or weakly interacting).

  9. Cosmology 1 Steve Wotton • Looking back in time • Universe contains fixed amount of energy (mass and radiation) • Space is expanding, universe is cooling. • kT = hc/λ = eV relates temperature (T), length (λ), accelerating potential (V) through fundamental constants k, h, c, e. • E.g 14TeV = 10-19m = 1017K (Note: size of proton = 10-15m) LHC analogies: A time machine that recreates conditions of early universe. A microscope that sees objects smaller than can be seen with light.

  10. Cosmology 2 Steve Wotton • The LHC will recreate the conditions of the early Universe. • Provides evidence of the processes that are assumed to operate. • May explain: • Dark matter. • Matter-antimatter asymmetry. • Mechanisms driving evolution of early universe. • The origin of mass. • The unification of all known forces.

  11. Detection techniques Steve Wotton • A discussion of techniques used in particle detectors…

  12. Ring-Imaging Cherenkov Detectors Steve Wotton • Identifying particles using Cherenkov radiation… • Cerenkov worksheet • RICH animator

  13. Cosmic Ray detection Steve Wotton • A practical demonstration of detection of high energy particles in the classroom…

  14. Other connections Steve Wotton • Medical imaging • Photomultiplier tubes • MRI • Radio-isotopes production in accelerators • Proton cancer therapy • Security scanning • Image Intensifiers • X-ray • Gamma-ray • Cosmic-ray • Non-destructive testing • Cosmic rays or neutrinos (“X-raying” the Pyramids) • Fragile/valuable objects • Paintings • Sculptures • Wine • Archaeological remains • Engineering

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