This is quark confinement IB Physics – Particle PhysicsĢ9 Gluon colour Quarks change colour through gluon exchange. Therefore isolated quarks and quarks cannot be observed. Gluons are themselves coloured Gluons bind quarks together Force between quarks increases as quarks are separated. IB Physics – Particle PhysicsĢ8 Gluons Bosons with spin = 1 and zero mass You should be able to draw Feynman diagrams for the following interactions Electron scattering Beta decay Pion decay Electron – positron annhilation Pair production Muon decay Quark interactions Photon – photon scattering IB Physics – Particle PhysicsĢ0 Pion - Decay Pion 1 Decay Pion + DecaryĢ6 Learn these ones Draw the Feynman diagram for beta (-) decayĬolor force and strong force are essentially the same thing Colour force binds quarks together in hadrons by exchange of gluons Strong force binds colour-neutral particles together e.g. IB Physics – Particle Physicsġ6 Strong interactions Annotate to show colour and flavour The quark gluon vertices could also show colour flow as quarks interact. IB Physics – Particle Physicsġ3 Weak Vertices Ws, Z and gluons video IB Physics – Particle Physicsġ5 Strong vertices The left hand side represents BEFORE and the right hand side represents AFTER The gluon can be regarded as a pathway through which colour charge is exchanged between quarks and antiquarks. Note that the time still flows from left to right and a backwards facing arrow represents an antiparticle travelling forwards in time. Probability of taking place process = (amplitude)2 IB Physics – Particle Physicsġ1 EM vertex IB Physics – Particle Physicsġ2 Basic em interactions By rotating the arms of the vertices, the following interaction possibilities are generated. For the em interaction The amplitude of the diagram is the product of the interaction strength for each vertex i.e. The picture represents a mathematical process called the amplitude. QED Video IB Physics – Particle Physicsĥ What is happening here? a.) Electron absorbs a photon and accelerates (changes direction) b.) Electron emits a photon and changes directionĩ Rotate the vertex slightly to show a real interactionįeynman diagrams may be used to calculate probabilities for fundamental processes. IB Physics – Particle Physicsįorces are explained by Emission/absorption of particles A particle is emitted “ spontaneously” Where does the energy to create this particle come from? (Uncertainty video) New law called the Heisenberg Uncertainty Principle The particle is known as a virtual particle. Vertices are linked by a line representing an exchange particle Charge and colour are conserved at each vertex. Arrows from right to left represent antiparticles moving forward in time. Time flows from left to right Arrows from left to right represent particles moving forward in time. Quarks or leptons are solid straight lines Exchange particles are either wavy (Photons, W, Z) or curly (gluons). These represent a lepton – lepton or quark-quark transition. IB Physics – Particle PhysicsĮach vertex has an arrow going in and one going out. There is an electromagnetic interaction vertex, a weak interaction vertex and a strong interaction vertex. We can use the vertices in a non-mathematical way to illustrate how quarks and leptons interact with each other. 2 Feynman Vertices Each of the three basic interactions can be described using a symbol called a Feynman vertex.
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