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Physics - Quarks Presentation (2013)
Transcript of Physics - Quarks Presentation (2013)
Free neutrons decay in 15 minutes Protons and neutrons are the only stable hadrons (usually bound in an atomic nucleus) Protons are composed of two up and one down quarks(uud)
Neutrons are composed of two down and one up quark (udd) Same as baryons except with antiquarks Mesons Integer quantum spins (bosons) Does not obey Dependent on the quarks B = 1 Baryon number (B) always conserved
It is +1/3 for quarks and -1/3 for antiquarks B = 0 Three quarks Quark/antiquark pair Pions Same as mesons except with antiquarks Since up quarks have an electric charge of +1/3 and down quarks have an electric charge of -1/3, protons have a net charge of 1 and neutrons of 0 vs Quarks Quantum Spin Pauli Exclusion Principle Electric Charge Baryon Number Antiparticle Baryons with very short lifespans
Can have charges like +2, +1, 0, or -1 Kaons Produced in high energy collisions between hadrons
No quantum spin
Unstable, decays in billionths of a second Discovered by using a cloud chamber
Strange quark and up/down anti-quark
Negatively charged or neutral You thought it was over... You were wrong. In 1968, scientists found that all of the particles were made of fundamental particles called quarks Boson Everything The Standard Model Matter
Protons, neutrons, and electrons Forces
Not subject to
Photon, W and Z, gluon, Higg's, graviton Elementary particle of
Pauli Exclusion Principle
Examples Properties Leptons Neutrinos have almost no mass and a neutral charge
Produced by the sun
Hard to detect since they pass through the earth Exist as solitary particles
Electron, muon, tauon have electrical charge -1
Electron neutrino, muon neutrino, and tauon neutrino are neutral
Do not interact with strong force
Interact via weak force
Heavy leptons decay almost instantly Neutrinos Neutrino Timeline Neutrino proposed by Pauli to explain beta decay 1930 electron neutrino indirectly detected 1956 1962 1970 1975 muon neutrino indirectly detected First direct detection of neutrino taoun neutrino indirectly detected The Strong Interaction Quarks interact with each other constantly via the strong force, which is mediated by gluons A red, green, and blue quark, as in a baryon The blue quark emits a blue/antigreen gluon and changes to green The green quark absorbs the gluon and changes to blue Total colour charge is always conserved Gluons Carry force (boson) like photons, except for the strong force Anything with a colour charge interacts with the strong force
Gluons have colour charge too, so they interact with the strong force Quarks Fundamental constituents of matter
Supported by hadronization
Cannot exist alone because of strong force and QCD 1st (lightest)
3rd (heaviest) Generation Name (u) Up
(b) Bottom Electric Charge Quantum Spin +2/3
1/2 Fermion All composite particles must be colour neutral Two ways to be colour neutral Gluons have 8 types Gluons have a probability of being in a certain state Scatter experiments in 50’s and 60’s discovered many particles known as the particle zoo A Brief History of Quarks A myriad of new particles were being discovered, and the old system of neutrons, protons and electrons being the fundamental particles couldn’t explain it 1960 1968 Murray Gell-Mann and George Zweig proposed the idea of 3 ‘quarks’ (up down and strange), fundamental particles that made up these other particles, however this idea was not widely accepted because quarks had not been observed James Bjorken and Richard Feynman discover proof of the existence of quarks in an experiment similar to Rutherford’s gold foil experiment. They bombarded protons with electrons, and noticed the scatter pattern was similar to the scattering Rutherford observed. 1964 Scientists Samuel Ting and Burton Richter, working independently and with completely different methods, announce the discovery of the 4th quark, the charm quark on the same day 1974 Bottom quark is discovered by Leon Lederman 1977 Top Quark is discovered at Fermilab 1995 Other Large Hadrons Baryons with three u and/or d quarks are N's (I = 12) or Δ's (I = 32). Baryons with two u and/or d quarks are 's (I = 0) or 's (I = 1).
If the third quark is heavy, its identity is given by a subscript Baryons with one u or d quark are 's (I = 12).
One or two subscripts are used if one or both of the remaining quarks are heavy There are over 200 combinations of baryons/mesons.
Most of these decay almost instantly into other quarks, and eventually leptons Baryons with no u or d quarks are Ω's (I = 0).
Subscripts are used to indicate any heavy quark content. The Strong Interaction +1, 0, -1 The Higgs Boson Possible Combinations 140 120