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Quanta to Quarks

QtoQ06-ju. Quanta to Quarks. Quantum, atomic, and sub-atomic physics; three parallel, yet strongly interacting topics We will concentrate on the “standard model” Highlight features and look at milestones and some of the background. QtoQ06-ju. Quanta to Quarks – Nuclear path 1.

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Quanta to Quarks

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  1. QtoQ06-ju Quanta to Quarks • Quantum, atomic, and sub-atomic physics; three parallel, yet strongly interacting topics • We will concentrate on the “standard model” • Highlight features and look at milestones and some of the background.

  2. QtoQ06-ju Quanta to Quarks – Nuclear path 1 • Becquerel 1896 radiation • Rutherford 1911 atom • Pauli 1930 neutrino • Chadwick 1932 neutron • Heisenberg 1932 Nucleus = n and p • Hahn and Strassman 1938 fission Nuclei and nucleons probe nucleus

  3. QtoQ06-ju Rutherford scattering 6 MeV alpha Closest distance for head–on approach

  4. QtoQ06-ju Detectors for scattering of electrons by protons and neutrons. Results consistent with nucleons having a substructure = quarks

  5. QtoQ06-ju Chadwick detection of the neutron Note:- charged particles not detected between beryllium and paraffin so photon or something else

  6. QtoQ06-ju Chadwick detection of the neutron Lead plate Note:- charged particles not detected between beryllium and paraffin so photon or something else… Radiation not stopped by inserted lead plate, so must be another neutral particle

  7. QtoQ06-ju Heisenberg model of nucleus:-made up of protons and neutrons Nucleus:- Z protons (atomic number) N neutrons Total A = Z + N (mass number) nucleons Number of protons Z Number of neutrons N

  8. QtoQ06-ju Various decay modes of nucleus Beta minus decay X(A,Z) => Y(A,Z+1) + e- + n protons Beta plus decay X(A,Z) => Y(A,Z-1) + e+ + n Alpha decay X(A,Z) => Y(A-4,Z-2) +a neutrons

  9. QtoQ06-ju Alpha decay-1 Alpha decay is a two body decay Both the alpha and the recoil nucleus have the same momentum in opposite directions. The alphas always get the same proportion of the available energy, Q And hence have the same range in matter

  10. Beta decay QtoQ06-ju Beta decay In beta decay the electrons have a range of energies even though the total energy available is the same. Pauli proposed that there is a third, undetected (hence neutral), particle which shares the energy and balances the momentum. The maximum electron energy is nearly the total available and so the third particle must have a very low mass. Energy spectrum of electron

  11. Powell 1947 pion pi => mu => electron decay observed Strange particles 1947-1950 Anti-particle – baryons 1955 Reines - neutrino detected 1956 QtoQ06-ju Quanta to Quarks – Nuclear path 2 Too many particles for all to be fundamental

  12. QtoQ06-ju Quanta to Quarks – Nuclear path 3 • Gell-Mann/Zweig 1964 Quark model • Weinberg/Salam 1967 electroweak • Glashow 1970 charm in theory • Richter/Ting J/y 1974 charm observed • Perl 1975 tau observed Standard Model emerges

  13. QtoQ06-ju Quanta to Quarks – Nuclear path 4 • Lederman U 1977 bottom observed • Rubbia 1983 W’s and Z0 • CDF 1995 top observed 1991-1992 Evidence indicates that there are only three generations of leptons from study of Z0.

  14. QtoQ06-ju Inward bound object and size • grain, 1 mm • virus, 100 nm • atom, 100 pm • nucleus, 10 fm • nucleon, 1 fm • quark, <1 am 1 am = 10-18 m

  15. Inward bound QtoQ06-ju Inward Bound • object and size • grain, 1 mm • virus, 100 nm • atom, 100 pm • nucleus, 10 fm • nucleon, 1 fm • quark, <1 am From DESY site

  16. QtoQ06-ju How can we examine small objects ? By the light or particles they emit or reflect For very small objects the wavelength of the light or particle plays an important role

  17. QtoQ06-ju Scattering – wavelength dependence Diffraction of waves Note that spread of pattern depends on l/a : For l < a pattern depends on structure of object. For l > a pattern independent of structure of object

  18. QtoQ06-ju Particle diffraction Similar diffraction behaviour is observed for scattering of electrons, neutrons by nuclei and crystals etc. Wavelength of particle given by the de Broglie relationship:- Eg. A 1GeV electron has a wavelength (1.23 fm) about the same as the diameter of a nucleon. ( note:- for ET >> mc2 , l = l photon with same ET )

  19. QtoQ06-ju Accelerator -1 CERN LEP e+e- Up to~ 200GeV+200GeV LHC Pp 8Tev+8Tev 8.6 km diameter CERN photo

  20. QtoQ06-ju Accelerator -2 CERN LEP LHC Tunnel Beam pipes etc under construction CERN photo

  21. QtoQ06-ju Detectors - ATLAS at CERN physicist CERN photo

  22. QtoQ06-ju Visualization of particles tracks - 1

  23. QtoQ06-ju The standard model • The standard model describes the universe in terms of a set of different kinds of particles and the interactions between them. • 12 particles (and their 12 antiparticles) • 6 leptons and their 6 antileptons • 6 quarks and their 6 antiquarks • 4 interaction forces:- • gravity, electromagnetic, • weak, fundamental strong

  24. name symbol charge MeV/c2 m/mproton electron e- -e 0.511 0.0055 electron neutrino ne 0 ~ 0 mu-minus m -e 105.66 0.1126 mu-neutrino nm 0 0 tau-minus t -e 1777 1.894 tau-neutrino nt 0 ~ 0 QtoQ06-ju the leptons – charge and mass

  25. name symbol charge mass MeV/c2 m/mproton e-plus or positron e+ +e 0.511 0.0055 electron antineutrino ne 0 ~ 0 mu-plus m+ +e 105.66 0.1126 mu antineutrino nm 0 ~ 0 tau-plus t+ +e 1777 1.894 tau antineutrino nt 0 ~ 0 QtoQ06-ju anti-leptons- charge and mass

  26. QtoQ06-ju Classification of particles – particles/anti particles Origin:- particles of exactly the same mass but opposite charge Later found to have other quantum numbers with opposite values Symbol:- either the electric charge as a superscript eg: p- and p+, e- and e+ or particle P anti-particle (often said as P-bar) Neutral particles/anti-particles:- some are the same (Majorana) eg p0and some are different (Dirac) eg neutron, neutrino

  27. QtoQ06-ju The first anti-particles:- positrons, 1932 - Anderson 63 MeV positron upwards emerges with 23 MeV) 3 electrons (bend to left) and 3 positrons ( bend to right)

  28. lepton lepton number le lm lt anti-lepton number le lm lt electron e- 1 0 0 -1 0 0 electron neutrino ne 1 0 0 -10 0 mu m 0 1 0 0-10 mu-neutrino nm 0 1 0 0-10 tau t 0 0 1 0 0-1 tau-neutrino nt 0 0 1 0 0-1 QtoQ06-ju lepton numbers

  29. QtoQ06-ju Decay p+ => m+ => e+ m+ => nm +e+ + p+ => m+ + nm Note lepton numbers are conserved

  30. name symbol charge e mass MeV/c2 m/mproton down d -1/3 ~ 3 up u +2/3 ~ 6 strange s -1/3 100 0.1 charm c +2/3 1250 1.3 bottom b -1/3 4500 4.8 top t +2/3 175000 187 QtoQ06-ju quarks – charge and mass

  31. QtoQ06-ju q = +2e/3 q = -e/3 Quark picture 1983 according to Frank Close“Cosmic Onion” Heinemann Educational Books1983 Top-quark found 1995

  32. name symbol charge e mass MeV/c2 m/mproton anti- down d -1/3 ~ 3 anti-up u +2/3 ~ 6 anti-strange s -1/3 100 0.1 anti-charm c +2/3 1250 1.3 anti-bottom b -1/3 4500 4.8 anti-top t +2/3 175000 187 QtoQ06-ju Anti-quark - charge and mass

  33. quark quark flavour numbers qd qu qs qc qb qt anti-quark flavour numbers qd qu qs qc qb qt down d 1 0 0 0 0 0 -1 0 0 0 0 0 up u 0 1 0 0 0 0 0 -1 0 0 0 0 strange s 0 0-10 0 0 0 010 0 0 charm c 0 0 010 0 0 0 0 -10 0 bottom b 0 0 0 0-10 0 0 0 01 0 top t 0 0 0 0 01 0 0 0 0 0 -1 QtoQ06-ju quarks – flavour numbers

  34. QtoQ06-ju leptons and quarks - masses p Generations 1 2 3

  35. force exchange boson "charge" range mass m/mp how many different kinds? gravity graviton mass infinite zero one electro- magnetic photon electric infinite zero one weak W+ W- Z0 weak 1 am 85.7 85.7 97.2 three Fundamental strong gluon colour infinite zero eight QtoQ06-ju Fundamental forces

  36. gravity weak electro-magnetic strong charged leptons y y y n neutral leptons y y n n quarks y y y y photons y n y n Z0 y y n n W+, W- y y y n gluons y n n y QtoQ06-ju forces acting between particles

  37. QtoQ06-ju Conservation laws - 1 The following quantities are conserved in all interactions Ie:- the total before must be the same as the total afterwards • Charge • Energy • Linear momentum • Angular momentum

  38. QtoQ06-ju Conservation laws - 2 The following quantities are conserved in interactions as indicated:- S strong; E electromagnetic; W weak • Baryon number y y y • Lepton flavour numbers y y y • Quark flavour numbers y yn • Colour yn/a n/a S E W

  39. QtoQ06-ju Classification of particles:photons, leptons, mesons and baryons • Originally described mass. • Photons no mass • Leptons light 0.5 MeV/c2 • Mesons medium 100-500 MeV/c2 • Baryons heavy > 900 MeV/c2 Still useful:- turns out that this also describes structure and quark content.

  40. QtoQ06-ju Classification of particles – baryons and mesons and hadrons hadrons Baryons Contain quarks Mesons a quark and an anti-quark three quarks or three anti-quarks (anti baryons)

  41. QtoQ06-ju Classification of particles – baryons and mesons and hadrons hadrons Baryons Mesons valence quarks gluons and sea quarks a quark and an anti-quark three quarks or three anti-quarks (anti baryons)

  42. QtoQ06-ju Baryons:- proton and the neutron d u u the proton uud + sea quarks and gluons the neutron udd + sea quarks and gluons d d u

  43. QtoQ06-ju mesons:- the pion family p+p0p- u:d-bar u:u-bar u-bar:d d:d-bar

  44. QtoQ06-ju “colour - 1” Chromodynamics :- theory of the strong interaction, colour plays the same role as charge in electrodynamics. Need three colours, but hadrons have to be colourless Use red, green and blue (parallel to TV and photo and print) Anti-colours = white – colour ; cyan, magenta and yellow Gluons have a colour and an anti colour

  45. QtoQ06-ju “colour - 2” Quarks have colour, anti-quarks have anti-colour Baryons:- one (valence) quark of each colour (anti-baryons have three anti-colours) Mesons:- quark(colour)+anti-quark(anti-colour) Leptons, photons, W’s, Z0 do not have a colour

  46. QtoQ06-ju Classification of particles - generations quarks leptons First generation: Second generation: Third generation: The upper member of each doublet is more positive

  47. QtoQ06-ju Classification of particles – fermions and bosons Fermions obey the Pauli exclusion principle:- “two particles with the same quantum numbers can not occupy the same quantum state” Bosons don’t:- “any number of identical bosons can occupy the same quantum state” Another way of saying this is:- “Fermions follow Fermi/dirac statistics, bosons follow Bose/Einstein statistics”

  48. QtoQ06-ju Classification of particles – fermions and bosons Fermions:- leptons, quarks, neutron, proton and other baryons Bosons:- photons, gluons, W’s and Z0 mesons A nucleus can be either depending on its spin.

  49. QtoQ06-ju Classification of particles – fermions and bosons Fermions have half integral spin:- 1/2, 3/2, 5/2, 7/2 ….. Bosons have integral spin:- 0, 1, 2, 3 …. Spin magnitude and its orientation are quantum numbers, as are the allowed projections onto a preferred direction. Eg spin 3/2 : -3/2, -1/2, +1/2, +3/2 spin 2: -2, -1, 0, +1, +2 Are two different quantum states +1/2 -1/2

  50. QtoQ06-ju Standard model and Nuclear Physics The nucleons remain as individual particles in the quantum well formed by the other nucleons in the nucleus Alpha, gamma decays, fission and fusion are reactions at the nuclear level.They are the result of nucleon to nucleon interactions via the “strong nuclear force” Beta decay is an interaction at the quark level

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