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Particle Physics: Status and Perspectives Part 1: Particles

Particle Physics: Status and Perspectives Part 1: Particles. SS 2014. Manfred Jeitler. Overview (1). what are elementary particles? the first particles to be discovered historical overview a few formulas relativistic kinematics quantum mechanics and the Dirac equation

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Particle Physics: Status and Perspectives Part 1: Particles

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  1. Particle Physics: Status and PerspectivesPart 1: Particles SS 2014 Manfred Jeitler

  2. Overview (1) • what are elementary particles? • the first particles to be discovered • historical overview • a few formulas • relativistic kinematics • quantum mechanics and the Dirac equation • common units in elementary particle physics • the Standard Model • detectors • accelerators

  3. Overview (2) • completing the Standard Model • the second generation (charm and J/ψ) • the third generation (beauty (bottom) and Υ (“upsilon”), top) • gauge bosons of electroweak interactions: the W and Z bosons • testing at the Precision Frontier: the magnetic moment of the leptons • the Higgs boson • fundamental symmetries and their violation • parity violation • CP-violation • T-violation

  4. Overview (3) • neutrinos and neutrino oscillations • particle physics and cosmology, open questions • the Energy Frontier and the Precision Frontier • Supersymmetry • dark matter • gravitational waves • slides and formulas at http://wwwhephy.oeaw.ac.at/u3w/j/jeitler/www/LECTURES/ParticlePhysics/

  5. Literature • A few useful books are: • Donald Perkins, Introduction to High Energy Physics • Otto Nachtmann, Elementary Particle Physics • You will find many other good books in your library • On recent experiments, much useful information can be found on the internet (Wikipedia, home pages of the various experiments etc.)

  6. What are (elementary) particles?

  7. e- the electron Thomson 1897

  8. J.J. Thomson’s “plum-pudding model” of the atom ... the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, ...

  9. e- p the proton Rutherford 1914 1897 1900-1924

  10. e- g p the photon Einstein Planck Compton 1900-1924 1897

  11. e- g p Chadwick n the neutron 1932 1914 1897 1900-1924

  12. e- g p n e+ the positron (anti-matter) Anderson Dirac 1932 1947 1914 1897 1937 1900-1924

  13. e- g p n e+ Who ordered this ? • Hess • Anderson, • Neddermeyer µ the muon 1937 1914 1897 1900-1924 1932

  14. muon lifetime • muon lifetime ~ 2.2 μs • speed of muons: almost speed of light • speed of light = ? • path travelled by muons = ?

  15. relativistic kinematics • elementary particles travel mostly at speeds close to speed of light • because their masses are small compared to typical energies •  (almost) always use relativistic kinematics • in particle physics, “special relativity” is sufficient most of the time • remember a few basic formulae !

  16. a bit of maths • Special Relativity • Quantum Mechanics • Dirac Equation

  17. relativistic kinematics v 1/γ 1

  18. the electron-volt (eV) + e- 1V - units: energy and mass • 10-4 eV: 3 K cosmic background radiation (~ 0.25 meV) • 10-2 eV: room temperature (~ 30 meV) • eV: ionisation energy for light atoms (13.6 eV in hydrogen) • 103 eV (keV): X-rays in heavy atoms • 106 eV (MeV): mass of electron me = 511 keV/c2 • 109 eV (GeV): mass of proton (~1GeV/c2) • ~ 100 GeV/c2: mass of W, Z • ~ 200 GeV/c2: mass of top • 1012 eV (TeV): range of present-day man-made accelerators • 1020 eV: highest energies seen for cosmic particles • 1028 eV (1019 GeV/c2): ~ Planck mass

  19. units: speed and distance • velocity: speed of light • ~ 3 * 108 m/s • ~ 30 cm/ns • approximately, all speeds are equal to the speed of light in high-energy particle physics ! • all particles are “relativistic” • distance: fm (femtometer) • 1 fm = 10-15 m • sometimes also called “Fermi”

  20. relations and constants • waves • λ * ν = c • ω = 2π ν • quantum mechanics • h Planck constant (“Planck’schesWirkungsquantum”) • h = h / 2π • hν =hω = E • numerical survival kit • c = h = 1 • as long as you need no “usual” units; and then, use: • c ~ 3 * 108 m/s speed of light • hc ~ 200 MeV * fm • ~ 6 * 1026 protons / kg (~ GeV / kg) Avogadro’s number • e ~ 1.6 × 10−19  As (coulomb) • 1 eV ~ 104  K Boltzmann’s constant • 1 Tesla = 10000 gauss

  21. “natural” units • c = h = 1 • c ~ length/time speed of light • hc ~ energy*length •  length ~ time ~ 1/energy • 1 GeV−1 ~ 10−16 m (=0.1 fm) ~ 10−24 s • V = -G m1m2 / r gravitational attraction •  G ~ m-2 • G = MPlanck-2particles with this mass would at ~proton-size distance have gravitational energy of ~proton mass • MPlanck ~ 1019 GeV • LPlanck = 1/MPlanck ~ 10-31 m • tPlanck = 1/MPlanck ~ 10-43 s

  22. gravitation is weak! • Vgrav = - G m1m2 / r gravitational potential = - MPlanck-2 m1m2 / r ~ - 10-38m1m2 / r • Velec = (1 / (4πε0) ) q1e q2e / r electrostatic potential = (e2 / (4πε0hc) )q1q2 / r = α q1q2 / r α = fine structure constant ~ (1/137) q1q2 / r ~ 10-2 q1q2 / r •  Vgrav/ Velec ~ 10-38/ 10-2 = 10-36

  23. e- g p n µ e+ Yukawa Powell p the pion 1947 1937 1914 1897 1900-1924 1932

  24. Force carriers gauge bosons L.J. Curtis Interaction between particles due to exchange of other (“virtual”) particles

  25. e- g p p n µ e+ n the neutrino Pauli Reines 1932 1947 1914 1897 1937 1900-1924

  26. L e- g K n p µ n p e+ S Rochester, Butler, ... „strange“ particles 1947-... 1947 1914 1932 1897 1937 1900-1924

  27. Too many particles!

  28. n m KL Kc Sc W- KS B D t p0 h S0 3s 1s 2s J/y D* 4s f w r the particle zoo life time (s) 100000 e- p n 1s 1 ms E=1eV m 1 µs KL Kc pc Sc 1 ns W- KS B D t 10-15s p0 h S0 3s 1s 2s J/y 10-20s D* 4s f w W±, Zo r 10-25s mass (GeV/c2)

  29. L e- g K n p p n µ e+ S In his Nobel prize speech in 1955, Willis Lamb expressed nicely the general attitude at the time: „I have heard it said that the finder of a new elementary particle used to be rewarded by a Nobel Prize, but that now such a discovery ought to be punished by a $10,000 fine.“ Lamb 1947-... 1947 1914 1932 1897 1937 1900-1924

  30. The “particle zoo” of the subatomic world Is there something analogous to the Periodic Table of the elements?

  31. Is there something missing? ? ? ? ? ? ? ?

  32. The periodic table today

  33. q q q q q g strong g t m u d u t u d c d d s d b u u e electromagnetic weak W, Z ? gravitation nm nt ne Wechselwirkungen Teilchen „Quarks“ „Leptonen“ Ladung stark 0 +2/3 -1 -1/3 schwach +1 0 +1/3 Proton Neutron

  34. u g strong g t m t b c s u d e electromagnetic weak W, Z ? gravitation nt nm ne d Wechselwirkungen Anti-Teilchen Ladung stark 0 -2/3 +1 +1/3 schwach +1 Pion (p)

  35. u u u u s s u u d d c u d D++ s L0 d K- p0 b D+ b  S+

  36. t ne nm nt interactions u c strong g strong g electromagnetic u u d d u d d s b m t e weak W, Z ? gravitation weak force carriers = bosons (spin 1) the Standard Model fermions (spin ½) leptons quarks charge 0 +2/3 -1 -1/3 +1 0 proton neutron baryons

  37. t ne nm nt u c g strong t d b c s u d s b m t e weak W, Z ? gravitation anti-particles leptons quarks interactions charge strong -2/3 nt ne nm 0 g +1 +1/3 e t electromagnetic m weak force carriers = bosons (spin 1)

  38. t ne nm nt u c g strong t d b c s u d s b m t e weak W, Z ? gravitation anti-particles leptons quarks interactions charge strong -2/3 nt ne nm 0 g +1 +1/3 e t electromagnetic m weak force carriers = bosons (spin 1)

  39. the 4 fundamental interactions Gravitation Strong Interaction Electromagnetism Weak Interaction

  40. lifetime and width • due to the uncertainty principle, the lifetime of a state (= unstable particle) and the accuracy, with which its mass (= rest energy) is reproduced at subsequent measurements, are correlated: Δt * ΔE ~ h • lifetime can be measured directly for fairly long-lived states ( > 10-16 s) • width can be measured directly for short-lived states (becomes immeasurably small for long-lived states) • both properties can always be converted into each other: τ = h/ ΓΓ = h/ τ • remember: hc~ 200 MeV ×fm c = 3 ~ 1023 fm/s  h~ 2/3  10-21 MeV ×s

  41. cross section • defined via scattering probability W = n . σ • n ... number of scatterers in beam • σ ... cross section of individual scatterer • naive picture: each scatterer has a certain “area” and is completely opaque • absorption cross section • can also be used for elastic scattering ... • into certain solid angle dΩ: dσ/dΩ • ... or particle transformation • differential cross section for a certain reaction • unit: “barn”: (10 fm)2 = 100 fm2 = 10-28 m2 = 10-24 cm2

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