Monday, Nov. 15, 2010 PHYS 3446, Fall 2010 Andrew Brandt 1PHYS 3446 – Lecture #19Monday, Nov. 15, 2010Dr. Andrew Brandt• More on AFP/Cerenkov• Particle Physics• Project Outlines Due• Classes 11/17, 11/22, 11/24?, 11/29 • Projects 12/1 12/3 (before lab) 12/6Project Assignments and tentative agendaWednesday Dec. 1• Solar Neutrino Deficit Baral-Lord• Long baseline neutrino experiments (neutrino mass) Butler-Mayfield• G-2 experiments Ouyang-Wright• HERA experiments: diffraction/large rapidity gaps Gray-WooFriday Dec. 3• Quark-Gluon Plasma (RHIC) Byrd-PryorMonday Dec. 6• Higgs Boson Theory Bridges-Corbin• Standard Model+Beyond the Standard Model Higgs Boson Searches at Dzero Absher-Dean-Shumate• Supersymmetry Theory Ibarra• Blackhole/Extra Dimension Searches at ATLAS Contreras-LaRoqueMonday, Nov. 15, 2010 2PHYS 3446, Fall 2010 Andrew BrandtMonday, Nov. 15, 2010 PHYS 3446, Fall 2010 Andrew Brandt3• What are elementary particles?– Particles that make up matter in the universe– Cannot be broken into smaller pieces– Cannot have extended size• The notion of “elementary particles” has changed from 1930’s through present– In the past, people thought protons, neutrons, pions, kaons, -mesons, etc. were elementary particles• What changed?– The increasing energies of accelerators allow the probing of smaller distance scales, revealing sub-structure• What is the energy needed to probe 0.1–fm?– From de Broglie Wavelength, we obtain Particle Physics Pcc2000 /MeV c197fm0.1fm MeVcMonday, Nov. 15, 2010 PHYS 3446, Fall 2010 Andrew Brandt 4• Classical forces:– Gravitational: every particle is subject to this force, including massless ones– Electromagnetic: only those with electrical charges– What are the ranges of these forces?• Infinite!!– What does this tell you?• Their force carriers are massless!!– What are the force carriers of these forces?• Gravity: graviton (not seen…yet)• Electromagnetism: PhotonsForces and Their Relative StrengthsMonday, Nov. 15, 2010 PHYS 3446, Fall 2010 Andrew Brandt 5• What other forces?– Strong forceHolds nucleus together– Weak forceResponsible for nuclear beta decay– What are their ranges?• Very short– What does this imply?• Their force carriers are massive (especially true for weak force)• All four forces can act at the same time!!! Forces and Their Relative StrengthsMonday, Nov. 15, 2010 PHYS 3446, Fall 2010 Andrew Brandt 6• The strengths can be obtained from the potential • Considering two protons separated by a distance r:Magnitude of Coulomb and gravitational potential are– q: magnitude of the momentum transfer• What do you observe?– The absolute values of the potential E decreases quadratically with increasing momentum transfer– The relative strength is independent of momentum transfer Relative Strengths of Forces2EMeVrr2NgGmVrr22EMeVrq22NgGmVrqFourier x-form Fourier x-form EMgVV22NeGm25221NeccGmc39 23621 1 10~10137 6.71GeVGeVMonday, Nov. 15, 2010 PHYS 3446, Fall 2010 Andrew Brandt 7• Using Yukawa potential form, the magnitudes of strong and weak potential can be written as– gWand gs: coupling constants or effective charges– mWand m : masses of force mediators• The values of the coupling constants can be estimated from experimentsRelative StrengthsSVrFourier x-form Fourier x-form 215SgcSVrWVrWVr20.004Wgc2Sgr2m c rce2Sg2 2 2q m c2Wgr2Wm c rce2Wg2 2 2Wq m cMonday, Nov. 15, 2010 PHYS 3446, Fall 2010 Andrew Brandt 8• We could think of as the strong force mediator w/• From observations of beta decays, • However there still is an explicit dependence on momentum transfer– Since we are considering two protons, we can replace the momentum transfer, q, with the mass of protonsRelative Strengthsm280 /Wm GeV c2 2 2 41pq c m c GeV2140 /MeV cMonday, Nov. 15, 2010 PHYS 3446, Fall 2010 Andrew Brandt 9• The relative strength between the Strong and EM potentials is• And that between EM and weak potentials isRelative StrengthsSEMVVEMWVV315 137 1 2 10241180 1.2 10137 0.004222 2 2 2Sgcqce q m c2422 2 4 2 2pSpmcgcce m c m c2 2 2222WWq m ceccgq2 4 2 222 2 4pWWpm c m ceccg m cSWVV72.4 10Monday, Nov. 15, 2010 PHYS 3446, Fall 2010 Andrew Brandt 10• The ranges of forces also affect interaction time– Typical time for Strong interaction ~10-24sec• What is this?• A time that takes light to traverse the size of a proton (~1 fm)– Typical time for EM force ~10-20– 10-16sec– Typical time for Weak force ~10-13– 10-6sec• The forces have different characteristic energy scales, which are used along with their interaction type to classify elementary particlesInteraction TimeMonday, Nov. 15, 2010 PHYS 3446, Fall 2010 Andrew Brandt 11• Prior to the quark model, all known elementary particles were divided in four groups depending on the nature of their interactionsElementary ParticlesMonday, Nov. 15, 2010 PHYS 3446, Fall 2010 Andrew Brandt 12• How do these particles interact??– All particles, including photons and neutrinos, participate in gravitational interactions– Photons can interact electromagnetically with any particles with electric charge– All charged leptons participate in both EM and weak interactions– Neutral leptons do not have EM couplings– All hadrons (Mesons and baryons) responds to the strong force and appears to participate in all the interactionsElementary Particles13• Bosons– All have integer spin angular momentum– All mesons are bosons• Fermions– All have half-integer spin angular momentum– All leptons and baryons are fermions• All particles have anti-particles– What are anti-particles?• Particles that have same mass as the normal particle but with opposite quantum numbers– What is the anti-particle of • A 0?• A neutron?• A K0?• A Neutrino?• An electronBosons, Fermions, Particles and
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