1 / 10

Physics 32: Elementary Particles

Physics 32: Elementary Particles. Christopher Chui. High-Energy Particles-1. Matter-wave: de Broglie wavelength, l = h/(mv) Van de Graaff generator and accelerator produce 30 MeV to accelerate particles. A source of H or He ions is accelerated towards the target

hadassah-duke
Download Presentation

Physics 32: Elementary Particles

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Physics 32: Elementary Particles Christopher Chui Physics 32: Elementary Particles - Christopher Chui

  2. High-Energy Particles-1 • Matter-wave: de Broglie wavelength, l = h/(mv) • Van de Graaff generator and accelerator produce 30 MeV to accelerate particles. A source of H or He ions is accelerated towards the target • Cyclotron uses a magnetic field to maintain charged ions, usually protons, in circular paths • Force due to magnetic field = qvB = ma = mv2/r • Period T = distance/speed = 2 pr/(qBr/m) = 2 pm/qB • A modified cyclotron (synchrocyclotron) allows complex electronics to decrease the frequency as the protons increases in speed to reach larger orbits Physics 32: Elementary Particles - Christopher Chui

  3. High-Energy Particles-2 • Synchrotron increases the magnetic field B as the particles speed up. Machines in Fermilab and CERN accelerate protons to energies of 500 GeV • Tevatron at Fermilab uses superconducting magnets to accelerate protons to 1000 GeV = 1 TeV • Synchrotron radiation causes energy loss • Linear accelerators accelerate electrons to 50 GeV • Colliding beams allow two beams of particles to collide head-on using storage rings up to 186 GeV Physics 32: Elementary Particles - Christopher Chui

  4. Yukawa Particle • In 1935 Yukawa predicted the existence of a new particle (meson) to mediate the strong nuclear force • For EM force between two particles, photons are exchanged to give rise to a force • Feynman diagram shows a photon acting as the carrier of the EM force between two electrons • Strong nuclear force = mc2 ~ hc/(2pd) • In 1947 meson was discovered in p+, p-, and p0 • Reactions: p+pp+p+ p0 andp+pp+n+ p+ • Particles presumed to transmit weak force: W+, W-, and Z0 were detected in 1983 • The quantum of gravitational force, graviton, has not been found Physics 32: Elementary Particles - Christopher Chui

  5. Four Forces in Nature • TYPE Relative Strength Field Particle • Strong nuclear 1 Gluons • Electromagnetic 10-2 Photon • Weak nuclear 10-6 W+, W-, Z0 • Gravitational 10-38 Graviton (?) Physics 32: Elementary Particles - Christopher Chui

  6. Stable Particles under Strong Decay • Category Name Symbol Antiparticle Spin Lifetime • Leptons electrons e- e+ ½ stable neutrino e nene’ ½ stable muons m-m+ ½ 2.2x10-6 neutrino mnmnm’ ½ stable tau t-t+ ½ 2.9X10-13 neutrino tntnt’ ½ stable • Hadrons(mesons) pion p+p- 0 2.6x10-8 kaon p 0 self 0 0.84x10-16 eta h0 self 0 5x10-19 • Baryons proton p p’ ½ stable neutron n n’ ½ 887 • G-bosons Photon g Self 1 stable W W+ W- 1 3x10-25 Z Z0 self 1 3x10-25 Physics 32: Elementary Particles - Christopher Chui

  7. Stability, Resonance, and Strange • Lifetime depends on which force is acting • Very short-lived particles are inferred from their decay products • Resonance refers to a large peak in the KE of particle bombardment, such as the D “particle” • Strange particles refer to reactions having twice as long half-lives as would be expected • Strangeness is conserved in strong interactions but not in weak Physics 32: Elementary Particles - Christopher Chui

  8. Quarks and Antiquarks • Proton = 2 ups + 1 down = 2/3 e +2/3 e – 1/3 e • Neutron = 1 up + 2 downs = 2/3 e – 1/3 e – 1/3 e • Meson pion = 1 u + 1 antidown= 2/3 e + 1/3 e • Antipion = 1 antiup + 1 down = -2/3 e – 1/3 e • Antikaon = 1 antiup + 1 strange= -2/3e –1/3e • Charmed quark has +2/3 e and C=1 • Top and bottom quarks are 3rd generation quarks • Electrons, protons, and neutrons are fermions (1/2 spin) for structure of matter; all others are called bosons (integer spin) for carriers of forces Physics 32: Elementary Particles - Christopher Chui

  9. QCD, and Electroweak Theory • Quarks have 6 flavors: u, d, s, c, b, t • Quarks might have color charge • Strong force between quarks is color force • QCD is the force that acts between color charges • Strong force between 2 hadrons is a force between the quarks are called gluons • Color force increases with increasing distance! • When 2 quarks approach each other, the force between them becomes very small—asymptotic freedom • Gauge theory attempts to unify the weak and electromagnetic interactions, which are seen as 2 diff manifestations of a single electroweak interaction Physics 32: Elementary Particles - Christopher Chui

  10. GUT • GUT attempts to unify electroweak theory into QCD • On a scale of 10-30 m, the EM, weak, and strong forces appear to work on 1 class of particle—leptons and quarks; baryons and lepton numbers would not be conserved • Lepton could become a quark through X bosons with a mass of 1014 GeV/c2 or 1014 times heavier than a proton • String theory attempts to unify all 4 forces of nature into a single theory • When supersymmetry is appliedsuperstring theory • Superstring theory predicts fermions would change into bosons, and all quarks have squark partners, and all leptons have slepton partners; bosonsphotinos and gluions. All these have not been detected yet Physics 32: Elementary Particles - Christopher Chui

More Related