Monday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu1PHYS 3446 – Lecture #21Monday, Nov. 27, 2006Dr. Jae Yu1. The Standard Model Quarks and LeptonsGauge BosonsSymmetry Breaking and the Higgs particleHiggs Search StrategyIssues in the Standard ModelNeutrino OscillationsMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu2• Workshop on Saturday, Dec. 2– 10am – 5pm– CPB 303 and other HEP areas• Write up due: Before the class Wednesday, Dec. 6• Remember to send me your talk slides sufficiently before the class on the day of your presentation• Will spend some time with Dr. Young-Kee Kim on Dec. 6, after your presentationsAnnouncementsMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu3• Monday, Dec. 4:1. Shane2. Daniel3. Heather4. Justin5. Cassie6. Layne• Wednesday, Dec. 6:1. Pierce2. Jessica3. James4. Matt5. LaurenPresentation ScheduleMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu4• Invert time from t Æ -t .• How about Newton’s equation of motion?– Invariant under time reversalTime ReversalrGpmr=GG T JJJGrG T JJJGmr p−=−GGLrp=×GGGt T JJJGt−222ˆdr CmFrdt r==GG()22222 2ˆ1dr dr CmmFrdt dt r−===GGG T JJJG T JJJG()()rprpL×−=−×=−GGGGGMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu5• Conversion of charge from Q Æ -Q .• Under this operation, particles become antiparticles• What happens to the Newton’s equation of motion?– Invariant under charge conjugateCharge Conjugate2ˆqEcrr=G C JJJG2ˆqcrEr−=−GQ C JJJGQ−222ˆdr CmFrdt r==GG()22222ˆ1dr qmrFdt r=− =GG C JJJG2ˆds rBcIr×=∫GG C JJJG()2ˆds rcI Br×−=−∫GGMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu6The Standard Model of Particle Physics• Prior to 70’s, low mass hadrons are thought to be the fundamental constituents of matter, despite some new particles that seemed to have new flavors– Even lightest hadrons, protons and neutrons, show some indication of substructure• Such as magnetic moment of the neutron – Raised questions whether they really are fundamental particles• In 1964 Gell-Mann and Zweig suggested independently that hadrons can be understood as composite of quark constituents– Recall that the quantum number assignments, such as strangeness,were only theoretical tools rather than real particle propertiesMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu7The Standard Model of Particle Physics• In late 60’s, Jerome Friedman, Henry Kendall and Rich Taylor designed an experiment with electron beam scattering off of hadrons and deuterium at SLAC (Stanford Linear Accelerator Center) – Data could be easily understood if protons and neutrons are composed of point-like objects with charges -1/3e and +2/3e.– A point-like electrons scattering off of point-like quark partons inside the nucleons and hadrons• Corresponds to modern day Rutherford scattering• Higher energies of the incident electrons could break apart the target particles, revealing the internal structureMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu8The Standard Model of Particle Physics• Elastic scatterings at high energies can be described well with the elastic form factors measured at low energies, why?– Since the interaction is elastic, particles behave as if they are point-like objects• Inelastic scatterings cannot be described well w/ elastic form factors since the target is broken apart– Inelastic scatterings of electrons with large momentum transfer (q2) provides opportunities to probe shorter distances, breaking apart nucleons– The fact that the form factor for inelastic scattering at large q2is independent of q2shows that there are point-like object in a nucleon• Bjorken scaling• Nucleons contain both quarks and glue particles (gluons) both described by individual characteristic momentum distributions (Parton Distribution Functions)Monday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu9The Standard Model of Particle Physics• By early 70’s, it was clear that hadrons (baryons and mesons) are not fundamental point-like objects• But leptons did not show any evidence of internal structure– Even at high energies they still do not show any structure– Can be regarded as elementary particles• The phenomenological understanding along with observation from electron scattering (Deep Inelastic Scattering, DIS) and the quark model• Resulted in the Standard Model that can describe three of the four known forces along with quarks, leptons and gauge bosons as the fundamental particlesMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu10Quarks and Leptons• In SM, there are three families of leptons– Î Increasing order of lepton masses– Convention used in strong isospin symmetry, higher member of multiplet carries higher electrical charge• And three families of quark constituents• All these fundamental particles are fermions w/ spin eeν−⎛⎞⎜⎟⎜⎟⎝⎠µνµ−⎛⎞⎜⎟⎜⎟⎝⎠τντ−⎛⎞⎜⎟⎜⎟⎝⎠ud⎛⎞⎜⎟⎝⎠cs⎛⎞⎜⎟⎝⎠tb⎛⎞⎜⎟⎝⎠+2/3-1/3Q12=0-1QMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu11Standard Model Elementary Particle Table• Assumes the following fundamental structure:• Total of 6 quarks, 6 leptons and 12 force mediators form the entire universeMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu12Quark Content of Mesons• Meson spins are measured to be integer. – They must consist of an even number of quarks – They can be described as bound states of quarks• Quark compositions of some mesons– Pions Strange mesonsπ+=π−=0π=udud()12uu dd−K+=K−=0K =0K =ususdsdsMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu13Quark Content of Baryons• Baryon spins are measured to be ½ integer. – They must consist of an odd number of quarks – They can be described as bound states of three quarks based on the studies of their properties• Quark compositions of some baryons– Nucleons Strange baryons Other Baryons– s=1 s=2• Since baryons have B=1, the quarks must have baryon number 1/3p =n =uududd0Λ=+Σ=0Σ=−Σ=udsuusudsdds0Ξ=−Ξ=ussdss++∆=uuuMonday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu14Need for Color Quantum Number• The baryon ∆++has an interesting characteristics– Its charge is +2, and spin is 3/2– Can consists of three u quarks Î These quarks in the ground state can have parallel spins to give ∆++3/2 spin– A trouble!! What is the trouble?• The three u-quarks are identical fermions and would be symmetric
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