PHYS 3446 Lecture 21 Monday Nov 27 2006 Dr Jae Yu 1 The Standard Model Quarks and Leptons Gauge Bosons Symmetry Breaking and the Higgs particle Higgs Search Strategy Issues in the Standard Model Neutrino Oscillations Monday Nov 27 2006 PHYS 3446 Fall 2006 Jae Yu 1 Announcements 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 presentations Monday Nov 27 2006 PHYS 3446 Fall 2006 Jae Yu 2 Presentation Schedule Monday Dec 4 1 2 3 4 5 6 Wednesday Dec 6 1 2 3 4 5 Monday Nov 27 2006 Shane Daniel Heather Justin Cassie Layne Pierce Jessica James Matt Lauren PHYS 3446 Fall 2006 Jae Yu 3 Time Reversal Invert time from t t Tur t t uu r r Tur r r uu r r r Tur mr p mr uu r r r r L r p uu Tur r r p r r r r p r p L How about Newton s equation of2 motion r 2r 2r r r C d r C d r 2 d r Tur m 1 2 m 2 F 2 r m 2 F 2 r uu dt r dt dt r Invariant under time reversal Monday Nov 27 2006 PHYS 3446 Fall 2006 Jae Yu 4 Charge Conjugate Conversion of charge from Q Q Cur Q Q uu r r q q E c 2 r uu Cur c 2 r E rr r r r r ds r ds r B cI Cur c I B uu 2 2 r r Under this operation particles become antiparticles What happens to the Newton s equation of motion 2r 2r 2 r r d r C d r q 2 Cur m 2 2 1 r F m 2 F 2 r uu dt r dt r Invariant under charge conjugate Monday Nov 27 2006 PHYS 3446 Fall 2006 Jae Yu 5 The 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 properties Monday Nov 27 2006 PHYS 3446 Fall 2006 Jae Yu 6 The 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 structure Monday Nov 27 2006 PHYS 3446 Fall 2006 Jae Yu 7 The 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 pointlike 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 q 2 provides opportunities to probe shorter distances breaking apart nucleons The fact that the form factor for inelastic scattering at large q 2 is independent of q2 shows 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 2006 8 Jae Yu The 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 particles Monday Nov 27 2006 PHYS 3446 Fall 2006 Jae Yu 9 Quarks and Leptons In SM there are three families of leptons ne e nt t 0 1 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 u d nm m Q c s t b Q 2 3 1 3 All these fundamental particles are fermions w spin Monday Nov 27 2006 PHYS 3446 Fall 2006 Jae Yu 1 h 2 10 Standard Model Elementary Particle Table Assumes the following fundamental structure Total of 6 quarks 6 leptons and 12 force mediators form the entire universe Monday Nov 27 2006 PHYS 3446 Fall 2006 Jae Yu 11 Quark 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 mesons K us p ud p ud K us 1 uu dd p 2 K 0 ds 0 Monday Nov 27 2006 K 0 ds PHYS 3446 Fall 2006 Jae Yu 12 Quark Content of Baryons Baryon spins are measured to be integer Quark compositions of some baryons 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 Nucleons Strange baryons s 1 s 2 Other Baryons 0 0 uds L D uuu uss p uud X S uus X dss n udd S0 uds S dds Since baryons have B 1 the quarks must have baryon number 1 3 Monday Nov 27 2006 PHYS 3446 Fall 2006 Jae Yu 13 Need 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 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 under exchange of any two of them This is incompatible to Pauli s exclusion principle What does this mean Quark parton model cannot describe the state So should we give up Monday Nov 27 2006 PHYS 3446 Fall 2006 Jae Yu 14 Need for Color Quantum Number Since the quark parton model works so well with other baryons and mesons …
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