09part1 - P461 - particles I 1 all fundamental with no...

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Unformatted text preview: P461 - particles I 1 all fundamental with no underlying structure Leptons+quarks spin while photon, W, Z, gluons spin 1 No QM theory for gravity Higher generations have larger mass P461 - particles I 2 When/where discovered Mostly Europe 1895-1920 Roentgen (sort of)1901 W/Z CERN 1983 Rubbia/vanderMeer1984 gluon DESY 1979 NO electron Europe 1895-1905 Thomson 1906 muon Harvard 1937 No tau SLAC 1975 Perl 1995 e US 1953 Reines/Cowan 1995 BNL 1962 Schwartz/Lederman/Steinberger 1988 FNAL 2000 NO u,d SLAC 1960s Friedman/Kendall/Taylor 1990 s mostly US 1950s NO c SLAC/BNL 1974 Richter/Ting 1976 b FNAL 1978 NO (Lederman) t FNAL 1995 NO muon Street+Stevenson had evidence but Piccione often gets credit in the 1940s as measured lifetime Nobel Prize? P461 - particles I 3 Couplings and Charges All charged particles interact electromagnetically All particles except gamma and gluon interact weakly (have nonzero weak charge) (partially semantics on photon as mixing defined in this way) A WWZ vertex exists Only quarks and gluons interact strongly; have non-zero strong charge (called color). This has been tested by: magnetic moment electron and muon H energy levels (Lamb shift) muonic atoms. Substitute muon for electron pi-mu atoms EM charge just electric charge q Weak charge weak isospin in i=1/2 doublets used for charged (W) and have I3-Aq for neutral current (Z) Strong charge color charge triplet red green blue P461 - particles I 4 Pi-mu coupling ) ( ) ( anomalies no K atom L + = + P461 - particles I 5 Strong Force and Hadrons p + p -> p + N* N* are excited states of proton or neutron (all of which are baryons) P = uud n = udd (bound by gluons) where u = up quark (charge 2/3) and d = down quark (charge -1/3) About 20 N states spin mass 938 2700 MeV About 20 states spin 3/2 Charges = uuu(2) uud(1) udd(0) ddd(-1) N, decay by strong interaction N b p/n + with lifetimes of 10-23 sec (pion is quark-antiquark meson). Identify by looking at the invariant mass and other kinematic distributions u d d d u u d u + ) ( 2 1 P461 - particles I 6 ISOSPIN Assume the strong force is ~identical between baryons (p,n,N*) and between three pions Introduce concept of Isospin with (p,n) forming an isopsin doublet I=1/2 and pions in an isopsin triplet I=1, and quarks (u,d) in a I=1/2 doublet Isospin isnt spin but has the same group algebra SU(2) as spin and so same quantum numbers and addition rules p n doublet and and I I I I pp pn np pn np nn Z z = = = + 1 2 1 2 2 2 3 1 1 1 1 1 1 2 1 2 1 2 1 2 / / ( ) ( ) P461 - particles I 7 Baryons and Mesons 3 quark combinations (like uud) are called baryons. Historically first understood for u,d,s quarks...
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This note was uploaded on 10/02/2009 for the course PHYS 460 taught by Professor Johnson,c during the Spring '08 term at Northern Illinois University.

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09part1 - P461 - particles I 1 all fundamental with no...

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