Elementary Particle Physics From Theory to Experiment
Carlos Wagner Physics Department, EFI and KICP, Univ. of Chicago HEP Division, Argonne National Laboratory
Society of Physics Students, Univ. of Chicago, Nov. 10, 2014 Particle Physics studies the smallest pieces of matter,
1 1/10.000 1/100.000 1/100.000.000
and their interactions.
Friday, November 2, 2012 Forces and Particles in Nature Gravitational Force Electromagnetic Force
Attractive force between 2 massive objects: Attracts particles of opposite charge
k e e F = 1 2 d2
1 G = 2 MPl Forces within atoms and between atoms Proportional to productStrong of masses Force + and - charges bind together Assumes interaction over a distance d and screen each other
==> comes from properties of spaceAtoms and timeare made fromElectrons protons, interact with protons via quantum neutrons and electrons. Strong nuclear forceof binds e.m. energy together : the photons protons and neutrons to form atoms nuclei Strong nuclear force binds! togethers! =1 m! = 0 protons and neutrons to form nuclei
protonD. I. S. of uuelectronsd formedwith Modeled protons by threeor by neutrons a theoryquarks, based bound on together Is very weak unless one ofneutron theat masses high energies is huge,udd shows by thatthe U(1)gluons gauge of thesymmetry strong interactions like the earth protons and neutrons SU (3) c are not fundamental
Friday,p November! u u d 2, 2012 formed by three quarks, bound together by n ! u d d the gluons of the strong interactions
Modeled by a theory based on SU ( 3 ) C gauge symmetry we see no free quarks Very strong at large distances confinement " in nature
! Weak Force Force Mediating particle transformations Observation of Beta decay demands a novel interaction
Weak Force Short range forces exist only inside the protons 2 and neutrons, with massive force carriers:
gauge bosons ! W and Z " MW d FW ! e / d Similar transformations explain the non-observation of heavier elementary particles in our everyday experience.
Modeled by SU (2)L gauge symmetry
assignsFriday, November 2 2, 2012isospin & u # &) L # charges ± 1 ''( $ ! $ ! 2 $d ! , $ e ! % "L % "L
Explains nuclear fusion in the Sun! and ultimately, Sunlight and ultimately, Sunlight Standard Model Particles
There are 12 fundamental gauge fields: But very di erent masses! 8 gluons, 3 Wµ’s and Bµ m3/m2 and m2/m1 a few tens or hundreds and 3 gauge couplings g1, g2, g3 3 mµ m me = 0.5 10 GeV, m 200, m 20 The matter fields: e µ 3 families of quarks and leptons with same Largest hierarchies 5 quantum numbers under gauge groups mt 175 GeV mt/me 10 ⇥ 9 neutrino masses smaller than as 10 GeV!
Only left handed fermions transform under the weak SM gauge group Lectures onSSupUe(3)rsymmetrSy U(2)L U(1)Y Carlos E.M. Wagner, Argonne and EFI Fermion