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1506 Chapter 33 | Particle Physics
Figure 33.25 In the Tevatron accelerator at Fermilab, protons and antiprotons collide at high energies, and some of those collisions could result in the production of a Higgs boson in association with a W boson. When the W boson decays to a high-energy lepton and a neutrino, the detector triggers on the lepton, whether it is an electron or a muon. (credit: D. J. Miller)
Summary
• Attempts to show unification of the four forces are called Grand Unified Theories (GUTs) and have been partially successful, with connections proven between EM and weak forces in electroweak theory.
• The strong force is carried by eight proposed particles called gluons, which are intimately connected to a quantum number called color—their governing theory is thus called quantum chromodynamics (QCD). Taken together, QCD and the electroweak theory are widely accepted as the Standard Model of particle physics.
• Unification of the strong force is expected at such high energies that it cannot be directly tested, but it may have observable consequences in the as-yet unobserved decay of the proton and topics to be discussed in the next chapter. Although unification of forces is generally anticipated, much remains to be done to prove its validity.
Glossary
baryon number: a conserved physical quantity that is zero for mesons and leptons and for baryons and antibaryons, respectively
baryons: hadrons that always decay to another baryon
boson: particle with zero or an integer value of intrinsic spin
bottom: a quark flavor
charm: a quark flavor, which is the counterpart of the strange quark
colliding beams: head-on collisions between particles moving in opposite directions
color: a quark flavor
conservation of total baryon number: a general rule based on the observation that the total number of nucleons was always conserved in nuclear reactions and decays
conservation of total electron family number: a general rule stating that the total electron family number stays the same through an interaction
conservation of total muon family number: a general rule stating that the total muon family number stays the same through an interaction
cyclotron: accelerator that uses fixed-frequency alternating electric fields and fixed magnets to accelerate particles in a circular spiral path
down: the second-lightest of all quarks
electron family number: the number that is assigned to all members of the electron family, or the number 0 that is
assigned to all particles not in the electron family
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