Particle Physics, quarks, and all that  updated October 3, 2005  D. Carrigan carrigan@fnal.gov (subject line must be sensible)

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standard model

The "Periodic Table" of elementary particles: The Standard Model

Many of the elementary particles and force carriers of nature have been discovered during the first part of our one hundred years. These particles include the quarks proposed by Gell-Mann and neutrinos first seen by Reines and Cowan with later contributions by Lederman, Schwartz, and Steinberger. Important discoveries at  Brookhaven National Laboratory, the Stanford Linear Accelerator Center, and Fermilab have shown that there are three generation of quarks and leptons. CERN discovered the W and Z, the enormously heavy intermediate bosons.

This complex set of particles and force carriers was forged into the Standard Model by many theorists including Glashow, Salam, and Weinberg.  This theory describes the famous link between the electric forces familiar from every day life and the weak forces of radioactivity. The addition of gluons (g) to the mix explains the forces that hold the atomic nucleus together.

A partial list of some of these discoveries is given at worldwide discoveries.

This simple table embodies nearly all the particle physics we see today at even the most powerful accelerators such as the Fermilab Tevatron. (A quick guide to the table appears at Standard Model.)

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The future for particle physics

The Standard Model explains much of what we know but there are many, many open questions. Understanding and answering these questions is the job of current and future accelerators and experimental and theoretical physicists. Theorists such as Chris Quigg on the left build models that extend physics beyond the standard model. In a 2004 lecture at Fermilab (slides and video) Quigg outlined many of these questions. For example Quigg asks are quarks and leptons elementary? What is the relationship of quarks to leptons? Are there new quarks and leptons? Are there new gauge interactions linking quarks and leptons? What is the nature of the new force that hides electroweak symmetry? Are there different kinds of matter? (Of energy?) Are there new forces of a novel kind? What do generations mean? What makes a top quark a top quark and an electron an electron? What is the (grand) unifying symmetry? ... These questions will probably challenge us for the next forty years and beyond. They could continue to have important implications for cosmology and links to the other great pillars of science.