by STEVEN WEINBERG
The July 4 announcement that the “Higgs boson” had been discovered at the CERN laboratory in Geneva made news around the world. Why all the fuss? New discoveries of elementary particles have been made from time to time without attracting all this attention. It is often said that this particle provides the crucial clue to how all the other elementary particles get their masses. True enough, but this takes some explanation.
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Since the early 1960s it has been known that it is possible for symmetries to be exact properties of the equations of a theory and yet not respected by observable physical quantities, like the values of particle masses. The consequences of such symmetry breaking were worked out in 1964 by Robert Brout and François Englert; by Peter Higgs; and by Gerald Guralnik, Carl Hagen and Tom Kibble, for a general class of theories that contain force-carrying particles, like the photon.
In 1967-8 the late Abdus Salam and I independently used this mathematics in formulating a specific theory, the modern unified theory of weak and electromagnetic forces that became part of the Standard Model. This theory predicted the masses of the W and Z particles, which were verified when these particles were discovered at CERN in 1983-84.
But just what is it that breaks the electroweak symmetry and thereby gives elementary particles their masses?
Salam and I assumed that the culprit is what are called scalar fields, which pervade all space. This is like what happens in a magnet: Even though the equations describing iron atoms don’t distinguish one direction in space from another, any magnetic field produced by the atoms will point in just one way. The symmetry-breaking fields in the Standard Model do not mark out directions in space — instead, they distinguish the weak from the electromagnetic forces, and give elementary particles their masses. Just as a magnetic field appears in iron when it cools and solidifies, these scalar fields appeared as the early universe expanded and cooled.
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For instance, the new particle was produced at CERN in collisions of protons that occur at a rate of over a hundred million collisions per second. To analyze the flood of data produced by all these collisions requires real time computing of unmatched power. Also, before the protons collide, they are accelerated to an energy over 3,000 times larger than the energy contained in their own masses while they go many times around a 27-kilometer circular tunnel. To keep them in their tracks requires enormously strong superconducting magnets, cooled by the world’s largest source of liquid helium. In previous work at CERN, elementary particle physicists developed a method of sharing data that has become the World Wide Web.
The New York Times for more
via Symmetry