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Massive Bosons


Predictions

Massive bosons seemed to get the electroweak theory into mathematical trouble, until 1971 when Gerard ‘t Hooft proved that it could make sensible predictions: a particle could change its identity by emitting a W+ or W- boson, or remain unchanged by emitting a neutral Z.

No Z events – called neutral currents – had ever been seen. Sheldon Glashow, John Illiopoulos and Luciano Maiani suggested that some would be suppressed because of an undiscovered quark. This was not universally accepted until Sam Ting and Burt Richter independently discovered the ‘charm’ quark in 1974, earning the 1976 Nobel physics prize.

But some neutral currents were not suppressed. Where were they?

Breakthrough

A major breakthrough came in 1973. At CERN, André Lagarrigue and his colleagues found evidence for neutral currents in Gargamelle bubble chamber pictures.

Intense beams of neutrinos and antineutrinos were fired through the liquid-filled chamber. Very infrequently a neutrino (or antineutrino) interacted with a particle and in some cases it survived. This proof that neutral currents existed was a triumph for theory and experiment.

Ideas

The idea of W and Z bosons weighing 80 GeV and 90 GeV respectively was not easily accepted. Could such massive elementary particles really exist? The ultimate proof would be to create them. How could enough energy be found?

Head-on collisions release much more energy than firing a particle into a stationary target. So Carlo Rubbia suggested turning an existing proton accelerator into a proton-antiproton collider.

The high energy Super Proton Synchrotron (SPS) at CERN had been running for only 2 years, but Rubbia convinced CERN’s Management that such a dramatic change of direction was a risk worth taking. In June 1978, the collider project got the go-ahead.

Next: Stochastic Cooling
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