Warped Passages - Lisa Randall [92]
With Mitch Golden, then a postdoc at Fermilab, I developed a more concise way to interpret experimental results about the weak interactions. Mitch and I showed how to systematically incorporate the effects of new heavy (as yet unseen) particles by adding only three new quantities to the Standard Model that would summarize all possible non-Standard Model contributions. I spent a few weeks trying to get it all straight, and the answers finally came together during one intense weekend of work. It was extremely rewarding to discover how all the processes that the Z-factories would measure could be elegantly related. Mitch and I felt we had developed a much clearer picture of how theory and measurements were related, and it was very satisfying. We were not alone in our discovery, however. Michael Peskin at SLAC and his postdoc Takeo Takeuchi did similar work concurrently, and others followed rapidly in our footsteps.
But the real success story concerns LEP tests of the Standard Model, which were incredibly precise. I won’t go into the details, but I will tell you two anecdotes that demonstrate their impressive sensitivity. The first is about finding the exact energy at which the positrons and electrons collided. The experimenters needed to know this energy to determine the precise value of the Z boson’s mass. They had to take into account everything that might affect the value of its energy. But even after they had accounted for everything they could think of, they noticed that the energy seemed to rise and fall slightly when they measured it at particular times. What was causing the variation?
Incredibly, it turned out to be tides in Lake Geneva. The level of the lake rose and fell with the tides and with the heavy rain that year. This in turn affected the nearby terrain, which slightly altered the distance over which the electrons and positrons traveled inside the collider. Once the tidal effect was factored in, the spurious time-dependent measurement of the mass of the Z went away.
The second anecdote is also quite impressive. Electrons and positrons in the collider are kept in place by strong magnetic fields, which in turn require a large amount of power. It seemed that, periodically, the electrons and positrons would become slightly misaligned, indicating some variation in the collider’s magnetic fields. A worker on the site observed that this variation correlated well with passages of the TGV, the express train that travels between Geneva and Paris. Apparently, there were power spikes associated with the French DC current that slightly disrupted the accelerator. Alain Blondel, a Parisian physicist working at CERN, told me the funniest part of this story. The experimenters had a real opportunity to absolutely confirm this hypothesis. Given that many of the TGV staff are French, there was inevitably a strike, so the experimenters were treated to a spike-free day!
What to Remember
The most important experimental tool for studying particle physics is the high-energy particle accelerator. High-energy colliders are particle accelerators that smash together particles; if they have enough energy, colliders produce particles that are otherwise too massive to exist in the world around us.
The Tevatron is the highest-energy collider currently in operation.
The Large Hadron Collider (LHC) in Switzerland, which will have about seven times the Tevatron’s energy and which will be built within a decade, will test many particle physics models.
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Symmetry: The Essential Organizing Principle
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Simple Minds
Athena uncaged three