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Robert Kutschke | Fermilab | USA

View Blog | Read Bio

The Quantum Mechanical Short-cut Through the Woods

Is there a prize for being the last blogger on the new Quantum Diaries to get started? Do I win? If my former thesis adviser is lurking out there, he will tell all within earshot, with a Scottish accent, softened only a little by years in Toronto, “You expected him to be on time? Why would he start now?”

So what I am up to? Last fall I joined with a group of other scientists working to develop a new experiment, named Mu2e, that we propose to build at Fermilab, a High Energy Physics lab just outside of Chicago. Fermilab is, today, on the cusp of a great transition; for about the past 20 years Fermilab’s Tevatron storage ring has worn the crown of the world’s highest energy colliding beam accelerator, a crown that will soon pass to the Large Hadron Collider (LHC) at CERN. Many of us at Fermilab seek to reinvent the lab for the post-Tevatron era and I will tell you about my part of that effort. Some of the other bloggers will talk about their efforts; Dave Schmitz already has one post on his experiment.

Our quest, is to look for a very rare decay of an elementary particle named a muon. Why are we doing this? It’s the quantum mechanical equivalent of taking the short-cut through the woods to Grandma’s house. The enormous body of data acquired by high energy physicists over the past 50 or so years suggests that new subatomic particles lie at the brink of discovery. Why have we not yet seen them? The most likely answer is that their masses are too high. One way to look for high mass particles is to build the mother of all accelerators, one with a high enough energy to produce the new particles directly. That was, for many years, the role of the Tevatron and it will soon be the role of the LHC. Another way to look for these particles is to exploit quantum mechanics, which tells us that very massive particles can make small changes to processes that take place at much lower energies. The magic words are virtual particles and loop diagrams; I have no idea how to make those words mean anything without giving the whole course. The most powerful such search is to look for a process that is forbidden, or almost forbidden, by physics we already understand; in such a case any signal at all is the sign of something new. That is the quantum mechanical short-cut through the woods: if physics breaks the right way, we can compete with the largest, highest energy accelerators by making very careful measurements using tools we already have.

That’s not to say it will be easy. When we traded away the need for very high energies, we received, in return, the need for exquisite understanding of our backgrounds. More on that another day. And I will find some drawings to add.

And one final comment, a followup on what Chris Ruiz and Anadi Canepa had to say about Vancouver. I spent much of two summers working at TRIUMF, a lab on the campus of the university of British Columbia. I have yet to solve the following mystery: is Vancouver, running away, the coolest city on the planet or would I have thought the same of whichever city in which I happened to spend the summers that I was 21 and 22?

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