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Robert Kutschke | Fermilab | USA

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How do you know when to Stop?

Monday, April 27th, 2009

I’m back. Some family matters came up unexpectedly. There was no way to keep all of the balls in the air at the same time so I had to decide which ones to drop. This was one of them.

For me, the hardest part about science is knowing when to stop, particularly when working on a paper that will be the last in series. One of the experiments I work on is the FOCUS experiment, which finished data taking about a decade ago and is just now finishing its last few papers.

For a little over one year now I have been chairing an internal review committee for a paper being written by a group of my colleagues on FOCUS. This is the way that high energy physics collaborations ensure quality control: a group of people who were not actively involved in a particular piece of work but who are experts in that sort of work in general or in related fields, are asked to review what has been done, offer suggestions for improvements and ultimately to say that the work passes the standards that the collaboration has set for itself. Only after passing this internal review will the paper be reviewed by the full collaboration and only after a vote of the full collaboration will the paper be sent to a journal.

During the course of an internal review it is normal that new ideas on how to improve the work are suggested. Some of these will be a small amount of work and of obvious benefit; these will be done. Others will be a large amount of work and of uncertain benefit; these are usually not done. But many ideas will be in the middle, the toughest sort being an idea that has a clear benefit but which will require a large amount of work or, perhaps, an unknown amount of work. Some ideas look simple at first but eventually lead to redoing a major part of the work.

So this is the hardest part. There are some good ideas that, in the end, just won’t be done. How do you know when to stop? Last week we decided to stop.

If all goes well, FOCUS will submit our 57th physics paper. Look for it on the arXiv.org server in 2 or 3 weeks.


Two things today

Thursday, April 2nd, 2009

In my opening post on Quantum Diaries I talked in very fuzzy terms about a new experiment at Fermilab, Mu2e.  We now have a real web site: http://mu2e.fnal.gov .  Have a look; the site is far from complete but I hope it’s enough to whet your appetites.  

Yesterday’s colloquium was both scientifically exciting and really fun to watch.  The speaker was Isabelle Grenier, from CEA/Paris VII, talking about early results from the satellite observatory formerly known as GLAST, now known as the Fermi Gamma-ray Space Telescope.  Their name has nothing to do with Fermilab, save that we both celebrate the accomplishments of Enrico Fermi. 

Their instrument has a much smaller point spread function than did its predecessors, which allows the identification of point sources that previously could not be resolved.  Morevover they cover the whole sky every 3 hours, which allows them to catch many transient effects.   They will have a lot of fun exploiting the power of this new instrument. I wish them every success and am looking forward to seeing many exciting results in the coming years.

Fermilab makes videos of all colloquia and each video usually shows up on the lab web site a few weeks after the colloquium was given: 


I highly recommend this one.


The Quantum Mechanical Short-cut Through the Woods

Tuesday, March 31st, 2009

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?