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Ken Bloom | USLHC | USA

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How do you know what is already known?

This blog post is not, not, not about the Higgs boson! Since, as Seth pointed out, there is nothing to say yet. What we do know, however, is that there will be a seminar at CERN on July 4 on the topic. The seminar is at 9 AM CERN time, which is 2 AM in Nebraska and 5 PM in Melbourne, when the ICHEP conference will be having its opening events. That’s where I’ll be that day, and I’m looking forward to watching the video stream with about six hundred of my closest friends in particle physics.

So instead of the Higgs, let’s talk about medieval literature. (Don’t run away yet!) My wife is a medievalist; she has done research on how medieval texts have been read and understood in different since then. Recently she was writing a book review on a new publication in this field, and she observed to me, “My own book is pretty heavily cited in Chapter 3.” That is, the author covered a lot of the same ground that she had already explored. But at least he knew about her work and cited it. Once, when she and I were at a conference of hers together, and one of her friends said over dinner that someone else had written his book — that is, someone else had really covered exactly the same ground, and didn’t even cite him!

This made me wonder — how exactly do we know what is already known in science? I don’t mean this in terms of knowing physical laws, but in knowing what sort of research has already taken place? Before you set out to do an experiment, how can you make sure that you are doing something that no one else has done before? If you are repeating someone else’s work (unknowingly, rather than to make an independent verification), that means that 1) the previous work didn’t get disseminated widely enough and 2) you are wasting your time, effort and money that could be directed at something more original.

I asked one of my colleagues who works in condensed matter physics about this issue, and she said that it can be a problem, but not as much as it used to be. Results in that discipline are published across a huge number of journals, some of which might be quite obscure. You would have to do an extensive literature search to make sure that you really knew what was out there, which could mean that you were very dependent on your university library to have access to all relevant information. However, this has changed thanks to improvements in information technology. Citation indexes have continued to improve, and online searches have made a huge difference in finding out what information is available.

Particle physics has actually been very far ahead of the curve on this, thanks to the hard working people in the Particle Data Group. The PDG’s history dates back to 1958, and since then they have been tracking pretty much every publication and measurement in particle physics. So as a particle physicist, I have never had to do a complicated literature search — I could always just consult the latest Review of Particle Properties (the 2012 edition has just been released) and find the current status of any measured quantity, not to mention the entire publication history behind it.

We should keep in mind that none of this comes for free — the PDG gets support from the US Department of Energy and National Science Foundation, who are also the sponsors of the US LHC blog. But why have we invested money in this data collection effort? I don’t know for sure but I will offer some speculations. I suspect that the original authors, led by Arthur Rosenfeld, didn’t know what they were getting into. At the time, there was a smaller number of particles to keep track of, but a sufficient amount that it seemed worthwhile to have their properties all written down in one place, especially since at that time there was no clear framework for their classification. As information in particle physics grew, collecting it surely became a much more daunting task, and it could not be done by a single person. But there is more to it than that — we like to believe that through successive measurements of a given physical quantity, we are making ever-better estimates of its true value. (Not that that is always so — one can find some interesting counterexamples.) The PDG also does the valuable work of making proper averages of all measurements to determine the most accurate values that can be obtained. The improved precision is needed to more throughly understand physical phenomena, and also to motivate future measurements. So I think that a lot of our rationale for a full accounting of all of the literature is related to our belief that we are really trying to get after something that is truly fundamental in our work.

Now, if there does turn out to be a Higgs boson, and if we do in fact manage to discover it shortly, then we will all be looking for the first “Higgs properties” section to appear in the PDG in 2014!

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