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Wednesday, August 16, 2006

Reading List: The Evidence for the Top Quark

Staley, Kent W. The Evidence for the Top Quark. Cambridge: Cambridge University Press, 2004. ISBN 0-521-82710-8.
A great deal of nonsense and intellectual nihilism has been committed in the name of “science studies”. Here, however, is an exemplary volume which shows not only how the process of scientific investigation should be studied, but also why. The work is based on the author's dissertation in philosophy, which explored the process leading to the September 1994 publication of the “Evidence for top quark production in pp collisions at √s = 1.8 TeV” paper in Physical Review D. This paper is a quintessential example of Big Science: more than four hundred authors, sixty pages of intricate argumentation from data produced by a detector weighing more than two thousand tons, and automated examination of millions and millions of collisions between protons and antiprotons accelerated to almost the speed of light by the Tevatron, all to search, over a period of months, for an elementary particle which cannot be observed in isolation, and finally reporting “evidence” for its existence (but not “discovery” or “observation”) based on a total of just twelve events “tagged” by three different algorithms, when a total of about 5.7 events would have been expected due to other causes (“background”) purely by chance alone.

Through extensive scrutiny of contemporary documents and interviews with participants in the collaboration which performed the experiment, the author provides a superb insight into how science on this scale is done, and the process by which the various kinds of expertise distributed throughout a large collaboration come together to arrive at the consensus they have found something worthy of publication. He explores the controversies about the paper both within the collaboration and subsequent to its publication, and evaluates claims that choices made by the experimenters may have a produced a bias in the results, and/or that choosing experimental “cuts” after having seen data from the detector might constitute “tuning on the signal”: physicist-speak for choosing the criteria for experimental success after having seen the results from the experiment, a violation of the “predesignation” principle usually assumed in statistical tests.

In the final two, more philosophical, chapters, the author introduces the concept of “Error-Statistical Evidence”, and evaluates the analysis in the “Evidence” paper in those terms, concluding that despite all the doubt and controversy, the decision making process was, in the end, ultimately objective. (And, of course, subsequent experimentation has shown the information reported in the Evidence paper to be have been essentially correct.)

Popular accounts of high energy physics sometimes gloss over the fantastically complicated and messy observations which go into a reported result to such an extent you might think experimenters are just waiting around looking at a screen waiting for a little ball to pop out with a “t” or whatever stencilled on the side. This book reveals the subtlety of the actual data from these experiments, and the intricate chain of reasoning from the multitudinous electronic signals issuing from a particle detector to the claim of having discovered a new particle. This is not, however, remotely a work of popularisation. While attempting to make the physics accessible to philosophers of science and the philosophy comprehensible to physicists, each will find the portions outside their own speciality tough going. A reader without a basic understanding of the standard model of particle physics and the principles of statistical hypothesis testing will probably end up bewildered and may not make it to the end, but those who do will be rewarded with a detailed understanding of high energy particle physics experiments and the operation of large collaborations of researchers which is difficult to obtain anywhere else.

Posted at August 16, 2006 18:00