Shifting Standards: Experiments in Particle Physics in the Twentieth Century
Allan Franklin
On July 4, 2012 the CMS and ATLAS collaborations at the Large Hadron Collider jointly announced the discovery of a new elementary particle, which resembled the Higgs boson, the last remaining undiscovered piece of the Standard Model of elementary particles. Both groups claimed to have observed a five-standard-deviation (five sigmas) effect above background, the gold standard for discovery in high-energy physics. In the Prologue to this book Franklin examines how this standard has changed from the early 1960s, when no such standard existed, to three, four, and finally five sigmas, the present standard. The body of the book also examines other changes in both the practice of experimental particle physics and in the reporting of their results. The discussion includes changes in the size and complexity of experimental apparatuses, the rates at which data can be produced, recorded, and analyzed, the size of the data sets, and the development of electronic and computational resources. Other issues discussed include the distinction between exclusion and selection of data, the appreciation and treatment of possible experimenter bias, recognition of “bad” data, changes in the writing style of papers and in the description of experimental apparatuses, and the progressive idealization of those apparatuses.
The issues are discussed by examining, in some detail, experimental papers on particle physics, which appeared at seven to ten year intervals in the twentieth century in Physical Review, the archival journal of the American Physical Society. These papers include some of the famous experiments of the twentieth century, including Robert Millikan’s measurement of the charge of the electron and the discovery of the neutrino by Frederick Reines, Clyde Cowan, and their collaborators. Other experiments are less well known. All of these experiments provided snapshots of experimental practice at various times in the twentieth century.