To conclude the series of postings on technical aspects of the Large Hadron Collider, tonight we will look at how physicists interpret the information they receive in their particle detectors.
The Science Museum (UK) has an online interactive activity called "The Hunt for Higgs," which uses the example of a Higgs boson, a particle many physicists expect to be found at the LHC. In this demonstration activity, viewers click on the animated image of a detector and are taken through the steps that would be involved in identifying a potential Higgs particle.
An important concept illustrated by the demonstration exercise is that massive particles -- such as the Higgs -- can be very short-lived, and can thus be detected only by the presence in the detector of combinations of other, lighter particles. As the demonstration indicates, however, the combinations are only ones physicists think might be the "signatures" of a Higgs.
The discovery of the top quark -- the heaviest of the quarks -- in 1995 serves as an excellent case study in how the existence of a highly tranient particle was inferred. According to the linked Wikipedia page on the top quark, "The Standard Model predicts its lifetime to be roughly 1×10 [to the]−25 [power] seconds...", which would be .0000000000000000000000001 of a second.
This Fermilab information page on the discovery of the top quark and the process of confirming its existence, is very useful. In particular, the two following headings on the Fermlab page are worth clicking on, for further detail: "Is it a top quark? The signature of a top event" and "How do we know when we've found the top quark?"
For all of the hype and expense of the LHC, it is important to note that it is not expected to offer the ultimate in detector clarity. Texas A&M University physicist Teruki Kamon, whom I once saw give a talk at Texas Tech, has a slide in some of his PowerPoint presentations that uses a photographic analogy to demonstrate the upgrades in information (quantity and quality) that will be available as researchers move from Fermilab's Tevatron to the LHC to the proposed International Linear Collider (ILC).
If you go to this slide show and then scroll down to page 3, you'll see a sequence of three depictions of the same picture (a girl jumping in the air, with her shadow showing below). At the Tevatron, according to this analogy, only perhaps the bottom one-fifth of the picture would be observable, and with a very fuzzy appearance, at that. At the LHC, the full picture would be available, but would still be fuzzy. Only at the ILC would the picture be both fully available and sharp.
The next set of LHC-related postings will discuss new types of particles and other phenomena that scientists hope to find.