Subatomic cubic zirconia

In a search for diamonds, one has to learn to how to remove the rest of the gems. Some, like the opal and freshwater pearl are easy to remove from the pile, since they look quite different. However, eventually you are left with gems that are indistinguishable from diamonds and you need to know just how many fakes there are. If the number of predicted fakes is 10 and you have 20 gems, you know you have some diamonds.

Nowadays the Tevatron is focused on searching for the very rare. These rare things often have a distinct signature in our detectors that allow us to identify them. The problem is that more common processes can sometimes mimic the signature of the collisions for which we’re searching, just as cubic zirconia can mimic diamonds. Given that the common processes can occur millions of times more often than the stuff we’re looking for, a tiny fraction of the common things can mimic the rare things and hide the real signature.

Physicists spend an awful lot of their time inventing selection criteria that allows them to keep the desired collisions (signal) and throw away the undesired look-alike stuff (background). However, there comes a point where the remaining background looks so much like signal that the selection criteria can’t remove one without also removing the other. We call this type of remaining background the irreducible background.

If you can’t further reduce the background, the next best thing is to know precisely how many background events to expect. If physics calculations predict that the background should contain 100 collisions with specific characteristics, and you see 150, those extra 50 events could be the sign of a discovery.

The most pressing new physics pursued by DZero is the search for the Higgs boson. One popular technique is to look for collisions in which a Higgs boson is produced at the same time as a W boson. The Higgs boson then decays into two bottom quarks, which produce jets of particles. Events with a W boson and two jets are a great place to start looking for Higgs bosons.

However, events with W bosons and jets are much more commonly produced by more ordinary mechanisms. A precise understanding of the simultaneous production of W bosons and jets by ordinary mechanisms is a crucial step in searching for the Higgs boson. Today’s analysis is a very careful study of these kinds of background events and represents a considerable improvement over earlier studies. In addition to helping with Higgs searches, this measurement is interesting in its own right as a study of collisions involving both the strong and weak nuclear forces. Physicists can also use it to understand the background in searches for other rare phenomena.

Don Lincoln

These physicists performed this analysis.
Modern physics analyses hinge on being able to generate many millions of simulated events to investigate how sensitive the analysis is to small variations in the data selection techniques. These physicists are responsible for submitting the computer jobs that generate these simulated events.