Do boson interactions break the rules?

Do photons and W and Z bosons interact with each other by the specific rules dictated by the Standard Model, or does their behavior indicate something unexpected?

The Standard Model dictates very specific rules that govern the way the photon (γ) and W and Z bosons interact with each other. In the Standard Model, the neutral photon and Z boson do not directly interact, but the charged W bosons can interact with each other or with the photon or the Z boson. Studying processes that include interactions between these force carriers gives physicists an opportunity to test whether the bosons are behaving by the Standard Model rules or cheating, like poker players passing cards beneath the table.

The interactions between photons and W and Z bosons can be modeled in a very general way by listing all of the possible couplings that could exist between those particles. The Standard Model predicts specific values for each of these triple boson couplings, but new physics could cause them to be something different. Measuring these couplings tests fundamental aspects of the Standard Model and places constraints on what new models of physics are possible.

At the Tevatron, triple boson couplings can be probed by WW, WZ or Wγ production. DZero scientists recently performed a comprehensive study of triple boson couplings, providing new limits for some channels and combining previous results from others across all three of these production modes. They provided new limits for events where either WW or WZ was produced and decayed into a lepton, neutrino and two jets and for events where a WZ was produced and decayed into three leptons and a neutrino. These results were combined with previous studies of WW and Wγ production to produce the most stringent limits on triple boson couplings from a hadron collider to date. No deviation from the predicted values was observed, so none of these players have been caught cheating under the Standard Model rules—at least for now!

—Mike Cooke

These physicists made major contributions to this analysis.
The offline-support team is responsible for providing the smooth and reliable storage and retrieval of data that is critical to performing physics analyses at DZero.