Illuminating the Z boson

DZero physicists looked for evidence of the Z boson directly emitting light, a process that is not part of the Standard Model.

According to the Standard Model, the Z boson lives its life in the dark. Lacking an electric charge, this weak force carrier is ignored by photons. Their only interactions are indirect, with their communication mediated by charged particles. They can only be produced at the same time if light is emitted by a charged particle that either helped make or was made by the Z boson.

But what if a Z boson could emit light, or a photon could emit a Z boson? While not part of the Standard Model, these interactions can be modeled and tested for by carefully studying events where both a Z boson and a high-energy photon are produced at the same time. This precision test of the Standard Model allows us to search for new physics in a generalized way, without needing to have a specific new theory in mind to perform the analysis.

Physicists at DZero have recently completed just such a detailed analysis of events with a photon and a Z boson. They started by making the most precise study of the production rate for these events by measuring it with respect to solitary Z boson production. This method improves the precision because a number of uncertainties in the measurement cancel out when using the ratio.

The analyzers went on to measure the production rate as a function of the properties of the photon and the Z boson plus photon system. Varying models of new physics would affect these distributions in different ways. Providing this full suite of measurements allows many theoretical models to be checked against the DZero data.

Finally, the analysis team searched for signs of the Z boson and photon directly interacting with each other. This would increase the production rate overall, but with a larger enhancement for events with the most momentum in the plane perpendicular to the Tevatron beams. With no signs of Z bosons interacting with photons, this analysis produced stringent limits on Z boson and photon couplings.

Mike Cooke

These physicists made major contributions to this analysis.
Thank you and happy holidays from all of us at DZero!