Counting jets to constrain physics models

The number of jets that appear in an event at DZero can reveal important information about the strong force.

Take a look at any given proton-antiproton collision recorded at DZero and you’re likely to spot a jet, but not the kind you’d find at an air show.

When a quark or a gluon is produced in a high-energy collision, it will turn into a spray of particles, called a jet, due to interactions with the strong force. This is the same force that binds quarks into protons, neutrons and many more exotic particles. By carefully counting the number of times that at least two jets were seen in DZero events and comparing that to the number of times that at least three jets were seen, we are able to better constrain models of the strong force by directly answering the question, “How often does a quark emit a gluon?”

It is difficult to calculate predictions of what jets might appear after a collision directly from the Standard Model. Instead, we use experimental data to constrain models of these interactions. One complication is that the proton itself is a bundle of quarks and gluons, and jet production is sensitive to the fraction of momentum that each of the proton’s pieces carries. Studying the ratio of the three-or-more jet production rate to the two-or-more jet production rate allows the strong force to be probed while minimizing the impact of the inner workings of the colliding proton and antiproton.

A recent analysis at DZero studies this ratio of jet production rates and compares them to the predictions from the latest theoretical models. The ratio is determined as a function of the largest-momentum jet, and the analysis is repeated for various cutoff values for the lowest-momentum jet. While no deviation was observed from the theoretical prediction, this result places important constraints on the way jets are modeled, which will be important to further our understanding of the strong force.

Mike Cooke

These physicists made major contributions to this analysis.
These physicists are the main administrators for the DZero Linux cluster, a crucial component of the DZero computing infrastructure that facilitates data analysis.