The bosons and the b’s

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Measuring how often a W boson and a bottom quark are produced together provides important constraints on models of the strong force.

Studies of the newly observed Higgs-like boson, measurements of the top quark and many searches for exotic physics cannot happen without first understanding the fundamental interactions that introduce certain naturally occurring background processes in the Standard Model: the bosons and the b‘s. The basic interactions that can create a W boson along with one or more bottom quarks are difficult to model, even though the process occurs with great frequency at hadron colliders. Calculations that involve the strong force are difficult to make in the Standard Model, so models that describe the interactions between quarks and other particles must be constrained by experiment. A recent result from DZero examines this particular production process, providing important input for further model development and a crucial cross-check of existing experimental results.

When a quark is produced after a high-energy collision, strong force interactions quickly turn it into a spray of particles, called a jet. The key to measuring how often W bosons are accompanied by bottom quarks is determining whether a jet is from a bottom quark in the first place. Most quarks turn into a jet immediately after being produced, but a bottom quark tends to form a composite particle that will travel about a millimeter before finally decaying and creating a jet. This small offset between the particles from a bottom-quark jet and the rest of the particles from a collision give analyzers the opportunity to identify bottom quarks. For this particular analysis, the analyzers built a special discriminant to separate events with a W boson and one or more bottom quark jets from those that include jets from lighter quarks.

The DZero analyzers measure a production rate that is consistent with that predicted by a number of existing theoretical models. Moreover, the 12 percent precision of this measurement will help significantly constrain these models, which have uncertainties of about 30 percent on their predictions. Improvements in modeling this process will allow for higher-precision measurements for many processes that include W bosons and bottom quark jets as a background.

Mike Cooke

These physicists made major contributions to this analysis.
The DZero Administrative Support Team plays an invaluable role in the organization and coordination of collaboration meetings, travel and special events.