W boson mass measurement limits Higgs hiding space

Improving the precision of the W boson mass measurement allows physicists to tighten the indirect constraints on the mass of the Higgs boson.

As the race to discover or exclude the Higgs boson nears the finish line, a new precision measurement of the W boson’s mass tightens the constraints on where the Higgs boson could be found. The Standard Model does not predict the mass of the W boson or the Higgs boson, but it does predict a specific relationship between those masses and the values of other experimental observables. This relationship can be used to indirectly constrain the mass of the Higgs boson. The precision measurements of the top quark and W boson masses are the most influential inputs to this constraint from the Tevatron.

Measuring the W boson mass to less than three parts in 10,000 requires a thorough understanding of the DZero detector. This analysis exclusively uses events where the W boson decayed into an electron and a neutrino. The identification and measurement of each of those decay products relies heavily on DZero’s calorimeter. The analysis team based the calorimeter energy response on a similar signal that doesn’t include neutrinos – the decay of a Z boson to two electrons. Then they carefully accounted for the impact of multiple proton-antiproton interactions during the same beam crossing and other effects that might influence the precision of the measurement.

Combining this new DZero measurement with the latest result from CDF improves the indirect Higgs boson mass constraints, which are based on precision measurements of related Standard Model observables. The new indirect constraints favor a Higgs boson mass of 94 GeV/c2 but allow for a range of compatible masses. The constraints leave less than a one in 20 chance that the mass is higher than 152 GeV/c2. The allowed range is compatible with the excess seen in the Tevatron Higgs boson search between 115 GeV/c2 and 135 GeV/c2. This W boson mass measurement uses just over half of the full Run II data set and will improve when the remaining data is included. The final measurement will become a legacy result of the Tevatron and play an important role in precision tests of the Standard Model for years to come.

—Mike Cooke

These physicists made major contributions to this analysis.

The missing transverse energy group (top row) and electron identification group (bottom row) refine and certify the definitions of neutrino and electron candidates, respectively, for the DZero collaboration. Their efforts help all analyses that use electrons and neutrinos, including the analysis above.