Shedding light on the Higgs

The Higgs boson does not directly interact with photons, but creates pairs of them through loops of other particles—perhaps including particles that have yet to be observed.

In the Standard Model, the Higgs boson interacts with other particles in proportion to their mass, yet its decay into pairs of massless photons is one of the most interesting and important channels to study. Not only was this one of the main discovery channels for the Higgs boson candidate observed last July, but it may also be the key to understanding if this new particle fits into the Standard Model or is the first glimpse of new physics. A recent result from DZero contributes to the ongoing efforts to determine the nature of this newly observed boson.

Because photons are massless, the only way for a Higgs boson to decay into a pair of them is through an intermediate “virtual” loop of massive particles, like top quarks (see graphic). Particles that exist but have yet to be discovered could affect the decay rate, giving physicists an opportunity to probe for new physics. Some new models of physics predict a version of the Higgs boson that disfavors its decay into quarks and leptons, and enhances its decay rate into photons.

To optimize their sensitivity, DZero analyzers classified events based on the quality of the observed photons and created samples with different background compositions. An event classifier was developed for each sample, using ten different variables that characterize the event to separate Higgs boson events from the background.

The improved techniques used in this analysis led to a 40 percent gain in sensitivity over the previous result from DZero. No significant excess of events was observed, as expected in this case since this single channel is only marginally sensitive to the Standard Model Higgs boson. The analyzers also tested the model where the Higgs disfavors decaying to quarks and leptons, excluding the mass range 100-113 GeV. Because it encodes important information about the interactions the Higgs boson has with other particles, this improved analysis will make important contributions to the combined Higgs boson results from DZero and the Tevatron.

Mike Cooke

These physicists made major contributions to this analysis.
After Tevatron operations concluded, the DZero detector was reconfigured into an exhibition area. The exhibition area coordinators oversee the efforts to share this piece of particle physics history and present fun and educational tours to the public.