Trade.Information

Relying on the buddy system.

The "buddy system" has been used for years as a way to keep children from wandering off. Staying close to a friend greatly reduces the chances of getting lost. Tevatron physicists are hoping they can also rely on this principle to find a particle that has eluded discovery for more than forty years: the Higgs boson.

Scientists currently believe a Higgs boson should have a relatively low mass, low enough that the Tevatron experiments could have a chance at observing it if it exists. However, at low masses, the Higgs prefers to decay to two bottom quarks. With this signature, the Higgs would likely be lost among the enormous background of similar events. But the Higgs could be produced along with a very distinctive friend: the W boson. By searching for these two buddies produced together, physicists have a better chance of catching a glimpse of the Higgs. The decay of the W boson to a lepton and neutrino provides a useful means to weed out many of the background events. Through a processes called "b-tagging," physicists can separate bottom quarks from lighter quarks with high efficiency and purity. The simultaneous observation of a lepton (electron or muon), missing transverse energy (signature of a neutrino) and two bottom quarks provides a less crowded landscape to search for a Higgs.

Physicists from the DZero experiment have searched for a Higgs boson accompanied by a W boson in one inverse femtobarn of data, and observed no evidence for signal. This result allows them to set the Tevatron's best limit on the rate of Higgs production in this channel at 1.1 to 1.4 picobarns, for Higgs masses from 105 to 145 GeV/c2. This limit is a factor of 10.6 from the Standard Model cross section prediction at a Higgs mass of 115 GeV/c2. By adding advanced search techniques like those used to find evidence for single top quark production (see the Result of the Week in the December 13, 2006 issue of Fermilab Today), DZero plans to push this limit even lower. By combining these results with additional search channels, DZero can further eliminate hiding places for the Higgs (new results to be announced tomorrow at the FNAL Wine & Cheese seminar). Hopefully, if we are successful in relying on the buddy system, the Higgs will never be lost again.

In pictures:
1.The ratio of 95% CL limits to the expected Standard Model cross section for associated W-boson plus Higgs production at the Tevatron.
2.The likelihood discriminant used in the Matrix Element search for associated W-boson plus Higgs production.
3.The good performance of the Level-3 trigger / Data Acquisition system at the DZero experiment ensures data is efficiently recorded for use in all analyses. L3/DAQ experts include: (front row, left to right) Yunhe Xie, Tulika Bose (Brown University), Thomas Gadfort, Aran Garcia-Bellido (University of Washington); and (back row) Andy Haas (Columbia Univesity). Not pictured: Gordon Watts (University of Washington) and Dave Cutts (Brown University).