iSGTW Feature - Higgs search at Tevatron

Feature - Friendly but fierce competition for the Higgs

This diagram plots the limit (at 95% confidence level) of Higgs production (y-axis) for different possible Higgs masses (x-axis). Each mark along the y-axis is a multiple of the Standard Model rate of Higgs production, and this rate is shown as a straight line at "1." The more data Fermilab scientists collect, the closer their observed limits will get to the Standard Model rate.

Notice that the "observed" line comes vertically closest to 1, the Standard Model rate, at 160 on the x-axis. Fermilab physicists have amassed nearly enough data to make a statement about whether the Higgs exists at the mass value 160 GeV/c2.

Image courtesy of the Tevatron New Phenomena & Higgs Working Group on behalf of CDF and D0

The two Tevatron experiments at Fermilab, CDF and D0, have nearly ruled out the hoped-for mass value for the Higgs boson-the particle regarded by some as one of the last big mysteries of the universe. Its discovery could help explain dark matter, dark energy and why particles have mass.

Against a tradition of friendly rivalry, the Higgs search provides sufficient motivation for these competitors to combine their analyses. Teams from each experiment run simulations on the Open Science Grid and compare their models to actual data. The process of combining results is a significant analysis in itself. The scientists must account for the unique uncertainties in each component of their different detectors.

"You don't want one group to say they've discovered the Higgs and, using the same data, the other group to say it's background," says CDF physicist Tom Junk. "That would be embarrassing."

Sharing hard-earned data requires trust.

"We spend almost the entire year dug down in our trenches, staring across at each other," says D0's Wade Fisher. "Now we're giving them our data, saying, 'Here, open up the hood and poke around the engine a bit'."

Through their combined efforts, the joint CDF/D0 collaboration has amassed enough data to state with 90% certainty-and likely 95% by year's end-that the Higgs does not have a mass of 160 GeV/c2.

That may seem a funny way to state a result, but it gets to the heart of the matter. The Large Hadron Collider, CERN's massive new accelerator, will be seven times more powerful than the Tevatron. Its Higgs "sweet spot," however, sits at 160 GeV/c2. If the Higgs isn't there, the CERN experiments will have to work harder to find it.

Members of the Higgs combination team. Gregorio Bernardi (D0, top left); Tom Junk; Mark Kruse (CDF, right); Wei-Ming Yao (CDF, bottom left).

Click on image to see clockwise from top left: Gregorio Bernardi (D0); Tom Junk (CDF), Mark Kruse (CDF), Matt Herndon (CDF); Nils Krumnack (CDF); Wade Fisher (D0); Wei-Ming Yao (CDF).

Image courtesy of the D0 and CDF collaborations.

Meanwhile, the Tevatron physicists will continue to accumulate and process data.

"Two years ago, we didn't appear to have much chance of finding the Higgs," said CDF's Mark Kruse. "The use of Open Science Grid resources has enabled us to run more simulated samples, and larger ones, which in turn has enabled us to exploit the data in increasingly sophisticated ways. I think people are starting to believe we have a realistic shot at the Higgs."

-Jennifer Lauren Lee, Fermilab