MIT Physics News Spotlight
How Do Eminent Physicists Tackle the Higgs Boson?
Robert Garisto, New York Times
In 2005, at a festive midsummer night’s banquet at Uppsala Castle in Sweden, I chose a seat across the table from two of the world’s leading experts on particle physics: the theorist Frank Wilczek, the previous year’s winner of the Nobel Prize in Physics, and Janet Conrad, a leading experimentalist.
As the northern sun lingered late into the evening, they talked animatedly about the origin of mass. And that conversation led to a bet about an elusive, long-sought, much theorized particle, with me as the bet’s keeper.
Now, with the Large Hadron Collider up and running at a lab outside Geneva, we may be close to settling that bet.
The Standard Model of particle physics, which has passed one test after another, rests on the beautiful idea that the forces of nature arise out of symmetries, which imply certain similarities between particles. But particles actually differ, notably by having different masses. So one of these symmetries must be “broken.”
In the Standard Model, particles have symmetry-breaking interactions with a kind of pervasive molasses called the Higgs field that imparts mass to them. The stronger the interaction, the heavier the particle.
So, Dr. Wilczek argued that night, when two particles at the L.H.C. collide at almost the speed of light, they will occasionally create a detectable excitation in the molasses — a particle that is to the Higgs field what a tsunami is to the ocean. That particle, so far undiscovered, would be the Higgs boson.
Dr. Conrad grinned. “What if the L.H.C. doesn’t find the Higgs?” she asked playfully.
Dr. Wilczek, whom I’ve never seen without a smile, was unperturbed. As twilight deepened and candelabras cast flickering shadows on the walls, he noted that precision experiments on other particles had shown that the Higgs boson has a mass that falls well within reach of the Large Hadron Collider.
He talked about the various unresolved problems of the Standard Model, and the hypothetical theory called supersymmetry, which connects particles of matter, called fermions, with particles that carry forces, called bosons.
Conversations around us grew louder as the wine flowed. Many theorists thought supersymmetry had the most compelling answers to those unresolved problems, and most supersymmetric models predicted the Higgs mass to be in the narrow range of 115 to 130 GeV (a giga-electron-volt is a unit of energy or mass; 1 GeV is a bit more than a proton’s mass).
Thus a compelling argument could be made that the Higgs had to exist, that the L.H.C. would find it, and that its mass would lie in a narrow range.
Dr. Conrad knew all this, of course, but she was enjoying the intellectual fencing match. She argued simply that experiments could disprove a compelling theoretical argument.
So they made a bet. And since Dr. Wilczek had a compelling theoretical argument on his side, he was happy to give her odds of 10 to 1. If the L.H.C. finds the Higgs boson with a mass below 150 GeV, he wins 10 Nobel chocolate coins (the pinnacle of Hanukkah gelt); if not, Dr. Conrad wins 100.
Because I’m an editor for the journal that published the original paper by Peter Higgs in 1964, as well as some of the two contestants’ most important papers, they decided to make me the bet’s adjudicator.
Since then, the Large Hadron Collider has been completed and has performed an extensive array of tests of the Standard Model. And it began to search for the Higgs boson, supersymmetric particles and other hypothetical particles.
Over the summer, the collider’s first substantial cache of data had few hints of anything new, and it was able to rule out almost the entire mass range for the Standard Model Higgs boson above 145 GeV. Some news articles speculated that the Higgs might not be found after all. So should Dr. Wilczek be worried?
No, not yet. The L.H.C. has simply confirmed that the Higgs isn’t where we thought it wasn’t. The favored mass window is still open. And if the Higgs is even slightly nonstandard, almost none of its mass range has yet been ruled out.
But the batch of data being analyzed right now should search some of the favored mass region, and all of it should be examined by the end of 2012. So the bet is likely to be resolved soon.
If Dr. Conrad wins, theorists will be scrambling for alternatives. Either way, experiment will have the last word — followed by the chocolate course.
Robert Garisto is a theoretical physicist and an editor of the journal Physical Review Letters.