Scientists put their heads together over the unbearable lightness of the Higgs mass

University of Maryland’s Raman Sundrum leads a discussion at the recent Nature Guiding Theory workshop. Photo: Joe Lykken

A confounding conundrum that has been needling particle physicists for decades was thrust to the fore when the Higgs boson discovery was announced in July 2012: The mass of the Higgs is absurdly low. Why?

Taken alone, the Higgs mass is expected to be 1019 GeV. That’s a 10 followed by 19 zeros. But something — some unknown behavior — must be locking in the Higgs mass at 125 GeV. According to the known laws of physics, it is no more natural that the Higgs weigh as little as 125 GeV than an ice cube remain at 0 degrees Celsius on a hot day or that a pencil stand alone on its tip for hours on end.

That there must be something else out there holding the Higgs in place is known as the naturalness principle. This has driven many of the new physics searches at the Large Hadron Collider, which have so far yielded null results.

At last month’s Nature Guiding Theory workshop, the first of its kind, more than 70 scientists hailing from across the United States, as well as from Europe and Asia, gathered at Fermilab to debate possible solutions to the massive problem.

“There were some radical ideas, but maybe radical is the order of the day,” said workshop co-organizer Prateek Agrawal of Fermilab. “Rotten tomatoes were brought up at every talk, but none were thrown. It was lively and well received.”

The ideas were necessarily far-reaching to be able to account for such a chasm between expectation and data.

Over the last few decades, scientists have published numerous schemes to balance the book on the Higgs mass. Extra dimensions might do it. So might supersymmetry, the idea that every known particle has a massive superpartner, or compositeness, the idea that particles thought to have no component parts might actually be divisible into smaller pieces after all. None of these have yet been found.

“We’re digging in the far-out nooks and crannies,” Agrawal said.

The workshop, funded by the URA Visiting Scholars program and supported by Fermilab’s Theory Group, gave scientists an opportunity to hash it all out, comparing their ideas against the data from the LHC experiments.

“Everybody approached this issue with a new sense of humility. We’re stuck in self-questioning and confusion,” said Fermilab’s Felix Yu, workshop co-organizer. “We want to know what the data is saying about this principle and whether it’s a good way of moving forward in this field.”

He added, “Being in this era — when it’s possible we have to upend decades of really foundational ways of thinking about this problem — is scary and exciting.”

Leah Hesla