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Navneet Krishnan, PhD student in the Department of Fundamental and Theoretical Physics. Photo: ANU Physics

Anomalous results in particle physics experiments could be a hint to the existence of another five Higgs bosons, calculations have shown.

In the sixties Peter Higgs predicted the existence of a scalar particle of the Higgs field, and estimated it would be very heavy: it took decades for a particle collider with sufficient energy to be developed – the Large Hadron Collider (LHC) – that could, by 2012, create a Higgs boson at the predicted mass of 126 GeV (about 200,000 times heavier than an electron).

But more was to come. In the late 2010s two different observations at the LHC hinted at a particle around 20 percent lighter than the Higgs boson. These lined up with an observation from the 1990s, at a predecessor to the LHC, the Large Electron-Positron Collider.

“Individually these observations were not important,” said Navneet Krishnan, PhD student in the Department of Fundamental and Theoretical Physics and co-author of a paper discussing  in Physical Review D.

“But together they're more interesting – there are three different decay routes that all amount to an energy of around 95 GeV.”

“So we decided to look at the models to see if any could give a plausible explanation.”

The current theoretical model for fundamental particles is the Standard Model. While it describes the 17 known particles, it has a number of shortcomings, such as an inability to explain why there is more matter than antimatter in the universe – that is, why we exist.

Navneet explored extensions to the Standard Model that involved creation of more Higgs bosons of different sizes. In fact, the Standard Model does already account for four Higgs bosons, (known as a doublet), three of which disappear due to interactions with other particles.

Other researchers had tried a model which adds a second doublet – totalling now eight Higgs bosons. However the calculated sizes did not match the new, comparatively light, observations, predicting pairs of bosons at much higher mass. So Navneet and collaborators added a ninth boson – a singlet – to the mix and turned the handle.

They found that two options of opposite parity existed, with the odd parity model fitting better. As with the existing Standard Model, three of the bosons have to disappear (their interactions give the W and Z bosons mass), which leaves six.

Apart from the known Higgs boson, of energy 126 GeV, and the new, unconfirmed particle at 96 GeV, the other four Higgs bosons would be of much higher energy

It’s possible particles that big could be created at the LHC; even if not, their decay pathways should contribute to the creation of smaller particles, which might amount to an observable signal, Navneet says.

“We might be able to spot it at the LHC. There is so much LHC data – it’s produced faster than we can analyse it.”

This article was first published by ANU Research School of Physics.