CERN

A physicist has a new hypothesis to explain the LHC's mysterious results

Not just one new particle...

FIONA MACDONALD
29 JUL 2016
 

Since March, physicists around the world have been getting cautiously excited about a series of strange flashes of energy detected by CERN's Large Hadron Collider (LHC).

Nothing is verified, but the results suggest that we're on the verge of finding the first particle outside the standard model of physics - the best set of equations we currently have to explain how the Universe works.

 

We're still waiting for more evidence from the LHC's latest run, but this new particle is generally predicted to be a subatomic particle with a mass six times heavier than the legendary Higgs boson. 

But a physicist from the University of Kansas has presented a slightly different hypothesis to explain the strange LHC results - known as the 750 GeV (giga-electron volts) excess.

Instead of just one new particle, he thinks we might have actually detected several of them.

The 750 GeV excess was announced at a conference in Italy in March. The result came about thanks to physicists smashing together protons with the LHC - something they do over and over again in order to find evidence of new subatomic particles in the debris of the collision.

Usually the standard model equations can explain the energy levels of the subatomic particles that splinter off from these collisions, even if we've never directly observed them before.

But, last year, a range of experiments at the CMS and ATLAS detectors picked up more high-energy photons (particles of light) than our current understanding of physics predicts.

 

Specifically, both experiments detected a spike at one particular energy level: 750 Gev, or 750 billion electron volts.

Further evidence is needed before researchers can say for sure what the strange signals were, but one of the leading explanations is that it could be a brand-new particle, one that is similar to the Higgs boson but around six times heavier.

This is based on the idea that the particle is what's called a "resonance" particle, which has a mass that triggers the 750 GeV signal.

"Every explanation of the 750 GeV excess needs a new particle," said physicist Kyoungchul Kong from the University of Kansas. "Most models assume one around 750 GeV."

But he's come up with a slightly different explanation. 

His hypothesis is that, instead of one new particle with a mass that triggers 750 GeV, the results could instead suggest the existence of a series of other, heavier particles, which decay into photons that are able to fake the signal at 750 GeV.

"The lifetime and mass of the particle could reveal something else beyond simply one extra particle, if it turns out to be a real signal," said Kong. "Yet we do not claim this as a discovery, and we need more data."

After the LHC excess was announced, the journal Physical Review Letters was flooded with submissions to explain the anomaly, but only four were published - including Kong's hypothesis.

That means that we're still a long way from knowing exactly what's going on here - if anything is happening at all. The signal could still turn out to be an artefact. 

Statistically speaking, the ATLAS data had around a 1-in-93 chance of being a fluke, which on its own wouldn't really be enough to bother presenting to the scientific community - researchers generally look for the 5-sigma standard, which means a 1-in-3.5 million odds of it being an accidental result.

But the fact that the CMS experiment picked up the same spike makes the results much more likely, and worthy of attention.

Still, we have very little information by which to explain these results just yet. Thankfully, an update on the excess will be presented next week at the annual International Conference on High Energy Physics in Chicago (alongside several lectures on physics "Beyond the Standard Model").

Until then, Kong admits that his explanation is only as good as anyone else's, but he put it out there simply to offer a different hypothesis to test and push the boundaries of our understanding.

"We explore ideas," said Kong about theoretical physicists. "Probably most of [the] ideas are wrong - but we learn from them, and we propose better ideas."

So for now, we wait. But if any of the hypotheses presented about this LHC excess turn out to be true, it's going to be a pretty huge deal.

And even if they don't, it'll still tell us a lot about physics, and could change our understanding of how the world works forever. 

"If this thing turns out to be real, it’s a 10 on the Richter scale of particle physics," physicist John Ellis from King’s College London - the former head of theory at CERN - who wasn't involved in the study, told The Guardian back in March.

"One’s excitometer gets totally broken."

We can't wait for next week.

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