It’s Official: The LHC Didn’t Find A New Particle

It’s Official: The LHC Didn’t Find A New Particle

Well, shoot. It’s been confirmed that early hints of a possible exotic new particle at the Large Hadron Collider in Switzerland have vanished. That disappointing news was announced last night at a physics conference in Chicago.

Image: CERN

It all started last December, when physicists at two LHC collaborations announced that they’d found tantalising traces of an exotic particle not predicted by the Standard Model of particle physics — perhaps a heavier cousin of the Higgs boson, or the elusive graviton, a quantum carrier of the force of gravity. Neither group’s reported finding was solid enough to claim discovery, but both reported hints of a signal in exactly the same spot in the data. So at least it seemed promising, and if it held up, it would be a very big deal.

From the start, everyone cautioned that these kinds of signals usually go away as new data is added the mix, and physicists have been madly analysing the new data ever since. A few weeks ago, rumours surfaced that, indeed, the signal was fading. But most people were still waiting to see the official results at the International Conference on High Energy Physics (ICHEP 2016), which kicked off yesterday in Chicago.

It’s hard to keep even null results under wraps for long. The paper from the CMS collaboration was accidentally posted to the conference proceedings yesterday, and the news spread like wildfire among physicists on Facebook and Twitter. Matt Buckley, a physicist at Rutgers University, told Gizmodo he hadn’t known the results had been posted in error when he sent out this series of tweets:

And it wasn’t long before the inevitable blog post appeared (although technically the Resonaances blog spilled the beans back on July 29).

Now all the data is officially in and yes, the rumours were true: The signal has faded away. Check out the gory details in the graph from the CMS experiment below. The blue squiggles represent the original 2015 data with the tantalising hints. The red represents the new data, and the black is both combined.

It’s Official: The LHC Didn’t Find A New Particle

And here’s the corresponding data plot from the ATLAS collaboration:

It’s Official: The LHC Didn’t Find A New Particle

Here’s another look at the ATLAS findings. On the left is the new data; on the right, new and old combined:

It’s Official: The LHC Didn’t Find A New Particle

Obviously particle physicists are in mourning today. “The loss of the 750 GeV diphoton resonance is a big blow to the particle physics community,” Adam Falkowski, a particle physicist who blogs at Resonaances under the pseudonym Jester, wrote. “We are currently going through the five stages of grief, everyone at their own pace.”

Others responded with more of a world-weary shrug. “It happens. I’m certainly disappointed, but hardly surprised,” physicist Matt Strassler wrote on his blog. “Funny things happen with small amounts of data.”

As for Buckley, “There’s always a certain segment of the theory community who likes to sit on the ground and tell sad stories about the death of kings when we don’t find anything,” he said. “It’s always the end of physics, it’s always a disaster. But no one made a mistake. The analyses are fine, statistics screwed us over. Having it not be true — it sucks. But we’ll survive and move on. Everyone in the field gets a couple of these under their belt.”

Sigh. So particle physicists won’t be popping champagne corks in celebration this weekend after all. But there’s plenty more results from the LHC that will be trickling out between now and the end of the year. And hey — at least our old friend the Higgs boson popped up again in the data, twice as fast as it did during the LHC’s first run.


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