New anomaly at the LHC

Has new ghost particle manifested at the Large Hadron Collider?, The Guardian, October 31:

Scientists at the Cern nuclear physics lab near Geneva are investigating whether a bizarre and unexpected new particle popped into existence during experiments at the Large Hadron Collider. Researchers on the machine’s multipurpose Compact Muon Solenoid (CMS) detector have spotted curious bumps in their data that may be the calling card of an unknown particle that has more than twice the mass of a carbon atom.

The prospect of such a mysterious particle has baffled physicists as much as it has excited them. At the moment, none of their favoured theories of reality include the particle, though many theorists are now hard at work on models that do. “I’d say theorists are excited and experimentalists are very sceptical,” said Alexandre Nikitenko, a theorist on the CMS team who worked on the data. “As a physicist I must be very critical, but as the author of this analysis I must have some optimism too.”

Senior scientists at the lab have scheduled a talk this Thursday at which Nikitenko and his colleague Yotam Soreq will discuss the work. They will describe how they spotted the bumps in CMS data while searching for evidence of a lighter cousin of the Higgs boson, the elusive particle that was discovered at the LHC in 2012.

This announcement – of a possibly new particle weighing about 28 GeV – is reminiscent of the 750 GeV affair. In late 2015, physicists spotted an anomalous bump in data collected by the LHC that suggested the existence of a previously unknown particle weighing about 67-times as much as the carbon atom. The data wasn’t qualitatively good enough for physicists to claim that they had evidence of a new particle, so they decided to get more.

This was December. By August next year (2016), before the new data was out, theoretical physicists had written and published over 500 papers on the arXiv preprint server on what the new particle could be and how theoretical models could have to be changed to make room for it. But at the 38th International Conference on High-Energy Physics, LHC scientists unveiled the new data said that the anomalous bump in the data had vanished and that what physicists had seen earlier was likely a random fluctuation in lower quality observations.

The new announcement of a 28 GeV particle seems set for a similar course of action. I’m not pronouncing that no new particle will be found – that’s for physicists to determine – but only writing in defence of those who would cover this event even though it seems relatively minor and like history’s repeating itself. Anomalies like these are worth writing about because of the Standard Model of particle physics, which has been historically so good at making predictions about particles’ properties that even small deviations from it are big news.

At the same time, it’s big news in a specific context with a specific caveat: that we might be chasing an ambulance here. For example, The Guardian only says that the anomalous signal will have to be verified by other experiments, leaving out the part where the signal that LHC scientists already have is pretty weak (4.2σ and 2.9σ (both local as opposed to global) in two tests in the 8 TeV data and 2.0σ and 1.4σ deficit in the 13 TeV data). It also doesn’t mention the 750 GeV affair even though the two narratives already appear to be congruent.

If journalists leave such details out, I’ve a feeling they’re going to give their readers the impression that this announcement is more significant than it actually is. (Call me a nitpicker but I’m sure being accurate will allow engaged readers to set reasonable expectations about what to expect in the story’s next chapter as well as keep them from becoming desensitised to journalistic hype.)

Those who’ve been following physics news will be aware of the ‘nightmare scenario’ assailing particle physics, and in this context there’s value in writing about what’s keeping particle physicists occupied – especially in their largest, most promising lab.

But thanks to the 750 GeV affair, most recently, we also know that what any scientist or journalist says or does right now is moot until LHC scientists present sounder data + confirmation of a positive/negative result. And journalists writing up these episodes without a caveat that properly contextualises where a new anomaly rests on the arc of a particle’s discovery will be disingenuous if they’re going to justify their coverage based on the argument that the outcome “could be” positive.

The outcome could be negative and we need to ensure the reader remembers that. Including the caveat is also a way to do that without completely obviating the space for a story itself.

Featured image: The CMS detector, the largest of the five detectors that straddle the LHC, and which spotted the anomalous signal corresponding at a particle at the 28 GeV mark. Credit: CERN.