Hint Of Crack In Standard Model Vanishes In Lhc Data

[ScienceNoob]

https://www.nature.com/articles/d41586-022-04545-z

I have no idea what this is about but it was Nature's top story. But i couldn't find it anywhere else so I was wondering if was even important?

[jim360]

The problem with posting this story is that I reckon, and I think I can say this without fear of contradiction, that there's precisely one person on AB who'd be able to say much about this, and they're writing this comment right now.

I'm not sure how much I can add to the explanation of what's going on beyond what the article said, although I'll have a go if you want to ask something more specific. I'm more interested in the fact that, outside the article you posted, this hasn't been picked up on at all from what I can see. And this despite, for example, these articles from last year:

https://www.bbc.co.uk/news/science-environment-56491033

https://www.theguardian.com/science/2021/mar/23/large-hadron-collider-scientists-particle-physics

https://www.thetimes.co.uk/article/cerns-naughty-quarks-chip-away-at-standard-physics-8n8m6chd7 ( https://archive.ph/vdqoo for non-paywall link)

and so on. In case it isn't clear immediately, all of these ar etalking about precisely the same thing, but an earlier (and, it turns out, flawed) measurement that made things look like the Standard Model (the basic theory of particle physics) wasn't working. The article you link to shows that it *is* working -- or, at least, that it isn't as obviously broken as it appeared.

It's perhaps typical of scientific journalism to focus on sensational discoveries, or possibilities of such discoveries, rather than the mundane story of "scientists make measurement that fits with what they were expecting actually". I'm reminded of another article, admittedly a relatively small one, from a few years back:

https://www.nature.com/articles/s41567-018-0325-3

In essence, the point is that, like radioactivity, particles in physics decay with some regularity -- the "half-life". And we'd like to predict this, and then also measure it. And for this particular particle, the old measurement was four times shorter than the newer measurements, but the old measurement was more in agreement with old predictions. And the new measurement was not. And this caused some concern amongst physicists, albeit relatively small group of them. But a new theoretical computation ( https://link.springer.com/article/10.1007/JHEP07(2022)058 ) shows that there isn't a problem after all, and the new experimental results are indeed "compatible" with the theory prediction. I have to say, looking at that paper, it would be a mistake to see it as definitive, partly because the uncertainties in the theory prediction are so large and partly because I think they've played a little fast and loose with what to do for some of the pieces of the calculation, but setting all that aside the point is that the "anomaly" gets attention, and the resolution very little.

This is human nature, of course: the unexpected is invariably more interesting. But an unfortunate side-effect is that popular science attention is almost always focused on the overly sensational, or on apparent problems -- the "scientists are baffled about [X]" story, in other words. But when it turns out that scientists understood it after all, or the problem goes away, rarely do people notice.

More to come...

[jim360]

As to this particular story: it *is* pretty important. Some measure of how important it is comes from the fact that the first paper on this measurement from the same experiment, in 2014, has already well over 1,200 citations across the last eight years or so, (see link below):

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.151601

I myself cited it twice, while a few people I know personally have cited it as many as 30 times. There was almost an entire industry about improving the ability to take this measurement (and a few other, related, anomalies) and find some way of explaining it with some "new physics". Those people will, presumably, be scratching their heads about what to make of it.

No doubt they'll turn to a few other muon-related anomalies from the last decade or so. Although, my personal bet is that many of those will end up disappearing too in the coming years. For my part, I was never invested enough in trying to explain these things for my career to be much affected by learning that the last however many years of my life have been spent trying to explain something that was in the event an experimental error.

But, those personal stories aside, it *is* a problem. Our best theory of particle physics is manifestly incomplete. And this (and a few other flukes) was our current best hint for where to look next in order to fix it. Physicists will be happy in a way to go back to the drawing board, but without a clear sign of where to look, and with so many variously attractive options from a mathematical point of view, it might be some time before they work out what the most promising line of research is in light of this result.

All hope isn't lost even here, though. As I understand the new paper, the experimentalists have repaired their analysis of systematic errors, but the result is still not exactly in agreement with theory. More data, and so less random uncertainty, might make the disagreement reappear again. Science is a never-ending process.