New force in nature?

Anyone have any insight into this? I’m delighted to see a new result - but I don’t know enough about the field to see any further than what the article says. Anyone? @Chronos ?@Asympotically_fat ?

" There is currently a one in a 40,000 chance that the result could be a statistical fluke - equating to a statistical level of confidence described as 4.1 sigma.

A level of 5 sigma, or a one in 3.5 million chance of the observation being a coincidence, is needed to claim a discovery.

Prof Mark Lancaster, who is the UK lead for the experiment, told BBC News: “We have found the interaction of muons are not in agreement with the Standard Model [the current widely-accepted theory to explain how the building blocks of the Universe behave].”

The University of Manchester researcher added: “Clearly, this is very exciting because it potentially points to a future with new laws of physics, new particles and a new force which we have not seen to date.”"

This is the first I’ve heard of this, but a few general comments:

First, any confidence level quoted is assuming independent random errors. But errors are not the same thing as mistakes. It’s highly unlikely that what we’re seeing is an error, but it’s considerably more likely that it’s a mistake. In fact, I’d say that it’s more likely than not to be a mistake, because mistakes are considerably more common than discoveries of fundamentally new physics. This is part of why anything in science must be replicable, by other experimenters using other apparatus, to be taken seriously. We’d also like to see if anyone can produce similar effects with electrons or tauons (which are both very similar to muons).

That said, second, if this isn’t a mistake: Muons are (so far as we know) subject only to the gravitational, electromagnetic, and weak forces, not to the strong force. Gravity is too weak to be remotely close to relevant, here, and we’ve got the electromagnetic and weak forces pinned down to a truly ludicrous degree of precision (or at least, we think we do). So if they’re really seeing muons do something they don’t entirely understand, then yes, they’ve found something big. This is in contrast to hadrons like protons: They’re subject to the strong force, which is only poorly understood, and so hadrons doing something not entirely understood is Tuesday.

Thank you.

PBS spacetime has a good summary of the experiment and results.

They are quite excited about it, but because it could potentially be an addition to the standard model. Not because it would mean a new force of nature. They think that the theoretical work of figuring out what such a result would mean has barely begun (rightly…no use wasting time explaining something that later turns out to have been bird poop on a supercooled solenoid (or whatever)).

Chronos is of course right that it’s most likely some systemic or analysis mistake. OTOH it is already confirmation for an earlier result, and that’s why some physicists have already shifted to second gear of excitement.

Thank you for that.

I remember a new “force” from maybe 30 years ago. It essentially opposed gravity as it was explained. And I think it was such that denser materials had slightly less gravitational attraction. So if you had 1 kg spheres of tungsten and beryllium and accounted for the different diameters the denser spheres had less attraction to each other then the lighter spheres. I think it was demonstrated with spheres hanging from very long thin wires and measuring their motion towards each other. And it may have had a catchy name like hyper-gravity of something.

I probably have the whole thing wrong but hopefully Chronos remembers the situation.

I vaguely remember that, but IIRC the results were never replicated and it was chalked up as experimental error.

According to the article in yesterday’s Times, it is an anomoly in the magnetic moment of the muon from what the standard model predicts. At least one critic of the results claims that their standard model computation was in error. Sounds unlikely but I don’t know anything more. I guess it will soon be sorted out.

Well, we know that some experiment at some point has to disagree with the standard model, as the standard model cannot be complete, as it doesn’t explain gravity, dark matter, or dark energy.

Trying to find where that disagreement is is hard, and that’s the reason for all these experiments. If the muon has a different measure than expected, then that’s somewhere that we can start looking for new particles or forces that can help us to expand the standard model to explain the things we currently cannot.

The electron’s dipole moment has agreed with theory for as closely as we can measure. The moun, however, is much more affected by virtual particle interactions, so they could show up more. The difference between what is expected, and what is measured is something that we are missing from the standard model. Whether that’s just some math that we did wrong, or a sign of something new, would be up to physicists and mathematicians to figure out.

I remember that - I was in college, and there were some rather sarcastic comments from people who had just gotten through a course of physics when the NYT reported “Hints of fifth force in universe challenge Galileo’s findings,” on 8 January 1986. I was in grad school when “cold fusion” broke - and by then actively on BITNET, so I saw the burst of discussion of that on sci.physics live.

I gather that the sensitivity of the muon to virtual particles is due to its mass (200 times greater than that of the electron) so I guess the effect on the tau would be even greater - but presumably the tau is harder to do the experiment on, right?

From what I saw, my understanding is that the sensativity goes up with the square of the mass, so a muon is 4000 time more sensitive than an electron.

The tau is even larger, 3477 times larger than an electron, giving about 12 million times more sensitivity.

Unfortunately, while a muon’s life is short, a tau’s is about ten million times shorter.

Microseconds are actually a pretty long time these days, and quite a bit can be accomplished in the lifetime of a muon. It will be a while before we are able to have a setup that allows any sort of useful measurement for the tau.

Tau are also a bit harder to make, but I think that the short lifetime is the main difficulty.

I think you mean 40,000 not 4000.

Carlo Rovelli is sceptical, and warns about the dangers of crying wolf.

I understand the excitement of my colleagues. Some of them spend their lives searching for the wolf. If they see a hint of the tail, they’ll be happy. But I also think that we scientists should be cautious. Journalists can be quick to translate a “could” into a “can” and a “can” into an “is”. The public may like to see us struggling, watching our excitement and our disappointment, but may also get bored by big announcements that then go nowhere. The risk is losing credibility.

If there’s a danger, it’s from headlines calling it the “new muon”, which is what this Gaurdian article ironically does.
When you consider how old the standard model is, the particle physics community has been tremendously restrained in not making announcements. There’s only been a handful, and one or two of those actually stood up (e.g. neutrino oscillation).

Most physicists interviewed about this potential discovery have indeed used stressed caution and a “wait and see” mentality. But unfortunately, some news sites have still reported it as “everything we know about physics may be wrong” and the like. The real problem is in how science gets reported, and sensationalized, often written by scientifically-illerate people for an audience that is largely scientifically illiterate.

I don’t know what the solution is, I’m just saying the problem is not primarily about physicists being hot heads.

I’m not investing in muon futures on margin and I’m keeping this in mind, too.

The neutrino speed of light thing turned out to be due to a cable jack not being properly plugged in. :slightly_frowning_face:

Yep. And if the muon thing turns out to be due to someone microwaving popcorn in the breakroom, I won’t be too surprised - just a little disappointed.

That’s true, but the most significant uncertain factor is due to a strong force effect, the hadronic vacuum polarization. And there, a case has indeed been made that the ‘accepted’ calculation is mistaken: an alternative based on lattice QCD techniques is consistent with the experimentally observed value, and has recently been published in Nature.

See also the discussion here.

Neat article on the difference between empirical and theoretical numbers