B Scientists may have discovered a new force of nature?

[ohwilleke]

Rovelli today Guardian
https://www.theguardian.com/comment...-discovery-physicists-headline-announcements?

Shorter Rovelli. Don't freak, it is probably just a fluke.

 

[artis]

@ohwilleke in your post #25 you mention the masses of up and down quarks and how they are used to calculate the sigma of the muon experiment ,

To give a more "real" example, one of the big differences between the prediction that says there is a 4.2 sigma distinction between experiment and prediction, and the one that says that there is only a 1.6 sigma distinction, is that the second prediction treats up and down quarks as having different masses, while the first one uses only the average mass of the up and down quarks. This slight tweak in the assumed masses of two Standard Model quarks makes a quite significant impact on the predicted discrepancy between theory and experiment, even though both the up quark and down quark masses are tiny (about 2.5% and 5% respectively, of the muon mass).

Pardon if this comes across as lazy but don't we know the mass of those quarks with certainty that we can use different numbers for different approaches?

 

[mfb]

Up and down quarks never appear in isolation, which makes it difficult to define what their mass is, and you get different answers (and large uncertainties) with different methods. Many calculations get much simpler if you neglect the small masses of up and down, or at least neglect their difference. But that's not what lead to the deviating theory predictions here. They used completely different approaches.

 

[DennisN]

A rather more technical take on the experiment itself is this 12 minute, fast moving video:

New Sixty Symbols video. Professors Ed Copeland and Tony Padilla discuss latest results in particle physics from Fermilab and the Large Hadron Collider.

Very interesting. Thanks for posting!

 

[ohwilleke]

But that's not what lead to the deviating theory predictions here. They used completely different approaches.

The approaches aren't completely different. Almost all of the difference comes from HVP and there are about five main differences between the two approaches. Using a 1+1+1+1 Lattice approach rather than a 2+1+1 Lattice approach is one of the significant differences.

 

[mfb]

I thought you were comparing it to the reference value that leads to a large discrepancy, not another lattice calculation. The sigma values suggested that.

 

[collinsmark]

A few words of caution about potential, new physics discoveries. Some historical examples are given. (The video leads up to the new anomalies discussed in this thread.)

 

[phinds]

Nice, informative discussion. Thanks for posting.

 

[CGandC]

If one wants to read quality scientific news with technicalities ( assuming the reader has BSc in physics ) , what kind of media can you recommend?

 

[weirdoguy]

https://arxiv.org/

 

[ohwilleke]

Blogs by credentialed physicists (Twitter feeds too).

 

[ChrisVer]

A few words of caution about potential, new physics discoveries. Some historical examples are given. (The video leads up to the new anomalies discussed in this thread.)

I really liked seeing the historical examples in her videos. I find it interesting that these are not talked about much, while most of the public discussion weight goes on the "holy grail" of 5σ... But these examples are a proof that what shines is not necessarily gold... So, it made me thinking:
What is the approach one would take after observing a 5 or even a 6σ deviation from the SM expectation? Wouldn't it be called it a discovery right away? I suppose, these are set by the collaborations or the analysists beforehand (the 5σ of HEP would put most of other sciences' null hypotheses results indestructible), but the point is that their claims would directly affect the theory community worldwide (they would have an indirect verification in hand that there is BSM).

For example FNAL said during their conferences that after unblinding, whatever their result would be, that's what would be published. So, supposing they had observed a 5σ deviation to Δαμ, would that be called an "observation of LFV" right away?
The latest example from particle physics was the Higgs discovery (OK and several other bound states that are observed by LHCb every now or then). For the Higgs, it looks like the case was to call it a discovery right away, but it could be because it's a special occasion (it appeared in different decay channels and in 2 "independent" experiments at the same time).

 

[mfb]

A deviation in g-2 doesn't have to be LFV. It can be anything.
Keep in mind that systematic uncertainties and theory uncertainties are not Gaussian - they have long tails. A 5 sigma systematics/theory error is far more likely than a 5 sigma statistical fluctuation. I would have expected a careful phrasing of the result. It's not like the discovery of the Higgs boson, which was dominated by statistical uncertainties that are well understood, and of course seen by two experiments that both had ~5 sigma.