Run the same calculations for the Muon, and... err... not so good, previously differing by 3.5 standard deviations.
Either the theory is wrong, or the experiments are wrong. The former is very interesting, because Muons are easy to experiment on, and if we can find "new physics" in something so ordinary, then it's an "accessible" regime for conditions that can be reproduced in a lab (albeit a big one).
This paper is saying that the discrepancy has been solved by using a more fancy set of computations and newer experiments at Fermilab.
In other words: No new exciting physics.
Still though, this is interesting because a mystery was solved, even if the answer is in some sense boring.
That's underselling an important point I think. Here's my understanding of it:
There have been two methods to provide the theoretical value, one based on calculating loop corrections, the so-called data-driven approach, and one based on lattice QCD.
From what I can gather, the point in the paper is rather that they stopped using the data-driven prediction, and relied solely on the lattice QCD prediction. This is unlike the previous paper where they combined the two predictions into one.
The former method requires a bunch of measured data as inputs, like how frequently many different interactions happens in nature (their cross-section). It requires more theoretical work, figuring out the loop correction formulas, and all those measurements, but once you have that you can relatively quickly compute the result.
What happened was that one very important cross-section was measured significantly better, but it disagreed with all former measurements. This despite very thorough cross-checking of the experiment. So when those new results were plugged in, the data-driven method gave a much worse prediction.
Meanwhile, the latter method is more brute-force, and relies on simulating QCD on a lattice[1]. A much more complex version of those water simulations used in movies and such. Due to how the physics is, it's very expensive to simulate, and thus the simulations haven't been quite good enough. Recent improvements to the method has changed that, making its predictions in line with the measured value.
The authors states fixing the data-driven method is of high importance, so hopefully this will be fully resolved in the future.
At least that's my armchair understanding.
Like no one really knows why we have three generations of particles and what that means or why they're so massive.
I only found out about hyperons [1] last year, where (at least) one down quark is replaced with a strange quark. And this matter has weird properties. IIRC the nuclei get smaller.
Many years ago I'd assumed it was only a matter of time until we make significant progress merging quantum mechanics and gravity but honestly, I'm starting to have doubts. The universe is under no obligation to make sense or give up its secrets. Just like in maths, some things may be unknowable.
So if the standard model is wrong, long live the right standard model. At least, perhaps until it takes a completely new paradigm to go further.
Why? The last time we got relativity and quantum mechanics which completely upended our standard of living and technological progress in the 20th century. Wouldn’t you be excited for finding out exactly how the current model is wrong and a better more accurate explanation for the workings of the universe?
or
Granted, but good luck trying to find a new model that matches the tested predictions QM/SM makes, AND reveals new physics you can hope to test.
