New ATLAS result weighs in on the W boson

A small but important piece of a giant machine puzzle.

[1]: https://www.youtube.com/watch?v=D28uSzCs7-k

[2]: https://ohwr.org/project/opt-adc-10k-32b-1cha/wikis/home

I think it's important to keep in mind is those cases certain models are being tested. In good science, you do experiments with certain models in mind, and of course associated models of your apparatus and machines themselves, and then you compare the results for consistency. You have to be very careful with any other additions in your statistical analysis that wasn't generated by the model, including the models of the machines (say some kind of 'epistemic uncertainty' or 'procedural uncertainty' or something like that) to correct after the fact, as I believe it potentially invalidates the base models by itself.

For example, say you measure gravity at sea level with 1 apparatus and report gravity is 9.9 +/- 0.1. Then you get a second apparatus, and measure 9.2 +/- 0.1 (i.e. something went wrong). The difference is significant. Then you realize there must be some error, so you add a 'experimental error parameter', which you can tune, and it has implications on both measurements: you adjust it until the uncertainties are compatible (which is to be expected from consistency of experiments), and arrive say at 9.9 +/- 0.6 and 9.2 +/- 0.6 for the first and second experiment. This new parameter clearly doesn't belong in the model, and there's no model for the parameter itself: there's no explanatory mechanism involved, only a new free parameter. Something you could say honestly, is that we known there's experimental error in one or both of the experiments, or the base models are significantly incorrect. But you can't say take an average of both results and say gravity is 9.55 +/- (..), because the existence of either experimental error or base model error (at least to a few sigma of certainty) invalidates this procedure -- that is, unless you just want a guess for some sort of immediate practical application and the "experimental error" is acceptable.

Another common and well known effect in experiments is knowing the result you want to get, and trying different "adjustments" or redoing analysis until (subconsciously or not) the analysis yields the result that agrees with previous observations. This has been reported by Feynman in his books. I believe some modern experiments shield against this by, among other ways, not seeing the results of an analysis until you're sure the experiments/analysis is good (so you can't fine tune the experiments analysis to get known results).

Once the contradictory Fermilab results were made available, what should the ATLAS group do? Well, one thing would be to double-check their own analysis, and it seems plausible that this is what led to the latest result. Using improved methods might just as well have revealed a problem as end up as it did, supporting the original analysis.

It's hard to predict what new technology can come of this. For example, who could have predicted the transistor?

I think the information gained is valuable in itself, but way smarter people than me will be looking way harder at it, and suddenly a real-world marketable application pops out. If we could predict it happening, that would be the pop.

Also, don't underestimate the massive amounts of learning being done in engineering just by designing experiments and building/maintaining accelerators. That, alone, might be worth it.

Not sure the world ever really cared either

[1] https://news.fnal.gov/2022/04/cdf-collaboration-at-fermilab-...

https://www.science20.com/tommaso_dorigo/is_the_cdf_w_mass_m...

https://www.science20.com/tommaso_dorigo/how_inconsistent_re...

The W boson doesn't live long enough to make it to the detector. All they can see are the decay products. The detector is like an onion, with different layers measuring the energies and/or momentum of different decay products.

So what a search like this is trying to do is look at these decay products, figure out which ones came from a W boson, combine the various energy and momentum measurements, and use that and relativity to determine the rest mass.

The measurement process always has some error, so you want to combine multiple measurements. This is how you get the statistical uncertainty. As an oversimplified example, imagine averaging multiple measurements. The more measurements you get, the smaller this error gets as your average gets closer to the true value. In actuality they're fitting some distribution to the mass measurements, but the same idea applies. The key thing is that the more data they collect, the smaller the statistical uncertainty gets.

But there's also systematic uncertainty. Lots of things contribute to this, and it's effectively an indicator of how well they understand the detector and how well they understand the decay process. For example, the various systems need to be calibrated to convert their measurements to actual energies and momentums. These calibrations aren't perfect, and so the measurements aren't perfect. Or, when they determine which events look like W boson decays, they might be selecting some small fraction of other processes, or rejecting events in a way that biases for higher or lower mass. These will throw off the final measurement. They try to correct for these, but there's never enough data to do so perfectly.

The key thing about systematic uncertainties are that no amount of measuring more decays will overcome them. There are other things you can do to bring them down, such as improving your detector simulations and doing additional calibrations. But there's a limit to how much they can bring this down.

As an example, imagine trying to measure the height of a building with a long measuring tape. You might measure it many times and then average it, and that would give you some very small statistical error. But you don't know that the measuring tape was printed completely accurately, you don't know that it isn't stretching due to gravity or temperatures, you don't know that you got the tape perfectly lined up with the building. Those are all systematic uncertanties, and so when you report your measurement, those will be included in your total uncertainty.

Any unknown physics is likely to be a very small effect, at least numerically. That small effect could require a radical change in the understanding of physics -- like the tiny, hard-to-measure difference between Newtonian gravity and general relativity.

Unfortunately, it's yet another case where a small apparent effect turned out to be just noise rather than an actual novelty.

The photon is the force carrier for hypercharge, and what we experience as electromagnetism on the macro scale is really a combination of hypercharge and the weak nuclear force.

Caveat: I haven't used this stuff in years, it's possible I am talking shit.