The importance of measurements

Having been pretty much bedridden with Covid for most of the week, I am now feeling much better. I still have those two lines on the thingy though, so today have added a cricket match to the list of missed things.

This is my first (known) bout of Covid since the start of the pandemic. Part of me was a little relieved to see the two lines appear on the lateral flow test. There have been a few times over the past years when I have felt rubbish but have come up with negative test results, and I had a nagging doubt I was somehow doing the test wrong.

Well, I wasn’t. Two very clear lines, consistently now for several days. So my comfort is that at least I have not been a bungling superspreader, falsely reassured by crap measurements.

Talking of measurements, he segued smoothly, there are two papers on the arXiv today I’d like to comment on.

The first is an ATLAS paper: Measurements of WW production in decay topologies inspired by searches for electroweak supersymmetry This is part of what I hope is a growing trend in physics at the Large Hadron Collider (LHC) throughout Run 3 (Physics collisions scheduled for 5 July! Don’t miss it!) and the subsequent high-luminosity running.

While we are of course on the lookout for physics beyond the Standard Model (for example the “electroweak supersymmetry” in that rather lengthy title), it may be that there is none within reach. In that case it is not enough for the legacy of the LHC to be “we looked for all the new theories we could think of and none of them were there”. We have to measure what is there, and quantify how well the Standard Model describes it.

This paper does just that. It identifies event configurations that might result from some supersymmetric processes, but which could also be generated by the Standard Model. It measures the rate (the cross section) and quantifies how well the Standard Model describes it.

The advantage of this approach, as opposed to just setting some limits on the supersymmetry stuff, is that if the Standard Model predictions improve in future, or if other new models we haven’t thought of yet predict similar configurations, these data can be reused to investigate that.

Model-independent measurements like this are building us a powerful library of results which can be used in many different studies (see some of these posts for more). In the end I hope we can get them, and the relevant predictions, into a state where a discrepancy would be taken as seriously as, for example, the discrepancy in the anomalous magnetic moment of the muon.

And that brings me to the second paper.

There’s a new lattice calculation of this quantity, which is consistent with a previous lattice result. Like that previous calculation, it is much less discrepant with the measurement than is the consensus prediction. This is disappointing in one way, because it reduces the likelihood of physics beyond the Standard Model being present in the measurement.

It is disappointing, even astonishing, in another way. The preprint doesn’t even cite the experimental papers, despite quoting their result. Doubtless this will be sorted out by the journal, but I still find it disturbing. Both the calculations and the measurements of the anomalous magnetic moment involve Herculean efforts. The lack of citation betrays a disconnect, or even a disrespect, that can’t be good for science.

And then back to the picture at the top. It is the Tatras mountains in Zakopane, where I spent last week at a school for Monte Carlo event generators – one of the areas where theory and experiment definitely come together, and respect each other. The school was brilliantly run by Krakow University, as part of the MCnet collaboration, until recently a UK-led EU-funded network. Remember them?

Anyway, it was a great week of physics, pool, beer and beautiful countryside.

And, it turns out, Covid. Oh well.

About Jon Butterworth

UCL Physics prof, works on LHC, writes (books, Cosmic Shambles and elsewhere). Citizen of England, UK, Europe & Nowhere, apparently.
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1 Response to The importance of measurements

  1. Peter Hobson says:

    My late father went to a conference (on gonadotrophins probably) in the Tatras in the 70’s and loved them so thanks for the memory. Totally agree with you comment about the paper that neglects to cite experimental evidence. What on earth were they thinking?

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