ATLAS reanalysis of W mass: Lower uncertainty, agrees with SM

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TL;DR Summary

ATLAS reduced the systematic uncertainties of its measurement. This puts the CDF measurement in even stronger disagreement with other experiments.

Improved ATLAS result weighs in on the W boson
Same dataset, but better analysis methods and some new results from elsewhere that could be used. Money plot from ATLAS:

This makes the CDF measurement an even weirder outlier than it was at the time of publication.

 

[Vanadium 50]

The primary difference is improvements in the event generation. It makes one wonder if there are similar improvements to be made at Tevatron energies.

 

[malawi_glenn]

The primary difference is improvements in the event generation

What are the improvements?

 

[Vanadium 50]

Without getting too technical, what you want is m(W). What you have is m(l + v) and you're missing the z-component of the neutrino. It takes some modeling to get from one to the other and those models contain inputs like proton structure.

As time passes, some of these models (or inputs) are disfavored by the data and new ones are created to take their place.

 

[malawi_glenn]

I have used pythia a lot.

Is it just the event generation of W -> l + v that has been improved or what else have they done?

If you have any technical references, I would be happy to read them

 

[Vanadium 50]

Pythia (at leas Pythia 6 out of the box) won't come close. The PDFs are ancient, the underlying event isn't right, and it won't get radiation of the lepton right.

This is kind of a part in 10,000 measurement. Takes lots of tuning and adjustment to get everything right.

 

[malawi_glenn]

Yeah I have also used Pythia with various pdfs. I guess I have to look more into the newest version of PHOTOS