an explainer video by David Tong, Cambridge UK
Moderators: kiore, The_Metatron, Blip
Its (the W boson) mass, one of the most important parameters in particle physics, is presently constrained by SM global fits to a relative precision of 0.01%, providing a strong motivation to test the SM by measuring the W boson mass to the same level of precision.
The Review summarizes much of particle physics and cosmology. Using data from previous
editions, plus 3,324 new measurements from 878 papers, we list, evaluate, and average
measured properties of gauge bosons and the recently discovered Higgs boson, leptons,
quarks, mesons, and baryons. We summarize searches for hypothetical particles such as
supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and
search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and …
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I started to work on the W boson mass in 2012 and it took us more than five years to publish a first measurement based on data of the ATLAS Experiment [2]. When I applied for funding for this project, one of the referees wrote that "this measurement is too complicated to be done in time and hence (s)he would not recommend funding". Luckily for me the other referees disagreed and I guess I have to thank the DFG and the Volkswagen foundation at this point that they were willing to take the risk. I have another anecdote on the W boson mass measurement, which illustrates its difficulty: We observed for quite some time some features in the our data, which we could not explain. Once one of my PhD students came into my office and told that he finally figured out this feature: the protons in the ATLAS detector do not collide heads-on but under a very small angle, allowing the not interacting protons to continue their travel through the LHC on the other side of the experiment. Indeed he was right - we have not been considering this effect in our simulations, however - after some calculations and speaking to the machine experts - it turned out that this effect induces a feature in our data, which is opposite in sign that we observe; so we have been left with an effect that was twice as large and unexplained. In the end it turned out to be caused by the deformation of the ATLAS detector by its own weight of more than 7000 tons over time. Enough of my memories - I just want to say with this that the W boson mass measurement is a difficult business.
So let's start to look at the new CDF measurement.
...continues
Sure am learning a lot today about the global electroweak fit - what gets called "the SM" on plots - from talking with my local muon g-2 lattice pals about the W boson result.
tl;dr this SM is not pure-theory, it also contains a lot of experimental results, with their own quirks
The_Piper wrote:Well I haven't heard of any experiments by neutral parties showing astrology to be correct. The standard model has experimental veracity to it.
aufbahrung wrote:It's a hard nut to crack but the standard model being basically astrology was bound to break at some point.
aufbahrung wrote:The_Piper wrote:Well I haven't heard of any experiments by neutral parties showing astrology to be correct. The standard model has experimental veracity to it.
I'm sure a astrological chart can be used to prove pi via some experiment. Still a astrological chart with no reason to exist outside of itself.
The CDF collaboration recently reported a new precise measurement of the W boson mass MW with a central value significantly larger than the SM prediction. We explore the effects of including this new measurement on a fit of the Standard Model (SM) to electroweak precision data. We characterize the tension of this new measurement with the SM and explore potential beyond the SM phenomena within the electroweak sector in terms of the oblique parameters S, T and U. We show that the large MW value can be accommodated in the fit by a large, nonzero value of U, which is difficult to construct in explicit models. Assuming U=0, the electroweak fit strongly prefers large, positive values of T. Finally, we study how the preferred values of the oblique parameters may be generated in the context of models affecting the electroweak sector at tree- and loop-level. In particular, we demonstrate that the preferred values of T and S can be generated with a real SU(2)L triplet scalar, the humble "swino," which can be heavy enough to evade current collider constraints, or by (multiple) species of a singlet-doublet fermion pair. We highlight challenges in constructing other simple models, such as a dark photon, for explaining a large MW value, and several directions for further study.
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