vendredi 24 août 2018

When you are in the field you know...

What means "I expect supersymmetry at the LHC"?

Now, you will invariably find people who said that due to naturalness new particles beyond the Higgs boson must be found at the LHC, but it’s hardly newsworthy unless it’s a core belief of the community involved. The community was never behind any statements of “must.” Also, the existence of bets that supersymmetry would be found at the LHC is far from proof that people felt it must be found, just as the existence of bets on Germany winning the 2018 World Cup of soccer was proof that the placer of the bet thought it was guaranteed Germany would win. 
Well, but a few very good people seem to have said that they were sure new physics or supersymmetry would be found. Among those very good people who said it, I am sure that they said it with an ever-present, unsaid, implicit softening background assumption that we all understood. A full version of what was meant and understood by such statements in the context of supersymmetry has usually been (maybe even always been), “If a minimal version of supersymmetry is correct and the Higgs potential is not finetuned to more than a few percent I fully expect that superpartners will show up at the LHC unless we are unlucky and the kinematics turn out to be too challenging, such as small mass splittings that we can’t trigger on very easily, etc.” But you really don’t want to say all those words every time you say, “I expect supersymmetry at the LHC.” When you’re in the field, you know. When you overhear or read it from the outside, you can easily misunderstand. There are an infinite number of “short hands” like that when you speak in a disciplinary field, and if you have to speak so carefully every time so that a robot can give it meaning then efficient communication really becomes impossible.
Naturalness, Supersymmetry, and Predictions for New Physics at the LHCJames D. Wells, 2018-07-03


Since when minimal supersymmetry has been under pressure from the simplest interpretations of naturalness?

... it was recognized very early on, and especially after LEP-2 [an e⁺e⁻ collider at CERN which looked for the Higgs boson and new physics without success, ending its run in 2000.] did not find superpartners, that minimal supersymmetric was under pressure from the simplest interpretations of naturalness. It had not found superpartners, which many expected, nor had it found the Higgs boson. To most who thought about such things, not having found the Higgs boson was the bigger worry. After all, LEP 2 did not get to very impressive energies at all to find superpartners, but the correlating scale of superpartners to the lower limit of 114 GeV for the Higgs mass was a cause for concern. [In supersymmetry, the Higgs boson mass is a function of superpartner masses — the higher the superpartner masses the higher the Higgs mass, in general. LEP’s mₕ > 114 GeV required superpartner masses to be unnaturally heavy in the eyes of some.]
In the face of null results from LEP 2 there were many directions to go: identify forms of supersymmetry that would give mh > 114 GeV without straining naturalness (e.g., adding an additional singlet Higgs boson, etc.), abandon supersymmetry (but other new physics ideas suffer from similar naturalness concerns), or abandon rigid naturalness criteria altogetherSince naturalness is not a hard-core data driven criteria, that’s a direction that several of us pursued, well before the LHC turned on. This now sometimes goes under the name of split supersymmetry. Its hallmark is to put more emphasis on data requirements and less emphasis on extra-empirical concerns. 
A prediction of abandoning naturalness in this approach was that there was no special reason to see supersymmetry at the LHC, but there was interesting new enhanced reasons to expect to see dark matter through annihilations in the center of the galaxy, and the electric dipole moment of the electrons might be within reach of experiment in the not-so-distant future, to name two examples...
Id. 

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