Particle Physicists begin to invent reasons to build next larger Particle Collider

Collider quilt. By Kate Findlay.
[Image: Symmetry Magazine]

Nigel Lockyer, the director of Fermilab, recently spoke to BBC about the benefits of building a next larger particle collider, one that reaches energies higher than the Large Hadron Collider (LHC).

Such a new collider could measure more precisely the properties of the Higgs-boson. But that’s not all, at least according to Lockyer. He claims he knows there is something new to discover too:

“Everybody believes there’s something there, but what we’re now starting to question is the scale of the new physics. At what energy does this new physics show up,” said Dr Lockyer. “From a simple calculation of the Higgs’ mass, there has to be new science. We just can’t give up on everything we know as an excuse for where we are now.”

First, let me note that “everybody believes” is an argument ad populum. It isn’t only non-scientific, it is also wrong because I don’t believe it, qed. But more importantly, the argument for why there has to be new science is wrong.

To begin with, we can’t calculate the Higgs mass; it’s a free parameter that is determined by measurement. Same with the Higgs mass as with the masses of all other elementary particles. But that’s a matter of imprecise phrasing, and I only bring it up because I’m an ass.

The argument Lockyer is referring to are calculations of quantum corrections to the Higgs-mass. Ie, he is making the good, old, argument from naturalness.

If that argument were right, we should have seen supersymmetric particles already. We didn’t. That’s why Giudice, head of the CERN theory division, has recently rung in the post-naturalness era. Even New Scientist took note of that. But maybe the news hasn’t yet arrived in the USA.

Naturalness arguments never had a solid mathematical basis. But so far you could have gotten away saying they are handy guides for theory development. Now, however, seeing that these guides were bad guides in that their predictions turned out incorrect, using arguments from naturalness is no longer scientifically justified. If it ever was. This means we have no reason to expect new science, not in the not-yet analyzed LHC data and not at a next larger collider.

Of course there could be something new. I am all in favor of building a larger collider and just see what happens. But please let’s stick to the facts: There is no reason to think a new discovery is around the corner.

I don’t think Lockyer deliberately lied to BBC. He’s an experimentalist and probably actually believes what the theorists tell him. He has all reasons for wanting to believe it. But really he should know better.

Much more worrisome than Lockyer’s false claim is that literally no one from the community tried to correct it. Heck, it’s like the head of NASA just told BBC we know there’s life on Mars! If that happened, astrophysicists would collectively vomit on social media. But particle physicists? They all keep their mouth shut if one of theirs spreads falsehoods. And you wonder why I say you can’t trust them?

Meanwhile Gordon Kane, a US-Particle physicist known for his unswerving support of supersymmetry, has made an interesting move: he discarded of naturalness arguments altogether.

You find this in a paper which appeared on the arXiv today. It seems to be a promotional piece that Kane wrote together with Stephen Hawking some months ago to advocate the Chinese Super Proton Proton Collider (SPPC).

Kane has claimed for 15 years or so that the LHC would have to see supersymmetric particles because of naturalness. Now that this didn’t work out, he has come up with a new reason for why a next larger collider should see something:

“Some people have said that the absence of superpartners or other phenomena at LHC so far makes discovery of superpartners unlikely. But history suggests otherwise. Once the [bottom] quark was found, in 1979, people argued that “naturally” the top quark would only be a few times heavier. In fact the top quark did exist, but was forty-one times heavier than the [bottom] quark, and was only found nearly twenty years later. If superpartners were forty-one times heavier than Z-bosons they would be too heavy to detect at LHC and its upgrades, but could be detected at SPPC.”

Indeed, nothing forbids superpartners to be forty-one times heavier than Z-bosons. Neither is there anything that forbids them to be four-thousand times heavier, or four billion times heavier. Indeed, they don’t even have to be there at all. Isn’t it beautiful?

Leaving aside that just because we can’t calculate the masses doesn’t mean they have to be near the discovery-threshold, the historical analogy doesn’t work for several reasons.

Most importantly, quarks come in pairs that are SU(2) doublets. This means once you have the bottom quark, you know it needs to have a partner. If there wouldn’t be one, you’d have to discontinue the symmetry of the standard model which was established with the lighter quarks. Supersymmetry, on contrast, has no evidence among the already known particles speaking in its favor.

Physicists also knew since the early 1970s that the weak nuclear force violates CP-invariance, which requires (at least) three generations of quarks. Because of this, the existence of both the bottom and top quark were already predicted in 1973.

Finally, for anomaly cancellation to work you need equally many leptons as quarks, and the tau and tau-neutrino (third generation of leptons) had been measured already in 1975 and 1977, respectively. (We also know the top quark mass can’t be too far away from the bottom quark mass, and the Higgs mass has to be close by the top quark mass, but this calculation wasn’t available in the 1970s.)

In brief this means if the top quark had not been found, the whole standard model wouldn’t have worked. The standard model, however, works just fine without supersymmetric particles. 

Of course Gordon Kane knows all this. But desperate times call for desperate measures I guess.

In the Kane-Hawking pamphlet we also read:

“In addition, a supersymmetric theory has the remarkable property that it can relate physics at our scale, where colliders take data, with the Planck scale, the natural scale for a fundamental physics theory, which may help in the efforts to find a deeper underlying theory.”

I don’t disagree with this. But it’s a funny statement because for 30 years or so we have been told that supersymmetry has the virtue of removing the sensitivity to Planck scale effects. So, actually the absence of naturalness holds much more promise to make that connection to higher energy. In other words, I say, the way out is through.

I wish I could say I’m surprised to see such wrong claims boldly being made in public. But then I only just wrote two weeks ago that the lobbying campaign is likely to start soon. And, lo and behold, here we go.

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In my book “Lost in Math” I analyze how particle physicists got into this mess and also offer some suggestions for how to move on.