A scientist's CERN LHC worst case scenario?

Factual Questions
1

Watching some science show the other day, random scientist 7-b said that the worst possible outcome to the LHC experiments would be finding the Higgs-Bossom and nothing else. That it would answer too many questions without opening new ones and that it would hinder future development of the field. Is that so?

I am thinking that the LHC is already booked for the entirety of its useful life and that it is meant to do a lot more than just the H-B thing. Right?

Is there any bigger collider at least on the dream stage of planning? What projects (currently envisioned) would a LHC flop hurt?

2

IANAPhysicist, but FWIW, I think it’s the Higgs boson.

3

Damn that Freud.

4

The scenario you describe is possible and would be one of the least useful outcomes. However, there are good reasons to expect new things to show up at LHC energies. Not finding anything new would, itself, be a surprise discovery. By its nature, though, that situation leaves you with very little to work with.

Possibilities, in order of (some physicists’) decreasing expectation:

  1. Higgs + more stuff (e.g., SUSY particles)
    Leaves you with the “more stuff” to investigate and learn from, in addition to the Higgs properties.

  2. Higgs + nothing else
    Hierarchy problem is back with a vengence; slews of supersymmetry theories go out the window, the space of dark matter candidates shrinks. Can probe the Higgs’s properties.

  3. nothing
    Shoots the standard model in the gut. Problem: nothing specific to work with – just “no Higgs, no nothing”. Makes progress tough.
    In all cases (although number 3 makes it harder), the observations will guide the design of the International Linear Collider (ILC). The ILC is to the LHC as the scalpel is to the meat axe. Once the LHC tells us roughly what the hell’s going on, the ILC can make precision studies of the Higgs and anything else discovered. The ILC would collide spin-polarized electrons and positrons, leading to very clean collisions. (The proton-proton collisions of the LHC are rather messy and uncontrollable.)

5

How soon can we expect to know something definitive from the testing? Will it be like “you’ve got boson”, or not, and then months of verification? I would expect it would go pretty quickly what with the electronical computers they have these days.

6

It depends on what nature has chosen for the masses of things. Interestingly, a light Higgs is not the easiest to find, not is a very heavy Higgs. A Higgs with a mass near the current lower limit would be made in abundance at the LHC, but its mass would mean that it would decay primarily to (bottom quark)+(anti-bottom quark) pairs. These quarks produce signatures known as quarks “jets” (showers of hadronic mess) whose parent flavor (i.e., bottom vs. top vs. up vs. down…) is tricky to identify. Thus, the bazillions of other processes which make jets get in the way of what you are looking for.

On the other extreme, a heavy Higgs has more favorable signatures in the detector, but they are not made as plentifully.

It turns out that the best case (in the ATLAS detector, for example’s sake) is if the Higgs mass is a bit above 160 GeV/c[sup]2[/sup]. This means the Higgs would be massive enough to decay into two W bosons (which in turn can decay into leptons, which are easy to pick out), but not so massive that you lose out in raw Higgs production. Such an ideal situation would lead to a publicized result in about a year (IMHO). Others may tell you it will be faster, but I think they underestimate how hard it will be to understand what the hell they’re looking at.

A less ideal situation may add another year before there is a clear Higgs signal. On the other hand, the more exotic possibilities could start showing up right away, but again I think it will take a good fraction of a year to sort out anything.

7

Thanks for the responses. Is there an outcome that would really boost string theory over the standard model?

8

And.

Is there an outcome that would really hurt funding and interest in the field (which seemed to be the concern of this scientist on the show)? I want to think that all cases still leave enough to be answered, and that the harder the question, the more it is worth investigating.

9

I think most people would define the destruction of the Earth as a worse outcome.

Is that risk past now that they’ve started running tests? Or is it still possible that we’ll all be destroyed once they crank it up a bit?

10

Yeah, this is why I called this thread “A **Scientist’s **WCS”. I am sure there are plenty other threads about doomsday for those with that concern (or you can start one more).

And no, this was just a quick check to make sure no screws were loose and no pipes were leaking. The non-black-hole-creation starts in late October, conveniently after the first few episodes of Heroes.

11

Boosting something over the standard model only takes seeing evidence for any non-standard model particle. (See note below.) But string theory isn’t the only non-standard-model framework. If something new is discovered, the first thing most people will do is scour the vast numbers of supersymmetric theories (some of which derive from string theory) looking for anything that has something to say about it. What it won’t look like is: “We have theories A, B, and C. If we see x, then A is true. If we see y, then B is true. (etc.)” Instead, the discoveries will eliminate some theories, make others look a bit sketchier, and leave others still consistent with all observations to date. But any new discovery beyond the Higgs will disfavor the standard model versus other options (including string theories.)

Keep in mind that there is still a gulf between string theory and experimental prediction. The situation is improving, but it isn’t the case that Joe Theorist’s string theory says you should see a 200 GeV/c[sup]2[/sup] gluino. Rather, Joe has perhaps shown that his string theory naturally leads to “an N=1 supersymmetric framework that includes supergravity and that has LSP masses as low as the electroweak breaking scale.” Completely separately, Jane Theorist (no relation) is working with such supersymmetric extensions to the standard model. She has one with a few dozen parameters which can be adjusted such that she would expect certain LHC observations. If the LHC does see something, Jane will see if her parameters can be set to explain it. If so:

  • Jane will publish: “My Such-and-such SUSY model can explain this LHC signal.”
  • Joe will publish: “My string theory leads to models that have the mathematical properties of Jane’s.”
  • Newpapers will publish: “String theory has been proven true!” :eek:

Note: You don’t need to actually see a new particle to disfavor the standard model, but that makes for a clean example. You could also see interaction rates or decay properties deviating from their expected trends.

Not really. There are certaintly outcomes that hurt funding for certain projects, but the spigot of funding in particle physics will still run at about the same rate. What I suspect is that the guy in your article is a big proponent of the International Linear Collider. If the LHC produces nothing, then it becomes very hard to justify the ILC as an immediate follow up, which to your guy means “funding is lost!” But in reality, the funding would just be redirected to other efforts in the field.

It’s true that the energy frontier is always the coolest to gab about, but neutrinos are big and dark matter is big and heavy ion physics is big and cosmology is big. In a few years, if nothing is starting to take shape at the LHC, you can bet that proposals for non-ILC next-step options will start coming out of the woodwork. (Muon storage rings, large underground laboratories, high-intensity proton beams…)

Don’t get me wrong – the LHC seeing nothing is most certaintly the worst case scenario. But if that unlikely outcome occurs, I won’t be any more or less worried about HEP (high energy physics) funding. Indeed, it’s not like the multi-billion-dollar ILC is a slam dunk to be funded anyway.

12

Aaaand here we are. This is probably the short answer to my original question.

Thanks for the detailed but digestible replies. This is a field where my interest to ask questions far exceeds my ability to understand the answers.

13

The String Model is still way too squishy for any experiment to have much relevance to it. Basically, everything you could possibly conceive of getting out of any experiment whatsoever is consistent in some way with the String Model.

It should be noted, though, that there are some theories with extra dimensions independent of the String Model, and some of those will be meaningfully tested by the LHC. The models which involve black hole formation, for instance, rely on the existence of extra dimensions with particular properties. So if we do form black holes, it’ll be a confirmation of those models (which would then be properly called theories). If we don’t form any black holes, then that’ll be an indication that, if extra dimensions do exist, they don’t have those particular properties.