What are the implications to physics if the recent Fermilab results hold up?

resident physicists,

There has been a lot of news about the data ‘bump’ found at Fermilab’s Tevatron accelerator. The results are not yet confirmed to high enough confidence to be considered a real discovery but there seems to be enough data to be attracting a lot of interest.

the results
a presentation of the results

I am not a physicist, but I do have a casual interest is QED and have read enough to have big picture understanding of the concepts. What I would like to understand is, if these results are confirmed, how much of our current understanding will need to be thrown out or at least revised.

I was first told about this ‘discovery’ by my brother in law who had been reading that the implications were profound enough to force a reevaluation of relativity, dark matter, dark energy and essentially put us back a century in terms of accepted theory. He isn’t a physicist either and I haven’t found those conclusions myself from what I’ve read. So what is the straight dope? How big of deal would this be? Would this shake the foundation of modern physics or would it just require a few tweaks that a non-physicist like myself wouldn’t even understand anyway?

The basic answer is that we don’t know. There’s simply not enough information from the current measurement to start saying anything more than it could be this or it could be that. If it really is a new particle, we’ll need to observe it in other channels to see how it interacts with things to really make sense of it.

A little background: CDF looked at proton-anti proton collisions where a particle called a W was produced along with two quarks or gluons. For various reasons, you don’t actually see the individual quarks or gluons, but instead they turn into what physicists call “jets”, which are basically a spray of particles in the detector. If you assume that the two jets come from the decay of a third particle, you can calculate the mass of that particle. If that was the case, you should get a large number of events where the two jets form something with roughly the same mass over and over, and if its not, the masses should be sort of randomly distributed. The challenge in this experiment is that whenever you collide protons, you get jets all over the place, so the backgrounds are incredibly high.

They do in fact see a number of events that line up at the same mass, to such an extent that would only expect randomly distributed masses to mimic that roughly 0.1% of the time. In particle physics, this is considered “evidence for” but not “discovery of” a new particle. What’s weird about this is that (a) the other experiment, D0, which runs under the same conditions, has not released anything saying they’ve seen it (b) there aren’t a whole lot of good ideas why a particle would only be observed in exactly this way, as we would have already seen it if it could be produced/decay in other ways. Both of these are not terribly good reasons to doubt the results as D0 could be frantically working on it right now and just haven’t published yet, and what we can come up with is not really a limiter on what is true.

There are a couple of things that would explain this result:

(1) Its simply not a new particle. 0.1% is not that small, and if you do enough measurements, you’ll see 0.1% effects sooner or later. There are other explanations too - if you mismeasure the energy of the jets (which is totally possible), you can make the peak appear or disappear. Now, you have to mismeasure them by roughly 3 or 4 times worse than CDF believes it can measure them to, but its still a possibility. Lastly, like I said before, the backgrounds are huge - get them slightly wrong and your signal completely vanishes. This will likely be confirmed or denied by D0’s results.

(2) Its a new particle that fits on top of the standard model. That is - all of what we know is right, there’s just more stuff out there that we haven’t found yet. There are many good theories (and some being made up in the last few days!) that can explain a new particle like that with no or minimal changes to the standard model. The way we figure out if this is the case is we look for the other particles those theories predict (they almost always predict more than one new one) or we look for the new particle decaying or being produced in different ways. This would certainly change how we view some of the tough questions, but is far from setting us back 100 years.

(3) The standard model is just totally wrong and something we take for granted is just not true. We know many things that decay to two jets, they’re just all the wrong mass. Maybe certain circumstances cause conservation of energy to just be wrong, and so things that are 90 GeV are decaying as if they are 140 GeV and this measurement just happened to hit the right circumstances. Who knows, right? This is a tougher nut to crack, but is still does not set us back 100 years. For example, when we discovered quantum mechanics, we knew Newtonian mechanics was just flat out wrong in some areas, but that doesn’t change the fact that in many, many other areas Newtonian mechanics is just fine. Similarly, even if this does mean there’s some super-duper Standard Model, the normal Standard Model will be just fine in many, many areas as well.

I haven’ seen anything saying this has any effect on relativity, dark matter, dark energy, or that it will put us back a century. From what I’ve read, it just affects the Standard Model.

Here’s a paper suggesting the new particle is a technipion, a particle that is possible if there is a fifth force, techncolor. From what I’ve read, this can provide a different mechanism for mass, and the Higgs boson isn’t necessary.

On preview, Krinthis just gave a most-likely better response, but I’ve got useful links, so I’ll post anyway.

Thanks for the great responses (to my first thread.) I didn’t think that the extreme interpretations could be correct. From what I understand this experiment’s results will be confirmed or rejected in pretty short order. Maybe this will be the start of a path to a more complete model, or a dead end. Either way, it’s always interesting to see the unexpected.

It wasn’t mentioned in the article you linked to, but in the NewScientist article on it,

So yeah, they should have a better idea “shortly”. Not sure if twice the data is enough to get them to the five sigma level they want.

There isn’t really anything that could ‘set us back 100 years’ – the theories we have are supported to extremely high precision, and it’s not that any experiment could suddenly turn up that just somehow invalidates all that. At the very least, our models would have to be a very good approximation to any models that are to supplant them in the future.

There are, of course, possible results that would force us to severely rethink the conceptual footing on which our current models rest – even though these models are right to a very high degree, they could be right for all the wrong reasons, in a similar sense that Newtonian mechanics managed to be a spectacularly good approximation (for everyday purposes) despite being founded on assumptions that are now generally acknowledged to be false (absolute space and time, etc.).

However, it’s unlikely that the Fermilab results, should they hold up, constitute such a discovery. For one, there’s several models extending the established ones such that the ‘bump’ can be accounted for – in particular, what seems to be talked about the most right now are two different ‘fifth force’ models. In one, the bump is caused by a Z’ boson, the force-carrying particle of a new force that interacts preferentially with quarks (as it would have already been seen if it interacted significantly with leptons – i.e. electron & co.); in the other, the bump is caused by a technipion, a bound state of techniquarks, which are fundamental particles in so-called technicolor models, which are called that because technically, they behave a lot like the ‘color’ force between quarks. :wink: Technicolor models are interesting in that they provide an alternative to the widely discussed Higgs mechanism for electroweak symmetry breaking, and giving the elementary particles their masses. The Z’ boson explanation has the advantage that it might take care of a couple of other recent anomalies that have been noted at the Tevatron, such as the so-called top/antitop asymmetry.

Oh, and another explanation has been proposed according to which the signal might be the first evidence of supersymmetry, albeit an unusual version of it. (To anybody willing to dig through the original papers, here’s the one proposing the Z’, here’s the technicolor one, and the supersymmetry one is here.)

So there’s not really a problem of having no explanation within (an extension of) currently accepted models; rather, the problem is having too many to choose between, which is probably going to be generic with many possible new physics signatures: damn near everything at all conceivable has been predicted by someone at some point.

EDIT: Well, that’s what I get for getting distracted by shiny things and then not previewing…

And now I even have to double-post because the edit expired! Anyway, Tommaso Dorigo has a very in-depth series of posts on his blog related to this; here’s the first one, which also provides a list of links to discussions elsewhere. He’s actually part of CDF, and his name is on the paper announcing the discovery, so what you read there is probably rather trustworthy.

Of course, the experiments at CERN will also shed light on this. If, for instance, they fail to detect the Higgs, even once they have an abundance of data collected at high energy, that would tend to support the technicolor hypothesis, or other hypotheses which do not require a Higgs boson. And of course, there’s also the possibility that they’ll detect this whatever-it-is, too (probably a pretty good chance, if this thing is real).