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.