A Fifth Fundamental Force?

On Wednesday April 6^th Fermilab at Chicago reported an anomaly. Their Tevatron accelerator smashes protons and antiprotons at relativistic speeds and measures what comes out. So here is what they found: for a particular collision-type which produces W and Z bosons (the force carriers of the weak force) as well as jets of other stuff, there was an overproduction of events at an energy of around 144 GeV. Sean Carroll at Cosmic Variance has graphs which illustrate this.

Such overproduction is often the signature of a new particle and the most likely candidate seemed to be something called the Z’ boson (not the fabled Higgs boson!). Fundamental bosons are force-carriers, so could this be the first evidence for a new kind of fundamental force?

String Theorist Lubos Motl commented wittily:  “The real question is: Why? There’s no excessively good reason for the Z’ boson to exist and no reason for it to not exist. We just usually prefer to believe in the non-existence unless we have a reason to do otherwise – unless we see a role that such a new particle could play. We don’t know of such a role.

“Of course, that doesn’t mean that the particle can’t exist. It surely means that such a new fifth force would remain a fifth wheel for some time. Imagine – people would say that there are five basic forces. One of them holds galaxies together and keeps us on the Earth; the other is responsible for all of chemistry, biology, and material science, not to speak about electromagnetic communication; the third force keeps atomic nuclei together; the fourth force causes some nuclei to beta-decay; and the fifth force adds 250 bizarre events at the Tevatron. ;-)”

Most likely the Tevatron results are a statistical artefact. The event-excess is significant at three-sigma (0.27% chance of it happening by chance) but as several people pointed out, if the jet energy measurement was off by 4% … the effect just goes away.

In any event, the Large Hadron Collider is now on the case, and the Fermilab people will be looking to acquire more data from the Tevatron right through to that facility’s close-down in October this year. But still, this may be the last you will hear of this particular story.