Science

A New Force Of Nature?

Fermilab and the Tevatron sit in the Illinois countryside near Chicago. i i

hide captionFermilab and the Tevatron sit in the Illinois countryside near Chicago.

AP
Fermilab and the Tevatron sit in the Illinois countryside near Chicago.

Fermilab and the Tevatron sit in the Illinois countryside near Chicago.

AP

The world of physics is abuzz with news coming from Fermilab. It's the largest particle physics laboratory in the United States and the place where I did my first postdoctoral fellowship. Scientists there have been very busy lately. For the past few months they have been pondering a bizarre and unexpected signal from one Fermilab's detectors, the giant CDF.

While the venerable Standard Model of particle physics — which summarizes all that we know of the world of subatomic particles and their interactions — predicts that the signal for a particular process should go down with energy, the data from Fermilab is showing a mysterious bump at about 144 times the mass of a proton. With results collected so far, the odds that the bump is just a false alarm are less that about 0.076 percent. The technical article describing the findings can be found here.

To most people, it may seem like a very small uncertainty, but in the world of particle physics the discovery of a new particle needs odds smaller than one in a million of being wrong. Data being currently analyzed by physicists working at Fermilab's second giant detector, the D0, could corroborate the finding. Or they could muddle things more. In order to get to such tiny uncertainty in a more definitive way, Fermilab will need help from its rival, the LHC, Large Hadron Collider, the current world-record holder for high-energy particle collisions. Although it would greatly help to keep the mighty Tevatron accelerator running a bit longer than September, when it is slated to shut down.

Why all the excitement? Any time a discovery deviates from expectations, science wins.

The bump being seen at Fermilab is surprising for mainly one reason: it's not what everyone was waiting to see. For decades, particle physicists have been pursuing two very elusive goals: the so-called Higgs particle, the particle that supposedly gives mass to all other massive particles in the Standard Model, and evidence of supersymmetry, a hypothetical symmetry of nature that doubles the numbers of existing elementary particles. In both cases, Fermilab's Tevatron accelerator can just brush the needed energy threshold to produce the desired new entities. Although finding the Higgs, or evidence for supersymmetry, would be very exciting, finding something unexpected is even more exciting.

As I wrote here last week, science needs to fail to move forward. That is, it needs to discover new phenomena that are not explained by current theories.

(Many commentators interpreted what I meant by failure in the wrong way. Of course discoveries proven correct, such as Newton's theory of gravity, remain correct. But they are seen as incomplete, unable to explain phenomena beyond their jurisdiction, so to speak.)

The bump seen in the data, if it prevails, may be an indication of another mechanism to give mass to particles: Technicolor. Essentially, Technicolor is somewhat similar to the strong nuclear force, which, according to the Standard Model, holds quarks together to make bigger particles such as the familiar protons and neutrons. Quarks carry a different kind of charge, called a color charge, such that protons and other particles made of quarks are "color neutral," that is, they can only combine quarks with the right combinations of colors.

(Likewise, atoms are electrically neutral since the electrons and the protons, having opposite electric charges, cancel each other out.)

Technicolor would be a new force of nature, a cousin to the strong nuclear force, which acts on "techni-quarks," holding them together to make all sorts of heavier particles. The one seen in Fermilab's data, if the theory is correct, is called a "techni-rho," that then decays into a lighter "techni-pion" and a W boson (this one is actually known to exist), generating the signal seen in the detector.

If Technicolor proves to be correct, the Higgs particle may be nothing more than a failed hypothesis. Current theories that attempt to unify the four forces of nature will also have to be revamped to include a fifth one.

Or there could be a different explanation.

As is typical of particle physics, and most areas of scientific research, new data generates a flurry of papers trying to make sense of it. Eventually, with more data and much discussion, scientists hone in on the correct answer. That's exactly how science should advance: experiments can confirm or contradict proposed hypotheses, or force scientists to invent completely new ones.

Time will tell if the bump found by CDF scientists is here to stay, or if it's only a very unlikely statistical fluke. (Or if it can be explained by a more mundane mechanism compatible with the Standard Model, also a possibility.) Either way, we will learn something about the world of the very small.

We will also learn, once again, that giving physical theories a sense of finality places physics in a vulnerable position it need not be in. It is better to always deem our explanations of the natural world as a work in progress.

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