Standard Model Takes A Dent

Anonymous Coward writes "According to New Scientist, researchers at Brookhaven NL have put a dent in the standard model of particle physics. Looks like a big deal and just what they've been waiting for - something to get their teeth into. Read the story here"

Comments

The universe needn't be infinitely complex.

[Christopher Thomas]

Every model is incomplete. "The suggests that the Standard Model is incomplete" -- Every model is finite and can not explain complete reality, which is infinitely complex. New and better models will always be invented. Hopefully they will come closer and closer to the limit (as in asymptote) - reality.

You are making a big assumption here - that reality is infinitely complex.

The universe may (or may not) be infinite in _size_, but that has no bearing on the complexity of the laws that govern it.

Behavior of the universe may look complicated, but again, this may very well be just complicated consequences of simple laws.

I see no reason to believe that the fundamental laws governing the universe wouldn't be very simple. Complexity is usually a sign that we've missed something fundamental going on.

Re:Curious.

[krlynch]

But the calculations of the cloud of virtual particles that surround the muon are insanely difficult. I'm curious if perhaps an error may lie in wait.

It is possible that an error lies in wait; I know that I make them all the time in these types of calculations :-)

That said, the calculations themselves are not really that difficult in principle; the procedure is quite rigorous and very well understood. Doing the calculations by hand is tedious and error prone, but most of these calculations today are automated. And they are usually done independently by multiple small groups of theorists, so that the results can be cross checked, and critiqued by interested observers. The odds of a major error hiding in the theoretical papers is very small. (There are of course some caveats, but they are technical and uninteresting, and they are, I believe, included in the theoretical error bars.

I think it might be a little early to begin the last rights for the standard model.

This is probably a good statement: the important thing to note about this new result is that it doesn't quite reach the level of scientific "certainty" (much like the noise from a few months ago out of LEP concerning the Higgs boson). This result differs from the Standard Model result by "2.6 sigma", whereas "scientific confidence" requires 3 sigma, and "scientific certainty" requires 5 sigma (which is MUCH MUCH stronger than 3 sigma, not the piddling difference it sounds like it is). What is truly interesting about this result is that, for the first time, we have a reliable result which differs from the SM result by so much. Get the paper and look at the last figure. If the experiment reaches its ultimate goal, and the central value doesn't move towards the SM value by too much, their ultimate result will definitely be greater than 3 sigma, and will probably exceed 5 sigma.

THAT's when we really rejoice :-)

they chose the muon for a reason

Actually, they chose it for a couple of reasons:

• the muon is a "lepton", so it doesn't feel the strong force. The strong force at low energies (like this experiment) is "non-perturbative" which makes the calculations much much tougher (for example, we still can't calculate the equivalent number for the proton with any certainty). Thus, if you work with leptons, you minimize the contributions from the strong force to the number you are measuring.
• it is easy to make polarized muons, which is a technical, but important property for this experiment.
• muons are almost stable: they live for about 64 microseconds in this experiment. Now, that may not sound like much, but given that most of the particles we study survive for 10^{-20} seconds or less -- that is the difference between a day and 10 times the age of the universe -- so, effectively, they live forever.
• they can only decay into electrons. This makes parts of the experiment really really easy, since they don't have any uncertainty from identification of the decay products.
• And finally, the most important reason: no one can figure out how to use anything else to do this measurement :-)

dents are both expectecd and welcome

[buga]

Even with the great experimental success of the standard model, physicists have known from the start that it was not complete. It has at least 19 arbitrary parameters. This is very far from most physicist dreams of a single coupling constant that governs every interaction in the universe. Note that the term "standard model" was used instead of "standard theory", when in fact it is really a scientific theory in every sense, to acknowledge the presence of these numerous free parameters.

Of course, even before this so called "dent", there is the fact that there is insufficient experimental data to confirm observation of th Higg's boson. But the previous success of the standard model leads us to believe that this confirmation will eventually come. And naturally, it was expected that at higher eneries the standard model will need to be replaced with something more general.

- Sim.