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.

Question

[alienmole]

This description at space.com made me wonder how sure you can be of the muon velocity, given its importance to the experiment, as described in point 3 on the linked page. Is this considered a significant area of uncertainty? More specifically, if the muon velocity were incorrect, such that their spin was being affected by the confinement field, would that be "easily" detectable in the results?

Good luck with your data analysis!

amateur particle science contributions

[alienmole]

It's probably not what you're looking for, but I'm sure there are ways to contribute by writing code for processing the enormous mountains of data that these experiments produce. Some of the scientific data processing and visualization apps are GPL'd or otherwise open, for example.

Not as much fun as generating TeV energies in your basement, though!

Not a real high confidence level yet

[apsmith]

While this is interesting, the disagreement is still not so far out of the range of experimental errors (2 sigmas) - I'd have been a lot more confident this really meant an indication of something beyond the standard model if it was 4 or 5 sigmas, or even a second experiment with different techniques was corroborating the measurement. Let's just hope it doesn't turn into another of those cases where they announced prematurely and it turns out there was really nothing there after all.

hmmm

[nomadic]

Shouldn't this story make the front page? I mean, I've seen a lot more mundane stuff make it...
--

Re:dents are both expectecd and welcome

[krlynch]

They didn't use taus because:

• taus don't live long enough to reach the necessary accuracy
• we can't make a polarized beam of taus
• taus have many, many more decay paths than do muons, making the analysis much much more difficult

I'm sure there are a number of other problems, but these are the real killers.

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 :-)

Re:Curious.

[bcrowell]

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. Appearently, their paper was only submitted to Phys. Rev. Letters Febuary 8th
The paper is here. If you check the references, the theoretical calculation (done by someone else) dates back to 1999. This kind of calculation was first done in the 1950's, so I think it's pretty well understood. They give a range of uncertainty on the theoretical value, and it's not significant compared to the statistical error bars in the experiment.

Tau would have produced a more measurable result (I assume), but crunching the numbers on it might be a nightmare
In the paper, they say that the effect scales as the square of the mass, so yes, the tau would have produced a bigger effect. I'd guess the reason they didn't use taus is simply that their accelerator didn't have enough energy to produce taus. I don't see why "crunching the numbers" would be an issue. If you have a computer program set up to calculate the g-2 of the electron or muon, then I think all you should really have to do is change one variable to calculate g-2 of the tau. Anyhow, this is an experimental paper. The relevant calculations have been understood for a long time.
The Assayer - free-information book reviews

Every model

[Josh Korson]

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.

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.

Re:Holy shit, it's starting to happen...

[rgclark]

Don't give up hope yet:

TABLETOP LASER ACCELERATORS ARE BRIGHTER AND FASTER
Physics News 510, November 1, 2000
http://newton.ex.ac.uk/aip/physnews.510.html

Table-Top Fusion
Significant Physics on a Small Scale
Creating fusion used to be best left to suns and high-priced devices. Now scientists have managed it with a mere million-dollar machine.
http://www.abcnews.go.com/sections/science/Daily Ne ws/tablefusion990324.html

Yankee Ingenuity: Dartmouth Physicists Convert A Microcope Into A Free-Electron Laser
http://www.sciencedaily.com/releases/1998/11/981 11 2075829.htm

Such "tabletop" accelerators are currently in the million dollar range. But given the interest of physicists to make use of such devices, the cost will probably in the 10 to 100 thousand dollar range within 10-20 years.

Bob Clark