Standard Model Takes A Dent 22
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"
The universe needn't be infinitely complex. (Score:3)
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:Question (Score:1)
Question (Score:2)
Good luck with your data analysis!
amateur particle science contributions (Score:2)
Not as much fun as generating TeV energies in your basement, though!
Not a real high confidence level yet (Score:2)
Ontopic Reply to Offtopic Post (Score:1)
Superstring theory (Score:1)
hmmm (Score:2)
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Re:dents are both expectecd and welcome (Score:2)
They didn't use taus because:
I'm sure there are a number of other problems, but these are the real killers.
Re:Curious. (Score:3)
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:
Holy shit, it's starting to happen... (Score:1)
Only a little OT: It's a shame that there isn't something amateur scientists could do that would be truly useful to particle physics. Amateur astronomers can watch for comets, novas, variable stars; birdwatchers can track migration patterns, watch for species far away from home or count local populations. I'd really like to be able to do something similar for particle physics, but while building my own cloud chamber would be really neat, the impression I get is that it would be just that: really neat, and not at all useful to science as a whole -- not when TeV accelerators are needed to really crack barriers...
Re:Holy shit, it's starting to happen... (Score:1)
Re:Curious. (Score:2)
The paper is here [bnl.gov]. 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 [theassayer.org] - free-information book reviews
Re:Holy shit, it's starting to happen... (Score:1)
One thing you might look at are lattice QCD calculations. People have figured out a way to do some low-energy strong force calculations (the ones that are traditionally very hard), but they take a lot of computing power, and some very impressive super-computers are being built to deal with them. I have no idea how much work has been put into it, but it might be very useful to produce a distributed system to do these calculations. Volunteers could contribute code and processor time.
Curious. (Score:1)
But on the other hand, they chose the muon for a reason.... Tau would have produced a more measurable result (I assume), but crunching the numbers on it might be a nightmare.... I guess it all boils down to how concrete the expectations are for the muon's interations with virtual particles. I guess that makes me curious, anyone know the answer?
Re:Superstring theory (Score:1)
Re:hmmm (Score:1)
First of all, we measure two quantities: the anomalous precession frequency of the spin (that is, how fast the spin rotates with respect to the momentum of the muons) AND the strength of the magnetic field in which the muons are stored. g-2 is proportional to the ratio of these two values. The other factors in the equation are fundamental constants that have also been measured very precisely. There are really very few theoretical assumptions embedded in the measurement itself (some single-particle relativistic electrodynamics of spin motion), so we aren't working backwards.
Second, the Standard Model consists of more than QED! At the level of statistics that we have, there are significant contributions from hadron loops (the strong interaction) and from W and Z bosons (the weak interaction).
Our "confidence level" is between 98 and 99 percent, a 2.6 standard deviation discrepancy. At this level, we do not claim that we have made a discovery. We've only found a very suggestive hint that there might be a discrepancy. In fact, although it's been fun, I would say that we've almost gotten an embarassing amount of publicity out of our result.
We don't test superstring theory at all. However, the more popular supersymmetry models can potentially lead to perturbations at the scale of our measurement.
Thanks,
Fred
Re:Not a real high confidence level yet (Score:1)
We have the data on tape to reduce the error estimate by about a factor of 2. Analyzing this data is going to be my thesis topic, and I look forward to sharing the result with you in a year or so.
By the way, one aspect of our analysis that hasn't been made apparent in some of the press reports is that it was done semi-blind. We measure the precession frequency and the magnetic field strength separately. Without both numbers, you can't get the physics result. Different teams analyze the two sets of data independently. Until the very end, hidden offsets are added to the numbers. This way, we can't bias the result by working towards (or away from!) a particular value.
Re:Question (Score:1)
The first answer to the question is that the magnetic field of the storage ring is chosen to store particles at the magic momentum. This field is very precisely calibrated and monitored, since it appears in the denominator of the expression by which we calculate the anomalous moment from the precession frequency. Particles that are moving much slower or faster spiral in or out of the ring without being stored.
We measure the momentum of the muons using what we call the "fast rotation." The muons are injected into our storage ring in a tight bunch. At early times after injection, the bunch structure modulates the time spectrum that we see in the detectors. We can measure the times at which we see the bunch pass by and from this determine the momentum distribution. The central value is correct.
Finally, the finite momentum spread (about 0.6 percent) of the beam means that some of the particles do have an momentum which differs from the magic momentum. We apply a correction for this; we determine it from computational simulations of the beam dynamics. The magnitude of the correction is about 0.5 parts per million (ppm), with an error estimate of less than 0.1 ppm. (Our result has an error estimate of 1.3 ppm, so the correction is small on this scale.)
Thanks,
Fred
Every model (Score:2)
dents are both expectecd and welcome (Score:3)
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... (Score:2)
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/Dail
Yankee Ingenuity: Dartmouth Physicists Convert A Microcope Into A Free-Electron Laser
http://www.sciencedaily.com/releases/1998/11/98
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