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Supersymmetry Theory Dealt a Blow
Dupple writes in with some news from the team at the Large Hadron Collider. "Researchers at the Large Hadron Collider have detected one of the rarest particle decays seen in Nature. The finding deals a significant blow to the theory of physics known as supersymmetry. Many researchers had hoped the LHC would have confirmed this by now. Supersymmetry, or SUSY, has gained popularity as a way to explain some of the inconsistencies in the traditional theory of subatomic physics known as the Standard Model. The new observation, reported at the Hadron Collider Physics conference in Kyoto, is not consistent with many of the most likely models of SUSY. Prof Chris Parke, who is the spokesperson for the UK Participation in the LHCb experiment, told BBC News: 'Supersymmetry may not be dead but these latest results have certainly put it into hospital.'"
The summary, like the article, jumps straight into "OMG CONFLICT" without bothering to tell us what's going on. From later in the article:
Researchers at the LHCb detector have dealt a serious blow to [supersymmetry]. They have measured the decay between a particle known as a Bs Meson into two particles known as muons. It is the first time that this decay has been observed and the team has calculated that for every billion times that the Bs Meson decays it only decays in this way three times. If superparticles were to exist the decay would happen far more often. This test is one of the "golden" tests for supersymmetry and it is one that on the face of it this hugely popular theory among physicists has failed. ...
The results are in fact completely in line with what one would expect from the Standard Model. There is already concern that the LHCb's sister detectors might have expected to have detected superparticles by now, yet none have been found so far.
But it sounds like this is only a problem for some variants of supersymmetry:
"If new physics exists, then it is hiding very well behind the Standard Model," commented Cambridge physicist Dr Marc-Olivier Bettler, a member of the analysis team. The result does not rule out the possibility that super particles exist. But according to Prof Parkes, "they are running out of places to hide". Supporters of supersymmetry, however, such as Prof John Ellis of King's College London said that the observation is "quite consistent with supersymmetry". "In fact," he said "(it) was actually expected in (some) supersymmetric models. I certainly won't lose any sleep over the result."
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In a nutshell: the Standard Model of particle physics, developed in the 60s and 70s, has once again been shown to be a remarkably robust and effective description of reality. Thus far, no proposed extension to the SM has been corroborated by any convincing evidence. However, there *are* problems with the SM - it's just the resolution of these problems is at present beyond us.
Can anyone explain some of the implications of this finding, for all the non-physicists on Slashdot?
It's going to be a hell of a lot harder to reroute tachyon particles through the main deflector dish.
Yes, specifically Bs Mesons (cue the "BS!" gags...) decaying into a muon pair.
In a fairly hand-wavy way, supersymmetry predicts we should see this quite a lot, but the experiment shows it happens far less frequently, implying the current version of SUSY is either incorrect or completely wrong.
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See? Your science doesn't have all the answers.
The binding energy is negative and lowers the mass of nuclei.
Yes ... and no.
Yes, the binding energy of protons and neutrons to each other lowers the mass of a nucleus, such that a carbon-12 atom has less mass than 6 separate protons and 6 separate neutrons, but there is also the binding energy of the three quarks within each proton and each neutron. That is a honking big positive number, such that most of the mass (somewhere close to 99%) is actually from the interaction (virtual gluons and such) between the quarks, rather than the rest mass of the quarks themselves. Since 99.9% of the mass of an atom comes from the protons and neutrons, about 99% of the mass of any object you interact with daily comes not from fundamental particles, but rather the energy of interaction between quarks.
So when the GP says "between and within protons and neutrons", he's correct, although dropping the "between" would make him slightly more accurate. I don't know enough about QCD to make any assessment of whether the Higgs field contributes significantly to the magnitude of that binding energy. (That is, if we had a zero-valued (or near-zero valued) Higgs field, would the magnitude of the quark binding energy (and thus the mass of everyday objects) be significantly different. )
Here is the paper: https://cdsweb.cern.ch/record/1493302/files/PAPER-2012-043.pdf
Some blogs discussing the significance of the result:
http://www.science20.com/quantum_diaries_survivor/lhcb_evidence_rare_decay_bs_dimuons-96311
http://motls.blogspot.com/2012/11/superstringy-compactifications.html#more
http://profmattstrassler.com/
Particle physics isn't my field, but neither the paper nor the blog posts seem to be interpreting it, as the BBC does, as evidence against supersymmetry.
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It always baffles me why everybody is so focused on developing completely new and revolutionary physics. The greatest progress has been made in refining the Standard Model, rather than replacing it. And it always amuses me when people exhibit surprise when the Standard Model holds up. There cannot be such complexity in the universe if the fundamentals are constantly in disarray.
Perhaps it's because Einstein was their role model, and nobody in the next hundred years is going to quite make the dent in physics as Einstein did even though everyone is going to try. Nobody remembers that there was 300 years between Newton and Einstein, and that people 300 years ago were just as smart and just as capable as people today, only with fewer opportunities for the unprivileged individual and slower methods of communication between intellectuals.
Unfortunately, wild theories and postulations are not going to get where people want to go. Einstein's revolution was sparked by a moment of insight. It's not something that can be forced out with extra hours pounding square pegs into round holes. It can be prepared for by building a solid foundation. But that amounts to keeping the rain barrels outside and ready to collect in a desert.
Forget the exotic theories (especially the untestable ones). Leave the speculation to the metaphysicists. Stick with the basics. Trying to initiate the next revolution in physics would be as futile as dancing for rain.
"If a nation expects to be ignorant and free in a state of civilization, it expects what never was and never will be."
The greatest progress has been made in refining the Standard Model, rather than replacing it.
Which is why a lot of folks were gunning for SUSY, because that's more or less exactly what is -- an extension, rather than a replacement, for the Standard Model.
In SUSY we keep everything we already know and love about the Standard model, but there is also a symetry where each existing particle has a partner with 1/2 spin difference.
Which as a consequence would apparently solve a number of known issues with the Standard Model -- which is attractive because we know the SM is good, but flawed -- and also provide possible solutions for other mysteries like Dark Matter.
So, basically, rulling out SUSY would be a setback for the (very reasonable and desireable) "refinement" model of advancing physics.
Maybe you're going off the fact that String Theory, a revolutionary new model of physics, also predicts SUSY?
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It can be thought of as an attempt to do probabilistic type arguments, when you don't have any data to do probability with.
Suppose that astronauts find a long abandoned alien base on the Moon. All equipment was carefully removed, but we know that the doors and corridors are all 4 meters wide and 3 meters high. It would be "natural" to assume that the aliens (or their machinery) were typically less, but not much less, than 3 meters tall. That could be wrong - maybe they are 1 meter birds who like room to fly in. Or maybe they are 4 meter giants who don't mind stooping. But, in the absence of any other evidence, it is a "natural" assumption. Such assumptions are very common in places like cosmology and quantum gravity.
One argument from naturalness is that dimensionless constants should "naturally" be near one, without a good reason to have some specific value. (The other "natural" is of course zero.).
Take the axion and CP violation. You can add a term to the QCD Lagrangian which violates Charge+Parity (or CP), which means that this term allows for particles and their antiparticles to behave differently. This term is multiplied by a constant denoted by theta, with theta = 0 meaning no CP violation. It turns out you can restrict theta to be 10^-10 experimentally. So, presumably, theta IS zero (as zero is a much more "natural" number than the really tiny 10^-10). The axion came from assuming that theta really described a new field (with a new particle, the axion), and was driven towards zero in the evolution of the universe. It seemed much more "natural" to say that "after about the first microsecond of the big bang theta is driven to be zero" than just saying "this constant is really tiny."
The reason I said that about the cosmological constant (lambda) is that it is about 0.7 and (in the same units) the standard model value for it is about 10^122. (Or,
in natural units, its current value is about 10^-122.) That is an extraordinary result. Many people were sure that lambda was exactly zero (as that could also be "natural,") but it isn't. Note that the value for the axion's theta is by contrast almost routine. If theta is like winning the lottery, lambda is like having every atom in the universe winning the lottery simultaneously for every nanosecond that the universe has existed. So, I regard these arguments as less persuasive than I did 20 years ago,
Einstein's revolution was sparked by a moment of insight.
Wrong, it was the result of long hard work by several people.
It all started when Maxwell's equations gave results that did not agree with newtonian physics. In an attempt to get at the root of things, Michelson and Morley created an experimental setup to measure the speed of light in different directions in a very precise way. To everyone's astonishment, these experiments indicated that the speed of light is a universal constant, which does not depend on either the movement of the light emitter nor the movement of the detector.
Which was exactly what Maxwell's equations had predicted to begin with! If there was a true intellectual giant here, it was Maxwell.
Several scientists started creating equations that made the results of the Michelson-Morley experiment compatible with classical mechanics. Einstein was just the most successful one, because his equations were more elegant and simpler than those of the others.
However, this does not mean Einstein was absolutely right, his theory was only the best one for that particular period. Today we know things he didn't know, just as Newton didn't know that the speed of light is constant.
For instance, there IS a fixed frame for the whole universe, the one in which the cosmic background is symmetrical. This background was discovered only in 1965.
There's also the horizon problem, which was discovered only in the 1970s. If we look at the sky in opposite directions, we see the same characteristics. We are looking at different regions of the universe that never had contact with each other since the creation of the universe. They are so far apart that even light couldn't have reached one from the other during the universe's lifetime. To solve this problem in a way that's compatible with einsteinian relativity, cosmologists came up with cosmic inflation, a rather ugly and contrived kludge.
Besides, relativity does not give results that are compatible with quantum physics, this has been demonstrated experimentally.
It's rather unfortunate that Einstein's theory is so elegant and precise, because it's certainly wrong when your size scales too much up or down.