The Large Hadron Collider may soon prove supersymmetry theory is wrong

Illustration for article titled The Large Hadron Collider may soon prove supersymmetry theory is wrong

Supersymmetry holds that all the subatomic particles we know have counterparts that are almost exactly the same, only much, much heavier. But the Large Hadron Collider hasn't found any supersymmetric particles yet, and they're running out of places to hide. Will we have to come up with a new model for subatomics?

The theory of supersymmetry is a favorite of many physicists because it elegantly explains a lot of basic mysteries about the subatomic world. The larger, unstable particles are responsible for the quantum fluctuations that would otherwise force the particles we're familiar with to be much, much more massive than they otherwise are. (This is a short version of the problem - for a more detailed explanation, check out this Nature article, or check out our own primer on undiscovered particles for more on the so-called sparticles.) Some of the supersymmetric particles could also be responsible for dark matter, and supersymmetry could be key to uniting all forces into one all-encompassing theory.

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But the Large Hadron Collider has now effectively ruled out masses for the sparticles below 700 gigaelectronvolts, and more and more mass ranges are getting eliminated all the time. This isn't just a practical problem. The tighter the mass range for the sparticles gets, the more physicists have to fine-tune their values to properly account for the observed quantum fluctuations. Scientists are averse to this sort of fine-tuning - indeed, the whole reason SUSY became popular in the first place was because it eliminated the need to fine-tune the mass value for the Higgs boson to resolve the fluctuation problem.

There's a lot of personal investment in the failure or success of supersymmetry, as physicist Alessandro Strumia explains:

"Privately, a lot of people think that the situation is not good for SUSY. This is a big political issue in our field. For some great physicists, it is the difference between getting a Nobel prize and admitting they spent their lives on the wrong track."

Still, if supersymmetry is ruled out - and there won't be consensus on that until the Large Hadron Collider finishes up its run in 2012 - that's hardly the end of the world for physicists. All it means is that another theory will be needed to resolve the problems with the standard models. Science isn't about being absolutely right - it's about constructing the best theories from the available evidence, and being willing to revise them as new evidence comes to light. Even if that means throwing out one of the most elegant, even beautiful theories physics has ever seen.

Via Nature.

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DISCUSSION

"Supersymmetry holds that all the subatomic particles we know have counterparts that are almost exactly the same, only much, much heavier."

At the risque of being considered brusque, no, the above is an incorrect statement.

Supersymmetric partners have the same mass (assuming supersymmetry isn't broken), but different spins (one is a boson, the other a fermion, with their spins differing by 1/2).

Assuming that supersymmetry exists then, even if it is a broken symmetry - as it must be since we don't observe partners with the same mass (that is, we only observe one particle of the pair, so the other must be more massive than what we can produce in the lab at this point) - it still isn't necessarily the case that all pairs of SUSY partners differ in mass by a huge amount.

And even if that was necessarily the case, the partners still differ in spin by 1/2, which gives them completely different behaviors, as different as they can be.

Thus, they could never be said to be "almost exactly the same, only much, much heavier."

Also, please change

"The larger, unstable particles are responsible..."

to

"The heavier, unstable particles are responsible..."

Elementary particles are neither large nor small; they have no geometrical size. Referring to them as large or small causes unnecessary confusion in the minds of those who are already confused by the overwhelming complexity of physics in general, and particle physics in particular.

"All it means is that another theory will be needed to resolve the problems with the standard models"

Standard Model, not standard models. Capitalized and singular, because it's a specific term referring to one specific theory, not a general term applying to several theories.

"There's a lot of personal investment in the failure or success of supersymmetry"

Very true, but that investment pales in comparison to the investment in string theory. If and when that turns out to be falsified, that's when we'll see some great physicists behaving like spoiled little children.