Poised to hunt for next particles
The Higgs boson has been found. But a search will soon start for an entire swarm of new particles – fundamental ones which can show whether the universe is supersymmetrical.
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When the now so famous Higgs particle, or Higgs boson, finally materialised in 2012, it seemed to the casual reader that the last piece of a jigsaw puzzle was in place. All the particles in our model of the universe had been accounted for.
In other words, scientists had found all the Lego bricks which they think we need to make the known universe, with energy, matter and whatnot.
But there is a chance that there is more. Much more.
Many physicists think we have only found one of two sets of such fundamental particles.
When CERN’s particle accelerator, the Large Hadron Collider (LHC) is fired up again at the end of 2014 there will be hopes of detecting the others.
This gigantic machine, which occupies a 27-km loop near Geneva, Switzerland, can theoretically create such particles. If so, it can confirm the suspicion among physicists that the universe is supersymmetrical
What does that mean?
Many symmetries
“The simplest example of symmetry is a sphere,” explains Professor Are Raklev at the University of Oslo’s Department of Physics. He starts at the bottom.
“The ball is the same, no matter how you turn it.”
A sphere has rotational symmetry. You turn it in any direction and you get the same shape. Spherical symmetry is just one example of symmetries in nature.
Another is cubic symmetry. A cube does not look the same independently of how you turn it. But it you rotate it 90 degrees you get the same picture as when you started. So it too has rotational symmetry.
“Physicists say that cubic symmetry is greater than the symmetry of the sphere. This is because more mathematics is needed to describe it.”
But Raklev points out that there are many more, much greater symmetries than the rotational symmetry of the cube
Einstein’s symmetry
For instance there is a colossal symmetry associated with Einstein’s special theory of relativity and the speed of light: Physics should be the same, no matter where it happens and at any given speed.
And this symmetry can be expanded to make it even larger, according to Raklev:
“Assume you are looking at something you think is a sphere, which appears to have simple symmetry. Then you notice that the surface actually consists of a myriad of tiny surfaces which form something almost spherical, but has a much more complicated symmetry.”
“In the same way, we are trying to see whether Einstein’s special theory of relativity has a larger and more complicated symmetry behind it.”
“The largest possible expansion of such symmetry is called supersymmetry.”
Many more particles
Okay. Our universe can be supersymmetrical. So what?
“Some physicists would be delighted,” says Raklev.
If our universe is supersymmetrical it would have some very special characteristics which can explain some of the unsolved mysteries of physics.
It would offer a solution as to why the mass of the Higgs boson is so tiny – according to calculations the particle should be a million billion times heavier. Supersymmetry can also provide a unified explanation for several of the fundamental forces in the universe.
But for many the sweetest thing it would do would be to supply the extra set of particles.
Dark matter
If the universe is supersymmetrical, all known particles should have a “shadow particle” partner, an associated particle which is more massive. When the universe was young and full of energy as many shadow particles were created as normal particles.
And the lightest of these particles matches the description of a culprit that is high on the wanted posters among astrophysicists: Dark matter.
Dark matter is a material that nobody has seen or directly observed. But there are strong arguments for why it must be here – all around us. If not, things would fall apart.
Spinning too fast
Measurements show that the galaxies throughout the universe don’t have sufficient mass to retain their shape.
Scientists have calculated the mass of stars, planets and all the other visible matter in galaxies. The gravitational force between these is what holds the galaxies together.
Galaxies swirl around like merry-go-rounds.
This slings out stars and other matter. The math doesn’t add up when scientists compare the mass of galaxies with the speed of their rotation. There just isn’t enough mass to keep the galaxy together. The stars on the outer arms of should be slung out into space on their own.
But this isn’t happening. So scientists reason that galaxies are filled with something invisible that has one noticeable quality – mass. This dark matter ensures that galaxies have enough mass and gravitational pull to stick together.
Only one supersymmetrical particle left
Computations of what we see in space hint of this mystical material that exists around us. But what is it made of?
It must consist of some unknown particle. This is where the extra particles in supersymmetry enter the fray.
“The lightest supersymmetrical particle is a good candidate for dark matter,” says Raklev.
This would also be the only supersymmetrical particle left in the universe.”
“The heavier supersymmetrical particles would be highly unstable,” explains Raklev.
As the energy in the universe drops with the passage of time, such particles disintegrate – they would break up and become lighter particles. Ultimately they would all consist of the lightest type, this particle which scientists suspect could be dark matter.
But so far this is all hypothetical and speculative. No scientists have found any supersymmetrical particles to date. Not even in the huge machine which could make it possible, the European
Organization for Nuclear Research (CERN)’s Large Hadron Collider.
None turning up
Enormous energy enables the LHC to make subatomic particles. Scientists have now created all the known particles of the universe, including the latest addition, the Higgs boson. But none of the attempts have produced any supersymmetrical particles.
“Actually we should have found some already,” says Raklev.
But even with the LHC at maximum power, none appeared. This could indicate that supersymmetrical particles are heavier than expected. Or that they don’t exist.
“Things are starting to get a bit uncomfortable for researchers now,” says the professor, who should know because his work is with supersymmetry.
“It will be exciting to see what happens when the LHC is turned back on again.”
Cannot be disproved
The enormous accelerator is currently down for an overhaul and upgrade. When it is switched on again at year’s end it will be capable of running at higher energies.
Maybe something will be found. Perhaps not. The problem is that even if supersymmetrical particles exist, maybe we can’t produce powerful enough collisions to detect them.
“If they are very heavy we won’t be able to produce them,” says Raklev.
“It was easier when the search was for the Higgs boson. There was an upper limit regarding how heavy it could be. If we didn’t find it before reaching that limit we could have concluded that it didn’t exist.”
But there is no comparable limit for the new particles. That means that with existing technology we can never disprove their existence – they can always be heavier. But if nothing turns up at LHC in the next few years, interest may decline.
“Some will probably continue looking for supersymmetrical particles. But there will probably be fewer physicists working on the project then,” predicts Raklev, and jokes:
“Then I guess I’ll have to shop around for another job.”
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Read the Norwegian version of this article at forskning.no
Translated by: Glenn Ostling
