CERN's Large Hadron Collider --"Has Awakened from 'Hibernation' To Renew Search for New Dimensions, Gravitons, and Tiny Black Holes"
The Large Hadron Collider (LHC) has awoken from 'hibernation' – and it's ready to flip the switch and hunt for new dimensions, pushing the boundaries of our knowledge of particle physics. During the past winter, the LHC took a break from smashing particles together at velocities approaching the speed of light and is now gearing up to get back to work.
In our everyday lives, we experience three spatial dimensions, and a fourth dimension of time. How could there be more? Einstein’s general theory of relativity tells us that space can expand, contract, and bend. Now if one dimension were to contract to a size smaller than an atom, it would be hidden from our view. But if we could look on a small enough scale, that hidden dimension might become visible again. Imagine a person walking on a tightrope. She can only move backward and forward; but not left and right, nor up and down, so she only sees one dimension. Ants living on a much smaller scale could move around the cable, in what would appear like an extra dimension to the tightrope-walker.
How could the LHC test for extra dimensions? One option would be to find evidence of particles that can exist only if extra dimensions are real. Theories that suggest extra dimensions predict that, in the same way as atoms have a low-energy ground state and excited high-energy states, there would be heavier versions of standard particles in other dimensions. These heavier versions of particles – called Kaluza-Klein states – would have exactly the same properties as standard particles (and so be visible to our detectors) but with a greater mass.
If CMS or ATLAS were to find a Z- or W-like particle (the Z and W bosons being carriers of the electroweak force) with a mass 100 times larger for instance, this might suggest the presence of extra dimensions. Such heavy particles can only be revealed at the high energies reached by the Large Hadron Collider (LHC).
Some theorists suggest that a particle called the “graviton” is associated with gravity in the same way as the photon is associated with the electromagnetic force. If gravitons exist, it should be possible to create them at the LHC, but they would rapidly disappear into extra dimensions. Collisions in particle accelerators always create balanced events – just like fireworks – with particles flying out in all directions.
A graviton might escape our detectors, leaving an empty zone that we notice as an imbalance in momentum and energy in the event. We would need to carefully study the properties of the missing object to work out whether it is a graviton escaping to another dimension or something else. This method of searching for missing energy in events is also used to look for dark matter or supersymmetric particles.
Another way of revealing extra dimensions would be through the production of “microscopic black holes”. What exactly CERN would detect would depend on the number of extra dimensions, the mass of the black hole, the size of the dimensions and the energy at which the black hole occurs.
If micro black holes do appear in the collisions created by the LHC, they would disintegrate rapidly, in around 10-27 seconds. They would decay into Standard Model or supersymmetric particles, creating events containing an exceptional number of tracks in our detectors, which we would easily spot. Finding more on any of these subjects would open the door to yet unknown possibilities.
During its annual shutdown, known as the Extended Year End Technical Stop (EYETS), the LHC was drained of liquid helium before engineers looked over the cooling and ventilation, vacuum, electrical and other systems. To prepare for its restart, scientists have been injecting helium back into the system which is being slowly cooled so the machine can be handed back to the operations teams.
"Now we have to make it work," said Stefanos Leontsinis, a postdoctoral researcher at the University of Colorado, Boulder. "We'll spend the next several weeks testing the components and preparing for the LHC restart."
When the LHC kicks into action next month, scientists will again try to push the boundaries of our knowledge of particle physics. These include searching for new dimensions, supersymmetric particles and potentially more subatomic particles, or even something that does not fit within the Standard Model of particle physics.
Image credits: CERN and NASA