The Large Hadron Collider (LHC), the world’s biggest particle smasher, will look for known unknowns such as dark matter, but also for so-called unknown unknowns that researchers have little idea about. That is according to Professor Fabiola Gianotti, the newly appointed Director-General of CERN, the European Organization for Nuclear Research, which helped identify the Higgs boson.
The LHC is due to restart early next year, what will it be able to teach us about dark matter?
‘I think that the LHC can tell us a lot about dark matter, whether or not we discover it. First of all, the LHC has a strong chance of being able to discover the particles that constitute dark matter. We know very well that all the particles that have been discovered until now do not have the right characteristics to be the dark matter particle.
‘The fact that we have observed the existence of dark matter indirectly clearly calls for new physics, for a new particle. If the LHC does not discover dark matter, of course, the negative answer will also be important. It will inform future plans for exploration of dark matter.’
How does the discovery of the Higgs boson impact on that search?
‘One of the important questions to be asking ourselves is: “does the dark matter particle get its mass through the Higgs boson mechanism or something else?” So this will be something we will have to study. Also, the Higgs boson itself can decay into dark matter particles and so studying the properties of the Higgs boson will allow us also to get indications about dark matter.’
‘Studying the properties of the Higgs boson will allow us also to get indications about dark matter.’
Professor Fabiola Gianotti, CERN
How exactly can smashing particles together find a dark matter particle?
‘There are various ways of producing and observing dark matter particles. If dark particles are dark in the sense that they interact extremely weakly with our instruments, the way to see them, for instance, will be to observe in our detector what we call missing energy. So, if you look at the energy in the initial state of the collision, this energy has to be conserved and you have to find the same energy in the final state. This is a very fundamental principle of nature – energy conservation. If you have some missing energy in the final state, this could be a very strong signal for dark matter particles.’
The LHC restarts next year. How confident are you that with the increased energy level that you have at that time, you’ll be able to find this missing energy or find some hint of dark matter?
‘I can’t tell. I am a research physicist so research is looking for the unknown, both the known unknown, like dark matter – we know it exists, we don’t know what it is, but we know that it’s an unknown – but also for the unknown unknown.
‘I can say I am confident because I am optimistic, but I cannot say more than that. And, of course, I would also like to stress that, for a researcher, surprise is always the best possible reward. So it would be good to find something totally unexpected.’
The Large Hadron Collider (LHC) is a 27 kilometre ring in which particles travel at close to the speed of light, suspended by superconducting magnets chilled to within a few degrees of absolute zero by liquid helium.
The underground collider, which straddles the French and Swiss border near Geneva, was built by CERN between 1998 and 2008, partly to prove or disprove the existence of the Higgs boson, a subatomic particle required for the Standard Model of physics.
Within three years of operation, researchers at CERN, whose work is partly funded by the EU, announced they had discovered a particle which could be the Higgs boson, and almost a year later they announced that they ‘strongly suspected’ the particle was indeed the Higgs.
Following this discovery, researchers shut the LHC down for maintenance and upgrades. They plan to restart the collider in early 2015 to run at almost double its current maximum energy.
For details, visit http://home.web.cern.ch/topics/large-hadron-collider
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