Visible matter – all the things that we can touch and see – accounts for only a small fraction of what makes up the universe. The vast majority of matter – about 85 % – is ‘dark’, which means that it does not emit or reflect light. While physicists are yet to observe any known particle interacting with dark matter, they are sure it is out there. “We infer that there is unaccounted matter because of the laws of gravity as we know them,” explains DARKJETS project coordinator Caterina Doglioni, senior researcher at Lund University in Sweden. “We just haven’t been able to understand what it is yet.” One hypothesis is that this dark matter is made up of particles that interact weakly with conventional particles. Some astrophysicists are trying to recreate dark matter in the lab, by smashing particles into each other. And one of the best places to do this is at the Large Hadron Collider (LHC), at the CERN laboratory in Geneva.
Fabric of the universe
The aim of the DARKJETS project, funded by the European Research Council was to contribute towards advancing our understanding of this most fundamental of questions – what our universe is made of. To do this, it focused on developing new techniques to analyse data. “When two particles collide, a ‘messenger’ particle that transmits the interaction between ordinary particles and dark matter particles can form,” adds Doglioni. “When we smash two particles together at the LHC, we are not looking for dark matter directly, but rather the existence of these new messenger particles, which could indicate the presence of dark matter.” To date, the challenge for scientists has been coping with the sheer amount of data that these interactions produce. “Often, there is simply too much data to record,” she says. “So, we wanted to see if we could analyse these interactions in a more efficient way.” To achieve this, the DARKJETS project pioneered a new data-taking technique for the ATLAS experiment at CERN. Critically, this technique avoids the need for enormous data resources. The technique applies real-time analysis algorithms to reduce data size, and only records what is relevant. This enables researchers to record more data, but with less need for storage. “Particle interactions can be strong – like, say, a huge magnet stuck on the fridge – or weak, like smaller magnets that fall off,” notes Doglioni. “In our search for dark matter, we are looking for weaker and weaker interactions, and to do that we will need more and more data. This is where real-time analysis techniques can really help.”
No signalling particles have yet been discovered that cannot be explained by the Standard Model of Particle Physics. This suggests that the search for dark matter continues. Nonetheless, Doglioni believes that physicists are on the right path. Being able to gather more and more relevant data can only increase the chances of detecting rare interactions between ordinary matter and dark matter. “We are still in the process of analysing data sets, and the method we developed is now a more established technique,” she says. Doglioni sees the search for dark matter as an existential quest. “It is not quite on the same scale as realising that the Earth is not the centre of the universe,” she concludes. “But discovering what 85 % of our universe is made of would be an incredible discovery.”
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