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| Dark Matter: Experiment to shed light on dark particles | Dark Matter: Experiment to shed light on dark particles |
| (about 2 hours later) | |
| By Rebecca Morelle Science reporter, BBC World Service | By Rebecca Morelle Science reporter, BBC World Service |
| In a man-made cavern, deep beneath a mountain, scientists are hoping to shed light on one of the most mysterious substances in our Universe - dark matter. | In a man-made cavern, deep beneath a mountain, scientists are hoping to shed light on one of the most mysterious substances in our Universe - dark matter. |
| The Gran Sasso National Laboratory seems more like a Bond villain's lair than a hub for world class physics. | The Gran Sasso National Laboratory seems more like a Bond villain's lair than a hub for world class physics. |
| It's buried under the highest peak of Italy's Gran Sasso mountain range; the entrance concealed behind a colossal steel door found halfway along a tunnel that cuts through the mountain. | It's buried under the highest peak of Italy's Gran Sasso mountain range; the entrance concealed behind a colossal steel door found halfway along a tunnel that cuts through the mountain. |
| But there's a good reason for its subterranean location. The 1,400m of rock above means that it is shielded from the cosmic rays that constantly bombard the surface of our planet. | But there's a good reason for its subterranean location. The 1,400m of rock above means that it is shielded from the cosmic rays that constantly bombard the surface of our planet. |
| It provides scientists with the "silence" they need to understand some of the strangest phenomena known to physics. | It provides scientists with the "silence" they need to understand some of the strangest phenomena known to physics. |
| Inside three vast halls, a raft of experiments are running - but with their latest addition, DarkSide50, scientists are setting their sights on dark matter. | Inside three vast halls, a raft of experiments are running - but with their latest addition, DarkSide50, scientists are setting their sights on dark matter. |
| Everything we know and can see in the Universe only makes up about 4% of the stuff that is out there. | Everything we know and can see in the Universe only makes up about 4% of the stuff that is out there. |
| The rest, scientists believe, comes in two enigmatic forms. | The rest, scientists believe, comes in two enigmatic forms. |
| They predict that about 73% of the Universe is made up of dark energy - a pervasive energy field that acts as a sort of anti-gravity to stop the Universe from contracting back in on itself. | They predict that about 73% of the Universe is made up of dark energy - a pervasive energy field that acts as a sort of anti-gravity to stop the Universe from contracting back in on itself. |
| The other 23%, researchers believe, comes in the form of dark matter. The challenge is that until now nobody has seen it. | The other 23%, researchers believe, comes in the form of dark matter. The challenge is that until now nobody has seen it. |
| What a WIMP | What a WIMP |
| Dr Chamkaur Ghag, a particle physicist from University College London, explains: "We think it is in the form of a particle. | Dr Chamkaur Ghag, a particle physicist from University College London, explains: "We think it is in the form of a particle. |
| "We have protons, neutrons and electrons and all these regular normal particles that you associate building things with. We think dark matter is a particle too, it's just an odd form of matter in the fact that we don't perceive it very readily. | "We have protons, neutrons and electrons and all these regular normal particles that you associate building things with. We think dark matter is a particle too, it's just an odd form of matter in the fact that we don't perceive it very readily. |
| "And that is because it doesn't feel the electromagnetic force - light doesn't bounce off it, we don't interact with it very strongly." | "And that is because it doesn't feel the electromagnetic force - light doesn't bounce off it, we don't interact with it very strongly." |
| Physicists have called these dark matter contenders Weakly Interacting Massive Particles - or WIMPS. | Physicists have called these dark matter contenders Weakly Interacting Massive Particles - or WIMPS. |
| They believe millions of them are passing through us every second without a trace. | They believe millions of them are passing through us every second without a trace. |
| But very occasionally one will bump into a piece of "regular" matter - and that is what they are hoping to detect with DarkSide50. | But very occasionally one will bump into a piece of "regular" matter - and that is what they are hoping to detect with DarkSide50. |
| Inside a house-sized tank, a large metal sphere holds a particle detector called a scintillator. | Inside a house-sized tank, a large metal sphere holds a particle detector called a scintillator. |
| This container is filled with 50kg of liquid argon and a thick layer of the element in its gas form. | |
| "If a dark matter particle comes in and hits the argon, the recoiling atom gets a kick of energy and it quickly tries to get rid of it," says Dr Ghag. | "If a dark matter particle comes in and hits the argon, the recoiling atom gets a kick of energy and it quickly tries to get rid of it," says Dr Ghag. |
| "In argon it gets rid of it by kicking out light; it sheds photons. | "In argon it gets rid of it by kicking out light; it sheds photons. |
| "But it also gives charge: some electrons that are liberated from the interaction site. And those electrons drift up into a gas layer, and when they hit the gas and you get another flash of light." | "But it also gives charge: some electrons that are liberated from the interaction site. And those electrons drift up into a gas layer, and when they hit the gas and you get another flash of light." |
| Until now, the hunt for dark matter has proved elusive. | Until now, the hunt for dark matter has proved elusive. |
| Some experiments claim to have seen signals of dark matter in the form of annual modulation. | Some experiments claim to have seen signals of dark matter in the form of annual modulation. |
| This is the idea that the number of these particles we should be detecting changes as the seasons change. | This is the idea that the number of these particles we should be detecting changes as the seasons change. |
| That's because as the Earth moves around the Sun, it is moving into a stationary field of dark matter - and for half the year it will be moving with the tide of dark matter - just like driving into the rain. But for the other half it will be moving against this tide and less dark matter will hit. | That's because as the Earth moves around the Sun, it is moving into a stationary field of dark matter - and for half the year it will be moving with the tide of dark matter - just like driving into the rain. But for the other half it will be moving against this tide and less dark matter will hit. |
| But other researchers have questioned attributing these seasonal variations that have been detected to dark matter. | But other researchers have questioned attributing these seasonal variations that have been detected to dark matter. |
| Other experiments have run for long periods of times without so much as a hint of the stuff. | Other experiments have run for long periods of times without so much as a hint of the stuff. |
| One, called XENON100, which is also in Gran Sasso, ran for the course of a year, but only saw two "events" - not enough to rule out that this might have been some stray background radiation. | One, called XENON100, which is also in Gran Sasso, ran for the course of a year, but only saw two "events" - not enough to rule out that this might have been some stray background radiation. |
| But with DarkSide50, there seems to be a new push to find some answers. | But with DarkSide50, there seems to be a new push to find some answers. |
| Alongside this experiment, another large detector - LUX - which is in a gold mine in South Dakota in the US will soon be coming online. | Alongside this experiment, another large detector - LUX - which is in a gold mine in South Dakota in the US will soon be coming online. |
| And in the next few years, scientists are planning even more ambitions detectors, such as XENON1T and LUX-Zeplin - they are hoping to find the first experimental evidence of these particles. | And in the next few years, scientists are planning even more ambitions detectors, such as XENON1T and LUX-Zeplin - they are hoping to find the first experimental evidence of these particles. |
| Aldo Ianni, from the DarkSide50 team, says: "Dark matter is really a major scientific goal at the present time. | Aldo Ianni, from the DarkSide50 team, says: "Dark matter is really a major scientific goal at the present time. |
| "It will help us understand a big fraction of our Universe that we don't understand at the present time. We know there is dark matter - but we have to understand what this dark matter is made of." | "It will help us understand a big fraction of our Universe that we don't understand at the present time. We know there is dark matter - but we have to understand what this dark matter is made of." |
| Fruitless search? | Fruitless search? |
| Professor Stefano Ragazzi, director of the Gran Sasso National Laboratory, hopes that the first glimpse of dark matter will be in his research facility. | Professor Stefano Ragazzi, director of the Gran Sasso National Laboratory, hopes that the first glimpse of dark matter will be in his research facility. |
| "There is competition amongst different experiments - so when you compete you prefer to win rather than coming second or third," he explains. | "There is competition amongst different experiments - so when you compete you prefer to win rather than coming second or third," he explains. |
| "The feeling is that dark matter could be just around the corner, so everybody is rushing to be the first to find it." | "The feeling is that dark matter could be just around the corner, so everybody is rushing to be the first to find it." |
| However, he admits that there is always the chance that these experiments may find nothing at all - and dark matter may not be in the form of WIMPs. | However, he admits that there is always the chance that these experiments may find nothing at all - and dark matter may not be in the form of WIMPs. |
| Professor Ragazzi says: "We may find that we have the wrong hypothesis… [dark matter] may be something completely different. | Professor Ragazzi says: "We may find that we have the wrong hypothesis… [dark matter] may be something completely different. |
| "But it may be even more interesting not finding dark matter than finding it." | "But it may be even more interesting not finding dark matter than finding it." |
| In the next few weeks DarkSide50 will be fully kitted out, the surrounding tank flooded with purified water, and then the scientists will have to watch and wait. | In the next few weeks DarkSide50 will be fully kitted out, the surrounding tank flooded with purified water, and then the scientists will have to watch and wait. |
| But Dr Ghag says despite the uncertainties, the potential reward of finding dark matter would be huge. | But Dr Ghag says despite the uncertainties, the potential reward of finding dark matter would be huge. |
| "If we did find dark matter, then we'd have done would be to solved one of nature's best kept secrets. And that would have been to have figured out what a quarter of the Universe is made of," he explains. | "If we did find dark matter, then we'd have done would be to solved one of nature's best kept secrets. And that would have been to have figured out what a quarter of the Universe is made of," he explains. |
| "That would be a revolutionary discovery - it would change our understanding of the Universe, the way it formed, and the way it will evolve." | "That would be a revolutionary discovery - it would change our understanding of the Universe, the way it formed, and the way it will evolve." |