by Staff Writers
Odense, Denmark (SPX) Dec 07, 2017
A whole lot of zig-zagging: Perhaps that is what happens when the universe's mysterious dark matter particles hit the Earth. SDU researchers can now show through simulations how it might look.
Planet Earth is constantly on the move, colliding with myriads of dark matter particles as it hurtles through space. Although no one has ever seen these mysterious particles, there is no question among physicists about their existence. That is why they have installed detectors around the globe in the hopes of detecting just a single one of them.
Dark matter particles can penetrate all other forms of matter, which means that they may even be able to traverse right through our planet without losing any energy whatsoever. On the other hand, their impact with ordinary matter that Earth is comprised of may hamper them slightly, resulting in a loss of energy.
"We just don't know, and that definitely doesn't make it any easier looking for them," said Timon Emken, a PhD student at the Centre for Cosmology and Particle Physics Phenomonology (CP3) at the University of Southern Denmark.
Where do the particles go?
The result was a program that can simulate the collision of dark matter particles with the Earth.
"Now, I can ask the computer to show me on the screen what happens when a dark matter particle hits Earth. For example, I can see on the screen which trajectory the particle would take from when it hits the surface of our planet until it leaves again," he said explained.
Weak or strong interactions?
In the standard paradigm, dark matter particles transverse the Earth with a very low probability of interacting with atoms inside the planet. However, underground detectors are tuned to do just that, i.e., to capture rare events of dark matter particle collisions with an atom inside a detector.
"But what if dark matter particles do not follow the standard paradigm? What if they actually interact strongly enough with ordinary atoms, that, as they cross the surface of the Earth and travel underground, lose enough energy to become undetectable? In that case, we will never spot them using standard techniques," said theoretical physicist and Associate Professor Chris Kouvaris from CP3.
Maybe today's dark matter detectors will never catch dark matter
DaMaSCUS simulates billions of dark matter particles that penetrate the Earth and scatter significantly with underground atoms, zig-zagging after every single collision.
"If this is the case, underground scatterings of dark matter particles with atoms might make the dark matter particles lose enough energy to be detectable in the underground detectors that we deploy today.
How do today's detectors work?
Today, there is a number of detectors placed approximately a couple of kilometres below the Earth's surface, and there is a very specific reason for their placement so far below ground: if dark matter interacts weakly with ordinary matter (as also the neutrinos do), only these two species can penetrate kilometres of the Earth's crust without being stopped.
This gives the advantage that deep site detectors evade contamination of the signal from unwanted cosmic and terrestrial radiation and background noise.
Why they may never catch dark matter
"In that case, it would make more sense to search for dark matter signals using detectors on the Earth's surface," he said said.
To overcome the problem of background noise," he said suggests that instead of trying to distinguish dark matter from background noise, one should look for a daily varying signal in surface or low depth detectors.
Maybe we should try this
The larger the distance travelled underground, the higher the probability of underground scattering. This is what creates the daily variation of the signal. The optimal location to exploit this effect is in the southern hemisphere at approximately 40 degrees latitude, i.e. in countries such as Argentina, Chile and New Zealand.
Using DaMaSCUS, Kouvaris and Emken can determine precisely the features (amplitude and phase) of this daily varying signal which can lead to the discovery of dark matter, if this scenario turns out to be true.
What lies ahead?
Paris (ESA) Nov 04, 2017
By pinning down, for the first time, the three-dimensional motions of individual stars in the nearby Sculptor dwarf galaxy, astronomers have shed new light on the distribution of invisible dark matter that pervades the galaxy. This study combined the positions of stars measured by ESA's Gaia mission with observations from the NASA/ESA Hubble Space Telescope taken twelve years earlier. Our ... read more
University of Southern Denmark
Stellar Chemistry, The Universe And All Within It
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