The search for dark matter is very exciting. Literally, it’s a bullet in the dark. Even though scientists are sure that dark matter exists – because all the normal matter in the universe cannot explain how galaxies come together – they don’t know what it is. They also don’t really know where he is (although they do have some ideas). They definitely don’t know what it looks like.
However, the physics community is keen to investigate this elusive particle because the dark side of our universe represents an alarming 95% of our universe when it counts. dark energy—an invisible force that accelerates the expansion of space.
But how does one analyze something without really knowing what to analyze? Well, there is one way. While we don’t yet know what dark matter is, scientists may slowly discover what it isn’t.
This is what several researchers dedicated to the study recently did by filtering data captured by detectors buried deep in a mine in Minnesota. While they haven’t found any evidence of dark matter, they say they have set one of the narrowest limits ever to detect this phenomenon one day. have a complete outline of their results published In June at the Physical Review of D.
“It’s all about the mindset in science, where a zero result can be just as positive,” Daniel Jardine, study co-author and postdoctoral researcher at Northwestern University, told Space.com. “Obviously it was cool to find dark matter, but we were able to intersect a new part of the dark matter parameter space.”
Related: “Hidden” photons could explain the mysterious dark matter
This latest discovery relates to the Super Cryogenic Dark Matter Search (SuperCDMS) collaboration, of which Jardin is a member.
In short, the team concluded that the experimental SuperCDMS detector can now exclude dark matter particles until approx About one-fifth the mass of a proton – and maybe even less mass.
“I’ve always loved chasing the unknown, and this is as big as it gets,” says Jardine. “I am very pleased that my career has brought me here, and however short it may be, I can always say that this result is the best in the world until another try inevitably follows.”
This composite image shows the galaxy cluster 1E 0657-56, also known as the “Bullet Cluster.” This cluster was formed after the collision of two large groups of galaxies, and is the most energetic event in the universe since the Big Bang. It is clear that most of the matter in the cluster (blue) is separated from normal matter (pink), providing direct evidence that nearly all of the matter in the cluster is dark in color. (Image credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optics: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lens maps: NASA/STScI; ESO WFI; Magellan/ Arizona/De Cloe et al.)
Wait, what is SuperCDMS?
To capture particle evidence of dark matter, the SuperCDMS collaboration worked with an experiment also known as SuperCDMS.
The experiment essentially harnesses the power of the detector to determine if and when dark matter particles (whatever they are) collide with the atomic nuclei of materials embedded within the detector itself, specifically germanium or silicon.
“I’ve been interested in outer space since I was a child because it makes everything on Earth seem so small and insignificant,” says Jardine. “Then I learned about dark matter and couldn’t believe that all the stars and galaxies and things we see in the night sky make up less than 5% of the universe.”
Getting a bit more technical, SuperCDMS can determine whether these dark matter particles are involved in what are known as “elastic collisions”. If they did, what would happen is that whatever energy the dark matter particle lost when it split apart would be transferred to the motion of the affected atomic nucleus. In turn, both bits will bounce back.
It would be like two billiard balls hitting each other only to bounce slightly backwards on the table, said study co-author Noah Korinsky, a scientist at the SLAC’s National Accelerator Laboratory.
But here’s the thing.
SuperCDMS apparently hasn’t discovered elastic collision yet – according to Jardin, we’ve heard about it now that such a discovery is likely to result in a Nobel Prize. But this research team, including Rob Calkins, research assistant professor at Southern Methodist University, asked an interesting question.
What if SuperCDMS catches another type of crash that no one has been looking for so far? Specifically, inelastic collisions.
Given these new findings, they must have come up with something.
“Searching for elastic collisions remains a key driver of SuperCDMS, but seeing inelastic collisions has paved the way for dark matter parameter spaces that were previously insensitive in experiments,” Jardine explained.
There are two possible ways inelastic dark matter collisions could occur. The first, according to the team, relates to something called radiasi braking radiation. In the detector, if these types of inelastic collisions occur, dark matter particles will transfer some of their energy to light particles, or photons, instead of just bouncing around as in the billiard ball example.
Whereas, on the other hand, inelastic collisions can occur via something called the midgal effect. If this discharge occurred, a dark matter particle hitting the nucleus would cause the nucleus to be knocked out of position, disrupting the distribution of the electron cloud. After returning to their place of origin, some of the flowing electrons will be removed.
At the risk of oversimplification, this means the team is looking for SuperCDMS signals from either flying photons or single-electronic hardcore.
“It’s not as easy as counting,” Jardine said. “This analysis uses the spectral shape to model the signal strength profile as well as some known background sources.”
And after all that, the search yielded no results – but the story didn’t end here.
Jardin continues, “Then we use statistics to answer the question, “What is the probability that we will see a signal with a known background? This question is repeated hundreds of thousands of times and we are left with a parameter space where we should be able to see the signal and we can’t.
Image of the 3-inch iZIP germanium detector used in the Soudan SuperCDMS dark matter experiment (associated with the Minnesotan mine). (Image credit: Matthew Cherry/SuperCDMS Collaboration)
There is always a silver lining
“There are about a billion dark matter particles passing by you every second, but they interact so rarely that you can’t tell,” Jardine said. “We’re looking for a 1 in a billion billion billion billion interaction opportunity.”
Although this golden ticket was not found, another form of treasure was revealed.
Above all, all the statistical studies on the SuperCDMS signal finally gave the team their conclusions about the potential low-mass limit for dark matter particles.
“Other dark matter experiments that weren’t as sensitive as SuperCDMS’s low-mass dark matter for elastic collisions published similar analyzes that broaden their reach and level the playing field. Reading that, we wondered how far we could go if we used the same method,” said Jardine.
In addition, he explained, the team also “added more analyzes such as more complex statistics and the inclusion of interactions with Earth.”
Yes, Earth
Perhaps even more impressive is the way the team calculated that all of Earth’s position in space could influence these dark matter signals.
As they pointed out, if dark matter interacts strongly enough with objects, it is likely to interact with everything in its path to our tiny Earth detectors beneath our soil. One of the things that is ready to interact is our planet’s atmosphere.
The team reasoned that if dark matter particles interacted with our atmosphere, the planetary shield would pick up some of the particle’s energy by the time we pick up the signal.
“Dark matter is thought to be more or less ubiquitous in a large sphere around the galaxy,” said Jardine. Our solar system is in the spiral arms of the Milky Way. That is, the earth rotates around the sun and the earth rotates on its own axis. This astronomical motion means Earth is passing through a sea of dark matter particles, but from our perspective, dark matter particles appear to be constantly bombarding Earth and our detectors.”
In doing so, the researchers realized that there was likely an upper energy limit that these interactive dark matter particles could penetrate – if they were reactive, that is.
By modeling things like the density of Earth’s atmosphere, working with geologists to find out what kind of rock is above the Minnesota mine where SuperCDMS is buried and many other variables, they have discovered the upper limit of dark matter energy.
“When you plug a line into some data, there are two parameters: the regression and the intercept,” says Jardine. “In this analysis, we have more than 50 criteria that match together.”
As for what’s next, Jardine says this Sherlock Holmes-style cutback will continue. And if any of those come to mind, emphasize a visual way of looking at a team’s score that puts things into perspective.
This is what Jardine means when he talks about parameter spaces. The black regions are the regions created with this new analysis. (Image credit: MF Albary et al.)
“This result – the black line – leaves some new parameter space that no one else has accessed before, but there is more open space on the left, less blocks up and down, which means less opportunity for interaction,” he says. This is getting harder and harder to investigate, but dark matter physicists are smart.
This dark matter hunter definitely reached for the stars and made a soft landing on the moon.
2023-08-21 13:31:40
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