Deeply under the French Alps, scientists chase dark matter

The mysterious substance called Dark Matter is intrinsically invisible. It cannot be directly observed – from the continuation, its presence is deduced by its gravitational influence on the universe, such as the link of the clusters of galaxies and move the stars around their galaxy faster than they should.

But new research published in Physical examination letters Use a “camera” to search for dark matter interactions, probing the nature of this elusive thing.

One hypothesis is that dark matter is made of still unknown particles which are subject to gravitational force but interact extremely weakly with ordinary matter, explains the University of Chicago Prof. Paolo will privacy, the spokesperson for the Damic-M (Dark Matter in CCDS at Modane) international collaboration, which conducted the study.

In recent decades, the search for black matter particles has concentrated on the Wimp, or to interact weakly massive particles, considered much heavier than a proton.

“But the Wimp have not been found so far, despite the extremely sensitive research by huge detectors weighing a ton, including the work of my colleague Luca Grandi with Xenonnnt,” said will Privite.

Experiences in the most advanced particle accelerators, including the experience of the Atlas to the great collision of Hadrons in CERN, also failed to find Wimp.

Astrophysicists now expand research to lighter particles, which requires exceptionally sensitive instruments because the signals produced by such low -energy mass particles would be almost impossible to detect.

The Damic-M experience is looking for these elusive signals at 5,000 feet below the surface of the French Alps. Although he did not find a dark matter in his initial race, the experience was able to exclude several this kind candidates known as the dark matter of “hidden sector”.

Hidden sector detector

Black matter detectors are designed around the premise that black matter particles will run up, on very rare occasions, will collide with a nucleus in one of the atoms of the detector. The decline in the nucleus can emit light electrons, shake electrons or shake the atom network, producing a signal.

A light particle of black matter is much more difficult to detect than heavy.

“A heavy particle hitting a nucleus is like a bowling ball striking another bowling ball – it will give considerable momentum,” said will Privite. “A light particle striking a nucleus would be like a ping-pong ball striking a bowling ball. This would not move it at all.”

However, the dark matter of the hidden sector would interact with electrons, which are thousands of times less massive than a nucleus.

“Now it’s like a ping-pong ball hitting another ping-pong ball,” said will Privite.

An instrument sensitive enough to detect simple electrons would be ideal for looking for dark matter in the hidden sector.

The DAMIC-M experience uses loading, or CCDS coupling devices, to achieve unprecedented sensitivity and resolution. Standard scientific CCDs are light -sensitive devices that convert photons into electrical loads, which are then transformed into a digital image.

They serve as “camera” astronomical telescopes. CCDs are also able to “imagine” particle interactions, which leave a trace of electrical loads in the device.

CCD DAMIC-Ms are much thicker to maximize the mass of the detector for interactions of black matter particles. The special CCDs of the experience are also able to read the skipper, an innovation that allows researchers to count electrons individually. The team is looking for pixels or clusters of adjacent pixels with only a few electrons – potentially indicating an interaction of dark matter.

These collisions are extremely rare and could be masked by signals from fundamental sources, such as the natural thermal fluctuations of the detector material. To help minimize this, CCD DAMIC -M are used at -220 ° F.

To alleviate the effects of external radiation, the detector is protected by several armor layers. Located in the underground laboratory of Modane under the French Alps, the detector is sheltered from cosmic rays of more than 5,000 feet of rock. To reduce the history of natural radioactive elements found in the walls of the cave, CCDs are surrounded by lead.

“Make fun,” said will be privileged, “we use an old lead, from a Roman ship cast and a Spanish galleon, because its radioactive contaminants have already broken down.”

For this study, the team built a prototype – the lower background, hosting two CCD modules and weighing only 26 grams – and has taken several thousand “photographs” over two and a half months. They then looked for these images of the clusters of pixels suggesting interactions of dark matter.

The team found 144 clusters with two electrons and a single group of four electrons – results compatible with the expected backgrounds.

“Thus, we have not yet discovered dark matter,” said will be privileged, although he added that the results are “more sensitive orders than any other experience, a notable achievement if we consider that they were obtained with a detector prototype and a small mass”.

As the research continues, the absence of a black matter interaction signal has deep implications for the nature of dark matter.

“Gel-in” or “gel-out”

In a potential, a simplified scenario of the evolution of the universe after Big Bang, dark matter and ordinary matter begin to balance and transform each other at equal rates.

As the universe expands and cools, it becomes more and more difficult for ordinary particles to meet each other and create a dark matter, which requires a high energy collision.

However, there is no energy for dark matter particles to meet and destroy themselves, transforming into ordinary matters, so that the abundance of dark matter would decrease quickly after the Big Bang. Finally, the particles of dark matter also become too spread out to engage and the quantity stabilizes that we measure today. This scenario is known as the “frost” of dark matter.

In another possible scenario, the particles of dark matter interact so weakly that dark and ordinary materials are never in balance. On rare occasions that dark matter is produced by ordinary matter interactions, it does not turn and increases in abundance.

The production of dark matter, as for the freezing scenario, is limited by the expansion of the universe, so that the quantity of dark matter finally stabilizes the quantity measured today. This scenario is known as the “frost” of dark matter.

The frost and freezing scenarios restrict the properties of dark matter – in particular its probability of mass and interaction – and theorists have predicted the properties according to which the dark matter of the hidden sector must be compatible with the freezing scenarios.

“These theoretical predictions are now surveyed for the first time by the result Null Damic-M,” said will Privite.

For the freezing scenario, a strict relationship exists between the quantity of dark matter today and its probability of interaction. This constraint allows researchers to make clear forecasts of the probability of a candidate particle to interact with the electrons of the detector and to produce a signal.

Because the team has not detected signals, the experience completely excludes several candidates in the hidden sector – they do not exist.

But for the freezing scenario, an absence of signal definitively excludes the existence of this candidate.

“The fact that we have not found dark matter in our data excludes that the particles of the hidden sector constitute the entirety of dark matter in the universe,” said will Private.

However, if the dark matter of the hidden sector exists, it could be a fraction of all dark matter, with something else comprising the rest.

Extent

After the success of the low-back room prototype, the complete DAMIC-M device should start collecting data in 2026.

The large -scale detector will be more likely to capture a rare interaction, said scientists, and the history will decrease considerably due to better shielding and less radioactive contaminants in the materials of the device.

“Our target is always the dark matter of the hidden sector, which we can find by composing a fraction of all dark matter, but also of Wimps and other candidates,” said will Private. “We expect Damic-M to be the main experience of the search for these low-mass black matter particles for several years to come.”