암흑물질 탐색, dark matter search

암흑물질 탐색을 위한 새로운 시도가 성공적인 첫걸음을 뗐다.

기초과학연구원은 지하실험 연구단이 이끄는 국내 공동연구진이 세계 최초로 상용 원자로를 활용해 가벼운 암흑물질을 직접 탐색하는 네온(NEON) 실험을 구현했다고 밝혔다.

이번 실험을 통해 기존 가속기 실험이나 천문학적 관측으로 접근하기 어려웠던 초경량 암흑물질을 탐색할 새로운 가능성을 열었다.


암흑물질은 우주의 질량·에너지 구성에서 약 27%를 차지하며, 천문학적 관측으로 그 존재가 강력히 제시됐다. 그러나 지금까지 암흑물질의 성질이나 상호작용을 직접적으로 관찰한 사례는 없다.

기존 암흑물질 탐색 연구는 약하게 상호작용하는 무거운 입자, 윔프(WIMP)를 중심으로 이뤄졌지만, 그 실험적 증거가 부족한 상황에서 가벼운 암흑물질과 암흑광자 같은 대안적인 후보가 주목받고 있다.

네온(NEON) 실험은 1~1000keV/c2(킬로전자볼트/광속제곱)의 초경량 영역의 암흑물질 탐구를 위해 설계된 독창적인 실험이다.

기존 가속기 기반 실험은 주로 윔프와 같은 무거운 입자의 탐색에 집중되어 있으며, 천문학적 관측은 암흑물질의 중력적 영향을 간접적으로 연구하는 방식이기 때문에 가벼운 암흑물질을 직접 탐색하는 데에는 한계가 있었다.

더욱이, 가벼운 암흑물질은 다른 물질과의 상호작용이 약해 자연 배경 방사선에 신호가 묻히기 쉽다. 배경 방사선을 최소화하고 정밀한 실험 설계가 필요한 이유다.

연구팀은 2.8 기가와트(GW) 열출력의 원자로에서 약 23.7미터 떨어진 지점에 탈륨 도핑 요오드화나트륨 섬광 검출기(NaI(Tl) 검출기)를 설치했다.

검출기는 배경 방사선을 최소화하도록 액체 섬광체, 납, 폴리에틸렌으로 구성된 다층 차폐 구조를 갖췄다.

이후 1년 4개월의 기간 동안 암흑물질 신호 데이터를 수집했으며, 원자로의 가동 기간 데이터와 정지 기간 데이터를 비교 분석하여 신호 데이터의 신뢰도를 높였다. 그 결과, 연구팀은 1~10keV 에너지 범위의 미세한 신호를 정밀히 분석하는 데 성공했다.


이번 실험은 원자로에서 발생하는 고에너지 광자가 암흑광자를 매개로 가벼운 암흑물질을 생성하고, 이 암흑물질이 전자와 상호작용할 가능성을 실험으로 직접 탐색한 연구다.

핵분열 과정에서 방출된 고에너지 광자가 전자와 상호작용하여 암흑광자가 생성될 수 있으며, 이 암흑광자는 가벼운 암흑물질로 붕괴할 수 있다는 이론적 제안이 있었으나, 실험적으로 검증되지 않았던 과정이 실제로 구현된 것이다.

특히, 암흑물질 신호와 배경 잡음을 구별하는 독창적 알고리즘을 데이터 분석에 도입해 신호 해석 능력을 크게 향상시켰다.

 

 

 

 

A new attempt to search for dark matter has taken a successful first step.

The Institute of Basic Science said that a joint Korean research team led by an underground experiment team has implemented the world's first neon experiment that directly explores light dark matter using commercial reactors.

The experiments open up new possibilities to explore ultra-light dark matter, which has been difficult to access with conventional accelerator experiments or astronomical observations.


Astronomical observations strongly suggested the existence of dark matter, which accounts for about 27% of the mass and energy composition of the universe. However, until now, there has been no direct observation of the nature or interaction of dark matter.

Existing dark matter exploration studies have centered on weakly interacting heavy particles, WIMPs, but in the absence of experimental evidence, alternative candidates such as light dark matter and dark photons are attracting attention.

Neon (NEON) experiments are original experiments designed for the exploration of dark matter in the ultra-light domain of between 1 and 1000 keV/c2 (kiloelectron volt/luminous square).

Existing accelerator-based experiments are mainly focused on the search for heavy particles such as wimps, and astronomical observations are a way to indirectly study the gravitational effects of dark matter, so there was a limit to the direct search for light dark matter.

Moreover, light dark matter has weak interaction with other matter, making it easy to bury a signal in the natural background radiation. This is why background radiation is minimized and precise experimental design is necessary.

The research team installed a thallium-doped sodium iodide scintillation detector (NaI(Tl) detector) about 23.7 meters away from the reactor with a 2.8 gigawatt (GW) heat output.

The detector has a multi-layered shielding structure consisting of liquid scintillators, lead and polyethylene to minimize background radiation.

Dark matter signal data were collected for a period of one year and four months after that, and the reliability of the signal data was increased by comparing and analyzing the reactor's operating period data and the shutdown period data. As a result, the research team succeeded in precisely analyzing microscopic signals in the energy range of 1-10 keV.


This experiment is a study that directly explored the possibility of high-energy photons from nuclear reactors generating light dark matter through dark photons and interacting with electrons.

There have been theoretical suggestions that high-energy photons emitted during fission can interact with electrons to produce dark photons, which can decay into light dark matter, but a process that has not been tested experimentally is actually implemented.

In particular, we have introduced an original algorithm to distinguish dark matter signals from background noise in data analysis, which significantly improves signal interpretation ability.