Search for dark matter with scientific balloon
Dec. 26, 2023 | Aerospace Project Research Associate, ISAS people
MIZUKOSHI Keita / Scientific Ballooning Research and Operation Group, ISAS
Research Summary
What are we and the substances around us ultimately made of? Ancient philosophers speculated about various origins through intuition, but through experimentation, we now understand that the world is composed of fundamental, indivisible elements known as elementary particles*1 . Up to this point, 17 elementary particles have been discovered, effectively explaining nearly all natural phenomena. This model of explaining the world with these 17 particles is referred to as the Standard Model. Numerous experiments confirming the Standard Model have consistently reported its validity, making it the current best framework. However, can the Standard Model truly account for everything in the universe? In fact, there are phenomena that cannot be explained by the Standard Model. One of them is dark matter.
Dark matter is an unknown source of gravity. Observing the cosmos, we understand that galaxies are being attracted by something we are not aware of. Yet, we are unable to directly perceive what is causing this attraction. This enigmatic entity is referred to as dark matter, but its true nature remains elusive. While the name conjures images of fictional characters (often portrayed as dark and eerie), it is, in reality, invisible. In fact, "invisible matter" might be a more accurate name, as the current nomenclature falls somewhat short. Nevertheless, without dark matter, the galaxies in our universe would not have the structural integrity they possess today, and perhaps we wouldn't even exist. Dark matter might be the final missing piece to understanding the world, possibly as an 18th elementary particle. Alternatively, it could represent a collective term for around 100 types of unknown elementary particles that we remain unaware of.
Although dark matter's existence is evident on a cosmic scale, detecting its interactions on Earth has proven challenging. For instance, assuming dark matter is about 100 times heavier than a proton, approximately 1,000,000 dark matter particles pass through an area of our palms each second. Even with substantial detectors like the Super-Kamiokande (50,000 tons of water) or XENONnT (6 tons of xenon), far larger than our palms, we have yet to observe a single interaction with matter. Earth-based observation is complicated by the fact that cosmic rays and radiation from unstable decaying atomic nuclei, present in ordinary matter, generate numerous reactions similar to those of dark matter. It's not simply a case of finding a needle in a haystack but rather navigating through a multitude of false reactions that obscure any genuine dark matter interactions.
Rather than seeking dark matter directly, my approach involves identifying antimatter*2 produced by dark matter, aiming to indirectly uncover dark matter's identity. Specifically, the antimatter counterpart known as antiprotons and antideuterons, if created by chance in the universe, would exist only in minuscule amounts. However, if dark matter exists, a significant number of antideuterons would be generated through its annihilation. I am involved in the GAPS experiment, which employs a long-duration balloon-borne instrument over Antarctica. By studying the tracks left by antideuterons, we aim to elucidate the quantity of antideuterons originating from dark matter. Since antimatter transform when they interact with Earth's atmosphere, we conduct experiments in areas with minimal air, facilitated by high-altitude balloon flights. Suppressing the shield effect due to Earth's magnetic field for detecting low-energy antiparticles, we conduct flights over Antarctica. Within the ISAS Scientific Ballooning Research and Operation Group, I contribute to the development and execution of balloon experiments. I'm also engaged in constructing the GAPS experiment's detectors, simulations, and thermal control systems, all in anticipation of detecting dark matter traces during our upcoming flight.
Terminologies
- *1 elementary particle : subatomic particle that is not composed of other particles
- *2 antimatter : Matter composed of particles with opposite charges or quantum numbers compared to regular matter.