TEAM NAI: NEUTRINOS
Irini Sakelliou
Adrianos: I know very well that neutrinos are tiny particles like the electron in an atom.
At the moment (2019), three “flavors” of neutrinos have been discovered: the muon neutrino (symbol νμ), the electron neutrino (symbol νe), and the tau neutrino (ντ). We still don’t know what else might show up!
431 Nefeli: Three ice cream cones! And we know there are more: chocolate, stracciatella, vanilla…
Adrianos: Sweets again? You need to understand that the question of why we’re made of matter and not antimatter is very serious.
At the beginning of the universe, when matter was created, the same amount of antimatter should have been created too.
98 Ianthi: So somewhere out there in the universe, there must be an anti-98 Ianthi and an anti-431 Nefeli? We better be careful not to hug our anti-selves!
Adrianos: You’re absolutely right. If 98 Ianthi and anti-98 Ianthi met, there would be a huge explosion, and both would be annihilated.
431 Nefeli: But that doesn’t happen in the universe. We know everything and everyone is made of matter.
Adrianos: Exactly. We haven’t discovered anything made entirely of antimatter. This imbalance between matter and antimatter might be explained by neutrinos.
431 Nefeli: Now I get why so many experiments try to detect neutrinos!
Adrianos: There’s one even in Greece, just outside Pylos. Shall we go find some neutrinos too?
Team NAI sets off for Pylos to discover neutrinos. They also want to understand why detecting them and measuring their properties is so important.
98 Ianthi: Adrianos, do you know where the neutrinos that reach Earth come from?
Adrianos: Mostly from the Sun. As it turns hydrogen into heavier elements, neutrinos are produced. These neutrinos leave the Sun undisturbed and reach Earth. There are other ways neutrinos can be produced, but the Sun is the main source.
431 Nefeli: Adrianos, let’s grab our little buckets and go collect neutrinos!
Adrianos: Where would you even find them? They don’t interact with anything — that’s how they pass through everything. Light can’t get through the densest regions of the universe, but neutrinos can! How will you convince them to sit inside your bucket?
98 Ianthi: True, they’re really hard to detect. But don’t crush my dreams. Isn’t that why we came to Pylos? To find and detect neutrinos? We want to see the giant neutrino telescope here.
Adrianos: Girls, listen — over a few trillion neutrinos pass through your body every second. Same for mine. We’d be extremely lucky if our bodies ever “notice” even a handful of them during our entire lifetime.
431 Nefeli: Did you bring your snorkel and flippers, Adrianos? We might need to dive into the sea.
Adrianos: There are other similar neutrino telescopes placed deep in the sea or inside the ice in Antarctica.
98 Ianthi: Adrianos, do you understand how neutrinos are detected?
Adrianos: To detect a neutrino, it has to collide with a particle that has an electric charge — either positive or negative. After the collision, the charged particle starts moving really fast. As it moves, it emits light. That light is what neutrino telescopes detect.
431 Nefeli: So that’s how scientists know a neutrino passed by?
Adrianos: Exactly! You’re getting it!
98 Ianthi: And to increase the chances of a neutrino colliding with a charged particle, we need to have a lot of charged particles in its path.
Adrianos: That’s probably why these telescopes are placed deep in the sea or in Antarctic ice — and also to reduce noise.
431 Nefeli: That’s also how the neutrino telescope near Pylos works, right?
Adrianos: That Greek telescope is called Nestor. As shown in the picture, it consists of twelve “floors.” Each floor is a hexagonal structure shaped like a star. Each floor has round “eyes,” and each eye contains a camera. These cameras record the light emitted by a charged particle.
The girls: You speak in such complicated ways, Adrianos! Where did you learn all this? Do you actually understand it?
Adrianos: I just like learning! For example, I read that in a similar experiment (IceCube in Antarctica), scientists detected 19 neutrinos from the object SN 1987A. Nineteen neutrinos! And they came from our neighboring galaxy. That galaxy is 163,000 light-years away — that’s 15,000,000,000,000,000 kilometers! So those 19 neutrinos traveled all that way and were finally detected in 2017 in Antarctic ice.
The girls: We hope Nestor finds some neutrinos too. But we think it’s not operating anymore…
Adrianos: I’ll ask and let you know. While you wait for an answer, watch this video. You can turn on Greek subtitles so it’s easier to understand!