Neutrinos

Neutrinos are tiny particles that exist everywhere in the Universe. They have no electric charge and interact very weakly with matter. Because of this, neutrinos can pass through large amounts of material, including the Earth, almost without being stopped.

Neutrinos are produced in many places, such as the Sun, cosmic-ray interactions in the atmosphere, exploding stars, and nuclear reactors. Even though they are extremely difficult to detect, they reach us in huge numbers and carry information from deep inside these sources.

Neutrinos come in three types, called flavors: electron, muon, and tau. For a long time, scientists believed that a neutrino would remain the same flavor forever. However, experiments showed that this is not true. As neutrinos travel, they can change from one flavor to another. This behavior is called neutrino oscillation.

In simple terms: a neutrino created as one type may be detected later as a different type. This discovery showed that neutrinos have mass and opened a new way to study both particle physics and the matter neutrinos pass through.

Neutrino oscillations depend on three main things:

• How far the neutrino travels,

• How much energy it has,

• The material it moves through.

When neutrinos travel through matter, such as the Earth, their oscillations are slightly modified. This means neutrinos are not only messengers from distant sources, but also sensitive probes of the medium they pass through. By carefully measuring neutrino oscillations, scientists can study neutrino properties and gain information about the Earth’s interior.

Neutrino Oscillation Tomography

Neutrino oscillation tomography uses changes in neutrino oscillations to study the inside of the Earth. Atmospheric neutrinos arrive at detectors from all directions. Some come from above, while others pass through the Earth’s mantle and core. As neutrinos travel through regions with different densities, their oscillation patterns change. By measuring these changes, scientists can learn how matter is distributed inside the Earth.

Neutrino Absorption Tomography

At very high energies, neutrinos interact more strongly with matter. Some of them are absorbed when they pass through dense parts of the Earth. Neutrino absorption tomography studies how the number of detected neutrinos depends on their direction and energy. Fewer neutrinos arriving from certain directions means they passed through denser regions. This technique is sensitive to the total amount of matter inside the Earth and works well together with neutrino oscillation tomography.