The largest structure ever in the history of mankind is being built for the smallest particle of matter known to mankind. Called the KM3Net Telescope, the structure will be a neutrino detector, taller than the Burj Khalifa, but buried under 3200 meters of water! The whole structure is the latest in the series of larger and larger neutrino detectors and will be the product of a pan-European contribution. It will be the second largest structure in human history, second only to the Great Wall of China.
The super-structure will consist of long cables, holding an optical modulus at the end of each. Each of these optical moduli is a standalone sensing unit, sensitive to light. It will consist of 31 photo-multiplier tubes (or PMTs), which are sensitive light-detectors. All of this will be sealed up as one unit inside a 17-inch glass sphere. The detector will consist of a huge number of such optical moduli!
Why neutrinos are such a headache!
Neutrinos are notoriously hard to detect. They interact only via the weak force (which is also responsible for the decay of heavy nuclei) with other particles and no other force. They leave no trails in the conventional detector chambers, as they are not charged. They do not affect other matter gravitationally, as they are massless (or have extremely small mass!). In order to detect them, the best strategy is to let it hit a proton and convert it into a neutron. This liberates a positron (or anti-electron). The positron emitted travels at such high speeds that it emits radiation called Cherenkov radiation. (Cherenkov radiation is the radiation emitted by a charged particle when it moves faster then light in that medium. Thus, here the electrons/positrons have to move faster than light moves in water). This radiation is detected by the PMT’s. The radiation comes in the form of a cone. This is how the neutrino is indirectly detected.
The KM3Net project is also a Cherenkov type detector, like the famous T2K detector in Japan, which is the largest right now.
Tall, Taller – Tallest!
The whole structure will be taller than the Burj Khalifa, the tallest building in the world. But, this will not be noticed, because it will be underwater. The chamber will be filled with water, as it has a high density of protons. It is meant to detect neutrinos coming through the Earth, and through the sea-floor. This is possible, since neutrinos interact very weakly.
Sometimes mountains have to be moved before the truth can emerge.