This summer, several thousand tons of sulfuric acid g were introduced into the ultra-pure water tank of the giant “Super Kamioka” detector, which is located one kilometer below the Japanese mine. The addition of this rare earth makes it possible to discover the elusive neutrinos that have produced supernova explosions since the birth of the universe.
detector Super Kamioka Ø SK It is a cylindrical tank with a diameter of 39.3 mx and a height of 41.4 m. 50,000 cubic meters of ultrapure water.It is located 1,000 m underground in the Kamioka Mine in Hiida City, Japan. Neutrino – Using 13,000 optical sensors in water – the most elusive particle in the universe.
The probe has been used to study the properties of the atmosphere, the sun and artificial neutrinos, especially the phenomenon of neutrino oscillation, which has won the 2015 Nobel Prize in Physics.
After completing the first phase of introduction from July to August, the experiment has now entered a new observation period. lin (Gd), Is part of the so-called rare earth elements.
Specifically, 13 tons of sulfuric acid octahydrate was added [Gd2(SO4)3 · 8H2O]This progress represents the culmination of nearly a decade of intensive R&D programs. Researchers from the Autonomous University of Madrid and the Canfranc Underground Laboratory participated in this research.
The addition of a certain percentage of g opens up the possibility of discovering the ocean known as “neutrinos” for the super-Kamioka.Supernova remnant neutrinoSupernova explosions have occurred since the beginning of the universe.
In addition, this element enhances SK’s ability to observe the neutrino bursts of any supernova in our galaxy, and significantly improves its ability to distinguish other basic processes (such as the distinction between atmospheric neutrinos and antineutrinos and artificial neutrinos). Observations).
Neutrinos from supernova explosions
Supernova explosions occur in stars 8 times the mass of the sun at the end of their life. They are one of the most active phenomena in the universe. The energy released in the first 10 seconds of the explosion is equal to 300 times the total energy released by the sun during its entire lifetime of 10 billion years.
About 99% of the energy is emitted in the form of neutrinos, and the remaining 1% is used to rupture stars. The light produced by the explosion only accounts for 0.01% of the total energy. Therefore, neutrinos carry much more information than light about the nature of these explosions.
The formation of neutrinos in supernova remnants. /SK/UAM
So far, after the explosion of SN1987A in the Large Magellanic Cloud, supernova neutrinos have only been observed once. The Kamiokande experiment, the predecessor of the Super Kamioka Death Squad, detected 11 neutrino events at the time.
Although the number of observed events is small, it is sufficient to show that the estimated total energy and duration (approximately 10 seconds) are consistent with the basic theoretical mechanism of supernova explosions.
Supernovae are ideal laboratories to verify the basic laws of physics, because their mechanism (which has a mathematical relationship) involves the behavior of ultra-high-density matter with general relativity. Therefore, these neutrinos need more data.
The volume of Super-Kamiokande is about 15 times that of Kamiokande. Therefore, SK hopes to observe more neutrino events (about 8,000) from supernovae in the Milky Way. Such observations will greatly help clarify the mechanism of the explosion.
However, supernova explosions in our galaxy only occur once every 30 to 50 years, so maybe only one or two (or none) can be observed during SK operation. Therefore, to learn more about supernova explosions, it is important to study explosions in galaxies far away from the Milky Way.
Looking for neutrinos in supernova remnants
There are hundreds of billions of galaxies in the universe, and it is estimated that the number of supernovae occurring somewhere in the universe every second is on the order of magnitude. Since neutrinos are emitted in all these explosions, they will spread and accumulate in the universe. These supernova remnants neutrinos (SRNis also called Diffused supernova neutrino background.
According to theoretical calculations, thousands of neutrinos will pass through an area the size of a person’s hand every second. This is the number of neutrino interactions in the SK tank each year. Although these interactions have occurred within the detector since the beginning of the observation, they are indistinguishable from noise and cannot be determined so far.
In a supernova, all types of neutrinos (electron type, meson type, tau type and their antiparticles) are produced. Anti-microelectronics is the most reactive with the water in the SK detector and interacts with protons (hydrogen nuclei in hydrogen atoms).2 pcsO) and produce a positron and a neutron.
The electrons in the anti-tank are anti-neutrino interactions and expected signals. /SK/UAM
So far, because neutrons are not easy to find, SK only uses information from positrons to search for SRN. As a result, search sensitivity is limited by the interactions of thousands of cosmic rays and solar neutrinos, which generate similar signals, thereby limiting the few SRN events that are expected each year.
However, g has the highest affinity for neutron capture among all elements in nature, and its special feature is that a large amount of energy gamma rays are generated during the absorption process. By adding the neutrons generated in the SRN antineutrino interaction to the tank water, they are also captured by the Gd nuclei, thereby generating observable gamma rays.
Therefore, this interaction produces a characteristic signal: First, Luz Cherenkov The positrons in the tank are emitted, and then within a fraction of a millisecond later, Cherenkov light from gamma rays is generated within about 50 cm of the same position.
Since other interactions rarely produce such signals, SRN events can be isolated. This is the reason why g is added to Super Kamioka. When the concentration is 0.01%, the will capture 50% of the neutrons, but when the concentration is 0.1%, the number will become 90%.
The discovery of relic supernova neutrinos will enable people to study the general characteristics of supernova explosions, because the large number of neutrinos from them contributes to the SRN that is now reaching this huge detector. In addition, the measurement of the energy spectrum of the SRN will allow the study of the occurrence of supernovae throughout the history of the universe.
Supernova and black hole
On the other hand, in some supernovae, when the core of a massive star collapses due to gravity, a black hole is formed, which prevents the emission of light. However, even in this case, a large number of neutrinos are expected to be released.
Therefore, comparing the observed SRN signal strength with the optically observed supernova frequency can provide information about the formation speed of these black holes, which will also increase our understanding of the universe.
In the end, many heavy elements around us are thought to be produced during fusion reactions in massive stars, supernova explosions, and neutron stars (high-density objects formed after some supernova explosions). Therefore, research and research on supernova explosions will also make progress in this field.