Friday, January 21, 2022

Physicists first spot elusive ‘ghost particles’ at LHC

An important milestone in particle physics has just happened at the Large Hadron Collider (LHC).

For the first time, candidate neutrinos were discovered not only at the LHC, but also at any particle collider.

The six neutrino interactions detected with the FASERnu neutrino subdetector not only demonstrate the technology’s feasibility, but also open up new possibilities for studying these mysterious particles, especially at high energies.

“Prior to this project, there had never been any sign of neutrinos at the particle collider,” said physicist Jonathan Feng of the University of California, Irvine, co-director of the FASER collaboration.

“This significant breakthrough is a step towards a deeper understanding of these elusive particles and the role they play in the universe.”

Neutrinos are actually everywhere. These are some of the most abundant subatomic particles in the universe; but they carry no charge and have almost zero mass, therefore, although they move through the universe at almost the speed of light, they practically do not interact with it. Billions of things are going through you right now. For neutrinos, the rest of the universe is mostly incorporeal; that’s why they are also known as ghost particles.

Although they rarely communicate, it is not the same as never. Detectors such as the IceCube in Antarctica, the Super-Kamiokande in Japan, and the MiniBooNE at Fermilab in Illinois use sensitive photodetector arrays designed to capture fluxes of light, for example, when neutrinos interact with other particles in completely dark environments.

But for a long time, scientists also wanted to study the neutrinos produced in particle colliders. This is because the collider neutrinos, which occur mainly in hadron decay, are produced at very high energies that are not well understood. The discovery of the collider neutrino provides access to energies and types of neutrinos that are rarely seen elsewhere.

FASERnu is a so-called emulsion detector. Lead and tungsten plates alternate with emulsion layers: during particle experiments at the LHC, neutrinos can collide with nuclei in lead and tungsten plates, producing particles that leave traces in the emulsion layers, a bit like ionizing radiation leaves traces in a chamber Wilson.

The plates should be developed like photographic film. Physicists can then analyze the particle tracks to find out what produced them; whether it was a neutrino, and what was the “flavor” or type of neutrino. There are three types of neutrinos – electron, muonic and tau, as well as their antineutrino counterparts.

During the FASERnu pilot run in 2018, six candidate neutrino interactions were detected in the emulsion layers. This might not sound like a lot considering how many particles are produced in a single launch at the LHC, but it gave the collaboration two important pieces of information.

“First, he confirmed that the position in front of the ATLAS interaction point at the LHC is the correct location for detecting the collider neutrino,” Feng said. “Second, our efforts have demonstrated the effectiveness of using an emulsion detector to observe this kind of neutrino interactions.”

The pilot detector was a relatively small apparatus, weighing about 29 kg (64 lb). The team is currently working on the full version, weighing approximately 1,100 kg (over 2,400 lb). This device will be significantly more sensitive and will allow researchers to distinguish between the flavors of neutrinos and their antineutrino counterparts.

They expect the third series of LHC observations to produce 200 billion electron neutrinos, 6 trillion muon neutrinos, 9 billion tau neutrinos and their antineutrinos. Since we have only detected about 10 tau neutrinos to date, this is going to be a pretty big problem.

The collaboration is also eyeing even more elusive prey. They are pinning their hopes on detecting dark photons, which are currently hypothetical, but which may help uncover the nature of dark matter, the mysterious, directly undetectable mass that makes up most of the matter in the universe.

But the discovery of neutrinos alone is an extremely exciting step forward for our understanding of the fundamental components of the universe.

“Given the power of our new detector and its convenient location at CERN, we expect to be able to register over 10,000 neutrino interactions at the next LHC launch starting in 2022,” said physicist and astronomer David Kasper of the University of California, Irvine, project co-leader. FASER.

“We will find the highest energy neutrinos ever produced from an artificial source.”

Team research published in Physical view D

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