MAJORANA Collaboration scientists search for rule-breaking electrons

In a new study published innatural physics, scientists from the MAJORANA collaboration tested the stringency of charge conservation and the Pauli exclusion principle using underground detectors. Alessio Porcelli published a News & Views article about the study in the same journal.

Today, the Standard Model of particle physics is one of the two pillars of modern physics. It successfully explains three of the four fundamental forces as well as the behavior of subatomic particles.

Pauli’s exclusion principle and the law of conservation of charge are two principles arising from symmetries in the Standard Model. They have undergone many theoretical challenges and have been proven repeatedly to the point where they are considered axioms.

Now, researchers believe that slight violations of these principles could lead to physics beyond the Standard Model, such as exotic forms of matter.

The MAJORANA Collaboration is one such experiment. This project aims to explore neutrinoless double beta decay, a type of radioactive decay, in the hope of determining whether the neutrino is a Majorana particle.

The study was an international collaboration of scientists, including Dr. Clint Wiseman of the University of Washington and Dr. Inwook Kim of Lawrence Livermore National Laboratory in California, who were co-authors of the study. nature study.

Dr. Wiseman shared his motivation behind this pursuit in an interview with Phys.org, “When I first learned about quantum mechanics, I was taught to question unshakable principles. The principles of quantum mechanics (standard The cornerstone of the model) is very important to me.

“As we find new areas of physics to explore in the 21st century, it pays to return to these principles and try to push the limits of their correctness.”

Symmetries, conservation laws and Majorana particles

Mathematician Emmy Noether revealed the profound connection between symmetries and conservation laws. According to Noether’s theorem, every conservation law is closely related to the underlying symmetry in nature.

“Our inability to create or destroy charges without taking other factors into account has to do with this symmetry. The inability of more than two electrons to share the same quantum state represents an equally important natural antisymmetry that is fundamental to atomic matter. Large-scale behavior,” Dr. Wiseman explained.

If these principles are proven to be violated, it means a violation of fundamental symmetries.

“The fact that photons are experimentally verified to be massless is often taken as evidence that charge conservation is fundamentally true. However, theoretical extensions of the Standard Model, such as certain quantum gravity models, may include mechanisms that violate charge conservation.

“The Pauli exclusion principle is mathematically derived directly from the antisymmetric properties of the fermion wave function. As is the case with charge conservation, this may be violated in model frameworks beyond the standard,” Dr. Kim told Phys. org.

How does this relate to the ongoing work of the MAJORANA project? The Majorana particle, if it existed, would be its own particle. This is purely conjecture at the moment, but neutrinos may fit the description.

Neutrinos are very elusive particles, making their properties difficult to detect and study. One of the things scientists have been unable to determine is whether it is its own antiparticle, a Majorana particle.

The MAJORANA project is doing this by looking for an extremely rare process called neutrinoless double-beta decay.

Beta Decay and Underground Detectors

Beta decay, as mentioned earlier, is a radioactive decay process. During this process, neutrons decay into protons, positrons (called beta particles, which are antielectrons), and antineutrinos.

MAJORANA DEMONSTRATOR consists of a high-purity germanium (Ge) detector placed deep underground to avoid radiation that could interfere with it, such as cosmic rays. Germanium detectors are highly sensitive to the energy released during these beta decay reactions.

In double beta decay, two beta decays occur simultaneously and we get two antineutrinos as well as a proton and a beta particle. However, in the absence of neutrinos, as the name implies, we do not observe neutrinos.

This is because, if the neutrino is a Majorana particle, the neutrinos produced by one beta decay will cancel out the emission of antineutrinos (from another decay), resulting in no neutrino emission, and the Majorana particle The demonstrator will detect neutrino emissions.

The data sets obtained by the detector array formed the basis for researchers to study the charge conservation limit and the Pauli exclusion principle.

Test your limits

The researchers focused on three cases, the first testing charge conservation and the other two testing the Pauli exclusion principle.

Let’s start with the first test: charge nonconservation. In this case, the researchers are exploring electron decay within Ge atoms. If an electron decays, it leaves a hole in the atomic orbital, which is filled by electrons from a different orbital.

This process emits photons or X-rays, indicating that the charges have been balanced. However, the lack of emission would indicate that charge is not conserved.

For the Pauli exclusion principle, the researchers focused on Type I and Type III interactions of fermions (in this case, electrons).

In type I interaction, there is an interaction between the newly generated electron and fermion system. The electrons are produced by electron pair generation through gamma rays.

The aim now is to see whether this newly created electron will occupy a completely complete atomic orbital (as is the case with Ge atoms), violating Pauli’s exclusion principle regarding fermions occupying the same state. If this did happen, they would observe X-ray emission.

In the last case, type III interaction, the interaction occurs between fermions in the same system, that is, between electrons within Ge atoms. If an electron accidentally jumps from its orbit to another filled orbit, photons or X-rays are emitted, violating the Pauli principle.

Set new constraints and form a legend

The researchers found that all three scenarios worked as expected, with no violations.

“We found no evidence that these principles are violated, which sets tighter limits on new physical theories. The charge conservation limits are the most stringent since 1999,” said Dr. Wiseman.

The limit Dr. Wiseman is referring to here is the average lifetime of an electron decaying into three neutrinos (or dark matter), which they determined to be greater than 2.83 × 10²⁵ years, showing the high stability of electrons.

Furthermore, Dr. King added: “We did not find any signatures, which suggests that these two principles have very high precision – at least to the extent that current state-of-the-art technology can detect them. This further strengthens our understanding of these principles.” effectiveness.

The MAJORANA DEMONSTRATOR data set has proven to be incredibly versatile. The experiment is being expanded by merging with another germanium-based detector, Gerda, to form a larger collaboration called LEGEND.

“By operating a high-resolution germanium detector in an ultra-clean environment, LEGEND will further investigate various unexpected features beyond Standard Model physics,” said Dr. Kim.

Dr. Wiseman concluded: “The current results verify the accuracy of quantum mechanics and provide tighter constraints for future efforts to establish new physical theories. This will require more imagination, or as Feynman said: Imagination in bondage.

2024 Science X Network