PRL Found the shaft
A team led by theoretical physicists at the University of Minnesota-Twin Cities, in collaboration with experimental researchers at the Fermi National Accelerator Laboratory, recently discovered a new method for finding axions. The physicists' new strategy opens up previously unexplored opportunities for detecting axions in particle collider experiments.
The researchers' paper was published May 31 in Physical Review Letters under the title "First Constraints on Heavy QCD Axions with a Liquid Argon Time Projection Chamber Using the ArgoNeuT Experiment" and as Editor's Recommendation.
"As particle physicists, we are striving to develop our best understanding of nature," said Zhen Liu, co-author of the paper and assistant professor in the School of Physics and Astronomy at the University of Minnesota. "Over the past century, scientists have used established theoretical frameworks in the search for fundamental particles with great success. So it's extremely puzzling why neutrons don't couple to electric fields, as we expect them to in our known theories; if we do discover axions, it will be a huge advance in our fundamental understanding of the structure of nature."
There are many, many substances in nature that are made up of various atomic molecules, etc.; and atoms are made up of more fundamental particles, such as protons, neutrons, electrons, etc. In addition, the light produced by the sun and the magnetic field produced by a magnet, which are not physical fields, are also the substances that make up the universe. So, how many basic units of matter are there in the universe? As mentioned before, atoms can be divided into smaller protons, neutrons, and electrons, so can these particles be further subdivided?
These questions have been seriously studied by physicists decades ago, they proposed a set of theories called the "standard model", predicting all possible elementary particles, a total of 61 species.
This model includes three other fundamental forces besides gravity, and its predicted particles have been confirmed by experiments one after another, especially the discovery of the Higgs boson, the "angel particle", on July 4, 2012, which marks the unprecedented success of the Standard Model and is the closest universal model to the theory of everything. Even so, there are still unanswerable phenomena in the Standard Model, such as neutrino oscillations, the origin of dark matter, and the imbalance between positive and negative matter.
--The latter two of these questions are related to axions.
An axion is a hypothetical particle that theoretically interacts weakly with other matter and has a small mass, making it difficult to observe (if it exists at all).
Dark matter has many candidates for particles that are not included in the Standard Model, so a discovery would be another milestone in physics; its candidates for new particles include axions. The axion was not originally proposed to solve the dark matter problem, but was initially derived from the Peccei-Quinn theory proposed by theoretical physicists Roberto Peccei and Helen Quinn to solve the strong CP problem in quantum chromodynamics. They introduced a new dynamical scalar field to characterize the magnitude of the action that violates the charge-universe symmetry, a field that can naturally give very small parameter values, guaranteeing the conservation of symmetry, and thus solving the strong CP problem.
Later, Nobel Prize winners in physics Frank Wilczek and Steven Weinberg pointed out that this would introduce a new particle, the "axion" axon.
The introduction of the axion is essentially a requirement that it be weak, thus characterizing the very weak CP breaking, which results in a particle that theoretically interacts with almost no other particles and has a very small mass, about 10-11 to 10-9 orders of magnitude of the mass of the electron, and therefore is not conditioned to be observed in previous experiments.
The method proposed by the team now involves measuring the "decay" product - what happens when an unstable heavy particle transforms into multiple lighter particles. By reconstructing this decay backward from the muon orbit in the detector, the scientists believe they have a chance to find the axion and prove its existence.
One of the main tools for studying subatomic particles and possibly discovering new ones is the collider experiment. Essentially, scientists force beams of particles to collide: when they hit each other, the energy generated produces other particles, and researchers are able to analyze their properties through a detector.
With this research, we are expanding the ways we can search for axion particles," said Raymond Co, co-author of the paper and a postdoctoral fellow in the School of Physics and Astronomy at the University of Minnesota. People have never before used the decay of axions into muons as a way to search for axion particles in neutrino or collider experiments. This research opens up new possibilities that could pave the way for future efforts in our field."
The article concludes with the team stating, "We have presented the first search for heavy QCD axions in LArTPC using the ArgoNeuT experiment. This search can be extended to a variety of new heavy QCD axion models, paving the way for future heavy QCD axion searches at neutrino facilities; the developed technique can also be used to constrain other dark particle models with long-lived resonant decays."
Reference links:
[1] https://mp.weixin.qq.com/s/mN1ArkjERy3V7MHTcaA8iw
[2]https://arxiv.org/pdf/2207.08448.pdf
[3]https://phys.org/news/2023-06-particle-axions-puzzling-physics.html
