Scientists are looking for „new physics” beyond the Standard Model

Even a well-established theory such as the standard model is not accurate all the time, and there are instances where its predictions are violated.

Our understanding of the subatomic world is based on the Standard Model, which describes all known elementary particles and their interactions. The success with which scientists have been able to relate its predictions to experiment has become one of the most important and fundamental theories in physics.

However, even a well-established theory such as the standard model is not accurate all the time, and there are instances where its predictions are violated or contradicted. This presents an exciting prospect, suggesting that some changes to the theory are needed, and may lead to the discovery of „new physics”, particularly new types of physical processes, particles and interactions.

To find out, two groups of American scientists have presented ideas on how to use the behavior of atoms and molecules to look for deviations from the standard model, especially aspects of this behavior related to the spin of electrons.

Deflections by electron spin

One can think of electrons as small, spinning tops spinning on a vertical axis. The rate at which they oscillate or change direction – a phenomenon called spin precession – depends on which particles, atoms and molecules they interact with and what laws those interactions obey. Studying deviations in the electron spin preview can help uncover physics beyond the standard model.

their study Published in ScienceResearchers led by Nicholas Hützler, an assistant professor of physics at Caltech, developed an experiment to study electron spin in molecules of calcium monohydroxide.

They chose this molecule because one of its electrons is sensitive to an applied magnetic field, and measuring its spin precession under the influence of a magnet would help test the validity of the standard model with very high precision.

To do this, the molecules were cooled to absolute zero (-273°C) to minimize the effect of temperature fluctuations on the experimental results and the spin forward was measured by irradiating the molecules with electromagnetic waves at a specially selected wavelength.

Although the team did not detect any deviations from the standard model this time – a sensational discovery on par with the discovery of the Higgs boson or gravitational waves – this new method of looking for deviations is a breakthrough.

Hutzler and his team proposed improvements to their experiment to get to a point where they could one day detect deviations from the standard model in the properties of electron spin precession. Molecules with highly sensitive electrons and better protection from external electromagnetic fields that affect results.

Using the problem goes further

Building on this work, another team of researchers led by Chi Zhang, the David and Ellen Lee Postdoctoral Scholar Research Associate in Physics at Caltech, proposed using the problem to further improve the accuracy of the method developed by Hutsler and his colleagues.

Entanglement is an incredible quantum phenomenon in which objects once in contact can store information about each other, even if they are separated by arbitrarily large distances. Also, the state of one object can be changed by manipulating the state of another.

their study Published in Physical review lettersThe team developed a method to trap molecules of calcium monohydroxide used by Hützler’s group, which solves a limitation by making the system less sensitive to fluctuations in external electromagnetic fields, since entanglement affects the behavior of the entire system and therefore increases. The accuracy of measuring the precession rate of their electrons.

„It’s like anchoring rubber ducks together,” Hutzler said Report. “If you want to measure the movement of ducks across a tank, if you line them up completely, they will be less sensitive to the background noise of splashing water. They are more sensitive to something you want to measure, such as the flow of current, because they all respond to it collectively.

„We want to be sensitive to the structure of the molecules,” Zhang said. „Uncontrolled electric and magnetic fields from the experimental setup lead to our measurements, but now we have a new protocol for trapping molecules in a way that is less sensitive to noise.”

In the next steps, putting these proposals into practice, the experiments will not require complex experimental facilities – cold molecules, lasers and a detector. This is significant because deviations from the Standard Model are typically studied using large particle accelerators such as the 27-kilometer-long Large Hadron Collider, which require large amounts of money, effort, and time to build and modify.

If these proposals and theoretical calculations turn out to be correct, scientists will have a very powerful method for studying nature at the most fundamental level.

„With the advantages of complexity, researchers can push these experiments to explore exciting fields of new physics,” Hutzler concluded.

References: Chi Zhang et al., Quantum-enhanced metrology for molecular symmetry breaking using decoherence-free subspaces, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.131.193602; Loïc Anderegg et al., Quantum confinement of entangled polyatomic molecules for eEDM searches, Science (2023). DOI: 10.1126/science.adg8155

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