Wednesday, August 17, 2022

Physicists discover never-before seen particle sitting on a tabletop

HomeNewsPhysicists discover never-before seen particle sitting on a tabletop
This newly-discovered particle could account for dark matter.

Researchers have found a new particle that is the Higgs boson’s magnetic cousin. Unlike the discovery of the Higgs boson, which needed the incredible particle-accelerating power of the Large Hadron Collider (LHC), the axial Higgs boson was discovered with an experiment that could fit on a tiny kitchen countertop.

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In addition to being a first in and of itself, this magnetic cousin of the Higgs boson — the particle responsible for giving other particles mass — might be a candidate for dark matter, which accounts for 85 percent t of the total mass of the universe but is only revealed by gravity.

“When my student showed me the data I thought she must be wrong,” Kenneth Burch, a professor of physics at Boston College and lead researcher of the team that made the discovery, said. “It’s not every day you find a new particle sitting on your tabletop.”

The axial Higgs boson differs from the Higgs boson, which was initially identified at the LHC in 2012 by the ATLAS and CMS detectors, in that it contains a magnetic moment, a magnetic strength or direction that generates a magnetic field. As such, it necessitates a more sophisticated theory than its non-magnetic mass-granting relative.

According to the Standard Model of particle physics, particles come from many fields that pervade the cosmos, and some of these particles shape the basic forces of the universe. Photons, for instance, mediate electromagnetism, whereas W and Z bosons mediate the weak nuclear force, which regulates nuclear disintegration at the subatomic level. Nevertheless, when the cosmos was young and hot, electromagnetic and weak force were the same thing, and these particles were almost identical. Physicists refer to this phenomenon as “symmetry breaking.” As the cosmos cooled, the electroweak force broke, causing the W and Z bosons to develop mass and act significantly differently from photons. But how precisely could these particles with weak force mediation get so heavy?

These particles, it turns out, interacted with a distinct field known as the Higgs field. This field’s perturbations gave rise to the Higgs boson and gave the W and Z bosons their mass.

When such symmetry is violated in nature, the Higgs boson is created. “However, often only one symmetry is violated at a time,” Burch explained, therefore the Higgs is solely characterised by its energy.

The hypothesis underlying the axial Higgs boson is more difficult.

“In the case of the axial Higgs boson, it appears multiple symmetries are broken together, leading to a new form of the theory and a Higgs mode [the specific oscillations of a quantum field like the Higgs field] that requires multiple parameters to describe it: specifically, energy and magnetic momentum,” Burch said.

Burch and colleagues described the new magnetic Higgs cousin in a study published in the journal Nature on Wednesday (June 8). Burch explained that the original Higgs boson does not couple directly with light, so it must be created by smashing other particles together with enormous magnets and high-powered lasers, while also cooling samples to extremely low temperatures. The presence of the Higgs is shown by the disintegration of the original particles into those that exist only momentarily.

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In contrast, the axial Higgs boson emerged when quantum materials at ambient temperature emulated a certain set of oscillations known as the axial Higgs mode. The researchers then observed the particle via light scattering.

“We found the axial Higgs boson using a tabletop optics experiment which sits on a table measuring about 1 x 1 meters by focusing on a material with a unique combination of properties,” Burch continued. “Specifically we used rare-earth Tritelluride (RTe3) [a quantum material with a highly 2D crystal structure]. The electrons in RTe3 self-organize into a wave where the density of the charge is periodically enhanced or reduced.”

The axial Higgs mode is produced when the magnitude of these charge density waves, which occur above room temperature, is changed over time.

In the latest work, the axial Higgs mode was generated by delivering laser light of a single hue into an RTe3 crystal. In a process known as Raman scattering, the light dispersed and changed to a colour with a lower frequency, and the energy lost during the colour shift generated the axial Higgs mode. The scientists next rotated the crystal and discovered that the axial Higgs mode also regulates the angular momentum of the electrons in the material, or the rate at which they travel in a circle, indicating that this mode must also be magnetic.

“Originally we were simply investigating the light scattering properties of this material. When carefully examining the symmetry of the response  —  how it differed as we rotated the sample  —  we discovered anomalous changes that were the initial hints of something new,” Burch explained. “As such, it is the first such magnetic Higgs to be discovered and indicates the collective behavior of the electrons in RTe3 is unlike any state previously seen in nature.”

In the past, particle scientists have predicted an axial Higgs mode and used it to explain dark matter, but this is the first time it has been observed. Scientists have never before detected a condition with numerous broken symmetries.

A symmetric system that seems identical in all directions breaks symmetry when it becomes asymmetric. The University of Oregon advises comparing this to a spinning coin with two potential states. Eventually, the coin will land on its head or tail side, releasing energy and becoming asymmetrical.

Excitingly, if this double symmetry-breaking is consistent with existing physics theories, it may be possible to create hitherto unknown particles that might account for dark matter.

“The basic idea is that to explain dark matter you need a theory consistent with existing particle experiments, but producing new particles that have not yet been seen,” Burch said. 

Adding this additional symmetry-breaking through the axial Higgs wave is one method to do this, he explained. Burch stated that although being anticipated by physicists, the team’s finding of the axial Higgs boson was unexpected, and they spent a year seeking to validate their observations.