Posts Tagged ‘matter’

by Mike McCrae

Everything in our Universe is held together or pushed apart by four fundamental forces: gravity, electromagnetism, and two nuclear interactions. Physicists now think they’ve spotted the actions of a fifth physical force emerging from a helium atom.

It’s not the first time researchers claim to have caught a glimpse of it, either. A few years ago, they saw it in the decay of an isotope of beryllium. Now the same team has seen a second example of the mysterious force at play – and the particle they think is carrying it, which they’re calling X17.

If the discovery is confirmed, not only could learning more about X17 let us better understand the forces that govern our Universe, it could also help scientists solve the dark matter problem once and for all.

Attila Krasznahorkay and his colleagues from the Institute for Nuclear Research in Hungary suspected something weird was going on back in 2016, after analysing the way an excited beryllium-8 emits light as it decays.

If that light is energetic enough, it transforms into an electron and a positron, which push away from one another at a predictable angle before zooming off.

Based on the law of conservation of energy, as the energy of the light producing the two particles increases, the angle between them should decrease. Statistically speaking, at least.

Oddly, this isn’t quite what Krasznahorkay and his team saw. Among their tally of angles there was an unexpected rise in the number of electrons and positrons separating at an angle of 140 degrees.

The study seemed robust enough, and soon attracted the attention of other researchers around the globe who suggested that a whole new particle could be responsible for the anomaly.

Not just any old particle; its characteristics suggested it had to be a completely new kind of fundamental boson.

That’s no small claim. We currently know of four fundamental forces, and we know that three of them have bosons carrying their messages of attraction and repulsion.

The force of gravity is carried by a hypothetical particle known as a ‘graviton’, but sadly scientists have not yet detected it.

This new boson couldn’t possibly be one of the particles carrying the four known forces, thanks to its distinctive mass of (17 megaelectronvolts, or about 33 times that of an electron), and tiny life span (of about 10 to the minus 14 seconds … but hey, it’s long enough to smile for the camera).

So all signs point to the boson being the carrier of some new, fifth force. But physics isn’t keen on celebrating prematurely. Finding a new particle is always big news in physics, and warrants a lot of scrutiny. Not to mention repeated experiment.

Fortunately, Krasznahorkay’s team haven’t exactly been sitting on their laurels over the past few years. They’ve since changed focus from looking at the decay of beryllium-8 to a change in the state of an excited helium nucleus.

Similar to their previous discovery, the researchers found pairs of electrons and positrons separating at an angle that didn’t match currently accepted models. This time, the number was closer to 115 degrees.

Working backwards, the team calculated the helium’s nucleus could also have produced a short-lived boson with a mass just under 17 megaelectronvolts.

To keep it simple, they’re calling it X17. It’s a long way from being an official particle we can add to any models of matter.

While 2016’s experiment was accepted into the respectable journal, Physical Review Letters, this latest study is yet to be peer reviewed. You can read the findings yourself on arXiv, where they’ve been uploaded to be scrutinised by others in the field.

But if this strange boson isn’t just an illusion caused by some experimental blip, the fact it interacts with neutrons hints at a force that acts nothing like the traditional four.

With the ghostly pull of dark matter posing one of the biggest mysteries in physics today, a completely new fundamental particle could point to a solution we’re all craving, providing a way to connect the matter we can see with the matter we can’t.

In fact, a number of dark matter experiments have been keeping an eye out for a 17 megavolt oddball particle. So far they’ve found nothing, but with plenty of room left to explore, it’s too early to rule anything out.

Rearranging the Standard Model of known forces and their particles to make room for a new member of the family would be a massive shift, and not a change to make lightly.

Still, something like X17 could be just what we’re looking for.

This research is available on arXiv ahead of peer review: https://arxiv.org/abs/1910.10459

https://www.sciencealert.com/physicists-claim-a-they-ve-found-even-more-evidence-of-a-new-force-of-nature

Since the 1930s scientists have been searching for particles that are simultaneously matter and antimatter. Now physicists have found strong evidence for one such entity inside a superconducting material. The discovery could represent the first so-called Majorana particle, and may help researchers encode information for quantum computers.

Physicists think that every particle of matter has an antimatter counterpart with equal mass but opposite charge. When matter meets its antimatter equivalent, the two annihilate one another. But some particles might be their own antimatter partners, according to a 1937 prediction by Italian physicist Ettore Majorana. For the first time researchers say they have imaged one of these Majorana particles, and report their findings in the October 3 Science.

The new Majorana particle showed up inside a superconductor, a material in which the free movement of electrons allows electricity to flow without resistance. The research team, led by Ali Yazdani of Princeton University, placed a long chain of iron atoms, which are magnetic, on top of a superconductor made of lead. Normally, magnetism disrupts superconductors, which depend on a lack of magnetic fields for their electrons to flow unimpeded. But in this case the magnetic chain turned into a special type of superconductor in which electrons next to one another in the chain coordinated their spins to simultaneously satisfy the requirements of magnetism and superconductivity. Each of these pairs can be thought of as an electron and an antielectron, with a negative and a positive charge, respectively. That arrangement, however, leaves one electron at each end of the chain without a neighbor to pair with, causing them to take on the properties of both electrons and antielectrons—in other words, Majorana particles.

As opposed to particles found in a vacuum, unattached to other matter, these Majoranas are what’s called “emergent particles.” They emerge from the collective properties of the surrounding matter and could not exist outside the superconductor.

The new study shows a convincing signature of Majorana particles, says Leo Kouwenhoven of the Delft University of Technology in the Netherlands who was not involved in the research but previously found signs of Majorana particles in a different superconductor arrangement. “But to really speak of full proof, unambiguous evidence, I think you have to do a DNA test.” Such a test, he says, must show the particles do not obey the normal laws of the two known classes of particles in nature—fermions (protons, electrons and most other particles we are familiar with) and bosons (photons and other force-carrying particles, including the Higgs boson). “The great thing about Majoranas is that they are potentially a new class of particle,” Kouwenhoven adds. “If you find a new class of particles, that really would add a new chapter to physics.”

Physicist Jason Alicea of California Institute of Technology, who also did not participate in the research, said the study offers “compelling evidence” for Majorana particles but that “we should keep in mind possible alternative explanations—even if there are no immediately obvious candidates.” He praised the experimental setup for its apparent ability to easily produce the elusive Majoranas. “One of the great virtues of their platform relative to earlier works is that it allowed the researchers to apply a new type of microscope to probe the detailed anatomy of the physics.”

The discovery could have implications for searches for free Majorana particles outside of superconducting materials. Many physicists suspect neutrinos—very lightweight particles with the strange ability to alter their identities, or flavors—are Majorana particles, and experiments are ongoing to investigate whether this is the case. Now that we know Majorana particles can exist inside superconductors, it might not be surprising to find them in nature, Yazdani says. “Once you find the concept to be correct, it’s very likely that it shows up in another layer of physics. That’s what’s exciting.”

The finding could also be useful for constructing quantum computers that harness the laws of quantum mechanics to make calculations many times faster than conventional computers. One of the main issues in building a quantum computer is the susceptibility of quantum properties such as entanglement (a connection between two particles such that an action on one affects the other) to collapse due to outside interference. A particle chain with Majoranas capping each end would be somewhat immune to this danger, because damage would have to be done to both ends simultaneously to destroy any information encoded there. “You could build a quantum bit based on these Majoranas,” Yazdani says. ”The idea is that such a bit would be much more robust to the environment than the types of bits people have tried to make so far.”

http://www.scientificamerican.com/article/majorana-particle-matter-and-antimatter/