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Scientists may have discovered fifth force of nature, laboratory announces

With appearance of mysterious new particle X17, will physicists have to call time on hunt for dark matter?

Harry Cockburn
Wednesday 20 November 2019 17:48 GMT
Scientists may have discovered fifth force of nature, laboratory announces

It has long been recognised that there are four “fundamental forces” which govern nature.

The substance of our universe is pulled together, or pushed apart by these forces which are determined by the fact they do not appear to be reducible to more basic interactions between particles.

They include the gravitational and electromagnetic forces, which produce significant long-range interactions whose effects can be seen directly in everyday life.

And they also include forces known as the strong interactions and weak interactions, which produce forces at tiny, subatomic distances and govern nuclear physics.

Over the years, there have been many unsubstantiated claims of the existence of a fifth fundamental force, and as the long hunt for dark matter continues to prove fruitless, efforts to find new forces at play to help fill-in the gaps the standard model of particle physics can’t explain have increased.

Dark matter is a theoretical substance hypothesised to account for around 85 per cent of all mass in the universe, but has not yet been glimpsed.

But now, scientists in Hungary’s Atomki Nuclear Research Institute, believe they may have found more solid evidence of a previously unknown fifth fundamental force of nature.

Attila Krasznahorkay and his colleagues at Atomki first reported some surprising results in 2015 after studying the light emitted during the radioactive decay of beryllium-8, an unstable isotope.

Since beryllium-8’s discovery in the 1930s after the construction of the first particle accelerator in Cambridge, the existence of this unstable atom, and the unique way it decays has been the focus of numerous studies related to stellar nucleosynthesis – how nuclear fusion in stars forms elements.

In 2015, they found, when firing protons at the isotope lithium-7, which creates beryllium-8, the subsequent decay of the particles did not produce exactly the expected light emissions, and that a specific tiny “bump” occurs, which means for an unexplained reason, the electrons and positrons, which burst apart as the atom decays, were frequently pushing away from each other at exactly 140 degrees.

Various retests at the same lab confirmed the results, and a year later, the same experiment was repeated, with the same results in America.

It is thought that the moment the atom decays, excess energy among its constituent parts briefly creates a new unknown particle, which then almost immediately decays into a recognisable positron and electron pair.

But we are not all about to be turned inside out or flattened into a different dimension. The unknown particle, described as a “protophobic X boson”, is thought would carry a force that acts over microscopic distances not much greater than that of an atomic nucleus.

A “boson” is a particle which can carry forces.

The particle has been named X17, as its mass is calculated to be 17 megaelectronvolts.

But Dr Krasznahorkay now believes they have measured the same results in stable helium atoms, however, instead of the electrons and positrons in the helium atoms separating at 140 degrees, the angle was closer to 115 degrees.

“This feature is similar to the anomaly observed in 8Be, and seems to be in agreement with the X17 boson decay scenario,” the team writes in arXiv, where the research has been published, but has not yet been peer-reviewed.

If the particle’s existence is confirmed, it means physicists will have to finally reassess the interactions of the existing four fundamental forces of particle physics and make space for a fifth.

“We are expecting more, independent experimental results to come for the X17 particle in the coming years,” the research team concludes in its paper.

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