A Particle New To Physics Could Solve the Dark Matter Mystery

A team of scientists in Hungary currently published a paper that hints at the presence of a previously unknown subatomic particle. The group first reported finding traces of the particle in 2016, and they now report more traces in a different experiment.

If the outcomes are confirmed, the so-called X17 particle could help to explain the dark matter; the mysterious substance scientists think accounts for more than 80% of the mass in the universe. It might be the provider of a “fifth force” beyond the four accounted for in the typical model of physics (gravity, electromagnetism, the weak nuclear force, and the strong nuclear force).

Smashing atoms

Most scientists who hunt for new particles use enormous accelerators that smash subatomic particles together at high velocity and look at what comes out of the explosion. The biggest of these accelerators is the Huge Hadron Collider in Europe, where the Higgs boson– a particle scientists had been hunting for decades– was discovered in 2012.

Attila J. Krasznahorkay and also his colleagues at ATOMKI (the Institute of Nuclear Research in Debrecen, Hungary) get taken a different approach, conducting smaller experiments which fire the subatomic particles called protons at the nuclei of different atoms.

In 2016, they observed at pairs of electrons and also positrons (the antimatter version of electrons) created when beryllium-8 nuclei went from a high energy state to a reduced energy state.

They spotted a deviation from what they expected to observe when there was a big angle between the electrons and positrons. This anomaly could be best be explained if the nucleus emitted an unknown particle which later “split” into an electron and a positron.

This particle would have to be a boson, which is the sort of particle that carries force, and its mass would be around seventy million electron volts. That is about as heavy as thirty-four electrons, which is fairly lightweight for a particle like this. (The Higgs boson, for instance, is more than 10,000 times heavier.).

Because of its mass, Krasznahorkay and his group called the hypothetical particle X17. Now they have observed some weird behavior in helium-4 nuclei which can also be explained by the presence of X17.

This latest anomaly is statistically significant– a seven sigma confidence level, which means there is only a very small possibility the outcome occurred by chance. This is well beyond the usual 5-sigma standard for a new discovery, so the outcome would seem to suggest there is some brand-new physics here.

Checking and double checking

However, the brand-new announcement and the one in 2016 have been met with scepticism by the physics community– the sort of scepticism that did not exist when two groups simultaneously published the discovery of the Higgs boson in 2012.

So why is it so difficult for physicists to think a new lightweight boson like this could exist?

First, experiments of this sort are hard, and so is the analysis of the data. Signals could appear and disappear. Back in 2004, for example, the team in Debrecen found evidence they interpreted as the possible existence of an even lighter boson. However, when they repeated the experiment, the signal was gone.

Second, one requires to make sure the very presence of X17 is compatible with the outcomes from other experiments. In this case, both the 2016 outcome with beryllium and the new outcome with helium can be explained by the presence of X17. However, an independent check from an independent group is still necessary.

Krasznahorkay and his team first reported weak proof (at a three-sigma level) for a brand-new boson in 2012 at a workshop in Italy.

Since then, the group has repeated the experiment using upgraded equipment and successfully reproduced the beryllium-8 outcomes, which is reassuring, as are the new outcomes in helium-4. These new outcomes were presented at the HIAS 2019 symposium at the Australian National College in Canberra.

What does this have to do with dark matter?

Scientists think that most of the matter in the universe is invisible to us. So-called dark matter would just interact with normal matter very weakly. We could infer that it exists from its gravitational effects on distant stars and galaxies. However, it has never been detected in the laboratory.

So, where does X17 come in?

In 2003, in among us (Boehm) revealed that a particle like Xseventy could exist in work co-authored with Pierre Fayet and alone. It could carry force between dark matter particles in much the same way photons, or particles of light, do for ordinary matter.

In one of the scenarios I recommended, lightweight dark matter particles could sometimes process pairs of electrons and positrons in a form that is similar to what Krasznahorkay’s team has seen.

This situation has led to many searches in low-energy experiments, which have ruled out many possibilities. However, X17 has not yet been ruled out– in which case the Debrecen team may have indeed discovered how dark matter particles deal with our world.

More evidence required

While the results from Debrecen are fascinating, the physics community will not be convinced a brand-new particle has indeed been spotted until there is independent confirmation.

So we can expect a lot of experiments around the world that are looking for a new lightweight boson to begin hunting for evidence of X17 and its interaction with pairs of electrons and positrons.

If confirmation arrives, the subsequent discovery might be the dark matter particles themselves.

Read the originala article on The Conversation.