Researchers in Hungary have published the exciting new claim that they’ve discovered a new subatomic particle, but it’s nowhere near time to start talking about Nobel Prizes as CNN (and now everyone who syndicates them) has done.
Since 2015, the team at the Institute of Nuclear Research (Atomki) and the University of Debrecen claims to have spotted a mysterious correlation between pairs of subatomic particles in their particle accelerator in Hungary. The observation stands in stark contrast with theoretical prediction, and could be the signature of a previously unobserved force of nature. But, like all controversial new results, this one will require further vetting and independent confirmation before it becomes gospel.
Presently scientists have four fundamental forces accounted for: gravity, electromagnetism, the weak nuclear force (which is responsible for radioactive decay), and the strong nuclear force (which holds atomic nuclei together). While these explain the matter that physicists have already observed, we know that most of the universe’s mass seems to be “dark matter,” stuff that clearly exerts gravity on the surrounding space but has no easy particle-based explanation. Perhaps there are other forces that communicate between regular matter and this dark matter – or just other particles that scientists haven’t spotted yet.
Back in 2015, the team in Hungary published their first result on the arXiv physics preprint paper server. They struck lithium atoms with a proton beam, causing some of the lithium to suck up a proton, turn into a radioactive form of the element beryllium, and decay. After enough data taking, they observed that as the angular separation between electrons and their antimatter counterpart called positrons emitted by the beryllium decay increased, the number of pairs of these particles decreased as expected – but then spiked at 140 degrees. The discovery made headlines the next year when a team of physicists in the US (led by the physicist who told CNN that this was a no-brainer Nobel Prize) realised the anomaly might be explained by a new force particle, one that would also explain another ongoing anomaly observed in an experiment called the Muon g-2 experiment that measures magnetic properties of a particle called the muon. The team in Hungary named the particle X17, since it weighed 17 mega electron-volts (around 35 times the proton’s mass).
The new results now on the arXiv physics paper server seems to be another hint of this particle’s existence with a new and improved setup. This time, they struck a tritium target – basically very heavy hydrogen – with the proton beam, watched it suck up a proton and turn into a heavy form of helium, then decay. Once again, they saw a spike in the electron-positron pairs, this time at 115 degree separation.
This is exciting stuff! But no, it’s not a Nobel-worthy discovery yet, because that’s not how particle physics works. Independent teams must now dive in and try and reproduce this results to ensure there weren’t any experiment-specific sources of error producing the signal. Physicists are taking the claim seriously, though. The NA64 experiment at CERN found no evidence of the decay last year, though their search continues. Other upcoming searches are underway or proposed.
I don’t mean to rain on the parade – it would obviously be a huge deal if scientists discovered a new fundamental force. But strong claims require strong evidence, including, most importantly, independent verification from other particle physics experiments.
Featured image: Zarija Lukic/Lawrence Berkeley National Laboratory