Scientists at the Cern nuclear physics laboratory near Geneva have discovered a heavier version of the proton, the subatomic particle that sits at the heart of every known atom in the universe.
They spotted the particle in a shower of debris that lit up a detector at the Large Hadron Collider (LHC), located deep beneath the ground at Cern, which smashes protons together at close to the speed of light. The collisions recreate in microcosm conditions that prevailed just after the big bang, with the energy converting to particles that spray in all directions.
The newfound particle, which is four times heavier than the regular proton, should help physicists refine their understanding of the strong nuclear force that glues together the innards of all atomic nuclei. The force is unusual because it behaves like a rubber band, getting stronger as the distance between subatomic particles increases.
Physicists working on the LHCb experiment found the heavy proton after the detector was upgraded to make it more powerful.
“This is just the first of many expected insights that can be gained with the new LHCb detector,” said Prof Tim Gershon at the University of Warwick, who takes over as the LHCb international lead in July. “The improved detection capability allowed us to find the particle after only one year, while we could not see it in a decade of data collected with the original LHCb.”
Atoms of hydrogen, the simplest and most abundant element in the observable universe, contain only a proton and an electron. Protons, along with neutrons in heavier atoms, consist of elementary subatomic particles called quarks. A proton contains two up quarks and one down quark, but there are heavier, unstable versions of quarks known as charm, strange, top and bottom.
In the heavy proton detected at Cern, both up quarks are replaced with charm quarks. The particle, snappily named Xi-cc-plus, was revealed by its signature decay into other particles. After popping into existence, it does not hang around: scientists suspect it survives for less than a millionth of a millionth of a second before breaking down.
“The more we learn about these particles, the more we can learn about the strong force, and that is the same strong force that binds our protons and neutrons together,” said Prof Chris Parkes, a physicist at the University of Manchester.
The discovery comes as UK Research and Innovation(UKRI), the nation’s science funder, faces fierce criticism for its plans to pull £50m funding for the LHCb’s final upgrade in the 2030s. The revamp would ensure the detector made the most of a major transformation to the LHC that could substantially improve its discovery potential.
UK scientists working in particle physics, astronomy and nuclear physics have been told their grants will be slashed following cost overruns at major science facilities. Projects have also been hit, including the next LHCb upgrade and an electron-ion collider under development with researchers in the US.
Last week, Chi Onwurah, chair of the Commons science committee, sent a scathing letter to Prof Ian Chapman, chief executive of the UKRI, and Patrick Vallance, the science minister, calling the cuts “wholly unacceptable” and “a failure” by UKRI, the Science and Technology Facilities Council and the Department for Science, Innovation and Technology.
The letter demands “swift and decisive action” and asks whether the decision on the LHCb upgrade is final.
“It is so important that we can overcome the problems caused by the UKRI decision to deprioritise the funding for this project,” Gershon said. “No other experiment either running or planned will be able to do this physics.”
