Force that holds atoms together measured more precisely than ever
We know less about the strength of the strong force than of any of the other fundamental forces of nature, but researchers at CERN have now made the most precise measurement of it ever
By Leah Crane
2 October 2023
The ATLAS detector at CERN
Claudia Marcelloni and Max Brice/CERN
Researchers have measured the strong force, which binds together the particles that make up protons and neutrons, to the highest degree of precision ever. Despite being the most powerful of all the fundamental forces of nature, its strength is more uncertain than any of the others. Measuring it exactly is key to understanding the nature of the world around us.
The other fundamental forces – gravity, the electromagnetic force and the weak force – all get weaker as the particles they’re acting on get further apart. But the strong force gets even more powerful. This causes exotic effects that neutralise it, making it tough to measure directly.
“The only way we can observe the strong force is indirectly,” says Stefano Camarda at the CERN particle physics laboratory near Geneva, Switzerland. “This measurement is particularly difficult, and the improvement that we’ve had since the mid-80s has been quite slow.”
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Camarda and his colleagues used the ATLAS experiment at the Large Hadron Collider (LHC) to make a leap in precision, bringing the relative uncertainty in the force’s strength down to 0.8 per cent. “This measurement represents an improvement of a factor of 2 to 3 with respect to the previous best experimental measurements,” says Alberto Belloni at the University of Maryland.
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The researchers measured the strong force by slamming pairs of protons together, which produced a particle called a Z boson. If there were no force mediating the interactions between the protons, the final Z boson would be at a standstill. But the strong force imparted a small “kick” to this particle. Its resulting momentum depended on the strong force’s magnitude.