Researchers determined the pressure distribution inside the proton. They made the first measurement of a mechanical property of a subatomic particle. The team found that the proton’s building blocks, quarks, are subjected to an astounding pressure of 100 decillion Pascal (1035) near the center of a proton. How much pressure? It’s about 10 times greater than the pressure in the heart of a neutron star.
The result gives incredible insight into the distribution of the strong force inside the proton. The strong force holds the proton together. On top of that, the success of the experimental technique used opens the door for pioneering explorations of other mechanical properties of the proton.
Inside every proton in every atom in the universe is a pressure cooker environment that surpasses the atom-crushing heart of a neutron star. That’s according to the first measurement of a mechanical property of subatomic particles, the pressure distribution inside the proton, which was carried out by nuclear physicists at Jefferson Lab. Once thought impossible to obtain, this measurement is the result of a clever pairing of two theoretical frameworks with existing data. The first framework is the generalized parton distribution (GPD) that scientists use to create a 3D image of the proton’s structure as probed by the electromagnetic force. The second is the gravitational form factor of the proton, which represents the mechanical structure of the proton as probed by the gravitational force. The nuclear physicists used existing data from Jefferson Lab’s Continuous Electron Beam Accelerator Facility Large Acceptance Spectrometer to determine that the proton’s building blocks, the quarks, are subjected to a pressure of 100 decillion Pascal (1035) near the center of a proton, which is about 10 times greater than the pressure in the heart of a neutron star. The next step is to apply this revolutionary technique to even more precise data from the Continuous Electron Beam Accelerator Facility to reveal other mechanical properties of the ubiquitous proton, such as the internal shear forces and the proton’s mechanical radius.
This material is based on work supported by the Department of Energy, Office of Science, Office of Nuclear Physics.
V.D. Burkert, L. Elouadrhiri, and F.X. Girod, “The pressure distribution inside the proton.” Nature 557, 396 (2018). [DOI: 10.1038/s41586-018-0060-z]