The proton, one of the components of atomic nuclei, consists of fundamental particles called quarks and gluons. A team of physicists from the US Department of Energy's Thomas Jefferson National Accelerator Facility found extremely high pressure from the center of the proton to the outside and a much lower inward pressure near the proton periphery. They also found that quarks are exposed to a pressure of 10 35 pascals near the center of the proton, which is about ten times larger than the pressure in the heart of neutron stars, the most densely packed known objects in the universe. 19659002] The first measurement of the mechanical property of a subatomic particle shows the distribution of pressure inside the proton. Image credits: Thomas Jefferson's National Accelerator Facility ”
"The distribution of pressure within the proton is determined by the strong force, the force that connects three quarks into one proton, and our results also shed light on the distribution of strong forces within the proton "said Dr. Volker Burkert, first author of the study.
"We provide a way to visualize the magnitude and distribution of the strong force inside the proton proton, opening up a whole new direction in nuclear and particle physics that can be explored in the future."
Once considered impossible, this measurement is the result of a skilful pairing of two theoretical frameworks with existing data.
First, there are the generalized parton distributions; they allow physicists to create a 3D image of the proton structure as probed by the electromagnetic force.
The second is the gravitational form factors of the proton. These form factors describe what the mechanical structure of the proton would look like if researchers could study the proton via gravitational force.
The American physicist dr. Heinz Pagels, who developed the concept of gravitational form factors in 1966, was noted in a paper. They pointed out that due to the extreme weakness of the gravitational interaction, "there is very little hope of knowing anything about the detailed mechanical structure of a particle."
Recent theoretical work, however, has linked generalized particle distributions with the gravitational form Factors that allow the results of proton electromagnetic probes to replace gravitational probes.
"That's the beauty of it, you have this map that you think you'll never get, but here we are and fill in this electromagnetic probe," said co-author Dr. Latifa Elouadrhiri.
The electromagnetic probe consists of electron beams generated by the Continuous Electron Beam Accelerator Facility, a DOE Office of Science User Facility
These electrons are conducted into atomic nuclei where they are electromagnetically confined with the quarks within protons Interacting process called deep virtual Compton scattering.
An electron enters a proton and exchanges a virtual photon with a quark that transfers energy to the quark and proton. A short time later, the proton releases this energy by emitting another photon and working it intact. The process is analogous to the calculations that Dr. Pagels to find out how it would be possible to gravitationally study the proton via a hypothetical beam of gravitons.
Burkert, dr. Elouadrhiri and her colleague, dr. Francois-Xavier Girod, could exploit a similarity between the known electromagnetic and hypothetical gravity studies to come to their conclusion.
"There's a photon, and a photon comes out, and the pair of photons are both spin-1, giving us the same information as exchanging a graviton particle for spin-2," Dr. Girod.
"Well, now you can basically do the same thing we did in electromagnetic processes – but relative to the gravitational form factors that represent the mechanical structure of the proton."
The results appear in the journal Nature
VD Burkert et al. . 2018. The pressure distribution inside the proton. Nature 557: 396-399; doi: 10.1038 / s41586-018-0060-z