The U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility, Nuclear physicists have confirmed that the current description of proton structure isn’t perfect. A bump in the data in probes of the proton’s structure has been revealed by a new precision measurement of the proton’s electric polarizability.

Figure 1: A new precision measurement of the proton’s electric polarizability.

Figure 1 shows thatmore precise measurement has confirmed the presence of the anomaly and raises important questions about its origin. The research was published on October 19 in the journal Nature. [1]

It's understood that protons and other subatomic particles are, generally speaking, comprised of quarks, even smaller particles that carry fractional charges. The simplified, standard model contends protons contain two positively charged quarks, and one negatively charged quark.

The proton is a jumbled mess of countless quarks and antiquarks interacting with one another by exchanging gluons – a separate type of particle representing the strong force that holds quarks together to make up a proton.

At the Jefferson lab, the team bombarded liquid hydrogen with electrons to study the internal nature of the proton in each hydrogen atom, using virtual Compton scattering. The electrons interact with the hydrogen's protons, ultimately causing the proton's quarks to emit a photon.

Detectors measure how the electrons and photons scatter, to figure out the quarks' position and momentum. The information gives researchers an idea of the proton's internal structure, and a way to measure the proton's electric polarizability. [2]

Lower energy photons may bounce off the surface of the proton, while more energetic photons will blast inside the proton to interact with one of its quarks. Theory predicts that when these photon-quark interactions are plotted at from lower to higher energies, they will form a smooth curve.

Nikos Sparveris, at Temple University, said this simple picture didn't hold up to scrutiny. The measurements instead revealed an as-yet-unexplained bump.

"What we see is that there is some local enhancement to the magnitude of the polarizability. The polarizability decreases as the energy increases as expected. And, at some point, it appears to be coming temporarily up again before it will go down," he said.

The theory predicts that the more energetic electrons are more directly probing the strong force as it binds the quarks together to make the proton.The physicists said that the next step is to further tease out the details of this anomaly and conduct precision probes to check for other points of deviation and to provide more information about the anomaly's source. [3]

References:

1. https://scitechdaily.com/physicists-baffled-by-proton-structure-anomaly/
2. https://www.theregister.com/2022/10/23/physicists_proton_structure/
3. https://www.sciencedaily.com/releases/2022/10/221019111327.htm

Cite this article:

Sri Vasagi K (2022) A New Precision Measurement of the Proton's Electric Polarizability at the US, Anatechmaz, pp. 423