The value 0.0719 wo n’t mean much to most of us, but the way you’ve solved this measurement opens the window for some more than interesting possibilities for taking physics beyond the scope of the Standard Model.
In an international effort among scientists dubbed the Jefferson Lab Q-weak Collaboration , a team of physicists has taken advantage of a strange quirk of particle physics to obtain a robust measure of one of nature’s weakest fundamental forces.
Interactions between particles fall into four categories, which can also be combined at sufficiently high energies: nuclear forces, electromagnetic forces, weak forces, and forces of gravity.
Gravity is the first thing that comes to mind. It is also the weakest.
The other force we are familiar with is electromagnetism , which sees how opposing charges of protons and electrons are attracted through the mediation of light particles, called photons.
Then there is the strong nuclear force, which acts over small distances to bind together particles called quarks into protons and neutrons through the passage of a particle called a gluon.
Finally, there is a strange little “weak” nuclear force (or weak interaction) that transforms neutrons into protons.
Although not remotely as weak as gravity, the weak nuclear interaction represents only a fraction of the tug between the charges of a proton and an electron.
“ Measuring this effect has been difficult because the weak force is much weaker than the electromagnetic one, ” says Ross Young, from the University of Adelaide in the study published in the journal Nature.
The key here was to take advantage of a strange discovery made in the 1950s.
Most elements in physics follow some kind of balance or symmetry rule. On load, this would mean that if we suddenly swapped all the positives and negatives, everything would look more or less the same.
Likewise, if you rewind time, there is no indication that we would ever notice it.
The space is a little weirder. If we turned everything around in a giant universal mirror, most things would not change.
Exceptions
The weak nuclear force provides the only major exception. There is an inherent bias to the left and right in the decomposition of the particles involved with this force, which we would notice if the universe were turned all the way around. This violation of what we call the symmetry of parity forms the basis of this experiment on the weak force.
Spinning the electrons in one of two directions and throwing them at the protons causes them to bounce precisely, depending on the direction, or “helicity,” of their spin.
“The difference between the two helicity configurations is less than 300 per billion scattered electrons,” says Young. “By measuring this small difference very precisely, we were able to determine the weak charge on the proton.”
The results of the experiment match what would be expected based on the current picture of particle physics, the Standard Model.
“If the measurement had deviated from the prediction, it would be a strong signature for a new yet unknown type of force acting between fundamental particles,” Young clarifies.
Despite how robust the Standard Model is, there are still many loopholes where the nature of phenomena like dark energy and the theory of quantum gravity still remain shrouded in an enigma. We just need the right way to analyze these barely noticeable properties of our universe to find the clue.
Reference: Precision measurement of the weak charge of the proton, Nature (2018). The Jefferson Lab Qweak Collaboration DOI: 10.1038 / s41586-018-0096-0
