At long last, physicists have finally discovered what makes up the bulk of the proton’s mass, and in this case, it isn’t quarks that create the rather bulky heft of this subatomic particle.
As Science News reports, as protons are comprised of the tiny particles that are known as quarks, it only makes sense to believe that quarks give protons their mass. However, even if you add up the entirety of the mass of these quarks, it still doesn’t equal the mass of protons as there is still plenty of bulk left that is unaccounted for.
Thanks to new calculations, physicists now know that just nine percent of a proton’s mass comes from quarks. The rest of the mass of these protons is derived from different processes that are occurring inside of them. What physicists have learned is that the 938 million electron volts of mass that make up protons are due to the theory of quantum chromodynamics (QCD), which has to do with the complex mixing of particles that are found deep within protons.
It would be an impossibility to come up with calculations based simply on QCD, which is why physicists instead look to lattice QCD for results. It was through lattice QCD that physicists have been able to determine the mass of protons in the first place, but it is only recently that they have delved into what makes up this mass, according to theoretical physicist André Walker-Loud of Lawrence Berkeley National Laboratory in California, who stated, “It’s exciting because it’s a sign that we’ve really hit this new era.”
Only 9 percent of the subatomic particle’s bulk comes from the mass of its quarks. https://t.co/vPhvo7AEvZ
— Science News (@ScienceNews) November 26, 2018
While nine percent of a proton’s mass comes from quarks, a further 32 percent of its mass is derived from quarks that are moving around inside these protons, which creates a huge amount of energy. Other particles that live inside protons are gluons, and despite the fact that gluons have no mass themselves, these gluons help to hold the fabric of quarks together, and the energy it takes during this act accounts for yet another 36 percent of the mass of protons.
With just 23 percent mass remaining, physicists have determined that this is due to quantum effects that occur between gluons and quarks. It is due to these mysterious interactions that allow “QCD to flout a principle called scale invariance. In scale-invariant theories, stretching or shrinking space and time makes no difference to the theories’ results. Massive particles provide the theory with a scale, so when QCD defies scale invariance, protons also gain mass.”
The new study which demonstrates that the mass of protons comes from much more than just quarks has been published in Physical Review Letters.