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Protons are particles that exist in the nucleus of all atoms, with their number defining the elements themselves. Protons, however, are not fundamental particles. Rather, they are composite particles made up of smaller subatomic particles, namely two “up quarks” and one “down quark” bound together by force-carrying particles (bosons ) called “gluons.”
This structure isn’t certain, however, and quantum physics suggests that along with these three quarks, other particles should be “popping” into and out of existence at all times, affecting the mass of the proton. This includes other quarks and even quark-antiquark pairs.
This structure isn’t certain, however, and quantum physics suggests that along with these three quarks, other particles should be “popping” into and out of existence at all times, affecting the mass of the proton. This includes other quarks and even quark-antiquark pairs.
Now, by exploiting a high-precision determination of the quark-gluon content of the proton and by examining 35 years’ worth of data, particle physics data researchers have discovered evidence that the proton does contain intrinsic charm quarks.
What makes this result more extraordinary is that this flavor of quark is one-and-a-half times more massive than the proton itself. Yet when it is a component of the proton, the charm quark still only accounts for around half of the composite particle’s mass.
The Weirdness of Quantum Mechanics
This counter-intuitive setup is a consequence of the weirdness of quantum mechanics, the physics that governs the subatomic world. This requires thinking of the structure of a particle and what can be found within it as probabilistic in nature.
“There are six kinds of quarks in nature, three are lighter than the proton [up, down, and strange quarks] and three are heavier [charm, up, and down quarks],” Stefano Forte, NNPDF Collaboration team leader and professor of theoretical Physics at Milan University, tells the Nature Briefing podcast. “One would think that only the lighter quarks are inside the proton, but actually, the laws of quantum physics allow also for the heavier quarks to be inside the proton.”
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