"The idea that there must be something else in an atom's nucleus came from the fact that the number of protons didn't match an atom's atomic weight. For example, an oxygen atom contains 8 protons, but has an atomic weight of 16, suggesting that it contains 8 other particles. However, these mystery particles would have to be electrically neutral, since atoms normally have no overall electric charge (the negative charge of the electrons cancels out the positive charge of the protons)."
A problem I see in these various reports about particles and the Standard Model, how does the Big Bang creation story explain their origin and when did these particles get created in BB cosmology? Was it before the Planck time and Planck length era for the universe? During inflation? During some quick post-inflation epoch? Why should neutrons appear negative charge vs. another positive charge? What would that do for our universe we live in today and observe using our telescopes? Is all of this just a big cosmic accident based upon the BB cosmology and new physics used today?
Here are some recent reports by space.com that ask like questions here.
Protons are ubiquitous in the universe. They are found in the nuclei of all atoms and play a crucial role in how stars shine. Protons: The essential building blocks of atoms : Read more
Quarks are elementary particles that are the building blocks of all visible matter in the universe. Explore them in more detail here. Quarks: What are they? : Read more
Lagrange found that the difference between an object's kinetic energy and potential energy unlocked something deeply profound about the universe. What makes Newton's laws work? Here's the simple trick. : Read more