# Questions tagged [quarks]

The quark model postulates that the hadrons such as protons and neutrons have an inner structure; quarks.

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### Can the Strong CP problem be explained by the cancellation of quark electric dipoles by dipoles from some as yet undetected matter surrounding quarks?

I am not a mathematical physicist but from popular science articles I get the impression that CP violation occurs because quarks unexpectedly don't produce an electric dipole. If this is correct could ...
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### The other quarks also have some different properties or strange is the only one?

Particles that contain a strange quark decay more slowly, because of what we see in this answer. The other quarks, besides up and down, also have some particularity? E.g. according to Brumfiel, Geoff (...
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### Jet events and Deeep Inelastic Scattering (Scaling Behavior) at the same time?

I am a philosopher of physics, so I already apologize for potential ignorance. I have also graduated in physics, but I now analyze problems on another level and also forgot some of the mathematical ...
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### Why does the up and anti-up quark combine into a pion and not a photon?

im currently studying a level particle physics and im confused about this. Particle annihilation occours when a particle meets its corresponding particle, converting their mass energy into two photons,...
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### Why do protons not show a "classical" mass defect?

An atomic nucleus consists of protons and neutrons, held together by the strong nuclear force (i.e. gluons). The heavier a nucleus gets, the more neutrons have to be added to overcome the increasing ...
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I have encountered myself with the following definition for $\pi$-fields as quark bilinears: $$\pi^a = i\bar{q}\tau^a \gamma_5 q \ ,\quad\text{with }\ q = \left(\begin{array}{c}u\\d\end{array}\right) ... • 601 3 votes 1 answer 105 views ### Why can't we insist that the strong interactions must preserve CP? I'm having some trouble wrapping my head around the strong CP problem. I know that the non-trivial vacuum structure of QCD induces the topological theta term in the strong sector of the SM, which is ... 12 votes 3 answers 4k views ### Why so much kinetic energy inside a proton? I'm reading 'Waves in an impossible sea' by Matt Strassler - a very good, popular science book, by the way - and he explains that the rest mass of a proton mostly comes from the kinetic energy of the ... • 699 1 vote 1 answer 98 views ### Quark condensate and VEV of \pi^0 In David Tong's lectures on the Standard Model I saw that there is a quark condensate, which is just a Vacuum Expectation Value (VEV) of the \bar{q}_{Li}\, q_{Ri} operator,$$ \left< \bar{q}_{Li}...
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I am trying to understand the different combinations of quarks in a hadron. I have seen that the positive pion is written as $\pi^{+}=u\bar{d}$, but I have not seen it written in the opposite order. ...