Questions tagged [quarks]

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

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Kinetic energy of quarks and mass of proton

I read that: Most of a proton mass comes from the energy of motion of its three quarks and from the energy carried by the gluons that keeps them confined together. Does kinetic energy of the three ...
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Finding $\Sigma$ wavefunctions from proton wavefunction. Any operator which can achieve this?

Knowing the isospin part of the wavefunction of the proton, it is possible to find that of the neutron by applying the isospin lowering operator $I_-$ which sits horizontally to the left of the proton ...
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Is there a law stating why a quark never decays weakly into a quark of the same weak-isospin ($T_3$)?

So I read multiple articles on weak isospin and one of them stated that "a quark never decays weakly into a quark of the same $T_3$". If this is true, can someone please explain what law ...
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Why does the Strange Quark have Strangeness -1?

I have been trying to find an explanation for the strange quarks negative strangeness value, I understand the term strangeness predates the quark model, but I'm unsure if terminology carry over is the ...
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How are we sure that the measured proton spin puzzle will be also observed similarly in the neutron thus a neutron spin puzzle?

The EMC experiment in 1988 using muons' deep inelastic scattering, has reported that the contribution of the valence quarks triplet (i.e. up-up-down) in the proton was measured to contribute as little ...
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Quantum chromodynamics - why are there no $rrb$ or $ggr$ terms?

$$\Psi_{colour}^{qqq} = \frac{1}{\sqrt{6}}(rgb + gbr + brg -grb - rbg - bgr)$$ My lecturer stated that there cannot be any $rrb$ or $ggr$ terms in the expression above. I would like to understand what ...
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Q\Quark Formation of the Latest Tetraquark

I was recently reading an article about a tetraquark combo TCC+ that was found and measured. The pic in the article looks wrong to me. It shows C antiU on top and a C antiD on the bottom. I know it ...
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Non-relativistic quark model, baryon masses and potential

Is there a simple non-relativistic quark model, based on which baryon masses, especially for the nucleon and the Delta resonance can be calculated? What is a reasonable non-relativistic potential? Is ...
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Sea of quarks-antiquarks-gluons? or a pond?

Please tell me where I go wrong in my understanding: If the valence quarks-gluons male up 1,5 % of total mass how can the remaining so-called sea contain "innumerable" virtual particles? At ...
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Do quarks have a non-zero electric dipole moment?

It is written here, in this PSE link that an electron has a measured perfect spherical charge density therefore a zero electric dipole moment (i.e. perfect monopole charge). My question is, are quarks ...
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Excited quark production

I found a Feynman diagram for excited quark production via an up quark and a gluon interacting (https://www.quantumdiaries.org/2015/02/04/lhc-run-ii-excited-quarks/). Is this quark gluon fusion and if ...
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Is sub-atomic particles (quarks) bunch of compressed photons? [closed]

According to theoretical physics,protons,neutrons and electrons are made up of sub particles called quarks which are the building block of matter (baryons). what if the quarks are bunch of compressed ...
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What's the difference between an electron and a quark?

Could you explain how QFT defines the peculiarity and differences, as to charge, between an electron and a quark? A quark has a fractional charge. Is the Coulomb force proportional to these charges? ...
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Is charge not quantized fundamentally and that is why we haven't come across magnetic monopole?

If protons are getting charged from quarks.. then the charge in quarks is fractional and not quantized. Does this mean that the charge we see is not fundamental? And the charges in quarks are just ...
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On the properties of $\Delta$ baryons

Considering the up and down quarks as an isospin doublet $|I, I_z\rangle$ $$ u=\left | \frac 1 2, \frac 1 2 \right\rangle, \qquad d=\left | \frac 1 2, - \frac 1 2 \right\rangle $$ their bound states ...
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Could the equal amounts of positive and electric charge point to equal amounts of matter and anti-matter?

The universe is electrically neutral because the electric charges of all quarks and leptons cancel. If particles are electrically charged, then there are equal amounts of positive and negative ...
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In the history of the development of the standard model was there a version in which quark-antiquark pairs or flux tubes were the fundamental particle [closed]

Based on the observations of color confinement and no free quarks, I'm wondering if instead of a having quarks as fundamental particles, during development of the Standard Model was there ever a ...
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Chirality vs Helicity in Top Quark Decay

I still have not had a good explanation of how a Right Handed Top Quark decays. As I understand it, helicity and chirality are both a part of spin. Does this mean that if either is left handed, the ...
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Nature of Transition Form Factor in Weak Decay

Can the Transition Form Factor in case of b to c quark level decay be imaginary? If yes what would be the significance of the real and the imaginary parts, and what would be the significance of the ...
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Do Quarks Exist?

Do Quarks Really Exist? Is there any experiment which can confirm the existence of Quarks and what kind of force is that which binds them to form neutron and proton?
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Feynman diagrams for neutral pion decay into electron-positron pair

The main Feynman diagram I've seen corresponding to this decay is the following: What I don't understand is why is it not possible for the up-antiup quarks that form the pion to annihilate into a ...
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Why do $Z$ or $H$ bosons can decay to a pair of quarks $t^+t^−$ with mass larger than boson in the inertial reference frame of boson?

The masses of $Z$ or $H$ bosons is less than the sum of the mass of two $t$ quarks. Why do $Z$ or $H$ bosons decay to a pair of quarks $t^+t^−$ with mass larger than boson in the inertial reference ...
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Can Top quarks change their spin direction?

Since we know there are right handed quarks, and that the Weak Force does not interact with Right Handed particles, if a quark cannot change its spin direction, how does the Top quark decay? If the ...
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By how much protons dipole moment inside a nucleus attenuate the culomb force between them?

By how much protons dipole moment inside a nucleus attenuate the culomb force between them? As up quarks repel more than down quarks the protons should be oriented with the positive side looking away ...
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Spin dependence of wavefunction of meson states bound by a certain potential

Lets assume two spin half particles, for example a charm quark and a charm anti-quark are bound by a spherical harmonic oscillator potential to form bound meson states. The possible ground state ...
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What are hadron parity partners?

I am studying Lattice QCD and there are many papers mentioning "Parity partners". What does this term mean?
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A gluon can have nine independent, bicolored states. How are some of the additions of these individual states, like $r\bar{r}+g\bar{g}+b\bar{b}$?

This came from the 25th page of the following pdf: http://www.gammaexplorer.com/wp-content/uploads/2014/03/Quarks-and-Leptons-An-Introductory-Course-in-Modern-Particle-Physics.pdf Sorry if I am asking ...
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Particles composed of square roots?

There are some particles which require square roots when telling their compositions. Mostly mesons, not baryons. e.g. $$ρ^0=\frac{u\bar{u}-d\bar{d}}{\sqrt{2}}.$$ Could you explain me how to make sense ...
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Fundamental reason for the color and flavor group to be the same?

The answer to this question might just be a straight-up "no, it's just a coincidence", but since coincidences are rarely a thing in physics, I thought I'd ask. Is there a fundamental reason ...
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Why is the chiral condensate a negative quantity?

The chiral condensate serves as an order parameter for the chiral phase transition. Thus, it is a finite quantity in one phase and vanishes in the other phase. It is given as a vacuum expectation ...
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Do Protons Have a Surface?

In searching for the radius of a proton, the Wikipedia page "Proton" states "Because protons are not fundamental particles, they possess a measurable size;...." As my physics is ...
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Ratio of neutron and proton structure functions

Experiments (e.g. Amaudruz et al. Nucl.Phys. B371, 3) show that the ratio of neutron and proton structure functions for x -> 1 is well below the value 2/3 expected from the quark charges and there ...
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Quark model wavefunction separability

When looking at the quark model we say we can write the wavefunction in 4 components, ie $$ |\Psi \rangle = |\Psi_{spatial} \rangle|\Psi_{spin} \rangle|\Psi_{flavour} \rangle|\Psi_{colour} \rangle \...
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Why are the quark quantum numbers $S$ and $B$ defined to be $-1$ for $s,b$ ($+1$ for $\bar s,\bar b$)?

For $s,c,b,t$ quarks we have quantum numbers $S,C,B,T$. (For $u,d$ quarks we usually specify charge and baryon number, though we could also specify $U,D$.) The quarks with charge $-1/3,~s$ and $b$, ...
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Could charm, bottom, and even top matter form under the right circumstances?

Strange matter forms because turning some of the down quarks into strange quarks unlocks lower energy levels, and this can lower the system's overall energy at high densities. If the density was ...
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What would happen to a quark if it could be isolated, into what particles it would change? [closed]

WP defines as quantum charge the $-\frac{1}{3} e$ charge value of the down quark and as elementary charge the -1e of the electron. The elementary quark particle cannot be isolated in the lab and its ...
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What makes up and down quarks so special?

One of the ways a lot of different mesons and baryons are grouped is by their up and down quark content. There's also isospin, which is admittedly a subset of a more general symmetry. But the ...
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Why is there a discrepancy between $m_n-m_p$ and $m_d-m_u$?

The difference in mass between a neutron and a proton is $1.3\space {\rm MeV}/c^2$, but the mass difference between an up quark and a down quark is $2.5\space{\rm MeV}/c^2$. How come the mass ...
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Finding the velocity of a bounded quark of a meson

How would you compute the velocity of one of the quarks of a meson, when we have no reference to a reaction or a collision? I initially thought we could use the conservation of energy and momentum to ...
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Could dark energy be a net repulsion from virtual colour-charged particles popping in and out of existence?

According to https://en.wikipedia.org/wiki/Dark_energy Dark Energy makes up 68% of "universal density" as the article expresses it. If there is a margin of error in that percentage which ...
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Do all hadrons experience the strong nuclear force?

In nuclear physics, nuclear force, also known as the residual strong force, is mediated by pions exchanged between protons and neutrons. It doesn't seem like this should be limited to protons and ...
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Indivisiblity of quarks

I have been researching the Standard Model of Particle Physics recently. According to the model, quarks are indivisible. Does this mean that quarks cannot be divided, or does it mean that if we were ...
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Explanation for exact amounts ratio between up,down quarks and electrons in a universe

As I've understood in the quark era $\approx (10^{-12} - 10^{-6}) \,\text{s}$ unified interaction has decoupled into Leptons and Quarks. Given that now Hydrogen+Helium atoms accounts for $97.9\%$ of ...
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Experimental evidence for quarks via Electron-Positron Annihilation – Color

To reproduce the correct R = Σ$q_i²$ of the experiments one has to multiply by a factor 3 corresponding to the three color charges, r, g, b. Isn’t this somewhat contradictory to statements such as ...
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Does "lifetime of up quark" have a physical meaning?

I saw this question about the lifetime of an up quark. As far as I know, free quarks are never observed in experiments. Then what is the significance of a statement like "the lifetime of an up ...
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Why do strangeness producing reactions have a small cross section?

My professor told me that kaon producing reactions have a small cross section compared to other nucleon collision reactions. The reason for that is the production of a strange quark but he didn't ...
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Parton Distribution Functions - Antiquarks?

In all the PDF plots that I have seen so far (e.g. https://arxiv.org/abs/1111.5452 Fig. $3$ and $4$) the PDFs for sea or charm quarks contained only the strange or charm quark, but not the $\bar{s}$ ...
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How to understand the missing transverse energy in the $t\bar{t}$ decay?

Let's consider the process $gg \rightarrow t\bar{t}$ and the subsequent decay of the $t$ quark into a $W^{-}b$ respectively. Now, if we consider the leptonic + jets decay mode of the $W^{-}$ boson, ...
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Are there any fusion reactions that reduce the number of baryons?

In the simplest of fusion reactions, two hydrogen nuclei fuse to form deuterium. Besides deuterium, we get a positron and an electron neutrino out of it. The positron combines with the extra electron ...
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In context of MSSM, what is stop mixing?

In context of MSSM, what is stop mixing and stop mixing parameter?
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