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0

To perhaps give an answer in a slightly different way, it's complicated. One must keep in mind that the decomposition of the angular momentum into spin and orbital components is model dependent. In the language of the renormalization group, it is scheme and scale dependent. If you probe a hadronic system at a given length scale (or, equivalently, energy) ...


0

Quarks as elementary particles are quantum mechanical entities. The same is true of electrons and protons. The hydrogen atom has the simplest quantum mechanical solution of how quantum mechanical particles are bound by attractive forces. This solution is a wave function, and it tells us that the electron is in a quantum mechanical probability locus around ...


12

From lattice calculations (see String Tension of Quark-Anti-Quark Pairs in Lattice QCD) it has been found that the string tension of the quarks, in the case of pions, is given by $$ \sqrt{\sigma}\sim460\ \mathrm{MeV} $$ which is equivalent to a length of $\sim 2.7\ \mathrm{fermi}$. In the case of the charmonium ($\bar c c$), the tension (see Charmonium ...


7

From the HyperPhysics site on Quarks: It is postulated that it may actually increase with distance at the rate of about 1 GeV per fermi. A free quark is not observed because by the time the separation is on an observable scale, the energy is far above the pair production energy for quark-antiquark pairs. For the U and D quarks the masses are 10s of MeV so ...


-1

This question appears to cover a fair amount of territory. I have asked a number of these types of questions. This seems to be asking what is the distinction between the say the s quark and the c quark in their doublet. The question of “why $SU(3)$” is another question, which in some ways includes the question of why there are 3 families of quarks. The ...


3

It is one of the experimental observations that led to the standard model of particle physics. The model has symmetries ( SU(3)xSU(2)xU(1) ) that build up the representations and these allow only for integer multiples charges, i.e. are consistent with observations. For example, why is there no meson existing of two up quarks, giving a charge of 4/3? ...


1

It turns out this diagram (one of eight) was given as an assignment in which we were to uncover the subtleties for ourselves. Considering the free quark propagator in isolation and then looking at the $1$PI correction associated with the gluonic correction (the self energy) , we see that this vanishes in dimensional regularisation with the result that the ...


2

Yes, nothing changes about the general rules if $m_u=m_d=0$. The CKM matrix is still the $SU(3)$ matrix transforming the up-type quark mass eigenstate to the up-electroweak-partners of the down-type quark mass eigenstates. The general CKM matrix distinguishes the phase. However, the CKM matrix becomes ambiguous and the number of generations is effectively ...


1

Let´s go: [1] From the DIS (Deep Inelastic Scattering) of eletron-proton, we can imagine that the photon exchanged in te process "sees" a parton (possible constituent of the proton) distribuition. We can imagine a cross-section of photons and that constituents of the proton. And we can analyze two situations: From a cross-section of longitudinal (scalar) ...


2

To complete David's answer, here is a two jet event in LEP, an e+e- collider, the ALEPH detector. The experiment is running on the Z mass. The central part of ALEPH consists of several different tracking detectors. The points where charged particles interact with the tracking detectors (hits) are shown as squares and the tracks fitted to the hits are ...


3

Hadronization still doesn't break conservation of energy and momentum. So getting the total energy, or the total momentum, of the quark-antiquark pair is easy: just add up the total energy and momentum of all the reaction products. To get the individual energy or momentum of one particle, i.e. just the quark (or antiquark), we rely on the fact that they ...


0

The parton model assumes that nucleons are composed of three valence quarks that share the momentum of the nucleon in an approximately equitative way. That means that the valence quark pdf's have a peak around $x = 1/3$, and have much lower values at $x \to 0$ and $x \to 1$. In addition to that, you have interactions between quarks (nowadays we know that ...


4

I'd say that this claim is specific for the current experiments at the LHC. We collide protons there, and the protons are made of quarks and gluons -- strongly interacting stuff. You can even say that there are already $b$-quarks in the proton. So, when the protons collide, this strongly interacting stuff produce events that are similar to the genuine $h\to ...


3

In order to get a good mass accuracy using the gamma gamma channel one needs to measure well the gamma energy in the electromagnetic calorimeter which can easily contain all the energy. The four vectors have measurement errors but not missing energy. b and b_bar decay weakly to a number of particles including neutrinos and the subsequent decays end on ...


0

You are not the first to try think that one more undelying onion level ( or matriuska) lies within what are considered fundamental particles at present. Back in the late 1970s when the quark model was established , preons were the next hypothesis as the subcomponents of quarks A number of physicists have attempted to develop a theory of "pre-quarks" ...


0

Electrons and other leptons are, as far as we know, fundamental. They are not made out of quarks, they are not made out of anything! Neither of your assertions has any empirical evidence going for it. However, it seems you are really asking for reasons for charge discretization, since you seem to get the idea of your assertions from the charges of electrons ...


4

Experimentally the charge distribution of protons and neutrons has been measured as a function of the radius. So the different charge content of the two nucleons does affect the distributions. As the other answer states this is the regime where only quantum chromodynamics models can attempt to describe the wavefunctions of the quarks within the ...


0

This is not a meaningful question. No, really, it isn't. Quarks don't exist as free charged objects on which we could take the classical limit and consider "forces" on them. They are confined, and occur only as constituents of bound states. In quantum mechanics, it doesn't make sense to ask whether the constituents of a bound state "repel" or "attract" each ...


2

As far as we know the classical (i.e. non-quantum) laws of gravity apply at all length scales. There are theoretical reasons to suppose that the classical description fails at scales approaching a Planck length, but this is far, far smaller than the size of a neutron. So inside a neutron we would expect the classical laws of gravity to apply, and in ...


0

In the absence of Yukawa couplings (only kinetic terms), the SM has the global flavor symmetry: $$G_{y=0} = U(N_f)^5=U(3)^5$$ Because there are 5 distinct representations in the SM (3 for quarks: $u_R$, $d_R$, $Q_L$; and 2 for leptons: $e_R$, $L_L$). However, $U(N) \sim SU(N)\times U(1)$, so the group can also be written as: $$G_{y=0} = SU(3)^5 \times ...


0

I often see $\mathrm{SU}{(3)}_\text{flavor}$. However, I have seen $$\mathrm{U}(3)_\mathrm L \times \mathrm{U}(3)_\mathrm R = \mathrm{SU}(3)_\mathrm L \times \mathrm{SU}(3)_\mathrm R \times \mathrm{U}(1)_\text{vector} \times \mathrm{U}(1)_\text{axial}$$ where the last one is broken by the quantum anomaly. See slide 14 in this lecture summary of Theoretical ...


2

Your $SU(3)\otimes SU(3)={\bf 1}\oplus {\bf 8}$ above is a chimaeric typo from hell. OK, I'll just give you the self-evident answers, but they would be meaningless junk numbers if you failed to reproduce them directly on the basis of your SU(3) text or the WP article which explains the rules and the Dynkin representation notation, D(p,q), which connects to ...


1

At lowest order, color screening comes from virtual quark/antiquark pairs, just like charge screening comes from electron/positron pairs in QCD. The diagram/effect is also referred to as 'vacuum polarization' and is shown below. Charge antiscreening comes from virtual gluon pairs; its diagram is below.



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