# Tagged Questions

0answers
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### Are Gribov copies responsible for the observed Mass-gap and color confinement properties of Pure Yang-Mills Theory?

New solutions to the existing problems are presented by the quantum mechanics and Einstein's theory of special relativity when treated together. The creation of particle/anti-particle pairs by quantum ...
1answer
54 views

### Asymptotic Freedom - Qualitative Explanation

I am doing a (mostly qualitative) course on Particle Physics, and am confused about the concept of asymptotic freedom. The lecture notes basically say that a quark may experience no force/be "unbound" ...
0answers
45 views

### What is equation of quark confinement, what is the process which called confined? [closed]

Quarks confined within larger particles such as proton, what is properties of quarks confinement? why quark confined, anyway!? divine purpose or what physical process?
0answers
57 views

### Final-state baryons in $p \bar p$ collisions in Pythia

I'm trying to simulate inclusive $\chi_c$ production in $p \bar p$ collisions at very low energies (~ 5.5 GeV) using Pythia8 event generator. Leaving aside problems bounded with applicability of ...
2answers
114 views

### Why is there a linear relationship between charge and isospin?

So the title basically says it all. Something that's really bothering me is the fact that the Gell-Mann Nishijima relationship can be extended to provide a linear relationship between charge and all ...
2answers
54 views

### Do the proton PDFs change much with Q?

Specifically, the second moments, do they change much from say 100 to 1000 GeV? Why or why not?
1answer
108 views

### What are the problems in quark-gluon plasma? [closed]

Someone (T.D.Lee?) said that quark-gluon plasma would (after 1980?) be very important to understand high-energy physics experiments. I read some description of this new state in wikipedia ...
2answers
103 views

### Is there something like Hawking radiation that makes protons emit component quarks?

If Hawking radiation can escape from black holes, could quarks perhaps become separated from protons despite it being "impossible" for that to happen?
2answers
96 views

### What maintains quark spin alignments in baryons?

What maintains quark spin alignments in baryons? The $uud$ proton and $udd$ neutron are both spin 1/2, implying that two of their spin 1/2 quarks are always parallel and the other is always opposed. ...
1answer
106 views

### Difference between Quark-Gluon Plasma and Color-Glass Condensate?

From the news. Apparently they are very similar, yet different.
1answer
62 views

### Is There Any Difference Between Strong Quarks Force and Strong Nuclear Force?

the spectrum of quarkonium and the comparison with positronium potential for the strong force is: $V(r) = - \frac{4}{3} \frac{\alpha_s(r) \hbar c}{r} + kr$ (where the constant $k$ determines the ...
1answer
257 views

### How does Delta baryon decay conserve angular momentum?

I'm a chemist so bear with me: I understand the Delta baryons $\Delta^{+}$ and $\Delta^{0}$ to be in some sense spin (and isospin) quartet states of the proton and neutron. These can decay straight ...
0answers
54 views

### In a composite Higgs, should the Z0 decay at the same rate that the neutral pion?

I am sorry to ask a question that obviously is a sum of separate questions about a process: Should the decay rate of Z0 be related to the decay of the "higgs" composite field it is eating? And, should ...
0answers
57 views

### Linear rising potential from a Gribov propagator

It is common wisdom that a gluon propagator (Gribov-)like $$G(p^2)=\frac{a+bp^2}{cp^4+dp^2+e}$$ should give rise to a linear rising potential. So far, I have not seen a proof of this and I would ...
1answer
90 views

### Parton Distribution Functions plot

I was looking at a plot of the parton distribution functions today and had a question. On the y axis, it seems like the value of x f(x) for gluons is greater than one at small x. I was under the ...
3answers
224 views

### Bound states in QCD: Why only bound states of 2 or 3 quarks and not more?

Why when people/textbooks talk about strong interaction, they talk only about bound states of 2 or 3 quarks to form baryons and mesons? Does the strong interaction allow bound states of more than 3 ...
1answer
67 views

### Has the mass of longitudinal and perpendicular spin 1 mesons been measured separately?

This might be a silly question. When the mass of a spin 1 meson is measured, is there a way to check whether it is the same for all polarizations? Is such a meson mass the same for longitudinal and ...
1answer
127 views

### Electromagnetic current-current correlators

Let the free electromagnetic current $J_\mu(x)$ be = $:\bar{\psi}(x)\gamma_\mu Q \psi(x):$ where $::$ is the normal ordering. In this expression why is $Q$ thought of as a "charge operator" instead ...
2answers
206 views

### Is there an explanation for the 3:2:1 ratio between the electron, up and down quark electric charges?

I understand that the NNG formula relates $Q$, $I_3$, and $Y$ and can be derived in QCD; does this unambiguously predict the electric charge ratios without making assumptions about the definitions of ...
1answer
129 views

### Similar masses and lifetimes of the $\Delta$ baryons

Why do the four spin 3/2 $\Delta$ baryons have nearly identical masses and lifetimes despite their very different $u$ and $d$ quark compositions?
1answer
67 views

### Colour decomposition of $n-$gluon tree amplitude

I have here a $SU(N_c)$ Yang-Mill's theory and let the index $i$, label the $n$-gluons, and $\{k_i, \lambda_i, a_i\}$ be its momenta, helicity and colour index and \$\cal{A}_n^{tree/1-loop}(\{k_i, ...
1answer
168 views

### Derivation of the effective potential between a quark and an anti-quark

Typically in particle physics books (not in QFT books!) I have often seen this statement that the potential between a heavy quark and its anti-quark can be "empirically" represented as \$V(r) = ...
1answer
283 views

### What's jet multiplicity?

That's a basic thing, but, surprisingly, it is very difficult to find concise explanation of: What is the definition of jet multiplicity? Why is it interesting?
1answer
186 views

### Why is it common to plot $xG(x,Q^2)$ and not simply $G(x,Q^2)$?

I'm trying to understand the modern description of high-energy scattering processes involving hadrons in the initial states. The phenomenological parton distributions functions play a central role, ...
4answers
1k views

### What are the details around the origin of the string theory?

It is well-known even among the lay public (thanks to popular books) that string theory first arose in the field of strong interactions where certain scattering amplitudes had properties that could be ...
2answers
984 views

### Is it pions or gluons that mediate the strong force between nucleons?

From my recent experience teaching high school students I've found that they are taught that the strong force between nucleons is mediated by virtual-pion exchange, whereas between quarks it's gluons. ...
1answer
1k views

### What is the significance of the QCD scale parameter $\Lambda$?

I see that it appears as a constant in the relation for the running of the strong coupling constant. What is its significance? Does it have to be established by experiment? Is it somehow a scale for ...
1answer
84 views

### Where can I get the most accurate measurements of parton distribution functions?

Where would I look to get the most accurate experimental values of parton distribution functions for the proton? I know these functions aren't measured directly, but I'd basically like to find a fit ...
5answers
4k views

### Is there an equation for the strong nuclear force?

The equation describing the force due to gravity is $$F = G \frac{m_1 m_2}{r^2}.$$ Similarly the force due to the electrostatic force is $$F = k \frac{q_1 q_2}{r^2}.$$ Is there a similar equation ...
2answers
683 views

### The contribution to mass from the dynamical breaking of chiral symmetry

The claim is often made that the discovery of the Higgs boson will give us information about the origin of mass. However, the bare masses of the up and down quarks are only around 5 MeV, quite a bit ...
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