Questions tagged [quarks]

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

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0answers
51 views

Exchange symmetry and angular momentum

My particle physics courses uses that exchange symmetry is related to the angular momentum of the constituent quarks in the quark model. We say that for baryons the total wavefunction is represented ...
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1answer
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Scattering $u\bar{d} - c\bar{b}$

I'm trying to define if the scattering $u\bar{d} \rightarrow c\bar{b}$ is possible in any of the fundamental interactions, I know that in QCD (channel t) is allowed because of the charge conservation, ...
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Top quark decay rate calculation $\Gamma(t\rightarrow W^+b)$

I'm trying to calculate the disintegration rate $\Gamma(t\rightarrow W^+b)$ from the Fermi Diagram: I know the lagrangian for the interaction would be: $$ -iF = \bar{u_b}\gamma^\mu P_Li\frac{g}{\...
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1answer
55 views

How to prove $Q_u = -2Q_d$ from $SU(5)$?

I'm a beginner, and I'm trying to figure out how to prove that charge of Up quark is equal to 2 times the charge of down quark from the 10 representation of $SU(5)$. Please help.
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Can flavor changing neutral currents occur

It says that flavor changing neutral currents are impossible. However I am just asking what would happen if a top quark emits a Z boson or a Higgs boson.
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Permitted bound states in extended QCD color group $SU(4)$

I'm very much curious about the possible quark combinations to form bound states in $SU(4)$ QCD. We already know Wilson has proven that only colorless combinations can arise in $SU(3)$ of these ...
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1answer
38 views

Charge anticharge superposition in nucleons

When a neutron converts itself into a proton, a negative quark changes into a positive quark. As the positive charge is geather than the negative ofcourse we must account for the expelled electron, it ...
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At the Big Bang, when particles were created, could free standing quarks (not bound in a hadron) have been created and remain alone today?

You can't pull a quark out of a hadron, but at time $T = 10^{-43}$ seconds or shortly thereafter, when all particles were created, wouldn't all quarks be individual, and not grouped into hadrons, (...
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Are there any mesons with one charm antiquark?

Is there a meson with one charm antiquark, $\bar{c}$, so that $C=-1$? Can they exist?
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Can you detect gravitational waves emitted by quark stars?

Quark stars are a bit like neutron stars, they have very large masses and small radii. Can we detect gravitational waves emitted in a binary of two quark stars or the gravitational waves from a not ...
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1answer
41 views

Can quarks in a proton be modeled as a Fermi gas?

I recently learned in one of my courses that a nucleus could be modeled as a Fermi gas. This led me to think about other fermions and whether or not I could mess around with them as well. Are the ...
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What can we conclude for the spin configuration of the quarks inside the baryon? [closed]

If yes, is there any way to reconcile this findings with Pauli's exclusion principle?
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1answer
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Are elementary particles as old as the universe?

Lets take quarks for example. Are the quarks - that constitute the universe - as old as the universe? Or are particles always created? Or were they all created when the universe was born?
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How to draw quark flow diagram when no flavour change occurs?

I've been asked to draw the quark flow diagram for $K^-p\rightarrow \pi^-\Sigma^+$, I did it like this: (Apologies for the handwriting) As you can see, I basically assumed that since the initial and ...
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1answer
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Quantum energy levels vs. mass

TL;DR given a system comprised of two bound particles with masses $m_1, m_2$, and given energies of bound states $E_n$ between the two particles according to the non-relativistic Schrodinger equation, ...
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1answer
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Simple “toy-model”-like explanation of quark confinement (QCD) and accompanying math

I have a qualitative understanding of quantum chromodynamics within nucleons and between nucleons, but I do not understand the math behind some of the physics like quark confinement. What is the math ...
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1answer
101 views

Why protons are stable but Neutrons not?

just read something about standard model and find it very interesting, proton is made of there subatomic particle U,U,D and neutron have U,D,D . electromagnetic force between U,U,D wants to rip apart ...
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1answer
54 views

Has a 3D chart of nuclides ever been published or proposed $(N, Z, S)$? What information might it show?

Phys.org's 'Strange' glimpse into neutron stars and symmetry violation leads to the new Nature Physics Letter Measurement of the mass difference and the binding energy of the hypertriton and ...
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How is Einstein-Bose condensation supposed to stabilize d*(2380)?

A recent paper suggests a new dark matter candidate: Einstein-Bose condensates of the hexaquark/dibaryon d*(2380) ($uuuddd$). The nice thing about this theory is that it does not require any new ...
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Understanding interaction between two quarks

Two protons and two electrons repel each other as they have same charge. Protons and electrons attract each other since they are oppositely charged. A single proton is made up of two up and one down ...
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1answer
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Why does the term $i\epsilon^{\alpha\mu\beta\nu}p_{\alpha}q_{\beta}$ vanish in the squared amplitude of the top decay?

I would like to calculate the squared of the amplitude of a top-decay $t-> Wb$. I know already the solution, but I can't get there: I get stuck with the Levi-Civita-Tensor on my way. Can you help ...
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Quark confinement mechanism

As far as I understood: Quark confinement states that observing individual quarks is not possible, color charged quarks are confined into hadrons. As we try to pull them apart, force between them ...
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1answer
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What would the propagator of the Feynamn diagram for $\bar{q}q \to \gamma \gamma$ be?

I am trying to draw the Feynman diagram at tree-level for: $$\bar{q}q \to \gamma\gamma $$ but I don't seem to understand what sort of propagator fits this diagram? I have seen in some places that a ...
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What is quark 'confinement' in the context of Yang-Mills Theory?

In the context of Yang Mills Theory, what is quark confinement? Please try to explain as simple as possible (obviously without being too general)
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How do I show that the tensor product of $\mathbf{3} \otimes \mathbf{\bar{3}}=\mathbf{1} \oplus \mathbf{8}$? [duplicate]

It's often stated that the tensor product of the representations of $SU(3)$ satisfies $\mathbf{3} \otimes \mathbf{\bar{3}}=\mathbf{1} \oplus \mathbf{8}$, and that this implies that if flavour $SU(3)$ ...
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1answer
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If quarks change colours constantly how are proton and neutron stable relatively?

Say for example a proton is composed of Up, Up and Down (valance) quarks and suppose the Down quark absorbs a gluon, Down quark must change colour in order to conserve colour charges but so must the ...
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1answer
53 views

Is there a neutral current interaction between an antineutrino and an anti-strange quark?

I'm doing some revision for an exam and was wondering what the Feynman diagram for a charged current interaction between an antistrange quark - residing in a proton - and an incoming antineutrino ...
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Why is a quarkonium any different from a meson?

Quarkonium states are bound states of a quark-antiquark pair but so do the mesons. What is the difference between a quarkonium (e.g., charmonium, and bottomonium) and a meson then? Why use a separate ...
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1answer
48 views

Do Quarks violate the law of energy conservation?

Look, I am not too knowledgeable in this area, but all I know is the following. So please bare with me. Idea Since Quarks are always in pairs and are bonded together by the Strong Force and cannot ...
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1answer
87 views

What's the definition of $\bar\psi$ in QCD?

This is a two part question. What is the definition of $\bar\psi$ in QCD? In QED I know that $\bar\psi=\psi^\dagger\gamma^0$, but in QCD we also have flavor and/or color space. In particular, I'm ...
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Why do Fermions (quarks specifically) have transversity while Bosons (gluons specifically) don't? [duplicate]

I hope this question isn't naive or anything of the sort but I am relatively new to this topic and this is the first question I ask on here. The Collins asymmetry which is exclusively a quark-...
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1answer
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How do gluons bind the quarks together within the hadrons and mesons?

I was trying to know about the strong nuclear force within the nucleus and the books and websites told me that it is the gluons which carry the force, and now I am curious how the gluons carry this ...
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1answer
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Quark Chirality Constraints in Nucleons

SW Engr here educating myself on particle physics, apologies in advance for any phrasing errors. I tried the google machine to no avail. Q: If only left handed matter fermions experience the weak ...
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4answers
106 views

Where do the mass and volume of the two quarks go when they create a meson?

A quark and an antiquark are fermionic particles with mass. Where do this said mass go when they bind to create a meson? If there's annihilation at play, how do mesons even be in the first place? ...
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1answer
63 views

Why can the masses of the Higgs and top quark determine whether we live in a false vacuum?

I read in the paper linked below that the ground state of the universe depends on the potential of the Higgs field, particularly the graph of the Higgs potential with its minima and maxima. I think I ...
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1answer
91 views

How do you reconcile quark masses with notion of confinement?

In trying to understand exactly what confinement means, I have been reading 't Hooft s original paper on 2D QCD at large $N$. In the paper he shows that the quark propagator pole is moved to infinity, ...
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Is there a reason, other than mass hierarchy, that we associate each quark generation with a particular lepton generation?

The Standard Model contains three generations of quarks, and three generations of leptons. We generally pair off these generations into the "light" generation ($e, \nu_e, u, d$), the "medium" ...
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1answer
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Quark-antiquark plasma and Fermi-Dirac statistics

I'm attempting to work my way through the following set of question: a) A plasma consists of an equilibrium mixture at temperature $T$ of quarks, $q$, (massless,relativistic, spin $\frac{1}{2}$, ...
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82 views

Why do this meson state (consisting with $ u,s,d$) are acceptable by nature?

I am new in Particle Physics and try to understand "Quark-Antiquark States:Meson article in Quarks & Leptons by Halzen and Martin(p=46) Why do this meson states are are acceptable by nature $$A=\...
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1answer
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What was above and below the QCD chiral symmetry breaking temperature?

Above a critical temperature in the Universe, there was probably a phase of unbroken approximate QCD chiral symmetry. Mathematically, the symmetry breaking is triggered when the operators $\bar{\psi}{\...
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Why aren't Delta and Omega particles stable?

Not only are they not stable their half-life is in the nanoseconds. Why are they so different from protons?
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Why don't hadrons form from quarks of all the same charge?

Why don't Hadrons ever form from quarks of all the same charge? For instance you never see 2 or 3 up quarks together with no down quarks or vice-versa.
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Quark Model Family

I have studied the baryon J=1/2 family.i did the $(Y,I_3) $ diagram and started from the highest weight $(\frac{1} {2} ,\frac{\sqrt{3} }{2}) $ which is the proton and used the operators $I_{+-} \ \ U_{...
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How would a quark star maintain degeneracy near the surface?

I'm still not exactly understanding how a quark star could possibly exist for more than a fraction of a second. Neutron stars are already hypothesized to have degenerate quark matter at their cores, ...
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2answers
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Does quarks always pulls each other?

Pions consist of quark and antiquark and strong force keeps them together. So color charge and anticolor charge attracts each other. But in proton we have 3 quarks and they also attract each other. It ...
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1answer
144 views

Why do the $c$, $b$ & $t$ quarks have strong hypercharge?

From the $SU(3)$ flavour symmetry we have quantum numbers for the up, down and strange quark, associated with the Eigenvalues of the Gell-Mann matrices $\lambda_3$ and $\lambda_8$. Namely $\lambda_3$ ...
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1answer
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If a particle and its antiparticle annihilate upon contact, how do they form bound states?

I am reading about some old discoveries in particle physics and early collider experiments from Perkin's Introduction to High Energy Physics. However, I didn't get the answers to all my questions. If ...
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How experiments differentiate between valence quarks and sea quarks

The picture that baryon consist of three quarks and mesons consist of a quark,anti-quark pair is inaccurate.However this simple picture is enough to explain many properties of the hadrons as mentioned ...
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$SU(3)$ $U$ and $V$ spin normalization

As we know the $SU(3)$ algebra can be written in terms of $3$ dependent $SU(2)$ algebras viz $(T_+,T_-,T_3),(U_+,U_-,U_3)$ and $(V_+,V_-,V_3)$. There action on a standard state is $\mid T_3,Y\rangle$ ...
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Could electric dipoles within hadrons provide an alternate explanation for strong force? [closed]

We all know that hadrons such as proton and neutrons are made up of quarks and not all of the quarks have the same charge. This would suggest that they have a positive and negative side. In the case ...

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