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Questions tagged [quarks]

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

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Why is the proton (uud) lighter than the $Δ^0$ (uud) baryon?

Neutron has quark composition udd with spin $\frac 12$. $\Delta^0$ baryon has quark composition udd with spin $3 \over 2$. On Wikipedia it says that $\Delta$ baryons have mass of approximately $1232 ...
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How can matter and anti-matter coexist in a meson?

Whilst learning about the nature of subatomic particles, I came along a pion zero meson. What really stumbled me was that the quark configuration of the particles was up and anti-up or down and anti-...
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If a particle decay has quark annihilation will it always emit a photon?

From what I can gather the decay $\pi^0 \rightarrow \gamma \gamma $ emits two photons because $\pi^0 $ has quark content $(u\bar u-d\bar d)/\sqrt{2} $, and the $u$ annihilates with $\bar u$, and $d$ ...
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How do leptons differ from one another?

All the leptons that I have come across have their native (matter) charges of -1 relative to the charge of an electron. Since they are all fundamental and are not made up of quarks, you can't ...
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If the combinations, in the context of particles which have identical interactions, are not orthogonal to each other?

I read from here If there are two or more particles which have identical interactions, then they may be interchanged without affecting the physics. Any (complex) linear combination of these two ...
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Quark flow diagram for $\rho^0 \rightarrow \pi^0+\gamma$

So $\pi^0=\frac{1}{\sqrt{2}}(u\bar{u}-d\bar{d})$ and $\rho^0=\frac{1}{\sqrt{2}}(u\bar{u}-d\bar{d})$ except with a higher angular momentum, this angular momentum is taken by the photon. How do I ...
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115 views

Difference between $W^-$ and $\pi^-$

Maybe it's a very naif question, but what is the difference between a $W^-$ and a $\pi^-$? I mean they both change a $d$ into a $u$ right? $d \rightarrow u W^- \quad \text{and} \quad d \rightarrow ...
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Why do quarks and gluons have colour?

I asked a question here a few days ago and got some fantastic answers so I'm going to continue. Let me preface this by saying I know quarks do not actually have 'colour', but colour is some sort of ...
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Naive question about lepton/quark energy states

I understand there are 3 energy states for quarks and leptons (electron, muon, tauon... Up, charm, top etc.) And we have 3 forces (not including gravity, em, strong and weak). This naively seems ...
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How are composite hadron fields related to elementary quark fields?

(This question is related to: A pedagogical exposition of the hadron physics?) I'm a mathematician who has been trying to learn quantum field theory for a while. I've gone through large parts of ...
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Spaghettification on quarks?

Imagine a nucleon falls into a black hole, I would expect the gravitational force acting on each quark to be drastically different but due colour confinement wouldn't there more pairs of quarks being ...
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Muon neutrino interacting with nucleon's quarks

I'm considering the muon neutrino/anti-quark interaction with the nucleons of ice in the IceCube experiment. The purpose is to decide which antiquarks are $\bar{q}$ and $\bar{q}'$. I have the ...
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54 views

How do quarks keep themselves apart?

I was chatting with user Dan Yand regarding my recent question about colour charges, it was mentioned in the comment section that particles with colour charges attract each other like or unlike hence ...
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1answer
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How does electron “orbit” nucleon unless 3 coloured charges act like positive charge?

Do quark(s) emit(s) electromagnetic wave otherwise how do(es) electron(s) form an orbital? Can colour charges somehow mimic electric charge? Btw I know quarks interact via strong nuclear force.
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How many anti/quarks can be squeezed inside a nucleon without upsetting exclusion principle?

I read about a nucleon with 3 Strange quarks which clearly violates PEP, however this was soon resolved by introducing colour charges. Then I read about colour confinement where surplus energy can be ...
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Muon neutrino and down quark interaction diagram

My questions concerns the IceCube experiment, in particular, the interaction between muon neutrino and the down quark. I've drawn the following Feynman diagrams: Are both diagrams correct? Can I say ...
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Temperature-dependence of quark potential in Abelian lattice gauge theory

I am working with Kapusta's "Finite-Temperature Field Theory" textbook, and am working through the first part of chapter 10. When building the correlator of the two quarks a distance $R$ apart in the ...
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If quarks can't be isolated in the first place, how did they become confined in the early universe?

On one hand, we know that quarks cannot exist in isolation. This is because the energy required to dissociate a quark-antiquark pair in a meson (or quarks in a hadron) will create a mesons (or hadrons)...
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Do antiquarks cancel quarks out?

I heard that antiquarks are just like antimatter. Does that mean that they cancel quarks out? If so, does that mean that there are more quarks than antiquarks?
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99 views

Commutator of a quark current

In Quantum Chromodynamics, when we take the limit in which the u, d and s quarks have no mass, there exists a global symmetry $G \equiv SU(3)_L \otimes SU(3)_R$ in flavour space. The corresponding ...
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1answer
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Is a nucleus a collection of quarks or a collection of neutrons and protons? [duplicate]

I do not much about particle physics. But people say that neutron and proton are composed of quarks, and in turn a nucleus is composed of neutrons and protons. Therefore, the question is, is this ...
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1answer
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The production of $b$ ($b$ bar) quarks

I have a question, please if there anyone helps me to understarnd how we distinguish the production pair of quarks $b$ ($b$ bar) it comes from a QCD background or comes from higgs decay?
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A question about isospin of pion and kaon

In Ch.18 of the textbook An Introduction to Quantum Field Theory by Peskin and Schroeder, on P.611 when discussing QCD renormalization of the weak interaction, two operators ${\cal O}^{1/2}$ and ${\...
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Is the electroweak $SU(2)$ gauge symmetry an exact symmetry in Standard Model before spontaneous symmetry breaking?

In Standard model, components of a $SU(2)$ doublet (for example $u$ and $d$) have different masses. This means there is no $SU(2)$ symmetry, but I think it is okay because the $SU(2)$ symmetry is ...
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Is it a coincidence that quarks have exactly -1/3 or 2/3 the electron's charge? [duplicate]

I have read these questions: Why do quarks have a fractional charge? Is there an explanation for the 3:2:1 ratio between the electron, up and down quark electric charges? Hypercharge for $U(1)$ ...
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Coefficients of Color Potential in Quarks [duplicate]

I was wondering if there was a relation between the fractional coefficients $$2/3, 1/3$$ obtained when calculating color potential for quarks and the value of electric charge for the up and down quark....
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What is the experimental evidence that the nucleons are made up of three quarks?

What is the experimental evidence that the nucleons are made up of three quarks? What is the point of saying that nucleons are made of quarks when there are also gluons inside it?
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what happens to positrons after pair production

what happens to positrons after pair production? There are two possible outcomes, but which one is true or most probable? The particle antiparticle pair have enough kinetic energy to overcome the ...
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When/ how were/are quarks formed?

We know that all particles can eventually be converted into energy. We know also that electrons were and still are formed by pair production from a 1MeV photon. Do physicists have yet any idea how ...
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1answer
145 views

Rho and Omega meson mixing

I am new to particle physics. So this might seem to be a trivial question. I read about $\omega$ and $\phi$ meson states being written in terms of octet and singlet state. In the same way, can $\...
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4answers
452 views

How can infinite density exist?

Thinking in mind, infinite density is where there is no space between particles correct me here if i'm wrong. Inside a blackhole at the core. So if there are 2 particles touching each other Then ...
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1answer
35 views

Fundamental and antifundamental representations, and hilbrt spaces

I am studying quarks $u$, $d$ and $s$. I know they can be represented by 3-vectors: We also have the antiquarks that are represented by the same 3-vectors: The difference between them is that when ...
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Wave function of two identical quarks

I'm asked to discuss what the ground state wave functions of $qq'Q$ would look like (a combination of two quarks and some spin 0 particle $Q$ which transforms like a singlet under flavor $SU(3)_F$ and ...
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A question about the notation of the Standard model

The ${\rm SU(2)_L}$ doublets, for example, the left-handed quark doublets $Q_{iL}\equiv(u_{iL}, d_{iL})^T$ are assigned quantum numbers $(\textbf{3},\textbf{2})_{+1/6}$, which means $Q_{iL}$ are ...
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What is meant by “the symmetry of an interaction”?

My understanding of a symmetry is this: apply an operation (e. g. parity inversion) to a system. If it behaves the same afterwards, it is symmetric under that operation. Now, quite often I see ...
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How does Bhabha scattering imply the existence of quark/lepton substructure?

In the 1983 journal article New Tests for Quark and Lepton Substructure which covers some science and mathematics behind quark and lepton composition (theoretical). It says: Bhabha-scattering ...
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Pulling quarks from one another creates a new pair of quarks? [duplicate]

It is said that the force between two quarks increases as they are pulled apart which is ultimately resisted by the strong nuclear force. Correct me if I'm wrong, but my physics teacher once said ...
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Deep inelastic scattering

Quarks can not observed directly in isolation so that they only can exist in the form of colorless hadron. So we may suggest some questions like "Is quark actually exist?", "Is it just mathematical ...
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What makes strange quarks stranger than any other quark?

Back in the 1950s, physicists noticed that certain heavy particles (sigma baryons, lambda baryons, & K mesons) have significantly longer lifetimes than physicists originally predicted just based ...
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Is the Lagrangian in the Standard Model exact or approximate?

We say that the Standard Model has $SU(3)_{C} \otimes SU(2)_{L} \otimes U(1)_{Y}$ symmetries. However, the $SU(2)_{L}$ symmetry of the doublet ($u, d$) is not exact because $u$ and $d$ have different ...
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How did the three quarks ($u, d, s$) acquire different masses?

If the three quarks $u, d, s$ had the same mass, they would have an $SU(3)$ flavor symmetry ($u, d, s$). This symmetry is broken because these three quarks have acquired different masses through ...
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106 views

Why do the right-handed up quark and down quark not form an $SU(2)$ doublet?

The left-handed up quark and down quark are an $SU(2)$ doublet $(u, d)_{L}$. Why do their right-handed counterparts, right-handed up quark and down quark, not form an $SU(2)$ doublet $(u, d)_{R}$?
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Are There Reasonable Definitions Of The Pole Masses Of Light Quarks?

For the heavy quarks and charged leptons, the "pole mass" of a fundamental particle is its mass (which varies as a function of energy scale in the Standard Model) when the energy scale it is evaluated ...
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What is the symmetry of the doublet ($u$, $d$)?

The up quark $u$ and down quark $d$ form a doublet ($u$, $d$). I know that they have a SU(2) symmetry. However, they also have a U(1) symmetry because they are regarded as two states of the same type ...
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1answer
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Is a quark‘s constituent mass affected by the chiral limit?

The up- and down quark’s constituent mass is usually taken to be around $300\,\text{MeV}\approx \tfrac{1}{3} m_\text{proton}$. Is this quantity affected by the chiral limit, where we let the quarks’ ...
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How many elementary particles are contained in a molecule of $H_2O$?

I was wondering about how many elementary particles form up one molecule of $H_2O$. What I thought of is the following: Hydrogen : 0 neutrons, 1 electron, 1 proton; electron is elementary and proton ...
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54 views

A fourth (sterile) neutrino existence and quark generations

Would the existence of a fourth (sterile) neutrino imply the existence of a fourth generation of quarks and a fourth lepton, beyond electrons, muons and tau particles?
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373 views

Most trivial neutral pion decay

Literature states neutral pion decay by QED cannot occur directly because the pion is uncharged. However, I cannot see why Photons are not allowed to interact with the Quarks directly. Please ...
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107 views

Prove that the singlet state of 3 quark flavors is fully antisymmetric

I have three quark flavors, according to group theory: $$3\otimes3\otimes3=10\oplus8\oplus8\oplus1$$ I have to show that the 1 is antisymmentric. My idea would be to try to construct the states ...
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QCD from chirally segregated, gauged $SU(3)_L \times SU(3)_R$?

There are already theory papers out there in which color $SU(3)_C$ is actually the diagonal subgroup of multiple $SU(3)$ factors. But due to a comment by @zooby, a new twist on this idea occurred to ...