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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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Can the Strong CP problem be explained by the cancellation of quark electric dipoles by dipoles from some as yet undetected matter surrounding quarks?

I am not a mathematical physicist but from popular science articles I get the impression that CP violation occurs because quarks unexpectedly don't produce an electric dipole. If this is correct could ...
DaveTheWave's user avatar
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The other quarks also have some different properties or strange is the only one?

Particles that contain a strange quark decay more slowly, because of what we see in this answer. The other quarks, besides up and down, also have some particularity? E.g. according to Brumfiel, Geoff (...
Nicolas Induzzi's user avatar
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Jet events and Deeep Inelastic Scattering (Scaling Behavior) at the same time?

I am a philosopher of physics, so I already apologize for potential ignorance. I have also graduated in physics, but I now analyze problems on another level and also forgot some of the mathematical ...
Dontwastetime's user avatar
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Why does the up and anti-up quark combine into a pion and not a photon?

im currently studying a level particle physics and im confused about this. Particle annihilation occours when a particle meets its corresponding particle, converting their mass energy into two photons,...
liv.ysf's user avatar
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1 answer
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Why is isospin utilized in determining the branching fraction of $K_1(1270)\to K\pi\pi$ final states?

The branching fraction of $\mathcal{B}_{K_1 \rightarrow K^{+} \pi^{+}\pi^{-}}$ is determined by $$\mathcal{B}_{K_1 \rightarrow K^{+} \pi^{+}\pi^{-}}=\frac{1}{3} \times \mathcal{B}_{K_1 \rightarrow K \...
realTyao's user avatar
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1 answer
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Are pure quark stars possible?

Has it been established that structures formed from quarks (like quark stars: https://en.wikipedia.org/wiki/Quark_star) are possible in principle ? I have read about the possibility that inside ...
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Can you explain the Georgi–Jarlskog mass relation?

I am trying to understand the Georgi Mass relation in $SU(5)$ As far as I was aware the symmetry breaking occurs only with the various charge quantum numbers (colour, weak charge, electromagnetic). So ...
bob's user avatar
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Isospin and quark composition of neutral pion

We have that the neutral pion has quark composition given by: $$\pi^0=\frac{u\bar{u}-d\bar{d}}{\sqrt{2}}$$ I want to justify this. This can be deduced by reasoning with isospin. We know that: $$|\pi^0\...
Leonardo's user avatar
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Why do protons not show a "classical" mass defect?

An atomic nucleus consists of protons and neutrons, held together by the strong nuclear force (i.e. gluons). The heavier a nucleus gets, the more neutrons have to be added to overcome the increasing ...
enzo's user avatar
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Understading dimensions in quark bilinears

I have encountered myself with the following definition for $\pi$-fields as quark bilinears: $$ \pi^a = i\bar{q}\tau^a \gamma_5 q \ ,\quad\text{with }\ q = \left(\begin{array}{c}u\\d\end{array}\right) ...
SrJaimito's user avatar
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Why can't we insist that the strong interactions must preserve $CP$?

I'm having some trouble wrapping my head around the strong $CP$ problem. I know that the non-trivial vacuum structure of QCD induces the topological theta term in the strong sector of the SM, which is ...
qavidfostertollace's user avatar
12 votes
3 answers
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Why so much kinetic energy inside a proton?

I'm reading 'Waves in an impossible sea' by Matt Strassler - a very good, popular science book, by the way - and he explains that the rest mass of a proton mostly comes from the kinetic energy of the ...
j4nd3r53n's user avatar
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Quark condensate and VEV of $\pi^0$

In David Tong's lectures on the Standard Model I saw that there is a quark condensate, which is just a Vacuum Expectation Value (VEV) of the $\bar{q}_{Li}\, q_{Ri}$ operator, $$ \left< \bar{q}_{Li}...
Gabriel Ybarra Marcaida's user avatar
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1 answer
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Quark Combination of Hadrons

I am trying to understand the different combinations of quarks in a hadron. I have seen that the positive pion is written as $\pi^{+}=u\bar{d}$, but I have not seen it written in the opposite order. ...
Anant Badal's user avatar
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1 answer
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Isospin doublet and quark content from contraction of quarks

Let's introduce a quark $SU(2)$ doublet. We are in the $m_u \approx m_d$ limit. So we have $$ q = \begin{pmatrix} u\\ d \end{pmatrix}. $$ Then we can construct the Nucleonic field $$ N := q q q = \...
Gabriel Ybarra Marcaida's user avatar
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Within a generation, fermion species' mass seems like it could have an effect on how many of the fundamental forces it interacts with. Is this true?

So, fermions all interact with the gravitational force and the weak force. All fermion species. Now, if you eliminate from that list, the particles that don't interact with electromagnetism, you ...
blacktopshaman's user avatar
1 vote
1 answer
118 views

Do all antiquarks carry and anti-color charge, or can they carry RGB color charges as well?

I know there are antiquarks with anticolor charges. Are there also antiquarks that instead carry color charges? Basically, which of these lists describes the types of quarks that there are: List one: ...
blacktopshaman's user avatar
1 vote
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How are $\pi$ Mesons Created in the Residual Strong Interaction?

Watching this episode of PBS Space Time, they run an animation of how pi mesons are exchanged by nucleons as the residual strong interaction to overcome proton electromagnetic repulsion. https://youtu....
IknoweD's user avatar
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How can a proton be stable if binding energy *increases* it's mass? [duplicate]

A hydrogen atom weighs 13.6eV less than a proton + electron. This missing energy, which is tiny compared to the rest mass of almost a GeV, was carried off by a photon when the atom formed. Nuclei show ...
Kevin Kostlan's user avatar
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Decoherence time of quarks

I have been reading papers on using top quark's use as a probe for new physics using quantum information theoretic observables such as concurrence. One of the reasons they provide for using a top ...
Lelouch's user avatar
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Are quarks real particles? Or only combination form of leptons inside nucleons? [duplicate]

There are not any free and independent quark in the nature. Collision of many particles inside most powerful accelerators could not produced any free and independent quark but result of collision ...
QQQ's user avatar
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Charge distribution of a proton

I've been studying high-school level physics and I noticed that protons are composed of up-up-down quarks. It is known that fields can be non-uniform due to geometries: Earth's gravity field is not ...
9m113konkurs's user avatar
1 vote
1 answer
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Quark charges - parton-distribution function - factor 5/18

I got the following from Thomson’s Modern Particle Physics and some other sources. The factor 5/18 distinguishing electron-DIS and neutrino scattering experiments is a basic proof for quarks and their ...
qatch's user avatar
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Youngs' tableau method and its relation with tensors

During my masters my prof. mentioned that the Youngs' tableau method can be used to calculate the number independent components of any arbitrary rank symmetric tensor in arbitrary dimensions. I wasn't ...
Sagar K. Biswal's user avatar
3 votes
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When do pairs of quarks form jets vs mesons?

For certain processes with low momentum transfer, such as the Kaon decay shown below, quarks will form bound states of mesons. Whereas for higher momentum-transfer processes, such as the decay of an ...
Jackson Burzynski's user avatar
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1 answer
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Confusion about irreps of $SU(N)$: is the "color charge" the same as spin 1?

Sorry if the question is too silly or not well stated, I am happy to clarify any point. Also, my presuppositions can be wrong. Consider a system of spin-$s$ particles: their spin operators $S_x$, $S_y$...
Matteo's user avatar
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Lagrangian for quarks and pions

I need to understand how starting from the free Lagrangian $$ \mathscr{L} = \bar{q}(i \not\partial - \hat{m})q $$ and based on the chiral angle associated with the pion field and the quark field ...
Jurandi Leão's user avatar
2 votes
1 answer
71 views

How relevant is the electric charge of quarks within hadrons?

Given that each quark flavor has a particular electric charge (i.e., either +2/3 or -1/3): how do these charges effect the internal dynamics of hadrons? Do the attractive and repulsive effects of ...
Thor Ether's user avatar
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1 answer
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How would I estimate the partial width for the decay of upsilon meson into an electron-positron pair?

I cam across a question that stated the total decay width for the phi meson was 4300 kev and the partial decay of it into an electron-positron pair was 1.3kev. How would I estimate the partial width ...
user2279603's user avatar
1 vote
1 answer
150 views

Why not put the anti-quarks in the conjugate representation?

The isospin doublet consisting of $u$ and $d$-quark is defined as $$ \begin{pmatrix} u\\ d \end{pmatrix}. \tag{1} $$ But the isospin doublet consisting of the antiquarks, $\bar{u}$ and $\bar{d}$, is ...
Solidification's user avatar
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0 answers
58 views

Kinetic energy of quarks in a proton

If we say that a proton has a kinetic energy of 50 GeV, can we say that each of the three quarks that compose it have roughly a mean energy of $\approx \frac{50}3=17$ GeV?
Ako's user avatar
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Is there a spin-1/2 hadron composed entirely of up quarks? [duplicate]

I am curious to know if there exists a spin-1/2 hadron that is composed of three up quarks. I understand that in quantum chromodynamics, baryons are formed of three quarks, each carrying a distinct ...
jkcwioqnkfdsoia's user avatar
1 vote
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What contributes most to the mass of the proton?

i'm a bit confused about the origin of the mass of the proton (or other hadrons). It is said that it stems from the renormalization of the current quarks, which have about 1/100 of the mass of the ...
Il Guercio's user avatar
1 vote
1 answer
129 views

How are the constituent quark masses determined?

I was wondering how the constituent quark masses are determined (in wikipedia they claim $m_{u/d,const}\approx 350 $ MeV), but how is this in practise determined or estimated? I could not find any ...
krabby patty's user avatar
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1 answer
180 views

Why does isospin symmetry survive chiral symmetry breaking?

In QCD there is a breaking of chiral symmetry such that, for the lightest quarks only, we have $$\langle \overline{u} u \rangle = \langle \overline{d} d \rangle = \mathrm{const.}$$ where the constant ...
Kris's user avatar
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1 answer
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Why is there a $u$ in the middle of the feynman diagram for a quark and an antiquark annihilating?

There is a feynman diagram in chapter 2 of Griffiths Introduction to elementary particles, where a pair annihilation is taking place. I am confused as before it was written that internal lines are ...
Anshish's user avatar
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Could the values of the CKM matrix be determined from the quark masses?

It seems like the values of the CKM matrix are somewhat related to the masses of the quarks. For example, the heavier the quark the less likely it is to change into another quark in a weak interaction....
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1 answer
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Why can't $uus$ and $uds$ quark content have $I = 1$ Isospin?

Well, I know the isospin singlet with $I=0$ and isospin triplet with $I = 1$. But for $I = 0$, why it must be $uds$ quark content rather than other assembly like $uus$ or $dds$? $ud$ can have $I = 0$ ...
thinking yang's user avatar
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0 answers
33 views

CKM Matrix Magnitude Question - Top to Bottom Greater than One?

In the CKM Matrix article on Wikipedia, the "standard" parameters for each matrix element are written with combinations of sines, cosines, and a complex exponential of 4 angle values. Using ...
18th Shard's user avatar
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0 answers
20 views

What is a polarized/unpolarized parton?

In QCD physics, certain partonic distributions like Generalized Parton Distributions (GPDs) and Transverse Momentum Distributions (TMDs) are defined for the case where the parton is either unpolarized,...
coopdog218's user avatar
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Which hadrons were present after the phase transition from the post-Big Bang QGP?

This question relates to the "hadron epoch" (after the initial quark-gluon plasma, but before the end of baryogenesis). My understanding is that the phase transition that ends the quark-...
SgtJohn74's user avatar
2 votes
1 answer
450 views

Why, in QCD, are quarks in the fundamental representation of $SU(3)$?

QCD is built from the notion that Dirac's Lagrangian should be invariant under gauge colour transformations. Here, quarks are elements of $\psi_{\alpha,f,c}(x)$, where $\alpha$, $f$ and $c$ stand for ...
orochi's user avatar
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1 answer
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Justifying the identification of eight gluons with the ${\bf 8}$ from ${\bf 3}\otimes{\bf 3}^*$

When we combine the fundamental ${\bf 3}$ and antifundamental ${\bf 3}^*$ of color $SU(3)$ of QCD i.e. single quark of three colors and a single antiquark of 3 anticolors, nine states are obtained. ...
Solidification's user avatar
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Can a sea quark swap places with a valence quark within a proton?

I understand that a proton is composed of three valence quarks and a very large number of sea quarks that briefly come into existence and then annihilate as quark-antiquark pairs. Is it possible for ...
Ryan's user avatar
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3 votes
1 answer
193 views

Would a black hole's event horizon split up a hadron into it's constituant quarks? Therefore creating free quarks?

As a thought experiment, say, for the sake of simplicity, we have a meson. This meson, which is traveling near light speed, is traveling towards a black hole. And skirts the event horizon in such a ...
Colonizor48's user avatar
2 votes
1 answer
329 views

Color vectors for antiquarks

For a single quark, the colour vectors are given by $$r=\begin{pmatrix} 1 \\ 0 \\0 \end{pmatrix} \qquad g=\begin{pmatrix} 0 \\ 1 \\ 0 \end{pmatrix} \qquad b=\begin{pmatrix} 0 \\ 0 \\ 1 \end{pmatrix}$$ ...
TaeNyFan's user avatar
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2 votes
1 answer
241 views

Why are vector mesons heavier than pseudoscalar mesons?

From the hyperfine calculation we find that the mass of the vector mesons are heavier than pseudoscalar meson, as the following proves. The magnetic moment is proportional to the spin and inversely ...
L L's user avatar
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0 answers
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Octet and decuplet baryon wavefunction

I read the octet and decuplet baryons symmetric and anti-symmetric wavefunction from 'Riazzudin and Fiazzudin's book. But I am little confused about the wavefunction of neutral sigma and Lambda baryon....
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1 vote
2 answers
175 views

Mass of $B$ Meson

This is a question from Griffith's Introduction to Elementary Particles, Chapter 2: The upsilon meson, $b\bar b$, is the bottom-quark analog to the $\psi$, $c\bar c$. Its mass is 9460 MeV/$c^2$ and ...
V Govind's user avatar
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0 answers
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How do I numerically compute the interquark potential from the correlation function of Polyakov Loops?

I know that the potential can be calculated in the following way: $$ aV(r) =-\ln(<\sum_{\textbf{x}} (P(\textbf{x}+R)P^{\dagger}(\textbf{x}))>)/N_T. $$ Now, suppone I have some procudure to ...
EigenAle's user avatar
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