Questions tagged [quarks]

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

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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) ...
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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
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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 ...
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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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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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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 ...
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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: ...
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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....
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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 ...
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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
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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 ...
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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
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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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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 $S_x$, $S_y$...
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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
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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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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
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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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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?
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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 ...
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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
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1 answer
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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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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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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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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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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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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
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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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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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Comprehensive references to learn about the flavor $SU(3)$ model of hadron classification

What are some comprehensive references to learn about the flavor $SU(3)$ model of hadron classification based on group theory? Textbooks, Lecture notes, videos anything will do. I need to learn this. ...
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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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2 votes
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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
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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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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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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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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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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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2 answers
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Is there something special about the $b$ quark?

I have seen many papers about measurements related to $b$ quarks, for example the forward-backward asymmetry of the $b$ quark or the decay width of $Z$ to $b \bar b$ pairs, but not so many for the ...
jmaguire's user avatar
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1 answer
328 views

Baryon wavefunctions

The textbook I am currently using states that when all quarks have the same flavor, there are no $J=1/2$ baryon wavefunctions for the ground state $l=0$. Is this an experimental result or is there a ...
jore1's user avatar
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1 answer
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'Elementary' particles (electrons) vs non-elementary particles (protons) regarding relativistic mass

Is there a possible slight difference between protons and electrons behaviour while they are accelerated at speeds that cause relativistic changes to their mass. Why am I asking that? Because for a ...
Krešimir Bradvica's user avatar
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1 answer
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$J=1/2$ and $J=3/2$ Baryons with $uds$ quarks

Why are there two different $J = \frac{1}{2}$ baryons with quark content $uds$ (the $\Lambda_{0}$ and $\Sigma_{0}$) but only one $J = \frac{3}{2}$ baryon (the $Σ_{*,0}$) with the same quark content? I ...
Archie C's user avatar
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2 answers
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Matter-antimatter conversion in quarks

If in beta plus decay, regular matter such as the up quark can decay into a positron, I have to wonder under high pressure, could it be possible for a quark to decay into the antiquark of its opposite?...
Jungwoon Song's user avatar
1 vote
2 answers
210 views

Quark structure of Baryons

I was studying Particle Physics then suddenly I came up with a question that why only Baryons are made up of three quarks, at first I thought to to conserve Baryon number which is $\frac{1}{3}$ for ...
Bishal Sarkar's user avatar
3 votes
1 answer
114 views

Could a fourth family of quarks and leptons account for dark matter?

In the early universe, could a family of quarks and leptons have formed an electrically neutral particle that is dark matter?
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What is the interaction between electrons and the electromagnetic field to give them charge?

*What is the interaction between a particle, like an electron, with the electromagnetic field that causes that particle to be charged? for example. If the positive charge of a proton comes from the ...
Jackson Wallace's user avatar

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