Why is it that when they have the artist's rendition of the Pentaquark it shows two downs, two ups, and one anti-strange quark? Is this or is this just for show? Follow up to this question: if this configuration is just for show, what is the Pentaquark truly made of?


4 Answers 4


A pentaquark is a particle made of five quarks. "Penta" means 'five' in Greek. Technically it could be made of any combination of quarks/antiquarks, though subject to some restrictions - see below.

Quarks are bound by the strong force. In the same way as the electromagnetic force sees the (electric) charge of particles and causes interactions only within charged matter, the strong force has an associated colour. Only coloured particles interact via the strong force. There are three colours: red, blue and green. These are just names, they have absolutely no optical/visual meaning - you could have called them 1, 2 and 3.

The defining feature of the strong interaction is that a free particle held together by it can only exist if it is colour neutral: i.e. if the total colour is 0. This can by either having, say, a blue quark being balanced by blue anti-quark, or by having all three colours at the same time - red+blue+green gives white=0, in analogy to visible light. This is known as colour confinement. The strong force is so powerful that particles subject to it cannot break free; when the colour charge is 0, however, they cease to feel it so they can move around and exist independently.

Quarks have colours. If you want a pentaquark you need to mix quarks and antiquarks of the correct colour in order to obtain an overall colour neutral system. E.g. a red, blue and green quark + a red and an anti-red quark. See here for pictures. EDIT: As the comments have stressed, this is actually the only viable configuration of the pentaquark: 4 quarks and an antiquark.

They usually show up, down and strange quarks because they are the lightest quarks and therefore the most likely to be produced. If they ever find a pentaquark (like they are claiming now at CERN), it is highly probably that it is made of u, d and s. You'd need higher energies to create heavier quarks.

  • 4
    $\begingroup$ "Technically it could be made of any combination of quarks/antiquarks, though subject to some restrictions." Er ... the restrictions are pretty important. It's really only possible for it to be four quarks and one anti-quark or the other way around. $\endgroup$ Jul 22, 2015 at 2:18
  • $\begingroup$ What dmckee said is true, and comes from Baryon number being 1/3 for quarks, -1/3 for anti-quarks, and a whole number for any physical particle. (And quite important) $\endgroup$
    – Omry
    Jul 22, 2015 at 6:22
  • $\begingroup$ Yeah well I explain the restrictions later on, I just wanted to stress the number five. I'll add a small edit $\endgroup$
    – SuperCiocia
    Jul 22, 2015 at 11:46

In Scientific American, they said it was this specific grouping as illustrated, though with arbitrary coloring. It briefly stated how it must involve which quarks based on decay channels. I lost my hardcopy of the magazine so I can't easily look upmthe quotation now.

I think it was not as you describe though... enter image description here

Yea, it's in Wikipedia now.

In July 2015, the LHCb collaboration identified pentaquarks in the Λ0 b→J/ψK− p channel, which represents the decay of the bottom lambda baryon (Λ0 b) into a J/ψ meson (J/ψ), a kaon (K− ) and a proton (p). The results showed that sometimes, instead of decaying directly into mesons and baryons, the Λ0 b decayed via intermediate pentaquark states. The two states, named P+ c(4380) and P+ c(4450), had individual statistical significances of 9 σ and 12 σ, respectively, and a combined significance of 15 σ — enough to claim a formal discovery. The analysis ruled out the possibility that the effect was caused by conventional particles. The two pentaquark states were both observed decaying strongly to J/ψp, hence must have a valence quark content of two up quarks, a down quark, a charm quark, and an anti-charm quark (uudcc), making them charmonium-pentaquarks.

(Emphasis mine)


I suggest you to read my answer here for a quick look into exotic hadrons. These particles mostly(at least so far) are very unstable appears for a short time and decay into another particles, hadrons and mesons. Hadrons made of 3 quarks and mesons one quark and its anti-matter. These unstable particles(resonances) have a quark content based on initial and final state particles. $$ \Lambda_b^0\rightarrow Resonance \rightarrow J/\psi p K^- $$
$J/\psi$ has a charmonium quark content $c \bar{c}$ where proton $uud$. And our penta-quark has five-leafed clover. enter image description here

But this not as easy as seen. There are lots of possibilities about quark content and you need to eliminate the others by technical analyzes. I strongly recommend the LCHb article for further details.

Today, researchers are confident about the exotic state, pentaquark and its form of quarks. What they should do further is studying the "internal mechanism" of the particle. I mean quark interactions of the particle. Further studies will be about whether this particle is tightly bound with strong gluonic interactions or softly bound via pion exchange as I showed in my previous answer.


The recent high-energy experiments have found the true pentaquark model of the proton: four quarks and an anti-quark. In fact these quarks may be highly-energetic electrons. Proton is pentaquark.




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