How CERN's discovery of exotic particles may affect astrophysics

April 11, 2014 by Brian Koberlein, Universe Today
The difference between a neutron star and a quark star. Credit: Chandra

You may have heard that CERN announced the discovery of a strange particle known as Z(4430). A paper summarizing the results has been published on the physics arxiv, which is a repository for preprint (not yet peer reviewed) physics papers. The new particle is about 4 times more massive than a proton, has a negative charge, and appears to be a theoretical particle known as a tetraquark. The results are still young, but if this discovery holds up it could have implications for our understanding of neutron stars.

The building blocks of matter are made of leptons (such as the electron and neutrinos) and quarks (which make up protons, neutrons, and other particles). Quarks are very different from other particles in that they have an electric charge that is 1/3 or 2/3 that of the electron and proton. They also possess a different kind of "charge" known as color. Just as electric charges interact through an electromagnetic force, color charges interact through the strong nuclear force. It is the color charge of quarks that works to hold the nuclei of atoms together. Color charge is much more complex than electric charge. With there is simply positive (+) and its opposite, negative (-). With color, there are three types (red, green, and blue) and their opposites (anti-red, anti-green, and anti-blue).

Because of the way the works, we can never observe a free . The strong force requires that quarks always group together to form a particle that is color neutral. For example, a proton consists of three quarks (two up and one down), where each quark is a different color. With visible light, adding red, green and blue light gives you white light, which is colorless. In the same way, combining a red, green and blue quark gives you a particle which is color neutral. This similarity to the color properties of light is why quark charge is named after colors.

A periodic table of elementary particles. Credit: Wikipedia

Combining a quark of each color into groups of three is one way to create a color neutral particle, and these are known as baryons. Protons and neutrons are the most common baryons. Another way to combine quarks is to pair a quark of a particular color with a quark of its anti-color. For example, a green quark and an anti-green quark could combine to form a color neutral particle. These two-quark particles are known as mesons, and were first discovered in 1947. For example, the positively charged pion consists of an up quark and an antiparticle down quark.

Under the rules of the strong force, there are other ways quarks could combine to form a neutral particle. One of these, the tetraquark, combines four quarks, where two particles have a particular color and the other two have the corresponding anti-colors. Others, such as the pentaquark (3 colors + a color anti-color pair) and the hexaquark (3 colors + 3 anti-colors) have been proposed. But so far all of these have been hypothetical. While such particles would be color neutral, it is also possible that they aren't stable and would simply decay into baryons and mesons.

There have been some experimental hints of tetraquarks, but this latest result is the strongest evidence of 4 quarks forming a color neutral particle. This means that quarks can combine in much more complex ways than we originally expected, and this has implications for the internal structure of .

Very simply, the traditional model of a neutron star is that it is made of neutrons. Neutrons consist of three quarks (two down and one up), but it is generally thought that particle interactions within a neutron star are interactions between neutrons. With the existence of tetraquarks, it is possible for neutrons within the core to interact strongly enough to create tetraquarks. This could even lead to the production of pentaquarks and hexaquarks, or even that quarks could interact individually without being bound into color neutral particles. This would produce a hypothetical object known as a quark star.

This is all hypothetical at this point, but verified evidence of tetraquarks will force astrophysicists to reexamine some the assumptions we have about the interiors of neutron stars.

Explore further: Quirky quark combination creates exotic new particle

More information: "Observation of the resonant character of the Z(4430)− state." R. Aaij, B. Adeva, M. Adinolfi, A. Affolder, Z. Ajaltouni, J. Albrecht, F. Alessio, M. Alexander, S. Ali, G. Alkhazov, P. Alvarez Cartelle, A.A. Alves Jr, S. Amato, S. Amerio, Y. Amhis, L. An, L. Anderlini, J. Anderson, R. Andreassen, M. Andreotti, J.E. Andrews, R.B. Appleby, O. Aquines Gutierrez, F. Archilli, A. Artamonov, M. Artuso, E. Aslanides, G. Auriemma, M. Baalouch, S. Bachmann, J.J. Back, A. Badalov, V. Balagura, W. Baldini, R.J. Barlow, C. Barschel, S. Barsuk, W. Barter, V. Batozskaya, Th. Bauer, A. Bay, L. Beaucourt, J. Beddow, F. Bedeschi, I. Bediaga, S. Belogurov, K. Belous, I. Belyaev, E. Ben-Haim, G. Bencivenni, S. Benson, J. Benton, A. Berezhnoy, R. Bernet, M.-O. Bettler, M. van Beuzekom, A. Bien, S. Bifani, T. Bird, A. Bizzeti, P.M. Bjørnstad, T. Blake, et al. arXiv:1404.1903v1 [hep-ex]

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3.3 / 5 (4) Apr 11, 2014
Well I believe that a QUARK star is very likely. IF the physics say it's possible, then nature usually finds a way, especially in cosmology. The next logical collapse after a Neutron star, is indeed a Quark star. Personally I suspect Quark stars (or Plank stars) or sat at the heart of Black Holes. A Quark stars extreme density would most likely create an event horizon surrounding it.
All personal belief of course but I would put money on it!!!
1 / 5 (1) Apr 11, 2014
Why did they change truth/beauty to top/bottom? Would it not be more engaging to revert to the original terms? Interested in responses to these non-physics questions since there must have been a pressure to change that; yet the words really don't "market" as well.
Apr 11, 2014
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not rated yet Apr 11, 2014
Via CKM matrix?
1.4 / 5 (7) Apr 12, 2014
These "exotic particles" seems to be energy fluxes of quantum vacuum which appear by particles collisions. They are momentary and do not have their own existence as for example electron, proton or foton. The same is with Higgs boson. Between Higgs boson and mass of the particles there is no direct epistemological correlation. Higgs boson is not proof for existence of Higgs field which is supposed to be rensposable foe mass of elementary particles.
Apr 12, 2014
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1 / 5 (9) Apr 12, 2014
There exists a very good book about CERNs way to produce discoveries:
The Higgs Fake - How Particle Physicists Fooled the Nobel Committee
It is worth to read.
5 / 5 (2) Apr 12, 2014
If you consider that the early universe was considered to be a quark gluon plasma, and that black holes are analogous to the singularity that started the universe (if indeed there was a singularity), then it makes sense that inside a black hole is a Quark star, perhaps consisting of a Quark Gluon Plasma, or quark multiplets, or combinations thereof. I'd even go as far as to suggest that the core of a black hole is a place of unification, and that all known forces are unified, again echoing the earliest times of our universe. Surely this must be considered given the extreme densities involved at the core.
not rated yet Apr 12, 2014
I for one would like to see an end to there being a singularity in the black hole. That would mean that they are unlike the big bang, because there the entire universe (that is, spacetime itself) was at "zero volume", versus just the materia in a black hole.

Just one thing is spinning black holes. They seem to curve the space around them, they have a spinning magnetic field, and what else. For that you need torque. (Strength to twist.) Normally, torque is measured in force * distance (e.g. newton meter, or for the units challenged, foot-pounds-force). Halve the distance and you need double the force. Make the distance zero, and you'd need infinite force.

If a black hole is a singularity, then its "internal width" is zero, so there's no room for the distance.

Much nicer would be to find quark stars, and thirty years from now, even some next step in this series, once we one day find that even quarks are built of something. :-)
not rated yet Apr 13, 2014
Not that it really matters, but I'm curious whether Z(4430) is -1/3 or -4/3 .. the article just says "negative charge" not the exact amount ... seems like a significant charge difference, but I guess it's still very possible they don't know.
5 / 5 (2) Apr 13, 2014
Not that it really matters, but I'm curious whether Z(4430) is -1/3 or -4/3 .. the article just says "negative charge" not the exact amount ... seems like a significant charge difference, but I guess it's still very possible they don't know.

It's -1. You can't have a free electric charge that's not a whole number (that would break QM). Believe me, had they found a fee partial charge you'd have heard about it on the evening news :)
5 / 5 (2) Apr 13, 2014
Besides, just look at the makeup they're proposing, these propertites don't come out of thin air like magic:

Charm and anti-charm (plus 2/3 plus -2/3 cancel out), leaving the down (-1/3) plus the ANTI-up (-2/3) = -3/3 or -1. It's all in the table above (and the understood "anti-table").
3 / 5 (2) Apr 13, 2014
Could a neutron star have a quark core?
5 / 5 (1) Apr 14, 2014
Why did they change truth/beauty to top/bottom? Would it not be more engaging to revert to the original terms? Interested in responses to these non-physics questions since there must have been a pressure to change that; yet the words really don't "market" as well.

The names are not that important :) As for marketing, although the "God particle" really sells well, I definitely prefer the "Higgs boson" instead...
5 / 5 (1) Apr 14, 2014
Could a neutron star have a quark core?

Sure. It should be possible to get intermediarte stages depending on the mass of the original star.
(Much like you should be able to get neutron stars that have a top layer of 'regular' atoms - or at least a proton-neutron-electron soup)
Apr 14, 2014
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