The Theoretical: Exotic Mesons and Multi-quarks, what are they?

The Theoretical: Exotic Mesons and Multi-quarks, what are they?

Credit and found: https://www.google.com/url?sa=i&url=https%3A%2F%2Findico.cern.ch%2Fevent%2F778351%2Fcontributions%2F3238815%2Fattachments%2F1764332%2F2863686%2FThornton_20181203_scotdist_glasgow.pdf&psig=AOvVaw0Z6hzuZOde11VPUEpoDUFN&ust=1634212835942000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCLDiyJ-N5vMCFQAAAAAdAAAAABAD

By: Ian Davis

Introduction:

I was introduced to exotic mesons during the midst of researching for Tachyons. I do not know much about them, but from what I can infer, it should be mesons and other particles composed of anti and regular quarks and gluons to create a pair that should not have existed. However, I see some instances in this work. Perhaps we have anti-pairs, maybe we have a "perfect" quark pairing reminiscent of strange matter, or maybe it is precarious as the weak force might make an appearance; time will tell. Let's get into it.

My Research:

From what we know about quarks, they have a color force, each color corresponds to each other, and they balance one another. As previously stated in other articles, red, green, and blue are all of which switch through the strong force and gluons, their force carriers. Each quark has its specific identity; they usually consist of the stable up and down quarks but can range to the other more unstable quarks like strange, charm, top, and bottom quarks. Each quark can pair up into a fermion as a tri-pair or three quarks altogether.

Credit and found: https://www.google.com/url?sa=i&url=https%3A%2F%2Fphysicsworld.com%2Fproton-contains-more-anti-down-quarks-than-anti-up%2F&psig=AOvVaw0sJ6Kg4U4Zsuyy5-cgF_X3&ust=1635290259650000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCKDw1IvZ5vMCFQAAAAAdAAAAABAD

So what are multi-quarks? Well, their existence is extraordinary, as they are exotic mesons, also known as general mesons, who could not fit the bill of the standard model due to their quantum numbers not being compatible, as well as most of them are exotic hadrons, having more than three quarks in their composition, either anti or regular. They are multiple types of mesons under this category like glueballs (only gluons, no quarks), tetraquarks (two ordinary quarks and two anti-quarks), a pentaquark (four regular quarks and one anti-quark), hybrid mesons (quark-antiquark pair with one or more gluons, almost like a flux tube with no shielding), and hadronic molecules (two-hybrid mesons forming either a pentaquark or a typical tetraquark) as they all have a hard time existing due to their ridiculous compositions. Classifying an exotic meson is pretty easy, as its composition comprises two types of quarks or the conventional and non-conventional quarks. The letter "q" represents the model's light, or more stable/conventional quarks like up, down, or strange. While the letter "Q" represents the heavier quarks that are less stable/non-conventional and include the top, bottom, and charm quarks. The denotation of the line above one of these letters shows an anti-version of said quark category, like "q and Q" would be a common representation.

Credit and found: https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.quantumdiaries.org%2F2012%2F01%2F20%2Fthats-right-count-them-4-quarks%2F&psig=AOvVaw1IclJYf4Ytu0xwftIN4uMg&ust=1635290324752000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCKiBi7TZ5vMCFQAAAAAdAAAAABAD

Glueballs, the most fascinating bunch, are a hypothetical composite particle that consists of solely gluons. Gluons are the gauge boson of the strong force and are a carrier for the color force (color charge), which will be why glueballs exist. Since they are a gauge boson for the strong force, they inevitably experience it themselves and therefore can mix with meson states. Due to their energy levels being within readable collider range, they should have been detected already; however, due to the mixing mentioned earlier with meson states, they are increasingly difficult to detect since they can basically hide. This is Hamiltonian mechanics, but in short, they mix within regular quark-antiquark pairs (mesons) and allow their hiding to occur; perhaps this is the reason why mesons can exist without annihilation. The candidate that has been spotted in isolation is known as which has the properties of a glueball. The discovery of a glueball would be significant because the predicted angular momentum is an astonishing 2 or 3 in the spin (ground states), which is not typical for any other particle in the standard model. Distinctive properties of the glueball are that they have a neutral QCD and a zero baryon number. 

Credit and found: https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.bnl.gov%2Fnewsroom%2Fnews.php%3Fa%3D218731&psig=AOvVaw346h3lG5RQeJcY7-Xu1u7k&ust=1635290382042000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCPji9c3Z5vMCFQAAAAAdAAAAABAJ

The tetraquark is an exotic meson only has 4 valence quarks or basically the raw number of body of quarks inside a hadron, but in this case, a meson (one example of what valence quarks mean is that a proton has three valence quarks, two ups, and one down) therefore having two quarks and two anti-quarks. The most common tetraquarks consist of two anti-quarks and two regular quarks, either a light quark or a heavy quark. However, multiple types of tetraquarks (with different MeV/c^2) have been observed. In most instances, there cannot be two anti-lights or two anti heavies in one tetraquark, as it has barely been observed and would not be stable. There can only be a heavy with a corresponding anti version and a light with a corresponding anti version. The earliest version observed was called X(3872), X as in temporary, and 3872 as in the MeV/C^2; as we can see, they are cumbersome due to their abnormal properties. However, in some instances, there have been detected heavy quarks and light quarks with other heavy and light quarks respectively, for example, Z(4430) that was discovered by the Belle experiment in 2007, had the composition of regular charm, anti charm, down quark and anti up quark, two heavies and two lights. One of the latest tests done in the LCHb, found a tetraquark of two regular charm quarks, then two anti-charms, showing that it can be composed of purely one type; in this instance, we have heavy. 

Credit and found: https://www.google.com/url?sa=i&url=http%3A%2F%2Fwww.sci-news.com%2Fphysics%2Ffour-new-tetraquarks-09481.html&psig=AOvVaw3Z93A9bc4nP05O7BspjpXR&ust=1635290472037000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCIjpnvLZ5vMCFQAAAAAdAAAAABAJ

The pentaquark has two categories of types: the "bags" and the "molecule," Both are human-made and have not been made by nature. As all quarks have a baryon number of +1/3 and their anti versions have -1/3, a pentaquark would have a total baryon number of 1 and therefore counts as a baryon. Since it has 5 quarks instead of the normal tri-quark, it is still classified as an exotic meson but also has the composition of 4 regular quarks and one anti-quark, typically light. In bags or a full circle of the five quarks, gluons are mediating all of them or about 7 in between (perhaps more), with the anti-quark typically posted outside the quark conglomeration.

Credit and found: https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.science.org%2Fdoi%2F10.1126%2Fscience.364.6444.917&psig=AOvVaw25O-29ToWmg1-3BgLINhmU&ust=1635290528390000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCLiPvIza5vMCFQAAAAAdAAAAABAD

For the molecule pentaquarks, or in full, "meson-baryon molecule" that have two spheres, one hanging off the other tumorously. This quark structure contains a three quark mechanism and another two-part mechanism; the three-part has three regular quarks, the other two have one anti-quark and one standard quark. 

Credit and found: https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.arabnews.com%2Fscience-technology%2Fnews%2F776441&psig=AOvVaw25O-29ToWmg1-3BgLINhmU&ust=1635290528390000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCLiPvIza5vMCFQAAAAAdAAAAABAb

How may the color force work in something like this? It has a bizarre way of canceling out each other. No matter what identity the quark takes on, there are basic principles. For a meson, they need to cancel out with one blue and one anti-blue, however in this instance, for a pentaquark, one quark pairs up with one color (ex: blue), one quark with another color (ex: red), two quarks with the same color (ex: green), and one anti-quark that counteracts the superior color (ex: antigreen.) Since the color binding is very weird, the binding between the five quarks is odd, as they are all tightly bound together.

For bags, they are easy to bind together due to their close proximity, however for molecules, it is theorized that they are bound together via pion exchange, also known as the strong force, which binds the three bags and the two bags together, but pretty weak due to distance. 

Credit and found: https://www.google.com/url?sa=i&url=http%3A%2F%2Fhyperphysics.phy-astr.gsu.edu%2Fhbase%2FParticles%2Fpquark.html&psig=AOvVaw25O-29ToWmg1-3BgLINhmU&ust=1635290528390000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCLiPvIza5vMCFQAAAAAdAAAAABAP

Other multi-quarks can include the hybrid mesons, with two quarks, one anti and one regular, connected by a gluon. They should have canceled out; however, the gluon is holding them together. The shape and idea are reminiscent of a quark flux tube held by color confinement (created by energy added to the process). They are meant only to keep quarks out of isolation since one quark can never be in isolation. The hybrid meson method is a little different since the gluons holding them together are a field that contains the entirety AROUND the quark pairs instead of a small field BETWEEN the quarks. The field is called an excited gluonic field and allows the color charge to continue, but differing between just two quarks, one anti and one not. 

Credit and found: https://www.google.com/url?sa=i&url=https%3A%2F%2Fmanoa.hawaii.edu%2Fnews%2Farticle.php%3FaId%3D1108&psig=AOvVaw2YpOl7o4R_ZHKrZifsGxP4&ust=1635290804572000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCLDJ1JLb5vMCFQAAAAAdAAAAABAD

There are cases of another type of molecule particle pair. Known as the hadronic molecule, if two-hybrid meson-like pairs pair up in a sort of tetraquark-like shape and form a kind of bubble using a large excited gluonic field, they can develop something resembling a tetraquark and a pentaquark molecule. The two pairs consist of double heavy quarks with one anti and one quark in each, like the hybrid meson. There have also been three quarks in one hybrid meson with two in the other; the three would consist of no anti and only regular quarks. Each pair has an "identity" of sorts, as one pair will take on a regular and anti version, for example, a pair will be named "Heavy-Meson" or "Heavy-Antimeson," most likely depending on which one has more MeV/c^2 will determine the stronger and overall identity (if one pair has a heavier anti-quark than the other pair, it will take on the identity of the antimeson) and will be aptly named different if it has three, like Doubly Heavy Baryon" since it has three quarks. I do not know if the hadronic molecule can still practice the color force, but the odds are is that it most likely can since it is an essential characteristic, just very weak since these are exotic. 

Credit and found: https://webific.ific.uv.es/web/en/content/hadronic-molecules

Not only are there quite a few quarks, but there happen to be a lot of gluons attempting to bind and start a field between and around the quarks, therefore making the entire thing heavy. However, the more compact the hadronic molecule gets, it can be classified as a compact tetraquark. More than likely, the individual hybrid meson fields will combine or get incredibly close. 

Credit and found: http://cpl.iphy.ac.cn/Y2020/V37/I10/101201

Finally, some conclusive numbers for the extra knowledgable folks are that the Lattice QCD predictions are that the lowest states for mass are: 0++ with the mass of 1611±163 MeV/c^2 and 2++ with a mass of 2232±310 MeV/c^2. But the  0−+ and the glueballs (0--) are all expected to lie above 2 GeV/c^2, but hybrid mesons 0−+, 1−+, 1−−, and 2−+ are all below the 2 GeV/c^2 cutoffs. The lattice was all quenched, and they did not mix with meson states. The 0++ conditions consist of glueballs and tetraquarks with their respective candidates found and tested upon. I will not include all subjects, but I will state that there have been quite a few. 

Credit and found: https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.researchgate.net%2Ffigure%2FPredictions-for-F-s-1-Q-2-from-the-fluctuation-model-LFHQCD-and-lattice-QCD-5-7_fig1_327644116&psig=AOvVaw0SJmVcL6u6lcQIKXKRpst9&ust=1635293681772000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCKiFxuvl5vMCFQAAAAAdAAAAABAI

Final Conclusion:

So, the Exotic Mesons and their currently theorized candidates are not set into stone; they are all basically theoretical but have been observed in many instances and still need further classification; these tests were very recent and are still being studied. However, they do all make sense are genuinely fascinating. We see that the tetraquark, a four quarked example, is still practicing color force but with anti additions. The pentaquark is a unique shape, as it can either have a bag shape or a molecule shape; both are very interesting as they can either be held together by pion exchange or by a color force with its anti equivalents. Same with hybrid mesons - as they are two quark pairs held together by a force field of sorts, a gluonic field that has been excited to wrap around the body of the pairs instead of in-between or as a connection. Even the glueball, one that is all gluons interchanging the color force but is relatively unknown and hard to detect, and the hadronic molecule is a complicated heavy molecule type of particle that uses two hybrid mesons surrounded by a field, all are very complex but still fascinating.

All of these abide by the rules of physics, but the way they form, stay together and have to decay shows that they are not natural and will most likely only be survivable in a lab and facility. They also have very abnormal weights, as the typical standard hadron has ~940 MeV/c2. Still, when these exotic mesons are included, they weigh into the thousands, meaning they are generally unsustainable. 

These have been proven to be authentic and can exist for some time; however, they will not naturally occur. There are many variations with different weights, types, colors, and mixing of both anti and regular quarks. Tests in the future will hopefully give insight into these fascinating particles.

Sources: 

1. https://link.springer.com/content/pdf/10.1140/epja/i2016-16001-x.pdf

2. https://lss.fnal.gov/archive/2018/conf/fermilab-conf-18-099-t.pdf

3. https://www.science.org/news/2019/06/exotic-particles-called-pentaquarks-may-be-less-weird-previously-thought

4. https://arxiv.org/abs/1502.07276

5. https://www.ibtimes.com/physicists-hunt-hybrid-mesons-understand-strong-nuclear-force-solve-quark-confinement-2534398

6. https://www.jlab.org/conferences/confinement/wed/gluonic_excitationsDudek.pdf

7. https://www.chemeurope.com/en/encyclopedia/Exotic_meson.html

8. https://g.co/kgs/mJGnTR

9. https://g.co/kgs/5t6xTr

10. https://www.thefreedictionary.com/valence+quark

11. https://webific.ific.uv.es/web/en/content/hadronic-molecules

12. http://cpl.iphy.ac.cn/Y2020/V37/I10/101201

Wikipedia links:

1. https://en.wikipedia.org/wiki/Exotic_meson#Lattice_predictions

2. https://en.wikipedia.org/wiki/Special_unitary_group#The_group_SU(3)

3. https://en.wikipedia.org/wiki/Gluon_field

4. https://en.wikipedia.org/wiki/Pentaquark

5. https://en.wikipedia.org/wiki/Tetraquark

6. https://en.wikipedia.org/wiki/Z(4430)

7. https://en.wikipedia.org/wiki/Exotic_hadron

8. https://en.wikipedia.org/wiki/Glueball

9. https://physicsworld.com/a/evidence-grows-for-tetraquarks/

10. https://en.wikipedia.org/wiki/State_of_matter

11. https://en.wikipedia.org/wiki/Hamiltonian_(quantum_mechanics)

12. https://en.wikipedia.org/wiki/Branches_of_physics

13. https://en.wikipedia.org/wiki/Color_confinement