LHCb unveils new particles

July 5, 2016, CERN
A view of the LHCb experimental cavern. Credit: Claudia Marcelloni/CERN

On 28 June, the LHCb collaboration reported the observation of three new "exotic" particles and the confirmation of the existence of a fourth one in data from the Large Hadron Collider (LHC). These particles seem to be formed by four quarks (the fundamental constituent of the matter inside all the atoms of the universe): two quarks and two antiquarks (that is, a tetraquark). Due to their non-standard quark content, the newly observed particles have been included in the broad category of so-called exotic particles, although their exact theoretical interpretation is still under study.

The quark model, proposed in 1964 by Murray Gell-Mann and George Zweig, is the most valid classification scheme of hadrons (all the composite particles) that has been found so far and it is part of the Standard Model of particle physics. In this model, hadrons are classified according to their quark content. However, it has been for a long-held mystery that all observed hadrons were formed either by a pair of quark-antiquark (mesons) or by three quarks (baryons) only. But, in the last decade several collaborations have found evidence of the existence of particles formed by more than three quarks. For example, in 2009 the CDF collaboration found one of these, called X(4140) – where the number in parentheses is its reconstructed mass in megaelectronvolts. This result was then confirmed later by a new CDF analysis, and by the CMS and D0 (link is external) collaborations.

Nevertheless, until now, the X(4140) quantum numbers – characteristic numbers with which the properties of a specific particle are identified – were not fully determined, and this ambiguity exposed the theoretical explanation to uncertainty. The LHCb collaboration could determine the X(4140) quantum numbers with high precision. This result has a large impact on the possible theoretical interpretations, and indeed it excludes some of the previously proposed theories on its nature.

LHCb unveils new particles
The image shows the data (black dots) of the mass distribution resulting from the association of the J/ψ and φ mesons, where the contribution of the four exotic particles is put into evidence by the four peaking structures at the bottom. Credit: CERN

While the X(4140) had already been seen, the observation of the three new with higher masses, called X(4274), X(4500) and X(4700), has been announced for the first time. Even though the four particles all contain the same quark composition, they each have a unique internal structure, mass and their own sets of .

These results are based on a detailed analysis of the decay of a B+ meson into mesons called J/ψ, φ and K+, where the new particles appear as intermediate ones decaying to a pair of J/ψ and φ mesons. To perform this research, the LHCb physicists used the full set of data collected during the first LHC run, from 2010 to 2012. The large signal yield efficiently collected with the LHCb detector has allowed LHCb scientists to discover those three new particles that were (literally, see the picture) peaking out from the data.

This news comes in addition to the discovery of the first two pentaquark by the LHCb collaboration last year.

Explore further: After a half century, the exotic pentaquark particle is found

More information: For more information, see lhcb-public.web.cern.ch/lhcb-p … .html#JpsiPhiExotics

Observation of J/ψφ structures consistent with exotic states from amplitude analysis of B+→J/ψφK+ decays. arxiv.org/abs/1606.07895

Amplitude analysis of B+→J/ψφK+ decays. arxiv.org/abs/1606.07898

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gculpex
3 / 5 (1) Jul 05, 2016
more quarks particles....
Da Schneib
5 / 5 (10) Jul 05, 2016
Very interesting. These particles could almost be called "bi-mesons," since they are essentially a combination of quark/antiquark pairs that form mesons. The full sets of quantum numbers will tell us more about QCD and the action of the color force.

Lots of reading to do here.
ursiny33
1 / 5 (5) Jul 05, 2016
Those quarks team up magnetically to each other to build mass, in a magnetic construction to evolve into the electron construction phases,
Da Schneib
5 / 5 (13) Jul 05, 2016
Errr, no. Quarks are held together in baryons by the color force, not EM. You know, that whole QCD thing that holds atomic nuclei together. Did you forget that atomic nuclei are all positive and neutral particles? And that they don't come apart despite all that positive charge? What do you suppose is holding them there? It sure ain't magnetism. It's not strong enough.
Mimath224
5 / 5 (5) Jul 05, 2016
@Da Schneib, yes interesting indeed but I don't find it surprising. As I have mentioned before on other threads the more scientists experiment with high (and higher) energies whatever the fundamental building property of particles is they will find 'it' combining and re-combining to produce so called exotic particles. Perhaps I'm being too simplistic in my lay mind, but it's like as if the scientists are gradually finding the intermediate steps on how this 'fundamental property' combines to finally produce stable entities. I really do think that there is a 'law' that governs how and what combinations are allowed and I'm confident they will be able to formulate it. My hope is that they do it within my lifetime,Ha!
Da Schneib
5 / 5 (4) Jul 09, 2016
@Mimath, I've been too busy to pay attention to this until now.

For these types of particles, there is indeed a law that governs how and what combinations are allowed. It's not a single law, but a whole bunch of laws. That's what we call a theory, and it's called "Quantum Chromodynamics," or QCD for short. However, it's very mathematically complex, and as a result it's not always easy for us to tell what it permits and forbids.

There are not one but six fundamental matter entities in this theory, called "quarks." In addition, there are also eight force entities, called "colored gluons," which mediate the color force (also called the strong force). We understand why there must be eight gluons, but we don't yet understand why there are six quarks.

[contd]
Da Schneib
5 / 5 (4) Jul 09, 2016
[contd]
A good way to understand the color force is to think of a force that has not one charge and its anticharge, like the EM force, but three charges and their anticharges. As with EM, like charges repel, and unlike charges attract. However, unlike EM, there are three charges and three anticharges, not just one. So if we name these three charges "red," "blue," and "green," then we see that red attracts antired, blue, antiblue, green, and antigreen charges, but repels other red charges.

Quarks carry red, blue, or green charges; antiquarks carry antired, antiblue, or antigreen charges.

Color charge is "confined;" this is because it is extremely strong, the strongest of all forces, and because there are not one type like EM and photons, but three types of force particles. Photons do not interact, because there is only one type; gluons, however, do interact because there are eight types.
[contd]
Da Schneib
5 / 5 (3) Jul 09, 2016
[contd]
As a result we never see a "bare" color charge; that is, we never see an individual quark. We can see two basic combinations: the three charges (or the three anticharges), and a charge and its anticharge.

What the experiment in this article shows is that it is possible for two pairs of charge-anticharge, i.e. two quark-antiquark pairs, to associate into a single particle.

Finally, it's worth mentioning that five-quark combinations are possible, and in fact were first discovered about a year ago. These are called "pentaquarks," and were discovered in this same detector, LHCb.
Da Schneib
5 / 5 (4) Jul 09, 2016
OK, so all of this begs the question, will we see 6- and 7- and higher order quark combinations?

We will at high enough energies, but they will not last long, because the 3- and 2-quark combinations are very stable and represent very low energy compared with these higher-order combinations; thus, it is energetically advantageous for the high-order ones to decay very quickly into the low-order ones. And in fact we already see this for the 4- and 5-quark combinations, which are very unstable and quickly decay into 2- and 3-quark particles.
Mimath224
5 / 5 (2) Jul 09, 2016
@Da Schneib Thank you for your explanation(s) and I do regularly search the net to try ( I say try, Ha!) to keep up to date.
However please note my wording particularly the use of the word 'property' which does NOT refer to particles (or the equivalent in other theories, 'wavicles' etc.) '....fundamental building property...combining and re-combining to produce so called exotic particles...'
perhaps I'm at fault for not explaining myself properly, so I'll try another approach.
I think it is agreed that electrons are fundamental particles, that is, they are not composed of 'quark, gluon' equivalent entities. My thoughts about this 'property' is that there must be a fundamental reason, or rule, as to why this 'property' or fundamental energy, produces, SAY electrons-positron pairs and not 'something' else. Here I am assuming that the 'property' that comprises the e/p pair is the same but it somehow combines differently with itself to produce the e and its anti-particle. Cont.
Mimath224
5 / 5 (2) Jul 09, 2016
Cont. That is I am going beyond, or deeper if you prefer, than the particles which might the product of pure energy. As scientist use ever more powerful machines that produce massive amounts of energy in collisions, what is the 'rule'/rules' that govern that energy to produce the particles detected, 'energy → (rule 1) particle → ... rule * stable particle combination.
'. I do feel that scientist are becoming closer and closer to this situation
I hope I have expressed myself properly.
Ha!, don't work to hard. Thanks for your time anyway.
nikola_milovic_378
Jul 10, 2016
This comment has been removed by a moderator.
nikola_milovic_378
Jul 10, 2016
This comment has been removed by a moderator.
Da Schneib
5 / 5 (4) Jul 10, 2016
@Mimath, this discovery may have profound implications regarding the matter-antimatter imbalance. I suggest you take in the "Family of Tetraquarks" article and read my comments there.

I also think that you are ignoring the fact that given enough energy, any particle/antiparticle pair may be created, and in fact is. For example, just because a proton collision at the LHC *can* produce, for example, a Higgs, doesn't mean that it always does; in fact, sometimes it produces your lowly e-p pair.
Protoplasmix
5 / 5 (5) Jul 10, 2016
Thanks for the good comments, Da Schneib, I wonder if it might also shed some light on the nature of neutronium (as in neutron stars) and maybe also possible phase(s) of matter in a maximally warped space-time, ie, inside an event horizon – what happens in gravitationally confined conditions where leptons and bosons don't matter? (pun not intended)
Da Schneib
5 / 5 (4) Jul 10, 2016
Thanks, @Proto. I don't think it will shed a great deal of light on neutron stars because the gravity isn't strong enough to affect the strong force, but I think it might on black holes.
Mimath224
5 / 5 (4) Jul 10, 2016
@Da Schneib, yes I understand and I have followed the Tetraquark family elsewhere but you do in fact make my point when you write '...any particle/antiparticle pair may be created, and in fact is' which is similar to what I'm suggesting. So I'm not ignoring this, I'm actually using it and what I'm asking, using your comment '...a Higgs, doesn't mean that it always does; in fact, sometimes it produces your lowly e-p pair.' is WHY? There must be a rule that governs the productions at the 'pre-particle' level....or is it a random process. Please, Da Schneib, I think you need to read what I've posted because you continue to talk about the particles as though they are not composed of anything whereas I am not.
Let me put it another way. Assuming that you and I accept the BB model of the universe and that at the unification epoch where the three quantum forces are unified. Cont.
Da Schneib
5 / 5 (4) Jul 10, 2016
It's a random process. But not really; it's constrained by the conservation laws. So it's only partly random.

No one's been able to come up with any constituents of the fundamental particles of the SM that agrees with observations with the exception to rishons for which there is no experimental evidence, and no one has seen a quark or an electron break down into smaller parts. If there are smaller parts in them, they're apparently confined. This is why I speak of them as "fundamental particles" and don't talk about constituents of them.

The closest anyone's come to what you're talking about is either rishons (see the Rishon Model article in Wikipedia) or string physics. IIRC you're familiar with both. Rishons suffers from a lack of experimental evidence, and string physics suffers so far from both a lack of contact with known physics and a lack of testability where it predicts something different from the SM.
Mimath224
5 / 5 (4) Jul 10, 2016
Cont. When the forces separate the QGP has not yet produced the Hadrons etc. that is before baryogenesis. But as a possible answer to my own question I wonder if I am 'going down the road' sphaleron (electroweak) theory but you might know more that than I do (or ever will). Sakharov conditions might be a route but then we are in the symmetry theory. That is, is it a complex form of (quantum) symmetry that governs what particles will be produced? That is, in your quote about the Higgs would you consider it to be symmetry that determines the particles produced which could be different even when LHC energies are the same?
Again, thanks for your time.
Da Schneib
5 / 5 (4) Jul 10, 2016
Mmmm, gravity is presumed to split off the unified force first; then comes the color force and at that point the hadrons form and the quarks are confined; however, there are still sphaleron processes at work that convert leptons and quarks back and forth. On the other hand, weak interactions are slow. So it's not clear to what extent they can affect baryogenesis.

The Higgs is the result of the breaking of the electroweak symmetry which comes even later.

Pretty much everyone thinks the Sakharov criteria must be met.

There is sufficient proven randomness in QM to make the processes that happen pure chance (regulated, as I said above, by conservation laws). Given what we already know this is the most parsimonious explanation.
Mimath224
5 / 5 (2) Jul 11, 2016
@Da Schneib Yes, thank you for your comments...most appreciated. I am aware of the rishon and string theories (though I repeat as a layman) and you're right, they too don't really fit my thoughts because I'd be asking the same questions. For example, if particles are (broadly speaking) vibrating strings I'd be asking 'strings of what?' or 'if something is vibrating what is that something? If that something is [say] 'pure energy' then do we have 'law' that determines what 'frequencies' make what?' I am thinking very loosely here and I'm sure you can think of better terminology.
The one thing I think we can all agree on that there is energy, although we might argue the details, I am asking what process causes that energy to become the particles we have come to accept. I have assumed here that e-, e- P+ etc. all have energy. You have given a partial answer with the comment of randomness and cons. laws which, for me, is 'something to be going on with'. cont
Mimath224
5 / 5 (2) Jul 11, 2016
Cont. Yes I didn't mention gravity because while 'I think' it has a definite role to play I really haven't asked the right questions to include it. As I am layman I also feel that certain things will escape me and gravity at the quantum level is one of them. That is to say, that if I consider gravity as a force then I meet the same problem as everybody else (mainstream). On the other hand thinking of quantum gravity as quantum 'geometry' then I get rather mixed up between what/where the 'geometry' is and the particles themselves. So I stop short because the next step might 'compactification' and that is not a route I can reconcile at present...later maybe...but not yet.
The other ingredient I left out was Time and I know my views on this are not mainstream (though I have mentioned it on other threads) so I think it is best left out on this occasion. Once again, thanks for your time. I certainly hope these scientist can continue their work...fascinating stuff.
Hyperfuzzy
not rated yet Jul 11, 2016
Great theory; but, I don't see the data as pertinent. This has a very simple explanation without any of this theory. It's like placing a blanket over a car shaped hill and defining the theory of a maserati. True, you might be able to build the maserati, but I doubt you could do it with quarks.

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