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What is the Y(4140)? The plot thickens April 6, 2009

Posted by dorigo in news, physics, science.
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I read with interest -but it would probably be more honest to say I browsed, since I could understand less than 50%- a preprint released three days ago on “The hidden charm decay of Y(4140) by the rescattering mechanism“, by Xiang Liu, from Peking University (now at Coimbra, PT). The Y particle has been recently discovered by CDF.

The existence of the several new resonances of masses above 3 GeV recently unearthed by B factories and by the CDF experiment poses a challenge to our interpretation of these states as simple quark-antiquark bound states, because of their properties -in particular, their decay pattern and their natural widths.

Already with the first “exotic” meson discovered a few years ago (and recently measured with great precision by CDF), the X(3872), the puzzle was evident: at a mass almost coincident with twice the mass of conventional charmed mesons (states which are labeled “D”, which are composed of two quarks: a charm and a up or down quark, like D^+ = c \bar d or D^\circ = c \bar u), the X was immediately suggested to be a molecular state of two D particles. I wrote an account of the studies of the nature of the X particle a few years ago if you are interested -but mind you, the advancements in this research field are quick, and I believe the material I wrote back then is a bit aged by now.

The paper by Liu tries to determine whether the interpretation of the Y particle as a pure second radial excitation of P-wave charmonium (\chi_{cJ}'', with J=0,1) holds water once the observed branching ratio of the Y into the final state seen by CDF (Y \to J/\psi \phi), and the measured decay width, are compared to a theoretical calculation.

The nice thing about the decay of the Y into the observed final state is that it occurs only through a so-called “rescattering” mechanism, by means of the diagrams shown in the graph below (the ones shown refer to the J=0 hypothesis of the \chi_{cJ}'', but similar diagrams are discussed for the J=1 state in the paper).

As you can see, the Y produces the two final state particles by means of a triangle loop of D mesons. These diagrams usually describe rare processes, and in fact Liu’s calculations end up finding a small branching fraction. I am unable to delve into the details of the computation, so I will just state the result: the typical values of the branching ratio B(Y \to J/\psi \phi) depend on a parameter, \alpha which, if taken in a “reasonable” range of values, provides estimates in the ballpark of a few 10^{-4}. This appears inconsistent with the observation provided by the CDF experiment.

Clearly, work is in progress here, so I would abstain from concluding anything definite on the matter. So, for now, let us call this an indication that the simple interpretation of the Y as a excited charmonium state is problematic.


1. singlino - April 6, 2009

Could it be new feature of QCD yet to be discovered (that is masked by the non petrterbativity of the theory at low energy) respensible for all those new (bound) states?

2. Luboš Motl - April 6, 2009

Isn’t it a bound state of a singlino, wino, neutralino, a five-times-wound D3-brane, and a black ring? 😉 I am sometimes uncertain about the legitimacy of all these “QCD surprises”.

All these states look pretty messy to me. Someone always says that he is shocked that some manifestly oversimplified hypothesis doesn’t seem to hold.

Take Marco Frasca. He also writes that it is shocking that a paper seems to indicate that QCD is not equivalent to a simple gluon exchange (which verbally sounds like a tree-level, or at most perturbative, QCD). Wow, what a shock that QCD goes beyond the tree level and perturbative series.

Similarly with your Y(4140). Why do the people a priori expect that similar states – apparently randomly chosen – are simple? 4140 MeV is a lot of energy for QCD. There’s a lot of room for many quarks, gluons, in all kinds of motion.

So all these things can naturally be “QCD molecules”, to say something complicated. But for strong coupling, there’s no qualitative gap between atoms and molecules, anyway, is there?

The gaps between different kinds of binding – and different kinds of excitations – appear in atomic physics because the electromagnetic fine structure constant that governs atomic physics is small, and the qualitatively different types of interactions and excitations have different powers of alpha, don’t they?

In QCD, the relevant “g” at the relevant distances is of order one, so there are no “qualitative classes”. So I am skeptical about any “very simple verbal” description of somewhat-generic heavy QCD states. Different ones can admit various ideal simplified descriptions – like configurations of the QCD strings etc. – but no picture is likely to be universal.

Of course that one particle can be a particular radial bound state of a simple kind. But without other hints, the probability is at most 1/N where N is the number of known candidate particles of a similar kind.

3. singlino - April 6, 2009

hi lubos, you mean by the legitimacy of studying them you mean studying them is practically useless? or pointless? in your opinion, could it be something like pentaquark state or something ? hadrons in QCD as far as i understand are bound states of 2 and 3 quarks because that is the minimal description, but nothing in principle prevent the existance of pentaquark bound states or some other exotics

4. singlino - April 6, 2009

what do you mean by “there is no qualitative classes” ?

5. mfrasca - April 6, 2009


I am saying something more. What you are saying reflects just the fact that your understanding of quantum field theory start and stop at weak perturbation theory. I am saying that what describes glue at small energies are excitations that have not spin one and are massive. Are these gluons beyond your tree level expansions?

I keep on finding your superficiality quite entertaining. As a matter of fact, you should spend most of your time apologizing around in the blogosphere. I keep on thinking that a person that was hired by Harvard should hold a higher profile.


6. Luboš Motl - April 7, 2009

Dear Marco, just on the contrary. Your surprise that QCD is more than just a perturbative expansion is caused by the fact that you imagine that QCD (and QFT) is just about perturbative expansions. Is this statement of mine surprising? It is actually a tautology.

You’re just another shallow obnoxious crackpot so it’s not shocking that your opinions who should be hired and what they should believe pretty much coincides with most of your “colleagues”. Just to make you really upset, such a job is being chosen from 66 candidates or so. They’re still holding the quality over there but it’s a struggle because idiots are trying to reshape physics departments at the broader Harvard, and in the whole world.

Singlino, complicated bound states can be divided according to their (conserved or almost exactly conserved) quantum numbers – like the spin, baryon number, various parities etc. – but they can’t be further and strictly subdivided into any finer (smaller) classes. That’s what I mean. A pentaquark is just an oversimplified word in an oversimplified model.

The basic pseudo-Goldstone bosons like pions are already far from being massless, but they are pretty good realizations of the idealized concept of a pseudo-Goldstone boson. As you go towards heavier states, these things are becoming more messy.

While it is OK to imagine that a pion is a quark-antiquark bound state, it’s already way too massive to be perfect, and the idealization becomes increasingly awkward as you go towards heavier states and resonances. You can’t calculate the number of quarks in a generic heavy hadron. There are really infinitely many quark-antiquark pairs and gluons in each hadron, and the idea that there are 5 of them is always just a very rough approximation, a mental model that can never get quite accurate even if one is lucky to get close.

The number of quarks (and antiquarks) is not conserved in QCD (separately), so one can’t classify bound state according to it. It’s not well-defined for mass eigenstates. The nucleus-like heavy states are actually microstates of a dual (AdS/CFT) black hole – which is a superior classical mental image. But one shouldn’t expect a simple verbal description for each black hole microstate.

7. mfrasca - April 7, 2009

Dear Lubos,

Currently I am an active researcher as my present file of publications is there to testify. You are not. So, by definition, you are the one belonging to the class of crackpots hanging around offending respectable people.

Of course, your answer is not about science as you miss significant arguments in a field where you cannot claim yourself an expert. I doubt you have the faintest idea of what people is doing about QCD and what is the emerging scenario. But your prejudices, now well rooted due to your long inactivity, can make you speak about almost everything pretending to be the expert of everything.

Things do not stay that way and you are an expert of nothing. I would like to see a paper of yours, with your now expressed “ideas” about QCD that can explain all low-energy phenomenology. This is a matter people is struggling with since a long time and involved some Nobel prize winners. But if you want to include also ‘t Hooft in your crackpot list just do it. In the end the value of your list will be practically zero.


8. Kea - April 7, 2009

The nucleus-like heavy states are actually microstates of a dual (AdS/CFT) black hole – which is a superior classical mental image.

Hi Lubos! Are those like those extremal black holes that Duff et al study using very elementary quantum information theory?

9. Luboš Motl - April 7, 2009

Dear Kea, I’ve read your musings about quantum information theory and Duff’s black holes.

So this is what I would tell you.

Duff et al. identified some nice simple formulae that are completely isomorphic to formulae that one uses to calculate interesting things with a few qubits in quantum information theory.

However, the real information inside the black holes that Duff et al. study is very different than those few bits. Black holes with macroscopic event horizons carry a huge amount of information – a lot of qubits – while the formulae only manipulate some quantum numbers describing these black holes, not the whole information.

Otherwise, if I had to answer your question above: the AdS black holes are not quite exactly identical to those that Duff et al. study. On the other hand, all black holes in all vacua of string theory are “qualitatively” the same type of objects.

So for example, if someone studies the analytic structure of scattering amplitudes, as induced by intermediate states, it doesn’t really matter whether they’re “Duff’s” extremal black holes or the AdS/CFT black holes dual to the large and heavy hadrons (similar to excited nuclei etc.).

10. Kea - April 7, 2009

However, the real information inside the black holes … is very different than those few bits.

Phew!! For one minute (or maybe some years) I was concerned that the reality of the inside (what is the inside, anyway? oh, so that’s the stuff that we didn’t know in the first place but somehow thought we had lost) of a black hole might not have much to do with Reality. But of course I’m a bit simple minded, as you know.

Why are you reading my blog, anyway?

11. dorigo - April 7, 2009

Tsk tsk kea, there are tons of reasons to reprimand Lubos, but reading your blog does not qualify as one 🙂


12. Luboš Motl - April 7, 2009

Dear Kea, I didn’t really want to talk about the black hole interior. By “inside” black hole, I meant the information carried by them. You may imagine that the information is carried by the event horizon itself – the very boundary of the interior or the exterior.

At any rate, the quantum-information-like formulae of Duff et al. know nothing about the geometry and causal structure of the black holes.

I am reading your blog because it periodically appears in my searches for keywords such as M-theory. Moreover, I have been always naturally looking for ideas on the boundary between science and fantasy. If you wish, I have always been searching for other new Einsteins and Einsteinesses.

Tommaso’s explanation should surely serve as a nice compliment although I would find it too misleading to copy the compliment from him. 😉

13. carlbrannen - April 7, 2009

Luboš, I don’t see why people concentrate so much on the event horizon. First, it’s not yet been seen in experiment, and second, the fact that things stops there is a classical result that applies only to certain choices of coordinates, i.e. Schwarzchild / Kerr. In Gullstrand-Painleve and their generalization to spinning black holes, test particles can fall through to the singularity.

QCD and QED are carried by massless bosons. One would expect their force to follow a 1/r^2 law but after quantum corrections, QCD becomes linear at long distances while QED is modified to be stronger the closer one gets to a charged point particle. One supposes you could do the same thing with general relativity, but backwards. Take GR as an effective force and see how it varies from Newton’s 1/r^2 law. Use that to tell you something about the quantum mechanics of gravitons. It was this idea that got me onto the horrible path of converting Schwarzschild and Painleve coordinates into a Newton force.

Kea, getting someone to agree with everything one says, is either an impossibility, or it’s due to one never saying anything significant. As unimportant amateurs, we should be happy that Luboš reads our stuff, and every now and then, appreciates something we’ve written. And that he speaks directly from his heart you should think of as a good thing, as compared to polite people who never read your stuff.

14. singlino - April 7, 2009

I think Nima Arkani Hamed is the new Einstein, the current Einstein is Witten

15. Blubos - April 7, 2009

Gentlemen, to a non-perturbative prefessional reading about BRST quantization and “massive” gluons please refer to the new paper by Sorella et al.:

16. Daniel de França MTd2 - April 8, 2009

“As unimportant *amateurs*, we should be happy that Luboš reads our stuff, and every now and then, appreciates something we’ve written.”

Are you being ironic, right? Kea is not an amateur anymore, to start with.

17. Matti Pitkänen - April 8, 2009

Dear Tommaso,

you say that X(3872) meson corresponds to a mass scale twice that for D meson. I have been teasing attentive colleagues year after year with this idiotic p-adic length scale hypothesis and its idiotic prediction that quarks appear in several mass scales differing by half octaves. Continuing this intolerable habit and without having bothered to kill the hypothesis myself: could it be that both charmed mystery mesons are octaves of standard ones;-)?

Matti Pitkanen

18. Luboš Motl - April 8, 2009

Dear Carl #13,

quite on the contrary. The event horizon is not only the most important locus of a black hole, but it is also entirely coordinate-independent. It is defined as the boundary between the interior and exterior, and the interior is made out of all points that can’t be connected to scri plus (future space outside the hole, at infinity) by any time-like trajectory. Note that this condition is independent of any coordinates.

It is also true that nothing is “felt” by the infalling observers at the horizon itself but that doesn’t change the fact that the locus is important from the viewpoint of the Universe. By indirect effects, the horizon is observable and that’s how we identify objects as black holes, see e.g.


The entropy is proportional to the horizon area, suggesting that it should be linked to degrees of freedom near the horizon (although this paradigm or this way of counting is not manifest in any solid microscopic counting of the entropy that is available).

On the other hand, the singularity is extreme, but can only be measured by the infalling observers, and they can’t measure anything too accurately because they’re gadgets are going to be crashed pretty quickly. This is not just a technical limitation. The degrees of freedom are presumably “really” evaporating near the singularity.

And yes, the 1/r^2 laws are corrected by quantum corrections that are partly calculable, partly measurable, and that constrain theories. However, no quantum corrections from 1/r^2 are measurable in GR. The corrections responsible e.g. for the Mercurcy perihelion precession are entirely classical, with no hbar. The quantum corrections start near the Planck scale only and they’re very small effects, indeed.

Otherwise, Carl, Daniel is right. The world is upside down. The amateurs and crackpots are going to be the new professionals and the professionals are going to be removed. The new dark ages are coming.


19. dorigo - April 8, 2009

Kea has never been an amateur. She has hard-earned a PhD, people.


20. Kea - April 8, 2009

Lubos: …but that doesn’t change the fact that the locus is important from the viewpoint of the Universe.

The problem I have with this statement is that it makes an assumption that I don’t buy into, which is to say that there is a fixed classical universe independent of observers. It is quite clear to me that my universe is a very different place to the universe even of other human beings. I do agree that any decent theory of gravity should eventually be able to derive classical black hole solutions, with horizons, within general relativity, but this is an uninteresting and purely classical scenario that makes no real use of quantum information (Hawking radiation being a rough explanation).

Now you also say that we detect BHs through the horizon, but surely this should be compared to how we detect particles in general, which is to say via a measurement theory that does not require such a barbaric ontology.

By the way, no one in quantum information theory would think that categories of Hilbert spaces were the end of the story for causality. As you rightly point out, that is just a beginning.

21. Luboš Motl - April 8, 2009

Dear Dr Kea, I didn’t say – or need – that the Universe was “fixed”. In fact, it is not fixed, it is dynamical.

Also, I didn’t say – or need – that the Universe is classical. In fact, it is quantum mechanical.

Third, the Universe is observed by observers. But there exist invariant quantities about it that are independent of the observers. The existence of horizons is an example.

Indeed, I have to assume that statements about geometry, constructed in the same way as those in classical geometry, must be possible. If they’re not possible, it makes no sense to talk – or argue – about different places in the Universe. Indeed, the existence of geometry is an approximation that doesn’t hold if things are studied at the Planckian accuracy.

But it’s a damn important approximation – for example, all of scientific and social scientific papers except for about 1000 papers about black hole microstates depend on the existence of space that can be described by classical geometrical terms.

I completely agree with you that at the quantum gravity level, there’s no special role played by the horizon. But in fact, there’s no role played by any other place in space – because places in space don’t exist at all. They’re derived concepts.

It’s not clear to me what is “barbarically ontological” about the detection of black hole horizons. Yes, black holes have different properties and different interactions with the environment than generic or light elementary particles. That’s why we detect them in different ways. Is that surprising?

Interesting to see a simple causal statement translated to the language of categories of Hilbert spaces. I wouldn’t be able to translate it back. 😉

22. Daniel de França MTd2 - April 8, 2009

“Kea has never been an amateur. She has hard-earned a PhD, people.”

I know, but I meant that even in the absurd case of calling someone amateur for not being paid to do research, despite of even having a PHD, is not true anymore in the case of Marni. But I think it is awesome that by just using her blog, and with a lot of effort and personal sacrifice, she could tell other people about her ideas. I deeply respect this aspect of her.

23. Daniel de França MTd2 - April 8, 2009

“Kea has never been an amateur. She has hard-earned a PhD, people.”

I know, but I meant that even in the absurd case of calling someone amateur for not being paid to do research, despite of even having a PHD, is not true anymore in the case of Marni. But I think it is awesome that by just using her blog, and with a lot of effort and personal sacrifice, she could tell other people about her ideas, and eventualy get paid to do what she loves the most. I deeply respect this aspect of her.

24. Blubos - April 8, 2009

“The nucleus-like heavy states are actually microstates of a dual (AdS/CFT) black hole – which is a superior classical mental image”
So, many thanks to the “idiots worldwide” that are preventing string-te(rr)orists, such as Lubos, to wide-spread this ugly-duals of QCD!

25. Luboš Motl - April 8, 2009

Dear Blubos,

the main culprit that should be blamed for – or, in your optics, credited with – the impossibility to teach AdS/CFT or other important things to most people is not the set of “idiots worldwide” but the human stupidity itself – for example yours.

And one shouldn’t be surprised that such stupidity exists. Many people, including Einstein, have figured out that only two things in the world are infinite – the Universe and human stupidity – and there are increasingly good reasons to doubt about the former. 😉 So you don’t need to thank anyone for the human stupidity – it’s a law of physics.

Best wishes

26. Blubos - April 8, 2009

Thanks dear Te(rr)orist,

however, you also failed to see I was thanking:
“…idiots are trying to reshape physics departments at the broader Harvard, and in the whole world.”
I think they are smart enough to see, after 3 decades, that the due place of stringers is at best at math. departments!
Best wishes


27. carlbrannen - April 9, 2009

Lubos, the link you gave in #18 doesn’t observe the event horizon of a black hole. It is a dream of astronomers to do this and arXiv is filled with proposals for new ways this might be done, for instance see 0809.3548 or 0902.4209.

The basic problem with applying quantum mechanical rules, such as entropy etc., to the event horizon is that it’s already well know that quantum mechanics and gravitation do not mix well. These sorts of calculations are fascinating to mathematicians but they have zero practical consequences, and are not any more likely to survive whatever the theory that unites quantum mechanics and gravitation (any more than calculations showing that classical electrons emit electromagnetic radiation and spiral into protons survived quantum mechanics).

“all points that can’t be connected to scri plus (future space outside the hole, at infinity) by any time-like trajectory”

This is a wonderful definition for a mathematician, but God is an engineer, and He defined the universe according to a simple set of differential equations that apply equally everywhere and at all times. That is, the universe is not composed of time-like trajectories, instead, time-like trajectories are a convenient method of reducing the complexity of certain parts of the universe to human understanding.

I say that to better understand the universe, we must lower our sights from the symmetries and other high level attributes of the differential equations, and instead contemplate the underlying equations, to the extent that we can guess them.

I’m not saying that the above quote is wrong; what I’m saying is that you don’t build machines out of things like this, or out of the various relativity principles. Machines are made out of differential equations; the Klein-Gordon equation is a better place to start. Symmetries are wonderful tools for solving differential equations, and they are also wonderful targets for machines to approximate, but they are not at the foundation of how machinery is constructed. At best they can only point the way and give little hints. At worst they confuse the user into believing in crap like wormholes, closed time-like circuits, etc. The stuff that goes on inside the event horizon is covered by the same differential equations that define the stuff that goes on outside it.

28. Luboš Motl - April 9, 2009

Dear Carl #27,

I am afraid that your reading skills are somewhat limited. Dmitry’s text I linked is based on the article


that explains, already in the abstract, that “Here we show that recent millimeter and infrared observations of Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, all but requires the existence of a horizon. Specifically, we show…”

So they do prove the horizon observationally.

Moreover, this is not “another” paper that is one among hundreds of similar “attempts”, as you say.

Instead, it is a paper by leaders in this subfield – of reverse engineering of black hole observations. Your main problem is that you pay much more attention to your preconceptions than to the things that you can actually observe or read. That would be fine if you knew more than the rest of the world which is clearly and unfortunately not the case. You know pretty much nothing about astrophysics, tests of GR, much like you know nothing about the analytical continuation and most other things, and unless you actually start to listen and learn, you will never know anything.

Your comments trying to close your eyes and not to see a sentence just because it contains the unwelcome (for you) term “timelike trajectory” is just another proof of your unlimited blindness and bigotry. Timelike trajectories are essential for “engineering” of the Universe as well as for the reverse engineering of observations of black holes while your attempts to throw away these important concepts are just rants of a bitter and stupid would-be philosopher.

What you write is just pure shit, much like what “Blubos” and other cheap biological and vitriolic stuff is writing. It probably makes no sense to try to explain anything to you because your brain is already saturated and you will never transcend your brutal mental limitations.

Best wishes

29. Kea - April 9, 2009

I don’t think God is an engineer that uses differential equations on a continuum space. Maybe she is an engineer that uses category theory. Lubos, in English the phrase all but requires [the horizon] does not equate to has observed [the horizon]. If you are so keen on discussing the Milky Way BH, perhaps you could describe, using string theory, the process that leads to the observed powerful proton jet.

30. carlbrannen - April 9, 2009

The problem with having an incomplete theory is that it provides a method of organizing observations which occludes the otherwise obvious. For Sag A, the problem is that, “The stellar winds from nearby massive stars provide sufficient material to support luminosities more than 11 orders of magnitude greater than that observed!” That is a pretty big clue, and is in some contradiction with the definition of the horizon from the same paper: “The primary astrophysical importance of a horizon is that the gravitational binding energy liberated by material as it accretes can be advected into the black hole without any further observational consequence.”

The problem with concentrating on high level symmetries and things that can be theoretically attributed to lie on the event horizon is that even if Kea is right, and God is not an Engineer, it’s still ludicrous to imagine that these high level symmetries are at the foundations of the construction of the universe. The foundations of mineralogy is not the 100+ crystal classes, it is atoms. The foundations of biology is not bilateral symmetry, or cladistics, it is DNA and chemistry. A sword is not constructed of ideal surfaces intersecting at an infinitely sharp edge, it is composed of atoms and its sharpness and symmetry is only a consequence of its intended use; to understand it one must understand metallurgy which is based on atoms.

31. dorigo - April 9, 2009

I thank all of you who contributed to this interesting thread. I abstained to comment since most of this is away from my area of expertise, but I did sit and watch it developing.


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