A bestiary of exotic hadrons
cerncourier.com
cerncourier.com
I'm glad this was mentioned, non-perturbative effects are not well understood and this is a big part of why it's worthwhile to study bound states of the strong force.
Not sure how bringing GR into the fray would help solve what essentially seems to be a computational complexity problem. Might actually make things worse.
1. The coupling constant of QCD is much higher than QED so contributions to the overall result from Feynman diagrams that have more vertices (the multiplicative factor of each element in the sum is proportional to the power of the number of vertices) don’t vanish as quickly as they do for QED
2. The gauge bosons in QCD (i.e. gluons) themselves have colour charge whereas those in QED (i.e. photons) do not have electrical charge.
I'm not sure what they mean by "Predictions rely on approximate analytical methods such as effective field theories." The predictions of LQCD are ab initio. Sometimes we fit EFTs to LQCD results, that's true. But EFTs are under control and have quantifiable uncertainties, they're not just willy-nilly approximations.
Not sure if it was deliberate or not, but yeah.
EDIT: got it, hardons
Can someone explain this to me?
Tcc(3875)+ can decay to a D0 and a D+, yes? And this is a strong decay?
I guess the reason Tbb doesn't have an equivalent strong decay to B mesons because of the sign difference -- that is, B0 and B+ would have anti-bs, not bs; and anti-B0 and anti-B+ would have negative charge?
And so the only major decay pathway is for the b itself to decay to a K+ (plus lepton noise), giving a temporary bu\s\u\d pentaquark, that then has uninhibited decays?
I guess what I'm asking is... is this the right way to think about this?
In weak decays, one or more of the original quarks or antiquarks will be converted in a quark or antiquark with a different flavor, which is a process that has a low probability of happening, so the weak decays happen less frequently, therefore the hadrons that can decay only through weak decays have a lifetime that is many orders of magnitude greater than the hadrons that can decay through strong decays (or electromagnetic decays, i.e. annihilation of quarks with the corresponding antiquarks).
D+ is c quark + d antiquark, D0 is c quark + u antiquark
Tcc(3875)+ is 2 c quarks + d antiquark + u antiquark
Therefore the 4 quarks/antiquarks in Tcc(3875)+ are the same as the 4 quarks/antiquarks in D0 + D+.
So this is a strong decay, because no quark or antiquark is converted into another kind of quark or antiquark.
For the Tbb- tetraquark, its composition would allow a similar strong decay into two b-quark + u or d antiquark hadrons, except that its binding energy is so great that the mass of the Tbb- tetraquark is smaller than the sum of the masses of the hadrons that would be produced during a strong decay (it is also smaller than the sum of masses of the hadrons that could be produced by an electromagnetic decay, see https://www.sciencedirect.com/science/article/pii/S037026931... ).
This forbids the strong decay and the electromagnetic decay, so the only admissible decay must be weak, where one of the b quarks will be converted into another kind of quark.
I speculate that in the coming decades or centuries, a new instrument may enable us to delve deeper into the atom and reveal that what we perceive now is merely a minuscule fraction of the whole picture.
Perhaps the notion that the subatomic world is as vast as the universe, as stated by Richard Feynman when he said "There’s plenty of room at the bottom.", holds more truth than we realize.
That's true and he knew this even at the time of this famous lecture. He was talking about that there is a plenty of room at the room for us to explore how can we use atoms in synthetic chemistry not into exploring the fundamental particles inside them . When we are talking about particle physics we are basically talking about the successor field of nuclear physics. It studies the interactions and particles inside the sub-atomic structure. Feynman's most interesting work - parton model- was one of the first innovative theoretical work in QCD and was one of milestone of development and validation of the quark model.
The idea that protons, neutrons, and other hadrons are composed of fundamental particles called quarks that come in six -flavors- (up, down, strange, charm, top, and bottom) and possess fractional electric charges. These quarks are bound together by the strong nuclear force, mediated by particles called gluons, and must combine in specific ways to form observable particles (mesons or baryons). One day this was a wild theory and needed a lot of work on validating this model experimentally.
They must be more like knots: https://en.wikipedia.org/wiki/Knot_(mathematics)
Quarks are small masses, gluons are strings connecting them, and the whole thing is in a rapid periodic motion.
> Like Mendeleev and Gell-Mann, we are at the beginning of a new field, in the taxonomy stage, discovering, studying and classifying exotic hadrons.
The chemistry of matter that's smaller than protons and larger than electrons is indeed a missing piece. But the real breakthru will be discovering a membrane that's impenetrable to those multiquarks.
In the case of NM we happened to have something that is often also computationally simple and efficient so we keep using it, but it is by no means a “correct theory”. just a useful model that is still useful.
i daresay it will continue to be useful for some things even if we eg discover that we are living in a simulation and manage to escape! As long as some part of us will continue to experience this reality it will be useful - the math is simple and gives good approximations in many cases.
EDIT: Like ironically I would say the planetary model has 1 unique utility, which is that for hydrogen-NMR it's useful to just assume that 1 electron is producing a little magnetic field like a Bohr model atom.
Take it or leave it :-)
Physics was all deterministic and objective. And then comes QM saying that there is no determinism and about the role of an observer, and comes GR saying there is no objective observer, because different observers can't agree about time and length.
I heard that physics professors in 19 century told their students that they had chosen the wrong career because physics was almost done. There were slight difficulties with electromagnetism, but they surely is going to be resolved in coming years. And then all that shiny and almost complete physics was blown up because very foundations of it were destroyed.
It was a paradigm shift. If it wasn't then what is? Copernicus? But the Ptolemaic astronomy did work and it works today. With its limitations of course, but it works. You can calculate positions of heavenly bodies with epicycles. Galilean laws of motions? But the laws of Aristotle works no worse then when Aristotle invented them.
"If awareness of anomaly plays a role in the emergence of new sorts of phenomena, it should surprise no one that a similar but more profound awareness is prerequisite to all acceptable changes of theory. On this point historical evidence is, I think, entirely unequivocal. The state of Ptolemaic astronomy was a scandal before Copernicus’ announcement. Galileo’s contributions to the study of motion depended closely upon difficulties discovered in Aristotle’s theory by scholastic critics. Newton’s new theory of light and color originated in the discovery that none of the existing pre-paradigm theories would account for the length of the spectrum, and the wave theory that replaced Newton’s was announced in the midst of growing concern about anomalies in the relation of diffraction and polarization effects to Newton’s theory. Thermodynamics was born from the collision of two existing nineteenth-century physical theories, and quantum mechanics from a variety of difficulties surrounding black-body radiation, specific heats, and the photoelectric effect.4 Furthermore, in all these cases except that of Newton the awareness of anomaly had lasted so long and penetrated so deep that one can appropriately describe the fields affected by it as in a state of growing crisis."
Later in the same chapter, he gives three examples of crises that led to paradigmatic revolutions: "a particularly famous case of paradigm change, the emergence of Copernican astronomy."; "the crisis that preceded the emergence of Lavoisier’s oxygen theory of combustion"; and "the late nineteenth century crisis in physics that prepared the way for the emergence of relativity theory."
Kuhn absolutely considered relativity and quantum mechanics to be examples of paradigmatic revolutions, just like Newtonian mechanics in the 17th Century and the earlier Copernican revolution.
If you want to argue that Kuhn was wrong about history, then you can do that (and I would at least partly agree); but if you want to claim Kuhn didn't say what he actually said, that's a different matter.
Is this stamp collecting? Do these exotic hadrons mean anything?
Given their horribly short lifespans, probably not much other than the fact that they manage to exist for however short a time might vindicate QFT a tad more (I'm assuming that QFT somewhat predicts their likelihood to show up).
Or maybe they'll bring a deeper understanding of the strong force.
But generally speaking, I feel you: lots of work and energy spent to create these exotic things, but that may or may not have an actual use or even meaning.
A lot of science is like this these days, it looks like we're hitting exponentially diminishing returns (as in: useful applications) in some areas of science.
However, even if you take the quote to mean what you imagined, it is unnecessarily cynical. LHC has advanced our understanding of physics.
[1]: https://www.theverge.com/2017/6/19/15831520/typos-large-hadr...