LHCb unveils new particles(home.cern)
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LHCb unveils new particles
http://home.cern/about/updates/2016/07/lhcb-unveils-new-particles
28 comments
> The underlying theory, QCD, predicts that free particles (hadrons)^1 are bound states of quarks, and in this case bound states of two quarks and two anti-quarks.
Even though we presume to know the dynamical equations of QCD exactly, I am pretty sure it was never shown rigorously that tetraquarks are possible under those equations.
Even though we presume to know the dynamical equations of QCD exactly, I am pretty sure it was never shown rigorously that tetraquarks are possible under those equations.
Could someone who knows a little more about physics please explain why physicists seem to fundamentally expect that there exists an upper bound on the number of types of particles in the universe?
I think you might have fallen for an easy misreading of the title. In fact, the new particles are still made from quarks, just as protons and neutrons as well as less quotidian matter like pions are. In that sense, it's not an increase in the "number of types of particles" in a similar sense that finding a new element is 'just' another configuration of electrons, protons, and neutrons.
Of course, it's still very interesting, particularly that these are apparently composed of quarks in a manner than previously particles had not been.
Of course, it's still very interesting, particularly that these are apparently composed of quarks in a manner than previously particles had not been.
Actually I think you might have fallen for an easy misreading of my question, because I specifically omitted the word "fundamental" before the word "particle" due to the fact that they are still made of quarks. The assumption in my question was that "particle" has a reasonable definition... unless you're suggesting it doesn't?
(Edit: slightly recorded comment to make it sound less sarcastic, since I wasn't trying to be. I actually do think it's completely possible that "particle" doesn't have a definition; I just didn't think it was likely that that was what was being said.)
(Edit: slightly recorded comment to make it sound less sarcastic, since I wasn't trying to be. I actually do think it's completely possible that "particle" doesn't have a definition; I just didn't think it was likely that that was what was being said.)
I certainly was taking a stab and tried to address what I thought you were most likely thinking about. It's hard to judge over text and I think my comment provided useful context for people reading it, even if you already knew it.
I'd also be interested in knowing whether particle physicists expect a finite number of quark-based particles and, if so, why.
I'd also be interested in knowing whether particle physicists expect a finite number of quark-based particles and, if so, why.
[deleted]
Technically that makes neutron stars a big particle
This result is interesting not because tetraquark states were not previously expected to exist, but because it allows us to verify whether theoretical predictions about them coincide with the experimental results. I don't think there was an expectation of hadrons being limited to two and three quarks only.
This explains and clarifies it, thanks a bunch!
The 'forces' which hold particles together only operate over a very short distance. There may technically be larger 'particles', but they would only exist for a tiny amount of time before exploding apart.
In the same way that you can reasonably say "I don't know how many kind of insects there are, but none of them get as big as BMW's." Within a certain range, it's hard to find insects in nature, but if they were big enough they'd be hard to miss.
I mean for all I know bigger insects could have existed at another time (or elsewhere in the galaxy...); that doesn't mean we think nature somehow fundamentally forbids them. Is the comparison really apt?
Why are you being such a jackass with your replies? You asked an ambiguous question not really relevant to the article, people are trying to answer, and you're attacking their answers for not addressing the exact meaning of your question. Do you want answers or not?
Maybe if you edited your original post to better explain the answer you're looking for, someone could give it to you.
My own guess, as not-a-physicist, is that physicists expect the predictions made by existing science and their hypotheses to eventually be observed through experimentation. Given what we know, we can predict that some particles/types of particles should exist; projects like the LHC are created to test these predictions.
Or to put it simply: physicists might expect an upper bound on particle types because the available science doesn't suggest there should be an unlimited number of types of particles.
Maybe if you edited your original post to better explain the answer you're looking for, someone could give it to you.
My own guess, as not-a-physicist, is that physicists expect the predictions made by existing science and their hypotheses to eventually be observed through experimentation. Given what we know, we can predict that some particles/types of particles should exist; projects like the LHC are created to test these predictions.
Or to put it simply: physicists might expect an upper bound on particle types because the available science doesn't suggest there should be an unlimited number of types of particles.
> Why are you being such a jackass with your replies?
I was completely serious that insects and particles don't really constitute an apt comparison, but if I was a jerk for pointing it out then my apologies.
I was completely serious that insects and particles don't really constitute an apt comparison, but if I was a jerk for pointing it out then my apologies.
The concept of observability is, but you seemed to miss that one in favor of focusing on the metaphor itself.
They don't. We just haven't seen many larger bound states yet.
Note that a tetraquark is different from two mesons, and a pentaquark is different from a baryon+meson.
As you increase the number of fundamental particles in a particle, modelling the exact mechanism of the bound state becomes harder. So for larger particles, we aren't even sure they should exist.
IIRC pentaquarks were something that theoretically were expected to exist, but were overall experimentally elusive.
Note that a tetraquark is different from two mesons, and a pentaquark is different from a baryon+meson.
As you increase the number of fundamental particles in a particle, modelling the exact mechanism of the bound state becomes harder. So for larger particles, we aren't even sure they should exist.
IIRC pentaquarks were something that theoretically were expected to exist, but were overall experimentally elusive.
Nobody knows for sure, but it seems to be somehow tied to the number of fundamental types in programming languages. And there is wispy evidence that the universe is written in JavaScript.
It all makes sense. The universe progressing toward heat death is a memory leak, and it causes a reboot every 10^10^10^56 years. Unfortunately there is no non-volatile memory.
> a reboot every 10^10^10^56 years
According to Don Page[1], that time (for our universe) is approximately 10^10^10^10^2.08 "Plank times, millenia, or whatever"[2].
[1] http://arxiv.org/abs/hep-th/9411193
[2] The units given in the paper (see [1], page 8)
Numberphile video about this paper: https://www.youtube.com/watch?v=1GCf29FPM4k
According to Don Page[1], that time (for our universe) is approximately 10^10^10^10^2.08 "Plank times, millenia, or whatever"[2].
[1] http://arxiv.org/abs/hep-th/9411193
[2] The units given in the paper (see [1], page 8)
Numberphile video about this paper: https://www.youtube.com/watch?v=1GCf29FPM4k
Ok, well
A.) It was clearly a joke. B.) That number was based off the Wikipedia heat death of the universe page reference for this: https://arxiv.org/abs/hep-th/0410270 C.) Regardless of the correct amount of time, no one will be there to verify it. We don't even understand enough yet to say with absolute confidence that heat death is the definitive final outcome of the universe.
But thanks for the reply :)
A.) It was clearly a joke. B.) That number was based off the Wikipedia heat death of the universe page reference for this: https://arxiv.org/abs/hep-th/0410270 C.) Regardless of the correct amount of time, no one will be there to verify it. We don't even understand enough yet to say with absolute confidence that heat death is the definitive final outcome of the universe.
But thanks for the reply :)
Lisp & Perl according to xkcd :P
https://imgs.xkcd.com/comics/lisp.jpg
https://imgs.xkcd.com/comics/lisp.jpg
> Perl
So that explains why nobody can figure out how the Universe works!
So that explains why nobody can figure out how the Universe works!
How many billions...and I feel like this is a completely useless fact.
All I see is that (again) models don't predict things, and they managed to make a slightly odd bit of dust. Every single other academic field has uses...this one seems to be filled with expensive errors.
All I see is that (again) models don't predict things, and they managed to make a slightly odd bit of dust. Every single other academic field has uses...this one seems to be filled with expensive errors.
Di-Photon excesses, Pentaquarks, The Higgs Boson!!! The LHC has just been an absolutely unmitigated success, and it's got plenty left to offer.
There are strongly substantiated rumors that the diphoton excess was a statistical fluctuation that has disappeared in the latest data. So, still no surprises out of the LHC overall.
I'd heard that about the Higgs to mu tau, but not the diphoton excess.
The phenomenologists on my floor are confident. Between ATLAS and CMS, one saw nothing and one actually saw a slight deficit (with much more data taken this run than in the last).
^1 A hadron is is made of quarks and gluons, which can only exist as bound states, such that they have no net strong charge. Contrast this with a lepton like the electron, that has no strong charge and can consequently exist as a free particle.