LHCb unveils new particles

http://home.cern/about/updates/2016/07/lhcb-unveils-new-particles

by joeyspn • 10 years ago

84 27 10 years ago

wfunction5• 10 years ago

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?

Aelinsaar4• 10 years ago

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.

wfunction5• 10 years ago

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?

juk4• 10 years ago

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.

calgoo• 10 years ago

Lisp & Perl according to xkcd :P

https://imgs.xkcd.com/comics/lisp.jpg

givinguflac2• 10 years ago

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.

tgb2• 10 years ago

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.

wfunction5• 10 years ago

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.)

CJefferson• 10 years ago

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.

nikic• 10 years ago

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.

wfunction5• 10 years ago

This explains and clarifies it, thanks a bunch!

Manishearth• 10 years ago

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.

Aelinsaar4• 10 years ago

Di-Photon excesses, Pentaquarks, The Higgs Boson!!! The LHC has just been an absolutely unmitigated success, and it's got plenty left to offer.

jessriedel3• 10 years ago

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.

Aelinsaar4• 10 years ago

I'd heard that about the Higgs to mu tau, but not the diphoton excess.

yk• 10 years ago

The title is slightly misleading, also in usual physicist speak right. The kind of particle here are made up of four quarks, and as far as I know were somewhat expected. 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. (Wether we should call everything we see in a collider a particle is a question, which I happily leave for philosophers to answer.)

^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.

jessriedel3• 10 years ago

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.

smaudet• 10 years ago

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.

LHCb unveils new particles

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