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

~~~
jessriedel
> 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.

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wfunction
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?

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juk4
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.

~~~
givinguflac
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.

~~~
pdkl95
> 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](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](https://www.youtube.com/watch?v=1GCf29FPM4k)

~~~
givinguflac
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](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 :)

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

~~~
jessriedel
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.

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

~~~
jessriedel
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).

