
Exotic four-neutron no-proton particle confirmed - mgalka
http://www.asianscientist.com/2016/01/in-the-lab/tokyo-tetraneutron-proton/
======
ars
I know it's the title of the article, but this is NOT confirmed!

There is a paper about it, and some hints it exists, but it has not risen to
the level of accepted particle.

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ch8230
Agreed. Until they eliminate other possibilities then it is not confirmed.

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friendzis
May be dumb, but first thing that popped into my mind reading the title was
"Whoa, element 0 discovered!"

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diskcat
voidium

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T-zex
Hoarium, to honor null refs! /s

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tosseraccount
He may not play dice, but He does program in ansi C.

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SideburnsOfDoom
They make no mention of how long the tetraneutron might stay around for. Are
we looking at whole seconds, or 10^-10 seconds of stability, or what?

~~~
sp332
It's short enough that it doesn't even touch the detector. The evidence is
that the energy from the four neutrons all shows up at once, instead of being
split among four individual neutrons.
[http://arstechnica.com/science/2016/02/no-protons-needed-
pos...](http://arstechnica.com/science/2016/02/no-protons-needed-possible-
discovery-of-a-four-neutron-particle/)

~~~
imglorp
So, more like formation flying than some kind of bond?

~~~
sp332
There would be a binding energy just like a normal nucleus. The question here
is whether they somehow violate the Pauli exclusion principle.

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Animats
Paywall.

Is this stable for some reasonable length of time, or is it one of those
"particles" with a lifetime in nanoseconds?

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pif
Hello, why writing "particles" with the quotes? Do you consider the reality of
a particle to be proportional to its lifetime? By the way, a nanosecond is a
very long time when you compare it to the lifetimes of some particles (with no
quotes)!

~~~
tfgg
Particles are sort of mathematically more poorly defined the shorter their
lifetime. But yes, a nanosecond is a long time in this context :)

~~~
pif
> Particles are sort of mathematically more poorly defined the shorter their
> lifetime.

This sentence doesn't make any sense to me. Could you please elaborate?

~~~
Benjamin_Dobell
I know nothing about the mathematics. But I think it's fair to say that in
general people tend think of particles as being a _stable_ unit of some sort.
So the term "particle" becomes less appropriate the less stable something is,
and time is often a factor when thinking about stability.

If someone were simply to slam 4 neutrons together, for how long would they
need to stay together for this to be deemed a real particle? I think it's for
this reason the original commenter quoted the use of the term "particle".

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zw123456
I know this is probably dumb on my part but am I the only one that had "dark
matter" pop into my mind?

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akiselev
There aren't any known arrangements of neutrons that are stable without
protons. Solo neutrons don't exist for longer than 10-20 minutes before
decaying into protons and I doubt these tetraneutrons exist for longer than a
few seconds unless they're moving at relativistic speeds (and even then, for
not much longer). Unless there is something drastically different going on in
the interstellar medium, neutrons as dark matter is extremely unlikely.

~~~
pc86
Is there an ELI5 about how a neutron decays into a proton? Aren't they
separate particles?

Or maybe an ELI-only-took-undergrad-physics-101? :)

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Manishearth
> Aren't they separate particles?

They are. Subatomic decay doesn't happen with particles "contained within"
other particles; a neutron does not contain a proton but can decay into a
proton, electron, and electron antineutrino via the W boson.

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blahDeeBlahBlah
Except neutrons are protons bound to electrons, so that's really just 4 of
each, so maybe this is just some exotic Beryllium, or a clump of degenerate
neutron gas as might escape from a dead-ish star.

~~~
ars
I can see why you would think that. But neutrons really are distinct
particles.

A neutron has 3 quarks in it, not 3 quarks plus an electron.

That down quark that became an up quark: An up quark is not a down quark plus
an electron.

~~~
raattgift
It gets a bit more complicated than that.

Matt Strassler has a couple relevant articles on his blog site.

The first goes deeper than the 3-quark simplification.

"What's a proton? First and foremost, it’s a mess. A total mess"

[http://profmattstrassler.com/articles-and-
posts/largehadronc...](http://profmattstrassler.com/articles-and-
posts/largehadroncolliderfaq/whats-a-proton-anyway/)

The second digs into both protons and neutrons

"So there are reasons to go further and describe things as I have elsewhere on
this website: a proton is made from three quarks (two up quarks and a down
quark), lots of gluons, and lots of quark-antiquark pairs (mostly up quarks
and down quarks, but also even a few strange quarks); they are all flying
around at very high speed (approaching or at the speed of light); and the
whole collection is held together by the strong nuclear force"

[http://profmattstrassler.com/articles-and-posts/particle-
phy...](http://profmattstrassler.com/articles-and-posts/particle-physics-
basics/the-structure-of-matter/protons-and-neutrons/)

And the third deals with neutron stability in nuclei, and specifically focuses
on the stability of the neutron inside a deuteron.

[http://profmattstrassler.com/articles-and-posts/particle-
phy...](http://profmattstrassler.com/articles-and-posts/particle-physics-
basics/mass-energy-matter-etc/the-energy-that-holds-things-together/neutron-
stability-in-atomic-nuclei/)

[forgive me for combining a reply to an earlier comment you made on neutron
stars]

We don't know the equation of state of a neutron star; most viable models have
substantial layering and an impressively busy energy-density flow. Most models
predict neutron stars to be very bright in neutrinos, although the brightness
is typically greatest at the outer layers rather than from the deeper ones
where one would expect a superfluid sea of degenerate neutrons to dominate
almost to the exclusion of everything else (e.g. there _may_ be small numbers
of superconducting protons floating around in it), and mechanisms which
produce the Pauli Exclusion Principle are non-negligible. Possible mechanisms
are somewhat constrained. How the density profile goes below the superfluid
layer is I think mainly speculation; there are BH-remnant-related reasons to
hope for a lattice crystal or some block-like structure of subatomic particles
forming an inner core.

JM Lattimer has a recent (2013) paper:
[http://arxiv.org/abs/1305.3510](http://arxiv.org/abs/1305.3510)

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elbigbad
The Strassler links are VERY good, thank you for posting. I'm especially
impressed that he answers comments on the posts in detail, even "stupid"
questions.

~~~
raattgift
I agree, Matt Strassler is a gifted communicator.

It's a tragedy that he has left full-time theoretical physics for greener
pastures as a result of the huge (as in double-digit percentages, and in some
cases more than a third) cuts in research budgets in the USA, coupled with his
desire to remain working in the States.

Unfortunately there are quite a few good working-scientist bloggers who have
been producing much reduced output as a result of lower funding in general.
Some have moved out of the USA and continue to blog. Some have had to focus
themselves on earning survival income by pushing out many grant proposals in
hopes of even partial funding, and simply cannot afford to take the time to
explain other scientsists' work to non-scientists. Some have, alas, mostly
stopped blogging altogether.

