
Physicists demonstrate existence of new subatomic structure - upen
https://las.iastate.edu/isu-physicists-help-demonstrate-existence-of-new-subatomic-structure/
======
TheRealPomax
Mmm, scientific click bait titling. More accurate would be "Physicists
demonstrate a theoretical subatomic structure in simulation". That's
important, to be sure, but it has nothing to do with demonstrating the
existence of a particle - we've determined something "should" exist based on
simulation and data-interpretation plenty of times, and many of those have
ended up being wrong. And that's good: good science comes from discovering
what _isn't_ true, but that makes it all the more silly to have this title on
the article. We've got the simulation worked out... now we need to see if it
holds up to reality. It might not. If so, that's valuable information.

~~~
jcoffland
Apparently you didn't read the article in full before criticizing it. The
article says that the simulation was used to verify real world observations
from a particle accelerator experiment in Japan.

~~~
johncolanduoni
"Verify" is a strong word. The RIKEN experiment didn't come close to the usual
standard of evidence for declaring a new particle exists, it just showed a
reaction for which creation of a tetraneutron is a possible explanation. There
need to be a lot more experiments (different ones, not just repeats of
RIKEN's) before anybody would be willing to declare tetraneutrons "exist".

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philipov
"On their own, neutrons are very unstable and will convert into protons —
positively charged subatomic particles — after ten minutes. " ... "For the
tetraneutron, this lifetime is only 5×10^(-22) seconds (a tiny fraction of a
billionth of a nanosecond). "

10 minutes is an eternity and 5×10^(-22) seconds is closer to what I'd
consider 'very unstable'

~~~
twic
> The research in Japan used a beam of Helium-8, Helium with 4 extra neutrons,
> colliding with a regular Helium-4 atom. The collision breaks up the Helium-8
> into another Helium-4 and a tetraneutron in its brief resonance state,
> before it, too, breaks apart, forming four lone neutrons.

I don't know how fast these particles were going in the experiment, but if
they were going at the speed of light, then the tetraneutron would make it 150
femtometres from the site of the collision before decaying. By way of
comparison, neutrons and protons are 1 - 2 fm across, and a uranium nucleus is
15 fm across [i]. So if the tetraneutron was actually going at a tenth of the
speed of light, it would barely make it a nucleus's diameter away before
exploding.

[i]
[https://en.wikipedia.org/wiki/Atomic_nucleus](https://en.wikipedia.org/wiki/Atomic_nucleus)

~~~
windsurfer
That's not how relativistic speeds work. If this was going near enough to the
speed of light, it could travel almost any distance before decaying. Time
dilation would be observed of the particle, where it would appear that time is
ticking slower for the particle compared to our own frame of reference.

~~~
chunky1994
Actually what the parent comment said would be correct. Time dilation and
length contraction do not arbitrarily change the proper distances that
particles travel at near light speeds.

As observers, the detectors would see precisely what we expect if we calculate
the distance using the detector's proper time when compared with the distance
we experimentally measure.

~~~
gus_massa
Mmm... I have the strange feeling that you both agree, let's write this with
more details to avoid confusion.

The half life of a static tetraneutron is (theoreticaly) 5E-22s.

If you are at a laboratory and the tetraneutron is moving at relativistic
speed, the apparent half life in the laboratory frame will increase
substantially.

To calculate the distance that the tetraneutron will travel you must multiply
the velocity x the apparent half life. I.E

d ~= v * 1/(1-v^2/c^2) * t_hl

where t_hl = 5E-22s = the half life of the tetraneuton

not the classic version that is

d_clasic_wrong = v * t_hl

For a more detailed explanation, with numbers and graphic you all can see the
analogue experiment with muons: [http://hyperphysics.phy-
astr.gsu.edu/hbase/relativ/muon.html](http://hyperphysics.phy-
astr.gsu.edu/hbase/relativ/muon.html)

\--

Anyway, IIRC a half life of 5E-22s is still very small. IIRC you can use a
bubble chamber or something similar to see the trajectory of the particles.
You can only see a collision and examine the debris and you will note that
when the collision has some specific energy you will get an unexpected excess
of collisions. You only can examine the direction and energy of the debris to
make a good guess of the intermediate steps of the collision and discover that
for a very short time you had a tetraneutron.

~~~
chunky1994
I do agree that time dilation occurs, what I disagreed with/corrected was with
this: _it could travel almost any distance before decaying_ , which I took to
imply that the lengthening of particle lifetimes was not measurable in the way
that you just pointed out.

In retrospect perhaps the parent comment was saying theoretically it could
travel any distance which is true, but doesn't really help in estimating
whether it could clear nuclear radii or not.

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coldcode
Physics is one science where the seemingly impossible winds up being possible
all the time. Strange to think people spend a good portion of their lives
studying things thought to not exist.

~~~
Manishearth
> where the seemingly impossible winds up being possible all the time.

No, it's where the possible is often portrayed as impossible by popular
reporting all the time.

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sctb
We've updated the link from
[http://sciencebulletin.org/archives/7339.html](http://sciencebulletin.org/archives/7339.html)
to this, which looks like the original source.

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GavinMcG
I read the headline as "demand" and thought this was a rather petulant
reaction to the "no new physics" development this year.

[https://home.cern/about/updates/2016/05/theory-
theoretical-p...](https://home.cern/about/updates/2016/05/theory-theoretical-
physics-crisis)

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maverick_iceman
The original paper [1].

[1] [https://arxiv.org/abs/1607.05631](https://arxiv.org/abs/1607.05631)

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poizan42
Is it really "subatomic" though? Seems more like it could be considered
isotope 4 of element zero.

~~~
johncolanduoni
Technically subatomic refers to the size of an atom with electrons, not a
nucleus (which is much smaller). It's especially appropriate here because
neutrons aren't electrically charged, so their interactions with other
particles are very short range.

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zer0gravity
I don't know, maybe this discovery has scientific value. But could it be the
sometimes scientists report small "breakthroughs" just so that they keep the
funding coming ?

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agumonkey
Still no turtles.

~~~
ozzmotik
it's subatomic particles all the way down i tell you!

~~~
jessaustin
I would have sworn I've seen an animation implying that at sufficient
magnification the whole thing loops around to galactic superclusters. Non-
intuitive, to be sure...

