
The plot thickens for a hypothetical “X17” particle - bigpumpkin
https://home.cern/news/news/physics/plot-thickens-hypothetical-x17-particle
======
dang
Recent related threads:

[https://news.ycombinator.com/item?id=21616084](https://news.ycombinator.com/item?id=21616084)

[https://news.ycombinator.com/item?id=21616381](https://news.ycombinator.com/item?id=21616381)

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jcroll
Good breakdown of why this is probably just noise
[https://www.forbes.com/sites/startswithabang/2019/11/26/this...](https://www.forbes.com/sites/startswithabang/2019/11/26/this-
is-why-the-x17-particle-and-a-new-fifth-force-probably-dont-
exist/#598bdf3d2e82)

~~~
justAnotherNET
I find it interesting that the top voted rebuttal to a CERN hosted article is
a Forbes one.

~~~
knzhou
You need to look at the source. Most Forbes content is bad, but this is Ethan
Siegel's blog, which is usually pretty good.

The CERN article is also good, and the two don't actually contradict each
other -- nobody is rebutting anybody else. An anomaly which has only a 5%
chance of holding up still _is_ extremely exciting. Probably not worth all the
media attention it randomly got, but definitely worth more investigation by
physicists.

~~~
saalweachter
It's that moment where they're about to draw the last number of this week's
lottery and you've matched every number so far.

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dmix
> Examining the number of electron–positron pairs at different angles of
> separation, the researchers found an unexpected surplus of pairs at a
> separation angle of about 140º.

I keep reading about this "angle" in regards to beryllium-8 and X17. Can
someone ELI5 for a non-physics person what it means for particles to come off
at a certain angle?

~~~
throwaway2048
Its pretty much what it sounds like, when there are particle collisions or
decays, the particles come off at certain characteristic angles relative to
the beam that are signatures of certain types decay and energies.

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

In this video, look for the forks that happen in the vapor trails being
generated, that is a particle collision, and the corresponding sort of angle
being talked about here.

[https://www.youtube.com/watch?v=-B2cvZgLToY](https://www.youtube.com/watch?v=-B2cvZgLToY)

This technique works because the air is essentially super saturated with
moisture, so even very slight atomic level disturbances will cause the water
to condense to form mini "clouds" (hence the term cloud chamber).

Its difficult to find videos about, but antimatter pair production will cause
patterns that look like this for instance

[https://i.stack.imgur.com/9CKRA.jpg](https://i.stack.imgur.com/9CKRA.jpg)

muons, electrons, and alpha particles of different energies will will cause
patterns that look like this

[https://i.stack.imgur.com/NwNcS.jpg](https://i.stack.imgur.com/NwNcS.jpg)

and so on.

Check out
[http://avtanski.net/projects/cc/virtual_cloud_chamber.html](http://avtanski.net/projects/cc/virtual_cloud_chamber.html)
and
[https://www.nucleonica.com/wiki/index.php?title=Help%3AVirtu...](https://www.nucleonica.com/wiki/index.php?title=Help%3AVirtual_Cloud_Chamber)
and see if you can identify some of the particles :)

~~~
dmix
Thanks very helpful, the angles being signatures to help determine what
forced/objects are involved makes a lot more sense to me now. That's always
been something I've struggled with in biology/chemistry and physics is the
higher level abstractions used to infer smaller phenomenons that are not as
easily observable.

I'm too used to compsci where it's more explicit and every "but why?" doesn't
lead you down a Wikipedia rabbit hole.

Edit: that cloud chamber video is very cool!

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peteradio
I find it interesting that there is no mention of NA64's sensitivity to the
particle. Is it possible to say from the Atomki institute experiments what is
the rate of production expected at NA64? Somehow LHCb will be able to refute
or confirm but only by 2023.

~~~
davrosthedalek
This talks might be interesting to you:
[https://indico.cern.ch/event/827066/contributions/3590884/at...](https://indico.cern.ch/event/827066/contributions/3590884/attachments/1938785/3213894/gninenko-
na64-pbc-05-11-2019.pdf) (see page 10)

There is hopefully also a DarkLight run at JLAB or something similar at MAMI
to test the remaining phase space.

~~~
peteradio
Thanks!

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fermuch
If you understand Spanish, here is a video of a complete and easy to grasp
introduction to what this new force is, what it means and how it was
discovered:

[https://youtu.be/u_O2hW2J8TE](https://youtu.be/u_O2hW2J8TE)

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jml7c5
Is there any new information in this article? I'm not seeing anything that
hasn't already been reported on.

~~~
jfengel
The "plot thickening" is that this is CERN's take on the matter, which has
been following it for years -- so to them, the same arxiv article constitutes
"new information" that came as just plain news to everybody else.

Other than that, there's nothing here you haven't seen before aside from a few
interesting quotes from CERN people.

