The plot thickens for a hypothetical “X17” particle | Hacker News Reader

The plot thickens for a hypothetical “X17” particle

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108 pointsbigpumpkin20 comments

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https://news.ycombinator.com/item?id=21616084

https://news.ycombinator.com/item?id=21616381

Good breakdown of why this is probably just noise https://www.forbes.com/sites/startswithabang/2019/11/26/this...

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

I case anyone wasn’t already aware - Forbes.com allows just about anyone to publish on their platform. Their editorial standards are FAR more lax than the print publication that shares its name.

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.

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.

> 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?

I might be mistaken but from my college chemistry I believe this is referring to VSEPR theory. Where electron pairs around a nucleus will push against each other to maximize the distance between other pairs in spherical space. So two electron pairs would be separated by 180° (line) and 3 by 120° (3 lines on same plane), 4 by 120° (tetrahedron) and so on.

So if it's 140° then something else is pushing against them as it should never be 140°.

Someone more knowledgeable correct me if I'm mistaken.

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

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

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

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

https://i.stack.imgur.com/NwNcS.jpg

and so on.

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

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!

Imagine a slow moving blob heading towards a target on a wall, a small charge causes it to explode at some point along its path to the wall. The larger the charge the wider the splatter. In this case, the mass is the analogy to that detonation charge. If that blob was photons alone (which are the standard model assumption) you'd expect a smooth decreasing amount of splatter as you go away from the center of the target, what they seem to be seeing is an unexpected increase around 115 - 140 degrees.

It's a literal angle, like you learned in geometry class. After the decay, two particles fly off in different directions. They mean the angle between those directions.

Apologies I meant what the significance of the particles bouncing off at certain angles, particularly down to the degree as others have mentioned the different ranges reported. My short google search earlier didn't help me much. Others have provided some links I will dig into.

You can use the angle (in conjunction with trig applied to various conservation principles such as conservation of momentum) in an attempt to derive quantities like mass.

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.

This talks might be interesting to you: https://indico.cern.ch/event/827066/contributions/3590884/at... (see page 10)

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

Thanks!

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

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

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.

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