6 ms·

The plot thickens for a hypothetical “X17” particle

108 points by bigpumpkin 7y ago

dang 7y ago
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
peteradio 7y ago
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 7y ago
  This talks might be interesting to you: https://indico.cern.ch/event/827066/contributions/3590884/attachments/1938785/3213894/gninenko-na64-pbc-05-11-2019.pdf 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.
  - peteradio 7y ago
    Thanks!
fermuch 7y ago
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
dmix 7y ago
> 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?
- xentripetal 7y ago
  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.
- throwaway2048 7y ago
  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%3AVirtual_Cloud_Chamber https://www.nucleonica.com/wiki/index.php?title=Help%3AVirtu... and see if you can identify some of the particles :)
  - dmix 7y ago
    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!
jcroll 7y ago
Good breakdown of why this is probably just noise https://www.forbes.com/sites/startswithabang/2019/11/26/this-is-why-the-x17-particle-and-a-new-fifth-force-probably-dont-exist/#598bdf3d2e82 https://www.forbes.com/sites/startswithabang/2019/11/26/this...
- justAnotherNET 7y ago
  I find it interesting that the top voted rebuttal to a CERN hosted article is a Forbes one.
  - knzhou 7y ago
    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 7y ago
      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.
  - alasdair_ 7y ago
    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.
- deleted 7y ago
  [deleted]
jml7c5 7y ago
Is there any new information in this article? I'm not seeing anything that hasn't already been reported on.
- jfengel 7y ago
  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.

108 points by bigpumpkin 7y ago

dang 7y ago

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

peteradio 7y ago

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 7y ago
This talks might be interesting to you: https://indico.cern.ch/event/827066/contributions/3590884/attachments/1938785/3213894/gninenko-na64-pbc-05-11-2019.pdf 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.
- peteradio 7y ago
  Thanks!

fermuch 7y ago

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

dmix 7y ago

> 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?

xentripetal 7y ago
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.
throwaway2048 7y ago
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%3AVirtual_Cloud_Chamber https://www.nucleonica.com/wiki/index.php?title=Help%3AVirtu... and see if you can identify some of the particles :)
- dmix 7y ago
  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!

jcroll 7y ago

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

justAnotherNET 7y ago
I find it interesting that the top voted rebuttal to a CERN hosted article is a Forbes one.
- knzhou 7y ago
  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 7y ago
    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.
- alasdair_ 7y ago
  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.
deleted 7y ago
[deleted]

jml7c5 7y ago

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

jfengel 7y ago
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.