4 ms·

NA62 spots two potential instances of rare particle decay

33 points by lelf 7y ago

317070 7y ago
Why is this result interesting? All of the particles involved are pretty exotic, and this is still fitting the Standard model. Can someone enlighten me?
- evanb 7y ago
  This kind of decay requires an overall neutral current that changes the strange quark to a down quark. No such current exists at tree level in the Standard Model---instead, strange has to turn into an up-type quark and from there into a down. So, anything from the SM that contributes to this process necessarily involves loops and has no large SM backgrounds. That makes it a very sensitive probe for searching for new physics. Everything seems consistent with the SM but that need not have been---certain kinds of new physics would have stood out in this decay channel. So, while it's not a discovery of a new particle, for example, it is a result that can tightly constrain conjectures.
JohnDeHope 7y ago
It seems like every article like this can be summarized as: this experiment or analysis could indicate physics beyond the standard model, we ran the experiment or analysis, and we found nothing unexpected. At this point I find myself asking what the ramifications would be if the standard model is correct and is all there is. It seems less worthwhile to wonder about alternatives to the standard model. Please correct my thinking.
- planck01 7y ago
  It can't be complete and all there is, because it doesn't explain everything we know exists. To simply quote wikipedia: "It does not fully explain baryon asymmetry, incorporate the full theory of gravitation as described by general relativity, or account for the accelerating expansion of the Universe as possibly described by dark energy. The model does not contain any viable dark matter particle that possesses all of the required properties deduced from observational cosmology. It also does not incorporate neutrino oscillations and their non-zero masses."
  - CharlesColeman 7y ago
    > It can't be complete and all there is, because it doesn't explain everything we know exists. However, it could very well be that a true scientific theory that explains those things is beyond our experimental verification, and the Standard Model (or something not much beyond it) will fit all particle accelerator observations made in the next thousand years or more.
    - nine_k 7y ago
      Fortunately we have astronomic events. No Earth-based experiment could emit gravitational waves strong enough to detect; good thing the Universe has plenty of black holes, and some of them merge.
      - CharlesColeman 7y ago
        > Fortunately we have astronomic events. That may help with some things, though it's not at all clear it's sufficient to verify a true theory that "explain[s] everything we know exists." It brings to mind the graviton, which I've read would be practically impossible to detect: you could detect one graviton every ten years with a Jupiter-mass detector placed very close to a neutron star, but the shielding needed to exclude the noise would cause it to collapse into a black hole.

33 points by lelf 7y ago

Why is this result interesting? All of the particles involved are pretty exotic, and this is still fitting the Standard model. Can someone enlighten me?

evanb 7y ago
This kind of decay requires an overall neutral current that changes the strange quark to a down quark. No such current exists at tree level in the Standard Model---instead, strange has to turn into an up-type quark and from there into a down. So, anything from the SM that contributes to this process necessarily involves loops and has no large SM backgrounds. That makes it a very sensitive probe for searching for new physics. Everything seems consistent with the SM but that need not have been---certain kinds of new physics would have stood out in this decay channel. So, while it's not a discovery of a new particle, for example, it is a result that can tightly constrain conjectures.

JohnDeHope 7y ago

It seems like every article like this can be summarized as: this experiment or analysis could indicate physics beyond the standard model, we ran the experiment or analysis, and we found nothing unexpected. At this point I find myself asking what the ramifications would be if the standard model is correct and is all there is. It seems less worthwhile to wonder about alternatives to the standard model. Please correct my thinking.

planck01 7y ago
It can't be complete and all there is, because it doesn't explain everything we know exists. To simply quote wikipedia: "It does not fully explain baryon asymmetry, incorporate the full theory of gravitation as described by general relativity, or account for the accelerating expansion of the Universe as possibly described by dark energy. The model does not contain any viable dark matter particle that possesses all of the required properties deduced from observational cosmology. It also does not incorporate neutrino oscillations and their non-zero masses."
- CharlesColeman 7y ago
  > It can't be complete and all there is, because it doesn't explain everything we know exists. However, it could very well be that a true scientific theory that explains those things is beyond our experimental verification, and the Standard Model (or something not much beyond it) will fit all particle accelerator observations made in the next thousand years or more.
  - nine_k 7y ago
    Fortunately we have astronomic events. No Earth-based experiment could emit gravitational waves strong enough to detect; good thing the Universe has plenty of black holes, and some of them merge.
    - CharlesColeman 7y ago
      > Fortunately we have astronomic events. That may help with some things, though it's not at all clear it's sufficient to verify a true theory that "explain[s] everything we know exists." It brings to mind the graviton, which I've read would be practically impossible to detect: you could detect one graviton every ten years with a Jupiter-mass detector placed very close to a neutron star, but the shielding needed to exclude the noise would cause it to collapse into a black hole.