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Comment by ephimetheus | Hacker News Reader

Neutrons are just as complex, they’re much harder to study though.

If i remember correctly Feynman said in one of his lectures that we know the mass of the electron with much greater precision than the proton, which may mean that it electrons are easier to study. I don't know if this is still true though.

Oh yes and so much so! Electrons are point-like (not composite like a proton) and interact only electroweakly (not strongly).

> point-like

Oh, your going to love this theory.

https://fondationlouisdebroglie.org/AFLB-222/MARK.TEX2.pdf

In summary, There is a way to model electrons as a twisted self enclosed em field.

A decent digest summary of the paper is this video

https://www.youtube.com/watch?v=hYyrgDEJLOA (Huygens Optics: Are Electrons made of Light? )

And neutrons are neither.

If it was possible to build a direct neutron accelerator/collider, I suspect we'd get some new physics pretty quickly.

Analysing hand-me-down neutron events from indirect collisions isn't quite as useful.

At ISIS (Oxford neutron source)…

Spallation generation: High-energy protons (~800 MeV) hit a heavy target, releasing a wide spectrum of fast neutrons up to hundreds of MeV. These are then moderated down to useful energies for experiments.

It’s not the LHC, sure. But I don’t see any reason (apart from “why bother”) why they can’t do spallation in Geneva. OK maybe there’s a cooling problem…

Spallation is the easy part

But neutrons can't go around a tube being guided by magnetic fields

Well my point is that the energy of the spallation neutrons is monotonically related to the energy of the protons hitting the Tungsten target ... although somewhat lower. I would consider these 100s MeV partiles to be (quite) high energy in contrast to the thermal neutrons alluded to elsewhere. Sure the spallation is lossy, but the result is still pretty high. And the physics is somewhat different with neutron experiments vs. protons... iiuc

There absolutely are direct neutron experiments, but they are much lower energy and have a different focus, partly because neutrons being neutral means they’re very hard to accelerate.

There’s an ultra cold neutron source at Paul Scherrer that is used to measure if the neutron has an electric dipole moment. This is complementary to high energy experiments.

Neutrons are not that different from protons. The decay from neutrons to protons is pretty well understood, and there’s no reason to think that the nature of quark/gluon interactions in a neutron are significantly different from those in a proton. What kind of new physics are you imagining we’d get?

Of course more experimental data is a good thing, but in this case it doesn’t seem obvious that it would lead to anything really new.

Why do you say they're "pretty well understood" when there's been a long-standing unresolved discrepancy between lifetime measurement techniques?

I think they mean that what happens when a neutron decays is well understood. One of the neutron's down quarks change to an up quark, facilitated by a virtual W boson with negative charge. The W boson is very unstable and immediately decays into an electron and an electron anti-neutrino, both of which are ejected leaving behind the former neutrino which is now a proton because of that quark change.

When that happens is less understood, hence the discrepancies you mentioned.

The same QCD theory that's used to model the proton models the neutron. Theoretically, our understanding of both is on the same footing.

The comment I replied to talked about "new physics". That's a term that's used in physics to describe physics beyond the Standard Model. Better experimental data about neutron internals could certainly help constrain the neutron lifetime, but that would be likely to be experimental constraints on existing physics, not new physics in the sense that the term is normally used.

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