Physicists Just Generated a Particle That Acts as Its Own Antiparticle | Hacker News Reader

Physicists Just Generated a Particle That Acts as Its Own Antiparticle

sciencealert.com

Ugh, science writing:

> Physicists Just Generated a Particle That Acts as Its Own Antiparticle

[...]

> Physicists now have the next best thing – a particle-like system that behaves just like the kind of matter Majorana predicted

If you talk with someone that works in solid state physics, they act as if these kind of particles were real as elementary particles. The most usual are holes [1] and phonons [2]. So it's standard notation in that area, but it may be confusing for the general public.

At least they didn't call it an "angel" particle, like in the previous submissions.

[1] https://en.wikipedia.org/wiki/Electron_hole

[2] https://en.wikipedia.org/wiki/Phonon

The distinction between fundamental particles and composite particles is more a statement about the extent of human knowledge rather than anything physical about those particles. That is, saying "this is a fundamental particle" tells you that we haven't discovered any constituent parts to it, not that there aren't any. Protons used to be fundamental particles until we discovered they were made of quarks, and quarks may yet turn out to be composite particles built from preons.

So yes, if you were attracted to this article because you thought they found a new fundamental particle, then it was clickbait. But the real point is that it's a Majorana fermion (with well-defined momentum eigenstates, a scattering matrix, etc.).

It's possible in the future that we discover neutrinos are Majorana fermions

https://en.wikipedia.org/wiki/Double_beta_decay#Neutrinoless...

at which time they will be "fundamental Majorana fermions"... and then discover after that the neutrinos are just composite particles.

https://arxiv.org/abs/1510.07988

(There are some subtleties here. Some quasi-particles don't have all the properties we normally associate with fundamental particles. And there are weak theoretical arguments that some fundamental particles can't be composite unless their constituents have properties that are subjectively inelegant.)

The gyromagnetic ration of a truly elementary particle is g=2. With the current theories, a electron has a cloud of virtual particles, but no internal structure. With this assumptions the theoretical value is approximately g=2+2.alfa/2pi+...~=2+1/(137*pi). The experimental value of the g of the electron agree with the theoretical value up to 14 digits, so it's a very good hint that the electron is really an elementary particle.

Obviously there can be future theory were the electron has internal structure, but it will be a breakthrough, not a small fix.

The theoretical and experimental value of g for a muon almost agree, but only 10 digits. So there is a small chance of something interesting there. But IIRC most people think that it may be a new particle in the cloud of virtual particles, not an internal structure of muons.

Protons and neutrons have internal structure, a lot of internal structure, so the value of g is a difficult to calculate number that is not 2. In particular, g=+5.6 and g=-3.8.

This is just a way of saying that we have probed the electron for internal structure to a significantly more precise level than the level necessary to reveal the known internal structure of nucleons. But it's just an upper bound. For all we know, the next accelerator (if there is one) could reveal composite structure just below the bound.

Yep, title is bad, better would be "Physicists Just Generated a Fermion That Acts as Its Own Antiparticle", or more concisely: "Physicists Just Generated a Majorana Fermion".

All bosons (e.g. photons) are their own antiparticle, so this is a rare instance of science writing where the headline is LESS interesting than the actual work done.

All bosons (e.g. photons) are their own antiparticle [...]

Are you sure? That doesn't sound right for charged bosons like the W bosons.

You're correct. The photon and the Z boson are each their own anti-particle. The rest of the force-carriers have distinct anti-particles.

Well up above the tropostrata

There is a region stark and stellar

Where, on a streak of anti-matter

Lived Dr. Edward Anti-Teller.

Remote from Fusion’s origin,

He lived unguessed and unawares

With all his antikith and kin,

And kept macassars on his chairs.

One morning, idling by the sea,

He spied a tin of monstrous girth

That bore three letters: A. E. C.

Out stepped a visitor from Earth.

Then, shouting gladly o’er the sands,

Met two who in their alien ways

Were like as lentils. Their right hands

Clasped, and the rest was gamma rays.

by Prof. Harold P. Furth (1930-2002)

Most of the discussion is here in this submission, but there are also two comments here: https://news.ycombinator.com/item?id=14817322

And there's another comment here: https://news.ycombinator.com/item?id=14818725

There are also other submissions:

https://news.ycombinator.com/item?id=14817206

https://news.ycombinator.com/item?id=14833208

https://news.ycombinator.com/item?id=14840123

I have personally been producing particles that are there own anti-particles since childhood. And, I continue to do so as I write this comment. Photons!

I guess it would be tough to keep these around in any substantial quantity.

It's not usually a problem to have a large number of photons?

Which are different because the result of a particle/antiparticle collision is the emission of photons so the quantity of photons is not changed by collisions.

Unless it can only become one of the properties at one time

> for every type of fundamental particle in the Universe there is the equivalent of an evil twin complete with an opposing charge

Do they have goatees?

So did I but I can't find it.....

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