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Ugh, science writing: > Physicists Just Generated a Particle That Acts as Its Own Antiparticle [...] > Physicists now have the next best thing – a particle-

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

lateadopter 9y ago
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.
- danbruc 9y ago
  All bosons (e.g. photons) are their own antiparticle [...] Are you sure? That doesn't sound right for charged bosons like the W bosons.
  - bjl 9y ago
    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.
gus_massa 9y ago
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 https://en.wikipedia.org/wiki/Electron_hole [2] https://en.wikipedia.org/wiki/Phonon https://en.wikipedia.org/wiki/Phonon
- jessriedel 9y ago
  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_double_beta_decay 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 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.)
  - gus_massa 9y ago
    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.

lateadopter 9y ago

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.

danbruc 9y ago
All bosons (e.g. photons) are their own antiparticle [...] Are you sure? That doesn't sound right for charged bosons like the W bosons.
- bjl 9y ago
  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.

gus_massa 9y ago

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

jessriedel 9y ago
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_double_beta_decay 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 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.)
- gus_massa 9y ago
  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.