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A question to particle physicists: I've always thought that matter and anti-matter qualifications applied only to charged particles. Neutrinos have no charge, s

by zvrba 6y ago

A question to particle physicists: I've always thought that matter and anti-matter qualifications applied only to charged particles. Neutrinos have no charge, so how can it have an antiparticle? Does there exist an "anti-neutron" as well?

bonzini 6y ago
Not a physicist but I can answer this. Antineutrinos have opposite lepton number compared to neutrinos. Lepton number is preserved by all particle reactions[1] so for example beta decay must produce an antineutrino (L=-1) in addition to an electron (L=1). Antineutrons also exist. Neutrons are composed of three quarks, uud (u has charge 1/3 and d had charge -2/3), while antineutrons are composed of two up antiquarks (charge -1/3) and one down antiquark (charge 2/3). And as in the case of neutrinos, neutrons have baryonic number 1 like protons and antineutrons have baryonic number -1 like antiproton a. Hence, for example, a beta decay will always turn a neutron into a proton and an antineutron into an antiproton (though the latter is theoretical). [1] More precisely there is a lepton number for each generation (electron/muon/tau) and all three are separately preserved.
_Microft 6y ago
This will blow your mind then: A Majorana fermion (/maɪəˈrɑːnə ˈfɛərmiːɒn/[1]), also referred to as a Majorana particle, is a fermion that is its own antiparticle. They were hypothesized by Ettore Majorana in 1937. The term is sometimes used in opposition to a Dirac fermion, which describes fermions that are not their own antiparticles., from https://en.wikipedia.org/wiki/Majorana_fermion https://en.wikipedia.org/wiki/Majorana_fermion
gus_massa 6y ago
Imagine that the relation between a particle and it's antiparticle is an abstract relation, and one of the easy to explain consequences is that they have the oposite charge. (Other consequence is that they have the same mass, but it's less interesting.) There is an anti-neutron https://en.wikipedia.org/wiki/Antineutron https://en.wikipedia.org/wiki/Antineutron I'm not sure of the details, but it should be easy to produce an antineutron beam, if you have the right equipment (perhaps like a particle acelerator worth a few million dollars :) ) Some random paper http://www.ph.unito.it/ccl/docenti/menichetti/CIVR/bressani.pdf http://www.ph.unito.it/ccl/docenti/menichetti/CIVR/bressani.... take a look at section 2.
T-A 6y ago
Neutrinos do have a charge, just not electric: https://en.wikipedia.org/wiki/Weak_interaction#Weak_isospin_and_weak_hypercharge https://en.wikipedia.org/wiki/Weak_interaction#Weak_isospin_...

by zvrba 6y ago

bonzini 6y ago

Not a physicist but I can answer this. Antineutrinos have opposite lepton number compared to neutrinos. Lepton number is preserved by all particle reactions[1] so for example beta decay must produce an antineutrino (L=-1) in addition to an electron (L=1). Antineutrons also exist. Neutrons are composed of three quarks, uud (u has charge 1/3 and d had charge -2/3), while antineutrons are composed of two up antiquarks (charge -1/3) and one down antiquark (charge 2/3). And as in the case of neutrinos, neutrons have baryonic number 1 like protons and antineutrons have baryonic number -1 like antiproton a. Hence, for example, a beta decay will always turn a neutron into a proton and an antineutron into an antiproton (though the latter is theoretical). [1] More precisely there is a lepton number for each generation (electron/muon/tau) and all three are separately preserved.

_Microft 6y ago

This will blow your mind then: A Majorana fermion (/maɪəˈrɑːnə ˈfɛərmiːɒn/[1]), also referred to as a Majorana particle, is a fermion that is its own antiparticle. They were hypothesized by Ettore Majorana in 1937. The term is sometimes used in opposition to a Dirac fermion, which describes fermions that are not their own antiparticles., from https://en.wikipedia.org/wiki/Majorana_fermion https://en.wikipedia.org/wiki/Majorana_fermion

gus_massa 6y ago

Imagine that the relation between a particle and it's antiparticle is an abstract relation, and one of the easy to explain consequences is that they have the oposite charge. (Other consequence is that they have the same mass, but it's less interesting.) There is an anti-neutron https://en.wikipedia.org/wiki/Antineutron https://en.wikipedia.org/wiki/Antineutron I'm not sure of the details, but it should be easy to produce an antineutron beam, if you have the right equipment (perhaps like a particle acelerator worth a few million dollars :) ) Some random paper http://www.ph.unito.it/ccl/docenti/menichetti/CIVR/bressani.pdf http://www.ph.unito.it/ccl/docenti/menichetti/CIVR/bressani.... take a look at section 2.

T-A 6y ago

Neutrinos do have a charge, just not electric: https://en.wikipedia.org/wiki/Weak_interaction#Weak_isospin_and_weak_hypercharge https://en.wikipedia.org/wiki/Weak_interaction#Weak_isospin_...