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Since an antiparticle by definition is a particle with the same mass but opposite charge, how is there such a thing as an antineutrino? A neutrino has 0 charge so could not have an opposite. So why does an antineutrino exist and how does it differ from a neutrino?

Charlie
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    "an antiparticle by definition is a particle with the same mass but opposite charge" - That's not the definition of an antiparticle; that's just two properties that antiparticles happen to have. – Tanner Swett Jun 12 '17 at 16:29
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    It does seem to be utterly identical to that other question. – Fattie Jun 12 '17 at 21:08

2 Answers2

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This is the table of elementary particles of the standard model of physics.

enter image description here

There exists the symmetric anti particle table, where the quantum numbers are such that added, particle + antiparticle the sum is zero.

The neutrinos carry the lepton number of the corresponding lepton, the antineutrinos the negative .

In addition neutrinos and antineutrinos, react to first order with the weak interaction only, are distinguished by chirality:

For each neutrino, there also exists a corresponding antiparticle, called an antineutrino, which also has no electric charge and half-integer spin. They are distinguished from the neutrinos by having opposite signs of lepton number and chirality. As of 2016, no evidence has been found for any other difference

The chirality difference, the way the spin of a fermion is oriented with respect to its motion, gives different interaction crossections; for example neutrino nucleon scattering versus antineutrino nucleon scattering.

doppelgreener
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anna v
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  • What does a lepton number represent? – Charlie Jun 12 '17 at 12:13
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    In the table there are three lepton numbers, electron, muon and tau. The represent the number of leptons, the way baryon number represents the number of nucleons. It is the reason that neutron( beta) decay goes into an e- and and antineutrino e and a proton, a three body decay instead of just a proton and an electron. Lepton number would beviolated otherwise. That is how the existence of neutrinos was established. – anna v Jun 12 '17 at 12:21
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    @Charlie It has been found that some quantities are conserved. What they represent is ... some quantity that is conserved. Interactions ... conserve those quantities. The product after and before ... remains the same. Some of them also impact how they interact in various interactions in ways that are not obviously related to the conservation of their number. – Yakk Jun 12 '17 at 14:46
  • I thought it is still not proven that neutrino isn't its own antiparticle. Is it settled now? – Vladimir F Героям слава Jun 12 '17 at 20:05
  • Wait isn't Z its own antiparticle? – Joshua Jun 13 '17 at 01:28
  • @VladimirF: It was, and then somebody noticed they can't be chiral if they're massive (which they are). That is, a left handed neutrino has a vantage point at which it appears right handed. Nobody knows how to fix the theory yet and the own-antipartical has a cult following again. – Joshua Jun 13 '17 at 01:30
  • @VladimirF from the chirality link "The resolution to this false paradox is that the chirality operator is equivalent to helicity for massless fields only, for which helicity is not frame-dependent. By contrast, for massive particles, chirality is not the same as helicity, so there is no frame dependence of the weak interaction: a particle that couples the weak force in one frame, does so in every frame." semantics, and a mathematical definition of chirality with gamma matrices – anna v Jun 13 '17 at 03:13
  • @Joshua bosons can be their own antiparticle , as the Z, if zero charge – anna v Jun 13 '17 at 03:16
  • @annav But from the same chirality link: "After the observation of neutrino oscillations, which imply that neutrinos are massive like all other fermions, the revised theories of the electroweak interaction now include both right- and left-handed neutrinos." That seems to be in disagreement with your answer. – Vladimir F Героям слава Jun 13 '17 at 06:56
  • @VladimirF Not really, just the way they interact changes , the operator does not change. They are just massive fermions as far as chirality goes, – anna v Jun 13 '17 at 07:46
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A neutrino has 0 charge so could not have an opposite

A (left-handed) neutrino has zero electric charge $Q$ but it is not uncharged.

The neutrino (anti-neutrino) has weak isospin charge $T_3$ of +1/2 (-1/2) and weak hypercharge $Y_W$ of -1 (+1).

The relationship of these three charges is given by

$$Q = T_3 + \frac{Y_W}{2}$$

and so, the neutrino is electrically neutral but not uncharged.

Alfred Centauri
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