Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Positron neutrino=electron antineutrino

  1. Apr 11, 2009 #1
    Hi everybody,

    Basically, the title of this thread says it all.

    My question is: Since all particles have an antiparticle and the positron is the electron's antiparticle, does that mean the positron-neutrino is the same as the electron-antineutrino?
    If not, is there such a thing as a positron-antineutrino?

    I'm a beginner when it comes to particle physics and I'm now just learning about it through website called particleadventure.org.
     
  2. jcsd
  3. Apr 11, 2009 #2

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    "Electron neutrino" is just the name of the thing, so it's anti-particle is called an anti-electron neutrino. You should view "anti-" as prefixing the whole name, not just the electron part. Anti-neutrinos don't have anything to do with the fermion they "belong" to, the "electron" in "electron neutrino" just refers to the generation of the standard model it belongs to (namely, that of which the fermion is called electron).
     
  4. Apr 11, 2009 #3

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    The 'electron' in the name electron-neutrino, refers to the generation it belongs to.

    The first generation of leptons are: Electron, Positron, Electron-Neutrino, Anti-electron-neutrino

    The Second is: Muon, Anti-muon, Muon-neutrino, Anti-muon-neutrino

    The peculiarity is that positron is just a fancy name for anti-electron.
     
  5. Apr 11, 2009 #4
    Thanks, now I know they are the same. I got thrown of cause the website called it a electron-anti-neutrino instead of a anti-electron-neutrino.
    I do have another question though;
    I know there are 3 types of neutrinos, but what's the difference between them. Is it they're mass?
    Also , how can there be anti-neutrinos when they don't have any electrical charge or strong charge?
     
    Last edited: Apr 11, 2009
  6. Apr 11, 2009 #5

    blechman

    User Avatar
    Science Advisor

    There is a theory that there are no "antineutrinos" - that is, the neutrino and ANTI-neutrino are the same particle, for each generation. These are called "Majorana neutrinos" and it is a very popular theory among neutrino physicists.

    To your next question: Assuming neutrinos are NOT Majorana, the CPT Theorem of Quantum Field Theory states that neutrinos and antineutrinos (or any particle-antiparticle pair) must have the same mass. The difference between (anti)neutrinos is that they carry "lepton quantum number" +1 (-1) respectively. Since we have not as yet seen (at least directly) lepton-number violation, that suggests that only certain types of neutrinos can come out of various experiments. For example: if you produce an electron (L=+1), then you must also produce an ANTI-neutrino to conserve lepton number.

    If neutrinos are Majorana, then lepton number would be violated and you can have very funny processes happening. This is an important constraint for incorporating Majorana neutrinos into the Standard Model. However, it can be done (in fact, it can be done very easily, especially if you believe in "Grand Unification").

    Hope that helps!
     
  7. Apr 11, 2009 #6
    I actually read about that theory a few minutes ago on Wikipedia.
    I'm not sure how to interpret your second answer, cause it's sound like another response to my second question. (It was helpful though).
    Concerning my first question;
    I know there are 3 types of neutrinos (not counting the anti-neutrinos): the electron-neutrino, the tau-neutrino and the muon-neutrino. What I wanted to know is what the difference is between those 3 neutrinos?

    If your second answer was a directed at my first question, could you please elaborate.
     
    Last edited: Apr 11, 2009
  8. Apr 11, 2009 #7

    blechman

    User Avatar
    Science Advisor

    sorry. you asked about the difference between neutrinos and their antiparticles. all i was trying to say was that if you believe in Majorana neutrinos, then there is NO difference.

    However, in the Standard Model, where neutrinos are massless, the difference between the particles is that they carry lepton number. In fact, they actually carry lepton-FLAVOR number (electron number, muon number, tau number), where L = E + M + T. So even though they are electrically neutral and color neutral, they are not "lepton number" neutral and there is a way to distinguish the neutrinos from antineutrinos.

    That answers your most recent question (electron neutrino has the quantum numbers E=1, M=0, T=0, etc).

    Of course, we now know that the neutrinos are NOT massless, so whether they have Majorana mass (which violates the lepton charge) or a lepton-number-conserving mass (known among particle physicists as "Dirac mass") is an open and hotly-debated question.

    Hope that helps.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook