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Neutrino flavor properties

  1. Jul 28, 2009 #1
    I'm a new grad student preparing to do some work on Daya Bay, and I'm basically taking in all the information on neutrinos that I can right now. It's pretty interesting stuff, but I was wondering if anyone has any thoughts on the following:

    Assuming I correctly understand that neutrino flavor is defined solely by the type of charged lepton involved in a CC intereaction also involving the neutrino, and also assuming that I correctly understand that a neutrino flavor is a superposition of three (maybe) mass eigenstates, then I believe it is safe to say that the mass of the neutrino involved in a CC interaction has nothing to do with the associated charged lepton. So I have to wonder, what property exactly is it that a neutrino possesses that influences the outcome of a CC interaction? Don't say flavor.

    I've looked around, and haven't been able to find a single instance where anyone has asked this question, much less attempted to speculate.

  2. jcsd
  3. Jul 28, 2009 #2
    Why not ?
  4. Jul 28, 2009 #3
    Because I'm looking for something a little less vague. I'm going to go out on a limb here and suppose that the term 'flavor' is less a lable of a type of neutrino and more a reference to the property that I'm trying to get at.

    I guess a better way to ask the question is, what, precisely, is flavor? Not the definition of flavor, but the actual physical attribute that it stands for.
  5. Jul 28, 2009 #4


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    Staff: Mentor

    You might as well ask, "what is electric charge?" or "what is color? [of a quark]"
  6. Jul 28, 2009 #5
    I guess I might as well. I didn't know if that's how it was, but I guess it is. Cool, thanks.

    I suppose that now I need to ask, is 'it is what it is' and acceptable answer, or a cop out? I'm off to find a philosophy board.
  7. Jul 28, 2009 #6
    The reason why we have three families almost duplicate to each other, except for their masses, mixing together in a seemingly arbitrary fashion, is not explained within the standard model. It is actually quite a discovery which came along together with the building of this model, and is left open as a puzzle. If that's your point, I guess we can only agree. If you have a technical question as to how this structure is implemented in neutrino interaction specifically, we can pick a reaction and write out the details of how the amplitude is calculated.

    Generally, if that may help, I can list a few references available readily. I post them in chronological order, so you may want to look at the latest references at the end first. I include previous ones mostly by personal taste and also because it is always desirable to have several points of view on the same question.

    The Standard Electroweak Theory and Beyond
    (G. Altarelli, Lectures given at the Nathiagali Summer School, Pakistan and the PSI Zuoz Summer School, July - August 2000)

    Neutrino Masses and Mixing: Evidence and Implications
    (M.C. Gonzalez-Garcia, Y. Nir, Rev.Mod.Phys.75:345-402,2003)

    TASI 2002 lectures on neutrinos
    (Yuval Grossman, Lectures given at the TASI 2002 Summer School, University of Colorado, Boulder, Colorado, June 2002)

    Neutrino physics overview
    (J. W. F. Valle, Review based on lectures at the Corfu Summer Institute on Elementary Particle Physics in September 2005.)

    The Standard Model of Electroweak Interactions
    (Antonio Pich, lectures given at the [...] 4th CERN - CLAF School of High Energy Physics, Vina del Mar, Chile, 18 February - 3 March 2007)

    Summary of the Electroweak and Beyond the Standard Model Working Group
    Prepared for XVI International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2008)

    Introduction to the Standard Model and Electroweak Physics
    (Paul Langacker, Lectures presented at TASI2008)

    Unanswered Questions in the Electroweak Theory
    (Chris Quigg, prepared for Annual Review of Nuclear and Particle Science)

    Also, if you prefer videos, you may want to check
    Neutrino Physics
    (Carlo Giuntu, Academic Training Lecture Regular Programme, CERN-TH 2009)
  8. Jul 28, 2009 #7


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    Gold Member

    Real simple now: What's the difference/relation between flavor and family in particle physics? I thought they were pretty much the same, with three of each, but I just read in wikipedia that there are six flavors of quarks and six flavors of leptons and that strong interactions conserve all flavors. I still think there are just three families.
    Jim Graber
  9. Jul 29, 2009 #8
    Humanino, one resource you didn't include that found very helpful was the neutrino summer school lecture series given at Fermilab over the past two months. There are about 32 hour-and-a-quarter long lectures. www.fnal.gov. Good stuff, man.

    And also, after giving it some thought, I agree that asking 'what is flavor' is like asking 'what is electric charge,' but I maintain that it's a valid question. Questions such as this have definitely been asked before, and solutions proposed. This is the kind of question that leads to discussions on action at a distance and such. Therefore, I press my query.

    Is there a flavor "field?" Are certain mass eigenstates more likely to give rise to certain flavors (more an oscillation question, which has probably been answered)? If so, what does that imply about the nature of flavor?

    I don't expect anyone to take me up on these questions, but it would be fun if someone did, I think. I'm not really interested in CC interaction dynamics, or mixing angles, or the mechanism of the MSW effect, or whatever. I'm interested in finding out what a neutrino is. This is why I'm on the neutrino project.
  10. Jul 30, 2009 #9
    There are three (maybe more, we're not sure) distinct kinds (flavors?) of neutrinos. Call them e, mu and tau. E neutrino only couples to electrons/positrons, etc.
    Neither of these kinds is a mass eigenstate. That simply means that there are terms in the "theory of everything" lagrangian that cross-couple different kinds of neutrinos to each other. So you start with the electron neutrino and you evolve it according to that lagrangian, and you get a superposition of e/mu/tau neutrinos. That is oscillation.

    Mathematically, each mass eigenstate is a superposition of flavor eigenstates, and conversely, each flavor eigenstate is a superposition of mass eigenstates. Just like, in a three-dimensional space, you can pick two different orthonormal bases and express members of either as linear combinations of the other one. Likewise, flavor and mass are just two different bases that correspond to two different types of neutrino interactions (weak interaction, which gives rise to flavor basis, and time evolution / self-interaction / higgs coupling / something else, which gives rise to mass basis ). At this point we aren't even quite sure as to the exact form of terms in the lagrangian which give rise to neutrino mass.

    There are three families of quarks and three families of leptons that we know of. Each family includes two quarks and two leptons. Strong interaction conserves families and flavors. Charged current weak interaction couples each up-type quark mass-state to each down-type quark mass state, and each charged lepton to each neutrino mass state.

    One major difference is that all quarks and all charged leptons are defined as mass eigenstates, whereas neutrinos are historically defined as states which couple to specific leptons. So, for quarks we have a CKM matrix which describes how weak interaction couples up-type quarks to down-type quarks, and for neutrinos we have something different.
    Last edited: Jul 30, 2009
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