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to me it’s not clear - that’s why I was asking. There is a lot of talking about method one and method two and so on in that paper. I am not an expert on this, so I find it kind of confusing. I am just puzzled that if there are different methods at all, shouldn’t there be an errorbar on that cross-section? Esp. if there are so little data points in the relevant energy region? If that cross-section was somewhat different wouldn’t it affect the number of expected events (not sure if it would do the same to the background since I am not sure exactly what contributes to that background). Best,

B.

Did I miss something? What does MiniBoonE have to do with Richard Dawkins’ The God Delusion?

[If neutrinos] really aren’t going at the speed of light, but even a bit less, then their spin can’t be inherently left-handed. Why not? Because, a sufficiently fast-moving observer could be moving past them, and would see a neutrino’s spin going the wrong way relative to its velocity.

This is correct, so there must be a right handed version of the neutrino. There is: the anti-neutrino. When you reverse the direction of a neutrino it changes helicity, but it also changes to an anti-neutrino, so no new particle needs to be added to the standard model to account for neutrino masses.

Although somewhat academic, we should probably think of the neutrinos as their own antiparticles (i.e. they don’t get arrows in Feynman diagrams) and allow them to come in both right and left handed versions. (In technical language, we should think of them as real four component spinors rather than complex two component spinors). This doesn’t require a dramatic change in thinking. When you hear “neutrino” just think “left-handed neutrino” and when you hear anti-neutrino think “right-handed neutrino.” We all know that mass terms mix right-handed and left-handed, so there’s nothing to worry about. (Except for lepton number, which is no longer well defined. No matter. Lepton number isn’t conserved anyway once you add neutrino masses).

Gavin

I.e. could you say a little about the cost/benefits of continuing at FNAL, vs. a new facility at SNS?

“The existence of nonzero neutrino masses somewhat complicates the situation. Neutrinos are produced in weak interactions as chirality eigenstates. However, chirality of a massive particle is not a constant of motion; helicity is, but the chirality operator does not share eigenstates with the helicity operator. Free neutrinos propagate as mixtures of left- and right-handed helicity states, with mixing amplitudes on the order of mν / E. This does not significantly affect the experiments, because neutrinos involved are nearly always ultrarelativistic, and thus mixing amplitudes are vanishingly small (for example, most solar neutrinos have energies on the order of 100 keV – 1 MeV, so the fraction of neutrinos with “wrong” helicity among them can’t exceed 10 − 10).”

See complete article here.

Isn’t that explained in the article by
Lipari?

http://www-boone.fnal.gov/cross-sections/boone_reference.html

is in the observed energy range? It is not really clear to me how much of the total cross-section is a fit and what is a calculation. thanks,

B.

I’m always excited to hear news from my old haunt Fermilab.  The latest is a terrific new result on neutrinos from the MiniBooNE experiment.  There’s a terrific explanation on Cosmic Variance by Heather Ray.  The new results move us clos…

1. According to the Standard Model, neutrinos are massless.

2. According to a number of different experiments, neutrinos appear to be oscillate their flavor, which only works if they have mass.

3. This should only be happening at a single energy range (why?), and we have 3 different ranges provided by different experiments. The MiniBooNE experiment has ruled out one of the ranges, which was suggested by the results of the LSND experiment. Does this mean we don’t know how to currently explain the LSND data?

Is this somewhat correct?

You are completely correct, and this effect is included in the theory of neutrino masses as appears in standard texts. The projection of the neutrino spin along its direction of motion is it’s “helicity”. There is another measure of the “handedness” of a relativistic spin one half-particle called “chirality” that is easily defined in terms of the matrices appearing in the Dirac equation, and this measure does NOT depend on the reference frame in which you observe the particle. For massless particles these measures of “handedness” agree, but for massive particles they can disagree for exactly the reason you describe, ie. by moving past the particle you can reverse it’s direction of motion, hence it’s apparent helicity. When a neutrino is created by the weak interaction it is always created in a state that is left-handed as measured by *chirality*. For a neutrino that is not exactly massless, this means that there is a small amplitude (proportional to it’s mass divided by its energy), and hence a small probability, that it actually was created in a state that is right-handed as measured by *helicity*. If you run along in the direction of the neutrino you will see a greater probability for it to be in the “wrong helicity” state, which agrees with what I wrote above because you see it with less energy in your reference frame, so the mass divided by the energy (which gives the “wrong helicity” amplitude, hence probability) is larger. I hope that this helps!

Will someone be kind, though, and mark on the very first chart with the green blur and the blue and red spots, what part of parameter space MiniBooNE allows? Or is that left as a homework exercise?