
Neutrino discovery–a step closer to finding charge-parity violation - jonbaer
https://phys.org/news/2017-06-neutrino-discoverya-closer-charge-parity-violation.html
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qubex
"Effect not big enough" implies a judgement about how much matter/antimatter
was available to begin with... a tiny effect is entirely sufficient to produce
the observable universe if one purports to begin with a truly colossal initial
amount of matter/antimatter.

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nimih
Since matter-antimatter annihilation produces radiation, what prevents us from
estimating the size of the effect by measuring the background radiation of the
universe and comparing it to the amount of observable matter?

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qubex
I presume the volume of the Universe. We can measure average density of
residual radiation but getting the total value of energy requires multiplying
by volume. Much of the universe's volume may be hidden behind a cosmological
horizon (basically, the idea that as the universe's rate of expansion
accelerates the greater the distance from us (Hubble's constant), eventually
the rate of expansion exceeds the _c_ and thus light from that part of the
universe can never reach us, making it unobservable).

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AnimalMuppet
Stupid question: Is neutrino oscillation deterministically sequential? That
is, does an electron neutrino always turn into a muon neutrino, which then
always turns into a tau neutrino, which then always turns into an electron
neutrino (or the reverse order)? Or does an electron neutrino sometimes turn
into a muon neutrino, and sometimes into a tau neutrino?

If it's sequential, and if the antineutrino sequences in the opposite order,
this effect could be explained just by the distance of the beam run being a
fraction of the oscillation distance such that it's hard to get anti electron
neutrinos, because at that distance, you're getting anti tau neutrinos
instead.

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frumiousirc
A neutrino is born in a weak eigen state (e,mu,tau) and propagates as a mass
eigen state (m1,m2,m3). The two bases are related by a rotation matrix of
three angles and three phases of which one, the CP violation phase, can in
principle be measured with long baseline neutrino experiments. The oscillation
happens because each mass state propagates at a different frequency. So while
a numu starts out with some fraction of m1, m2 and m3 states, it soon becomes
a different mixture which is neither nue, numu nor nutau. Instead, when the
neutrino interacts, it does so with some admixture probability of doing so in
the form of each possible flavor.

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qubex
So it's basically a Markov Chain kind of process, but on continuum of time
rather than in discrete steps?

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frumiousirc
I guess you could couch the concept in this way but I have not ran across this
approach to do calculations.

In vacuum the oscillation probability (ie, the vector holding probability
amplitude saying how much of "e-ness", "mu-ness" and "tau-ness" the neutrino
has over time) is analytic and almost trivial to apply.

In the presence of matter, forward elastic interactions with electrons in the
matter can "pop" or "reset" the neutrino back to a nue weak eigenstate. This
is the so-called "matter effect". If the density is constant one can rewrite
the oscillation probability formula into a form that is the same as the vacuum
one. So, again, easy to calculate.

When going through variable matter densities one must, to be proper, solve a
differential equation. Computationally, this is done by stepping the equation,
eg with Runge-Kutta. Happily for us humans doing experiments at home, if the
matter in question is the Earth then the fact that its matter density is close
to uniform in bands (crust, mantle, core) one can do a step-wise constant
density approximation that's pretty close to a full solution and much faster.

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gorhill
> implies that matter—including galaxies, stars, and even humans—should have
> been annihilated by the equal amounts of anti-matter.

That is an odd sentence: "Even humans" after enumerating "galaxies, stars".

