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Mass of an anti electron neutrino

by adimantium
Tags: anti, down quark, electron, mass, neutrino, up quark
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Oct4-13, 09:01 PM
P: 13
I can't seem to find the mass of an anti electron neutrino in MeV. I found that in beta radiation one down quark breaks into an up quark, an electron, and an anti electron neutrino. The mass in MeV of a down quark is 4.8, the mass of an up quark is 2.4 MeV, the mass in MeV of an electron is 0.511 MeV. So the mass of an anti electron neutrino should be 1.889 MeV. However I can't find a place to make sure I am right. Thank you and forgive me if i'm wrong.
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Oct4-13, 10:25 PM
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PF Gold
P: 2,602
Your calculation ignores the fact that the beta decay products typically carry kinetic energy. This makes it hard to use beta decay to measure the neutrino mass, since the neutrino masses are very small, probably around a few hundredths of an eV. The kinetic energy of the electron, for example, is typically at least a few % of its mass, so around a few thousand eV, which is around 5 orders of magnitude larger than the expected neutrino mass. An experiment would need a high sensitivity to measure the small neutrino mass.

Furthermore, because of neutrino oscillations, current experiments have not been able to measure the value of the electron neutrino flavor eigenstate.

There is a proposal for a new experiment sensitive to a mass of around ##0.2~\mathrm{eV}##. A review of this and other experiments is here. It may be possible in the next few years to have a direct measurement of a neutrino mass.
Oct5-13, 07:22 AM
P: 11,928
In addition to the good post of fzero: you cannot consider the quarks as isolated particles. The decay is a process of the whole nucleon or even the whole nucleus (if you don't have a free neutron). The released energy corresponds to the mass difference between initial and final nucleus (or neutron->proton for a free neutron).

Those light quark masses are problematic anyway - it is hard to measure them as you cannot see them as isolated quarks, and the values have a large uncertainty.

Aug30-14, 11:31 AM
P: 92
Mass of an anti electron neutrino

So the measurements that suggests that the electron neutrino may have a negative mass-squared value are wrong ?
Aug30-14, 12:15 PM
P: 919
which measurements gave such a thing? if such a thing exists then it's a tachyon.
Also a technique people use to measure the neutrino masses are the Kurie Plots:
For the negative masses you would be in the blue line of the Kurie Plot.
Aug30-14, 02:47 PM
P: 11,928
There are no measurements that are incompatible with real and positive neutrino masses.

And how is this related to the old thread from 2013?
Aug31-14, 12:20 AM
P: 92
I didnt want to open a new thread ...

So what are these guys talking about ?
"The unphysical result of the negative mass square of the electron neutrinos recently reported in several tritium β-decay experiments, is one of the most attractive subjects among remaining physical problems"
"In view of erroneous and unphysical mass results obtained by some earlier experiments in β-decay"
Aug31-14, 03:59 AM
P: 597
Beta decay experiments set out to determine the neutrino mass found their best fit was for negative mass squares. However, the result were still compatible with positive mass squares and so there was never really a big problem. The expriments are therefore not wrong, they are simply not sensitive enough to make a definite statement.

As is often the case, physicists like to theorize what could cause a result for which there is only a weak hint in case more precise measurements would confirm it.
Aug31-14, 04:34 PM
P: 11,928
Those are old measurements - the linked paper is from 1998 and refers to papers from 1991 to 1995.

A more recent and more precise measurement has been done in Mainz, they quote a squared mass of ##-1.6 \pm 2.5 \pm 2.1 eV^2## - this is an example where the best fit value is negative, but a small positive mass is well in agreement with the measurement (less than 1 sigma away).

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