# Search results

1. ### I Tau decays

Thanks a lot! So the W boson decays into an up/down pair, but for some reason that pair has a higher probability to form a rho meson than a pion? Iso ne of the reason related to the fact that the rho is a vector while the pion is a scalar, while W is a vector?
2. ### I Tau decays

Hello! Tau decay has a branching ratio to a charged pion + neutral pion + tau neutrino much bigger than to a charged pion and a tau neutrino. Based on consideration of available phase space, I would imagine that adding an extra pion would decrease the branching ratio. Why is this happening...
3. ### I How do you get polarized charged particles?

I meant, how can you use synchrotron radiation to polarize electrons? Would any polarized light source work (e.g. a laser)? Or is there something special about the synchrotron radiation?
4. ### I How do you get polarized charged particles?

Thanks! What exactly do you mean by "by synchrotron radiation"?
5. ### I How do you get polarized charged particles?

Hello! how does one produced big ensembles of polarized charged particles (electrons, protons, muons etc.) for certain experiments? In the case of neutral particles (for example the nucleus in an atom) this could be done using a magnetic field, but I guess this won't work that straightforward...
6. ### I T-odd vs T-violation

Thank you for this! I will check that paper. However I still have a question (again please check this paper), as I am still not sure how to reconcile these 2 definitions. So in equation (1), they use the same formula as you did: $$\vec{d}=\int\vec{r}\rho d^3r$$ According to your argument, this...
7. ### I T-odd vs T-violation

That doesn't answer my question. We know that nature is not T-symmetric so there is no way to assume it is. But my questions is simply is the electron dipole moment, defined the way it is in the papers I mentioned, T-odd or T-even (I tend to trust those papers with few hundred citations more...
8. ### I T-odd vs T-violation

Thank you for your reply. So given that the (say electron) EDM is proportional to the spin (see my previous post and the 2 papers I mentioned), it means that the EDM is also T-odd (I guess this is my only confusion right now)?
9. ### I T-odd vs T-violation

I am really confused now. As far as I know, Schiff moment comes from a not total screening of the (possible) EDM by the electron cloud. You don't have a Schiff moment for an electron. My questions is purely about the electron EDM, so I am not sure I understand the Schiff moment argument in the...
10. ### I T-odd vs T-violation

Oh, I see now what you mean by dynamics. Basically the EDM appears through some loop diagrams which in themselves reflects some dynamics of the system. I guess it makes sense, but that is really confusing, especially that Wikipedia page putting the classical image next to the quantum...
11. ### I T-odd vs T-violation

What exactly do you mean by dynamics in this case? Equation 1 follows from Wigner-Eckart theorem, which basically reflects how the angular momenta can couple in a system. We didn't enforce any rotational symmetry into that equation, it follows from the fact that the electron has spin. I don't...
12. ### I T-odd vs T-violation

I am not really sure I understand. Equation 1 says, for an electron, that the EDM and the spin are parallel (or anti-parallel). There is no dynamical assumption (if by dynamical you mean actual motion of the particle). The spin of the electron is not actually the electron rotating (i.e. the spin...
13. ### I T-odd vs T-violation

Thank you for this! Did you get a chance to check the paper I suggested? They use the same formula as you for the electric dipole (eq 1) and then, in the comments after equation 3 they state that the formula is T-odd (please check the paper, it would be easier to formulate my questions once we...
14. ### I T-odd vs T-violation

I am not totally sure what you mean. Of course T-violation is a quantum mechanical results. We can't have T-violation (or P, or C) at a macroscopical scale. My questions was of course QM/QFT related. But I am not sure what you mean by spin degrees of freedom. J is the angular momentum of the...
15. ### I T-odd vs T-violation

Please check the paper I put the link for. It shows why d is T-odd. Basically d is proportional to J (angular momentum), same as ##\mu##, so they have the same behavior. (I could type here the derivation from there but it's easier to just check the paper)
16. ### I T-odd vs T-violation

Thank you for your reply! Related to your previous reply: I didn't say that E (the electric field) is odd under T (it is even). I said that the dot product ##d\cdot E## is odd under T. Also I don't think you are right with: "the electric dipole moment is even and the magnetic dipole moment is...
17. ### I T-odd vs T-violation

Hello! I am a bit confused by the difference between T-odd and T-violation. For example, I read that the existence of a fundamental particle EDM is a violation of time symmetry. However, placing an electric dipole in an electric field, would produce a hamiltonian (non-relativistically, which is...
18. ### I Nuclear charge radius formula

I am not sure what you mean by that. If you mean that the charge radius might not always be the best parameter to use, then that is right. No one is claiming that, and there are of course other parameters that enters the calculations beside the nuclear charge radius. BUT, if you need that one...
19. ### I Nuclear charge radius formula

That's right. The formula you mentioned comes mainly from assuming that the nucleus is a liquid drop i.e. it has a constant density (initially the formula was simply ##r_0A^{1/3}##, with ##r_0## being a constant). People still use this formula in many situation simply because it is easier to use...
20. ### I Neutrons inside a nucleus

Oh I see. So basically the extra mass of the neutron must add more energy than the mass of the proton plus the coulomb repulsion (roughly), in order for beta decay to happen, right?
21. ### I Neutrons inside a nucleus

Hello! Why can't we have as many neutrons as we want inside a nucleus? I understand that for protons you have the Coulomb repulsion, but what leads to an increase of energy when adding more neutrons (which in turns lead to beta decay or fission)?