# Cherenkov radiation from neutral composite particles

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1. Oct 18, 2015

### Garlic

Hello everyone,
Can atomic or subatomic neutral composite particles that consist charged particles emit cherenkov radiation if they are polarised strongly enough (and are fast enough)?

2. Oct 18, 2015

### Staff: Mentor

It's not impossible, but long before you get your first Cherenkov photon the compound disintegrates from scattering in the medium, loses all its energy or does something else that has nothing to do with Cherenkov radiation.

3. Oct 19, 2015

### snorkack

What if the composite particle cannot disintegrate because of colour confinement?

Neutrons have a magnetic dipole moment. Do neutral mesons also possess magnetic dipole moments?

Neutrons are capable of elastic scattering off a proton via strong interaction. But electrons are not subject to strong interaction. What is the prevalent mechanism for elastic scattering of neutrons from electrons: electromagnetic interaction with the magnetic dipole moment, or weak interaction?

4. Oct 19, 2015

### Staff: Mentor

Color confinement doesn't prevent anything if there is sufficient energy. On the other hand, color confined objects are too small for Cherenkov radiation anyway.
I would expect that, unless there is a symmetry preventing it.

5. Oct 19, 2015

Staff Emeritus
Spin-0 mesons have a symmetry preventing it. (In which direction does the moment point?) Spin-1 and higher don't have this problem, but they are too short lived to have a substantial interaction with a magnetic field. The best you can usually do is measure a transition magnetic moment.

6. Oct 20, 2015

### snorkack

Hydrogen atom does have a magnetic dipole moment - despite having spin zero. The spins of proton and electron are opposite and equally half, so cancel to zero - the magnetic moments of proton and electron are unequal, and leave a net magnetic moment.
Why then cannot a meson with spin zero consisting of two different quarks possess a net magnetic moment?

7. Oct 20, 2015

Staff Emeritus
Are you sure? What is $\sqrt{l(l+1)}$ in this case?

8. Oct 20, 2015

### snorkack

What are you signifying with l here?

9. Oct 20, 2015

Staff Emeritus
L is total angular momentum. Zero for parahydrogen.

10. Oct 20, 2015

### snorkack

Indeed. Zero total angular momentum because the spins of electron and proton are antiparallel and equal. Whereas the magnetic momenta are unequal, and actually in the same direction.

If electron and proton can have net magnetic moment despite having spin summed to zero, why cannot two quarks which are not each other´s antiparticles have a net magnetic moment despite having spin summed to zero?

11. Oct 20, 2015

If you are in an eigenstate of total spin, the individual spins are in a state $\uparrow \downarrow + \downarrow \uparrow$. When you operate the magnetic moment operator on that wavefunction, you get zero.