Decay of pion

1. Mar 23, 2009

ruchika

Why the decay of neutral pion to electron positon pair is forbidden?

Last edited: Mar 23, 2009
2. Mar 23, 2009

humanino

Last edited: Mar 23, 2009
3. Mar 23, 2009

blechman

you know, way back when i wrote down on a test that this decay was forbidden. my professor has a good laugh: he told me that i just "disproved" his PhD thesis!

4. Mar 23, 2009

malawi_glenn

it is not forbidden, I did my Diploma thesis on that decay! ;-P

i.e I am in the same situation as blechman's teacher was ;-)

5. Mar 23, 2009

clem

The decay into electron-positron has to proceed through two virtual photons, one leading to the e-p pair and the other being absorbed by one of the pair. This makes the pi-->e p
rate much slower than the two gamma decay.
If the term "forbidden" is used in the way it is used in beta decay, then the e-p is
"forbidden", as confirmed by the experimental rate.

6. Mar 23, 2009

malawi_glenn

it is second order, so it depends on what one means by "forbidden"

7. Mar 23, 2009

humanino

Here I think it means that it violates helicity conservation (which is expected for the leading order in the Bjorken limit).

8. Mar 31, 2009

LongLiveYorke

Isn't it also helicity suppressed?

9. Mar 31, 2009

malawi_glenn

yes, see the post above yours =)