# Homework Help: Forbidden D meson decay

1. May 13, 2013

### sunrah

1. The problem statement, all variables and given/known data
Why is D*+(2010) → D+(1869)π0 allowed via the strong interaction but Ds*+(2110) → Ds+(1969)π0 forbidden.

The numbers in the brackets are masses in MeV.

2. Relevant equations

3. The attempt at a solution
My guess was that mass was not conserved, but if π0 is 135 MeV then it is. Strangeness is also conserved. Charge is also conserved. Isospin is also conserved. What else is there to consider?

2. May 14, 2013

### sunrah

ok so I see that for the allowed process we have:

$|c\bar{d}\rangle \longrightarrow |c\bar{d}\rangle|d\bar{d}\rangle$
for example and for the forbidden process we have:

$\\ |c\bar{s}\rangle \longrightarrow |c\bar{s}\rangle|d\bar{d}\rangle$

my question is does the first process conserve quarks? if so how? I think that the strong interaction can create a quark-antiquark pair from either an up or down quark. But the antidown on the left could create a π+ particle but where does the other down quark come from to make the D+ meson? thanks

Last edited: May 14, 2013
3. May 14, 2013

### sunrah

here is a stab at answering my own question.
in the first allowed process, the D*+ particle decays producing a $d\bar{d}$

pair via a gluon and then the $\bar{d}$ joins with the charm quark forming D*+ and the $d$-quark with

the $\bar{d}$-quark from the left hand side forming the pion. is that right?

but i still dont know why the second process is not allowed. i think it is allowed under the weak force but why and why not under the strong

thanks

Last edited: May 14, 2013