# Physics GCE Question - not allowed to use conservation of baryon/lepton number

1. Jan 22, 2012

### dalcde

1. The problem statement, all variables and given/known data
State and discuss how three conservation laws apply to this decay event (D0 -> K++$\pi^-$)

2. Relevant equations

3. The attempt at a solution
I talked about conservation of charge, lepton lepton number and baryon number. However, the marking scheme (actually the examiner's report) says "some lost marks by
trying to apply rules such as lepton number and strangeness." I believe it means that conservation of lepton number is regarded as wrong (and baryon number too, probably). Does anyone know why it is so (I know lepton numbers is silly here...)? Or is it my misunderstanding of the statement? (I have no problem with the "strangeness" part because it is not conserved by weak interactions)

Edit: This is question 18 b iv of GCE June 2011 Physics Unit 4.