Understanding the Forward Muon Deficit in Coherent Pion Production

Abstract

For any inelastic process $v_{\ell }+I\to {\ell }^{-}+F$ with $m_{\ell }=0$, the cross section at ${\theta }_{\ell }=0$ is given by Adler's PCAC theorem. Inclusion of the lepton mass has a dynamical effect (``PCAC-screening'') caused by interference of spin-zero (${\pi }^{+}$) and spin-one exchanges. This effect may be relevant to the forward suppression reported in recent experiments.

3 pages, 2 figures, presented at NuInt07, Fermilab, may 31 - june 3 2007