Helicity conservation and meson diffraction dissociation

Abstract

In a Deck-model description of meson diffraction dissociation, we study the contribution made to the low-mass enhancement by the vector-meson-exchange Deck amplitudes. The vector-exchange amplitudes are parametrized with the help of data on the electroproduction of $\rho$ mesons. Cross sections for vector exchange are compared to the standard pseudoscalar-meson-exchange Deck results and are found to be comparable in specific cases. A detailed spin and helicity amplitude analysis shows that the vector-exchange Deck amplitudes provide a low-mass system which satisfies approximate $s$-channel helicity conservation, whereas the pseudoscalar-exchange terms yield approximate $t$-channel helicity conservation. Combining the two contributions, we show that approximate $s$-channel helicity conservation holds in $\mathrm{Kp}\to \left(\rho K\right)p$ and in $\mathrm{Kp}\to \left(\omega K\right)p$. However, $t$-channel helicity conservation is expected in $\mathrm{Kp}\to \left(K^{*}\pi \right)p$, $\pi p\to \left(\rho \pi \right)p$, and $\mathrm{Kp}\to \left(\phi K\right)p$. These results agree with data. The relevance of these results to the interpretation of the $Q$-mesonresonance region is discussed.