As part of a measurement~\\cite{phiprl} of the cross section
of $\\phi$ meson photoproduction to high momentum transfer, we measured the
polar angular decay distribution of the outgoing $K^+$ in the
channel $\\phi \\rightarrow K^+K^-$ in the $\\phi$ center-of-mass
frame (the helicity frame). We find that $s$-channel helicity
conservation (SCHC) holds in the kinematical range where $t$-channel
exchange dominates (up to $-t \\sim 2.5$~GeV$^2$ for $E_{\\gamma}$~=~3.6 GeV).
Above this momentum, $u$-channel production of a $\\phi$
meson dominates and induces a violation of SCHC.
The deduced value of the $\\phi NN$ coupling constant lies in the upper range of
previously reported values. |
