Measurement of $J/\ddot{I}ˆ$ helicity distributions in inelastic photoproduction at HERA

Abstract

The $J/\ddot{I}ˆ$ decay angular distributions have been measured in inelastic photoproduction in $ep$ collisions with the ZEUS detector at HERA, using an integrated luminosity of 468 $p{b}^{-1}$. The range in photon-proton centre-of-mass energy, $W$, was 50 $<W<$ 180 $GeV$. The $J/\ddot{I}ˆ$ mesons were identified through their decay into muon pairs. The polar and azimuthal angles of the $\hat{I}{¼}^{+}$ were measured in the $J/\ddot{I}ˆ$ rest frame and compared to theoretical predictions at leading and next-to-leading order in QCD.

15 pages