High-mass dijet cross sections in photoproduction at HERA

Dijet differential cross sections for the reaction e/sup +/p to e/sup +/+jet+jet+X in the photoproduction regime have been measured with the ZEUS detector at HERA using an integrated luminosity of 42.7 pb/sup -1/. The cross sections are given for photon-proton centre-of-mass energies in the range 134 lt W lt 277 GeV. The differential cross sections as a function of the dijet mass, M/sup jj/, and of the dijet angular variables have been measured for 47 lt M/sup jj/ lt 160 GeV and compared to next-to-leading-order QCD calculations. The dijet events in the region 75 lt M/sup jj/ lt 100 GeV have been used to derive a 95% C.L. upper limit on the cross section for Z/sup 0/ photoproduction of sigma /sub e(+)p to e(+)Z(0)/X lt 5.9 ph. Upper limits on the photoproduction of new heavy resonances decaying into two jets are also presented for masses in the range between 60 GeV and 155 GeV