Inclusive η production at low transverse momentum in 63 GeV ppcollisions at the cern intersecting storage rings

The inclusive production of η-mesons in pp collisions at √ s=63GeV and ϑ_CM=90° has been measured for p_T<1.5GeV/c. The η/π ratio decreases from its previously measured asymptotic value of η/π ∼ 0.5 at high transverse momentum, to η/π ≈0.3 at P_T = 750MeV/c and η/π ≈ 0.01 at P_T=300MeV/c, in a way that consistent with phase-space considerations, e.g. m_T scaling. The η/π ratio, integrated from 0.2-1.5 GeV/ c, is found to be η/π=0.07±0.055.