Resonance production in central pp collisions at the CERN Omega Spectrometer

A study of resonance production in central pp collisions is presented as a function of several kinematical variables. In particular the difference in the transverse momentum (dP T) of the exchanged particles shows that undisputed q ¯ q mesons are suppressed at small dP T whereas glueball candidates are enhanced and in addition, the azimuthal angle φ gives information on the nature of the Pomeron. The Omega central production experiments (WA76, WA91 and WA102) were designed to study exclusive final states formed in the reaction pp−→p f X 0 p s , where the subscripts f and s refer to the fastest and slowest particles in the laboratory frame respectively and X 0 represents the central system. Such reactions are expected to be mediated by double exchange processes where both Pomeron and Reggeon exchange can occur. The trigger was designed to enhance double exchange processes with respect to single exchange and elastic processes. Details of the trigger conditions, the data processing and event selection have been given in previous publications [1]. The experiments have been performed at incident beam momenta of 85, 300 and 450 GeV/c, corresponding to centre-of-mass energies of [2] of the evolution of the different exchange mechanisms with centre of mass energy, exchange respectively. Hence we expect Double Pomeron Exchange (DPE) to be more significant at high energies, whereas the Reggeon-Reggeon and Reggeon-Pomeron mechanisms will be of decreasing importance. The decrease of the non-DPE cross section with energy can be inferred from data taken by the WA76 collaboration using pp interactions at √ s of 12.7 GeV and 23.8 GeV [3]. The π + π − mass spectra for the two cases show that the signal-to-background ratio for the ρ 0 (770) is much lower at high energy, and the WA76 collaboration report that the ratio of the ρ 0 (770) cross sections at 23.8 GeV and 12.7 GeV is 0.44 ± 0.07. Since isospin 1 states such as the ρ 0 (770) cannot be produced by DPE, the decrease of the ρ 0 (770) signal at high √ s is consistent with DPE becoming relatively more important with increasing energy with respect to other exchange processes. Due to the fact that there was no electromagnetic calorimeter in the WA76 experiment at √ s of 12.7 GeV, the s dependence of only a small number of states can be determined. The states for which the s dependence …