Sector of the 2++ mesons: Observation of the tensor glueball

Data of the Crystal Barrel and L3 collaborations clarified essentially the situation in the 2++ sector in the mass region up to 2400 MeV, demonstrating the linearity of (n, M2) trajectories, where n is the radial quantum number of a quark–antiquark state with mass M. We discuss these data and show that there exists a superfluous state for the (n, M2) trajectories: a broad resonance f2(2000). We pay special attention to the reactions in the mass region 1990–2400 MeV where, together with f2(2000), four relatively narrow resonances are seen: f2(1920), f2(2020), f2(2240), f2(2300). We analyze the branching ratios of all these resonances and show that only the decay couplings of the broad state f2(2000) → π0π0, ηη, ηη′ satisfy relations inherent in the glueball decay.