Search

We have studied the ππ andK systems centrally produced in proton proton collisions at 300 GeV/c and π+/p proton collisions at 85 GeV/c using the CERN Ω spectrometer. Clear evidence forS*/fo(975) production is observed. An analysis performed on the π+ π− mass spectrum in the 1.0 GeV region, using a coupled channel formalism, shows that it is possible to describe theS*/fo(975) effect with one single resonance once interference of theS*/fo(975) with theS-wave background is introduced. The resultingS*/fo(975) parameters aremo=979±4MeV,gπ=0.28±0.04,gK=0.56±0.18 corresponding to a pole position on sheet II at (1001±2)−i(36±4) MeV. Evidence is also found for a structure having a mass of 1472±12 MeV and a width of 195±33 MeV.

The reactionpp→pf(π+π−γ)ps, where theπ+π−γ system is centrally produced, has been studied at 300 GeV/c. Theπ+π−γ mass spectrum shows evidence for aρ0γ decay mode of theη′ (958) andf1 (1285). The branching ratio (f1(1285)→ηπ+π+)/(f1(1285)→ρ0γ) is found to be 5.0±0.7. No evidence is found for aρ0(770)γ decay mode of theE/f1 (1420) for which an upper limit BR (E/f1(1420)→ρ0γ)<0.08 at 95% CL is found.

The transverse momentum distributions for and ϕ (1020) have been studied in thept region between 2 and 4 GeV/c and central rapidity. The data analysed come from the WA77 experiment at CERN with a 300 GeV/c π− beam incident on a Be target. These distributions are well described by the functionpt−n withn∼8. A sample of simulated events from the Lund Monte Carlo in the same experimental conditions reproduces well the data.

We have performed a search for vector-vector final states centrally produced in proton proton interactions at 300 GeV/c using the CERN O spectrometer. Evidence is found for ??0 production in the reactionpp?pf(2p+2p-2p0)ps and for ?? production in the reactionpp?pf(2p+2p-2p0)ps. However no evidence is found for ?ø production in the reactionpp?pf(K+K-p+p-p0)ps.

We have studied the reactions where the system is centrally produced, at 85 GeV/c and 300 GeV/c using the CERN Omega spectrometer. A spin-parity analysis of theKS0K±p± system shows the presence of a strongJPC=1++ signal which we identify as theE/f1 (1420) meson. We also find evidence for the decayE/f1(1420)?KS0KS0p0 which determines theC-parity of this state to be positive. Alternative explanations of the data have been tested and ruled out. Hence we obtain the quantum numbers of theE/f1 (1420) to beIG(JPC)=0+(1+).

The reactionpp→pf(π+π−π0)ps, where the π+π−π0 system is centrally produced, has been studied at 300 GeV/c. The π+π−π0 mass spectrum shows evidence for the η, ω anda2 (1320) as well as an enhancement in thea1 (1260) region. A Dalitz plot analysis of the π+π−π0 system has been performed. Thea1 (1260) parameters coming from the fit of the 1+S wave arem=1208±15 MeV and Γ=430±50 MeV. No evidence is found for theh1(1170) orh1(1380).