Upper limits for the production of new light gauge bosons in 0 , and 0 decays have been obtained with the Crystal Barrel detector. The kinematically well-constrained reactions pp ! 0 0 P have been studied, where P 0 ; ; 0 decays through the emission of a single photon recoiling against a missing state X. X can be a long-lived weakly interacting particle or X !. This paper gives full detail of the analysis of our previous work and extends the search to 0 decay. No signal has been observed and branching ratio upper limits (90 % C:L:) of 6 10 ?5 have been obtained for masses of the gauge boson lying between 65 MeV and 125 MeV (0 decay), 6 10 ?5 , for X masses between 200 MeV and 525 MeV (decay), and 4 10 ?5 , for X masses between 50 MeV and 925 MeV (0 decay). The 0-decay limit represents a factor of 4 to 8 (depending on the X-mass) improvement when compared to the existing limit, whereas the and 0 decay limits have been measured for the rst time, thereby extending the M X range from 125 MeV up to 925 MeV.

We have measured the branching ratio for the radiative decay ω → ηγ with ω mesons produced in antiproton-proton annihilation at rest into π0ω and ηω. Taking into account ϱ - ω mixing we find a branching ratio B(ω → ηγ) = (6.6 ± 1.7) × 10−4, in accord with the constructive interference solution in other experiments. The upper-limit for the direct radiative decay ω → 3γ is 1.9 × 10−4 at 95% confidence level.

The distribution of m(π+π−) in the decay η′ → π+π−γ has been measured with the Crystal Barrel detector. The results are based on a total of 7392 observed η′ decays. The box anomaly constant is extracted from this and its value is found to agree well with theoretical expectations. The pseudoscalar nonet parameters (f1, f8 and θPS) are determined. Finally, we find that there is a problem of consistency between QCD and the standard VDM assumption.

A study of p̄-annihilation in liquid deuterium into π−π0π0 and a spectator-proton is presented. A cut on the proton-momentum of ≤ 100 MeV/c ensures that annihilation takes place on a quasi-free neutron. A partial wave analysis shows contributions from three vector mesons, with masses and widths of (763.7 ± 3.2; 152.8 ± 4.3), (1411 ± 14; 343 ± 20); (1780−29+37; 275 ± 45) MeV/c2, respectively.

The π+π− invariant mass distribution produced in pp annihilation at rest and recoiling against η mesons exhibits large interference between the amplitudes for ϱη and ωη production. The interference can be quantitatively described within the framework of ϱ-ω interference. We find full coherence between the ϱω-ωη production amplitudes and a vanishing relative production phase. The implications of this result for pp annihilation dynamics are discussed.

Crystal Barrel data on <(p)over bar p> --> 5 pi(0) at rest are presented. Mass spectra for 2 pi(0) combinations, 3 pi(0) and 4 pi(0) and decay angular distributions all differ significantly from phase space. We present several ways of fitting the data. All agree on the definite presence of the f(0)(1500), observed in its 4 pi(0) decay mode. It can decay into pi pi(1300) and into sigma sigma where sigma stands for the full pi pi S-wave amplitude.

The f0(1500) is observed in its KK decay mode in an amplitude analysis of high statistics data in pp annihilation at rest into π0KLKL. The mass and width is found to be (m, Γ) = (1515 ± 20, 105 ± 15) MeV. A comparison of the decay rate into 2π0 shows that this state cannot be dominantly ss. The f′2(1525) has been observed for the first time in pp annihilation and its production rate is consistent with the expectation from the OZI rule.

Data on\(\bar pp \to \eta \pi ^0 \pi ^0 \pi ^0 \) taken at beam momenta of 1.2 and 1.94 GeV/c reveal evidence for twoI=0J PC=2−+ resonances inηππ. The first, at 1645±14(stat.)±15(syst.) MeV with width 180 −21 +40 ±25 MeV, decays toα 2(1320)π withL=0. It may be interpreted as the\(q\bar q^1 \) D 2 partner ofπ 2(1670). A strong signal is also observed just above threshold inf 2(1270)η withL=0. It is 11–22 times stronger than is expected for the high mass tail of the 1645 MeV resonance. It can be fitted as a second 2−+ resonance at 1875±20±35 MeV with width 200±25±45 MeV. A third resonance havingJ PC=2++ is observed at 2135±20±45 MeV withΛ=250±25±45 MeV, decaying to botha 2(1320)π andf 2(1270)η withL=1. There is no evidence for resonances with decays toa 0(980)π, ση orf 0(980)η.

(p) over bar p annihilation is a very promising field in searches for interesting mesonic states. A wide variety of different mesonic final states is found with the Crystal Barrel detector. Many of these channels can be traced back to original (p) over bar p transitions into two mesons. This report summarizes Crystal Barrel results on two-body reactions found in (p) over bar p annihilation in flight into all neutral final states. The final states (p) over bar p --> 0(-)0(-) and (p) over bar p --> 0(-)omega (0(-) = pi(0), eta) for which partial wave analyses have been performed will be emphasized. The highest contributing angular momenta found in these analyses are J(max) = 3HBAR for 600 MeV/c, J(max) = 4HBAR for 1200 MeV/c, and J(max) = 6HBAR for 1940 MeV/c.

Upper limits for the production of new light gauge bosons in pi(0), eta and eta' decays have been obtained with the Crystal Barrel detector. The kinematically well-constrained reactions <(p)over bar p> --> eta(0) eta(0) P have been studied, where P = eta(0), eta eta' decays through the emission of a single photon recoiling against a missing state X. X can be a long-lived weakly interacting particle or it decays into <nu(nu)over bar>. The resulting branching ratio upper limits (90% C.L.) are: 6 x 10(-5) for masses M(X) of the missing particle X lying between 65 MeV/c(2) and 125 MeV/c(2) (pi(0) decay), 6 x 10(-5) for M(X) between 200 MeV/c(2) and 525 MeV/c(2) (eta decay), and 4 x 10(-5) for M(X) between 50 MeV/c(2) and 925 MeV/c(2) (eta/decay). The eta(0)-decay limit represents an improvement by a factor of 4 to 8 (depending on M(X)) when compared to the existing limit, whereas the eta and eta' decay limits have been measured the first time, thereby extending the M(X) range from 125MeV/c(2) up to 925 MeV/c(2).

A partial-wave analysis of the reaction p $($) over bar$$ p-->pi(0) pi(0) pi(0) has been performed using a high-quality high-statistics data set of 712 000 events. In addition to the f(0)(975) and f(0)(1300), the scalar resonance with mass m = (1500 +/- 15) MeV and width Gamma = (120 +/- 25) MeV is necessary to describe the data.