partial wave analysis of antiproton–proton annihilation data in flight at 900 MeV/c into π ^0π ^0η , π ^0ηη and K^+K^-π ^0 is presented. The data were taken at LEAR by the Crystal Barrel experiment in 1996. The three channels have been coupled together with ππ -scattering isospin I = 0 S- and D-wave as well as I = 1 P-wave data utilizing the K-matrix approach. Analyticity is treated using Chew–Mandelstam functions. In the fit all ingredients of the K-matrix, including resonance masses and widths, were treated as free parameters. In spite of the large number of parameters, the fit results are in the ballpark of the values published by the Particle Data Group. In the channel π ^0π ^0η a significant contribution of the spin exotic I^G=1^- J^PC=1^-+ π _1 -wave with a coupling to π ^0 η is observed. Furthermore the contributions of ϕ (1020) π ^0 and K^*(892)^± K^∓ in the channel K^+K^-π ^0 have been studied in detail. The differential production cross section for the two reactions and the spin-density-matrix elements for the ϕ (1020) and K^*(892)^± have been extracted. No spin-alignment is observed for both vector mesons. The spin density matrix elements have been also determined for the spin exotic wave.

Abstract A partial wave analysis of antiproton–proton annihilation data in flight at 900 $$\mathrm {MeV/}c$$ MeV/c into $${\pi ^0\pi ^0\eta }$$ π0π0η , $${\pi ^0\eta \eta }$$ π0ηη and $${K^+K^-\pi ^0}$$ K+K-π0 is presented. The data were taken at LEAR by the Crystal Barrel experiment in 1996. The three channels have been coupled together with $$\pi \pi $$ ππ -scattering isospin I = 0 S- and D-wave as well as I = 1 P-wave data utilizing the K-matrix approach. Analyticity is treated using Chew–Mandelstam functions. In the fit all ingredients of the K-matrix, including resonance masses and widths, were treated as free parameters. In spite of the large number of parameters, the fit results are in the ballpark of the values published by the Particle Data Group. In the channel $${\pi ^0\pi ^0\eta }$$ π0π0η a significant contribution of the spin exotic $$I^G=1^-$$ IG=1- $$J^{PC}=1^{-+}$$ JPC=1-+ $$\pi _1$$ π1 -wave with a coupling to $$\pi ^0 \eta $$ π0η is observed. Furthermore the contributions of $$\phi (1020) \pi ^0$$ ϕ(1020)π0 and $$K^*(892)^\pm K^\mp $$ K∗(892)±K∓ in the channel $${K^+K^-\pi ^0}$$ K+K-π0 have been studied in detail. The differential production cross section for the two reactions and the spin-density-matrix elements for the $$\phi (1020)$$ ϕ(1020) and $$K^*(892)^\pm $$ K∗(892)± have been extracted. No spin-alignment is observed for both vector mesons. The spin density matrix elements have been also determined for the spin exotic wave.

A partial wave analysis of antiproton-proton annihilation data in flight at 900 $MeV/c$ into $\pi^0 \pi^0 \eta$ , $\pi^0 \eta \eta$ and $K^+ K^- \pi^0$ is presented. The data were taken at LEAR by the Crystal Barrel experiment in 1996. The three channels have been coupled together with $\pi\pi$-scattering isospin I=0 S- and D-wave as well as I=1 P-wave data utilizing the K-matrix approach. Analyticity is treated using Chew-Mandelstam functions. In the fit all ingredients of the K-matrix, including resonance masses and widths, were treated as free parameters. In spite of the large number of parameters, the fit results are in the ballpark of the values published by the Particle Data Group. In the channel $\pi^0 \pi^0 \eta$ a significant contribution of the spin exotic $I^G=1^-$ $J^{PC}=1^{-+}$ $\pi_1$-wave with a coupling to $\pi^0 \eta$ is observed. Furthermore the contributions of $\phi(1020) \pi^0$ and $K^*(892)^\pm K^\mp$ in the channel $K^+ K^- \pi^0$ have been studied in detail. The differential production cross section for the two reactions and the spin-density-matrix elements for the $\phi(1020)$ and $K^*(892)^\pm$ have been extracted. No spin-alignment is observed for both vector mesons. The spin density matrix elements have been also determined for the spin exotic wave.

A search for the exclusive production of the Zc±(3900) hadron by virtual photons has been performed in the channel Zc±(3900)→J/ψπ±. The data cover the range from 7 GeV to 19 GeV in the centre-of-mass energy of the photon–nucleon system. The full set of the COMPASS data set collected with a muon beam between 2002 and 2011 has been used. An upper limit for the ratio BR(Zc±(3900)→J/ψπ±)×σγN→Zc±(3900)N/σγN→J/ψN of 3.7×10−3 has been established at the confidence level of 90%.

We describe partial-wave analyses of the systems π-ηand π-η' produced in interactions of a π- beam (190 GeV/c) with a liquid hydrogen target. The data were recorded during the 2008 COMPASS run, where a slow recoiling proton (|t|>0.1 GeV^2) was required by the trigger. We compare analyses of the π-ηand π-η' data. Significant contributions can be attributed to the resonances a_2(1320), observed in the D_+-wave, and a_4(2040), observed in the G_+-wave. Between the two systems, we find similar compositions of the even partial waves D_+ and G_+ after taking phase-space factors into account, but a much enhanced P_+-wave in π-η'. Relative phase-differences indicate a large incoherent contribution of in the P_+-wave of the η'π- system, but other interpretations are not excluded. The known resonances a_2(1320), a_4(2040) and their parameters could be extracted from the data; their branchings are found to roughly agree with predictions from ηη' mixing.

Data are presented on the reaction p̄p → ωωπ at rest from the Crystal Barrel detector. These data identify a strong signal due to f2(1565) → ωω. The relative production from initial p̄p states P2, P1 and S0 is well determined from ωω decay angular correlations; P-state annihilation dominates strongly. A combined fit is made with data on p̄p → 3π at rest, where f2(1565) → ππ is observed. A Flatté formula is fitted to the f2(1565), including the s-dependence of decay widths to ωω and ρρ. The data then determine the K-matrix mass, M = 1598± 11(stat)± 9(syst) MeV. The decay width to 2π is very small, of order 2% of the total width. We investigate the f2(1565) through its decays to ωω in the process p̄p → ωωπ at rest. Data on p̄p → 3π at rest are also used to estimate relative widths to ππ and ωω. The first clear identification of the f2(1565) was by May et al. in the Asterix experiment on p̄p → πππ at rest [1,2]. Subsequently, it has been identified by the Obelix collaboration in n̄p → πππ [3], and in Crystal Barrel data on p̄p → 3π at rest [4,5]. However, it has become clear that the f2(1565) also couples strongly to ωω (and therefore probably to ρρ). Abele et al. [6] found a strong cusp in the ππ D-wave at the ωω threshold in the 3π data. This led to the identification of f2(1565) as the same 2 + resonance as observed by GAMS [7] and VES [8] in ωω just above threshold. Their results are listed under f2(1640) by the Particle Data Group (PDG) [9], who also list other sightings there and under f2(1565). The properties of this resonance have remained elusive. Here, we show that it is important to fit with a Flatté formula which includes the s-dependence of decays to ππ, ρρ and ωω; there is a sharp cusp at 1564 MeV due to the opening of the ωω channel. In outline, the elements in the analysis are as follows. Firstly, ωω correlations in the Crystal Barrel data on the ωωπ channel determine well the relative amounts of annihilation from initial states S0, P1 and P2. Secondly, earlier Crystal Barrel data on the 3π 0 channel determine well the lower edge of the resonance. Both of these sets of data are readily fitted with a Breit-Wigner amplitude which includes the s-dependence of widths for decays to ρρ, ωω and ππ. However, Now at IHEP, Beijing 100039, China

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.

Antiproton-proton annihilation into 0 has been studied with the Crystal Barrel spectrometer at CERN at an incident beam momentum of 1.94 GeV/c. The data were taken with a trigger requiring neutral nal states. A new isovector state, the a2(1660) decaying to 0 , is observed. In the invariant mass region around 2.1 GeV=c 2 , strong production of a heavy resonance is required, but our analysis does not distinguish between J P = 0 + , 2 + and 4 +. The production of the f0(1500) in reactions in ight is also observed.

Prominent KK¯ resonances observed in the in-flight annihilation of p¯p into K+K−π0 include f2(1270), f0(1500), f2′(1525), ϕ(1680)/ρ(1700) and a state at 1750 MeV/c2 consistent with f0(1710). The reaction cross sections σ(p¯p→X(K+K−)π0) are obtained by means of a partial wave analysis. When these are combined with known KK¯ partial widths, the resulting production rates of presumably non-nn¯ states, X=f0(1710) and f2′(1525), are found to be suppressed by an order of magnitude compared to f0(1500) and f2(1270), respectively.

Five scalar isoscalar (f(0)) mesons below 1.8 GeV/c(2) are experimentally established according to the Review of Particle Physics 2004. Five f(0) ground states are theoretically expected, below 1.8 GeV/c(2): two q (q) over bar, two q(2)(q) over bar (2) and a glueball. There is no safe prediction how these states mix. Two of the 5 observed f(0) resonances are very broad and their mass, width and decay branching ratios have large uncertainties; we cannot even exclude they belong to a single superwide resonance. The glueball can be mixed into any of the 5 or 4 observed f(0) mesons. Although the f(0) sector is at the most difficult edge of meson spectroscopy, there is hope to obtain consistent experimental results allowing to determine the composition of the observed mesons if experimenters agree on a suitable formalism to extract resonance parameters in this complex environment.

We report on a study of four reactions in \(\bar{\mathrm p}{\mathrm p}\) annihilation at rest, of \(\bar{\mathrm p}{\mathrm p} \rightarrow 2\pi^ + 2\pi^-\eta\) , \(\bar{\mathrm p}{\mathrm p} \rightarrow 2\pi^ + 2\pi^- 2\pi^0\) , \(\bar{\mathrm p}{\mathrm p} \rightarrow 2\pi^ + 2\pi^-\gamma\) and \(\bar{\mathrm p}{\mathrm p}\rightarrow 4\pi^0\eta\). The \(\eta'\) and the \(\eta\) (1440) are seen in their decays into \(\pi^ + \pi^-\eta\), \(\pi^0\pi^0\eta\) and \(\pi^ + \pi^-\gamma\) ; no signal is seen in the \(4\pi\) invariant mass distribution. Branching ratios for \(\eta'\) and \(\eta\) (1440) production and decay into the different channels are determined. In particular we derive the ratio \(\Gamma_{\eta (1440)\rightarrow\pi^ + \pi^-\gamma}/ \Gamma_{\eta (1440)\rightarrow\pi^ + \pi^-\eta} = 0.111\pm 0.064\).

. We report on a study of four reactions in p̅p annihilation at rest, of p̅p→ 2π^ + 2π^-η , p̅p→ 2π^ + 2π^- 2π^0 , p̅p→ 2π^ + 2π^-γ and p̅p→ 4π^0η . The η' and the η (1440) are seen in their decays into π^ + π^-η , π^0π^0η and π^ + π^-γ ; no signal is seen in the 4π invariant mass distribution. Branching ratios for η' and η (1440) production and decay into the different channels are determined. In particular we derive the ratio Γ_η (1440)→π^ + π^-γ/ Γ_η (1440)→π^ + π^-η = 0.111± 0.064 .

Data are presented on antiproton neutron annihilation at rest into omegapi (-) pi(0) taken with the Crystal Barrel detector at LEAR (CERN) using a liquid deuterium target. The partial wave analysis shows evidence for at least two omegapi vector resonances above the rho(770) ground-state. Possible evidence for a third rho' state with a mass around 1180 MeV is discussed. The results are compared to model dependent predictions concerning the nature of the rho' states. (C) 2004 Elsevier B.V. All rights reserved.

Annihilation of antiprotons and protons at rest into neutral particles has been studied with the Crystal Barrel detector at LEAR. Annihilation frequencies are determined for final states containing π0, η, η′ and ω mesons using a liquid and a room temperature, 12 bar, gaseous hydrogen target. Including annihilation frequencies for production of neutral kaons from other experiments, the identified reactions for annihilation in liquid hydrogen add up to a branching fraction of (3.56±0.28)% per annihilation compared to the frequency of (3.50±0.30)% with which we observe the all-neutral decay modes inclusively. Since the exclusive final states are normalized to the Crystal Barrel measurement of the π0π0 branching ratio, the latter result is strongly supported by this present study.