A study of the pi^0pi^0 system produced in charge exchange and central collisions

A study of the $\pi^0\pi^0$ system produced in charge exchange $\pi^-p$ collisions at 38 and 100 GeV/c and in central $pp$ interactions at 450 GeV/c has been carried out. The $S$ wave has rather a complicated structure in both processes indicating the existence of several scalar resonances. The $f_0(980)$ and $f_0(1500)$ appear as dips at 1 and 1.5 GeV in the $S$ wave for charge exchange reaction, and as shoulders at these masses in the $S$ wave for central production. The production of the $f_0(980)$, $f_0(1300)$ and $f_0(1500)$ in the reaction $pp \to p_f\pi^0\pi^0p_s$ as a function of the $dP_{T}$ kinematical filter shows the behaviour differed from what has been observed for the undisputed $q\bar{q}$ mesons. An extra $f_0(2000)$ state is seen in the $S$ wave for charge exchange reaction as a dip at 2 GeV. Resonances with higher spins, $f_2(1270)$, $f_4(2050)$ and $f_6(2510)$, have also been studied. All the three mesons are produced in the reaction $\pi^-p\to\pi^0\pi^0{n}$ mainly via an one-pion exchange for small $-t$, whereas a natural-parity exchange domimates for large $-t$. The behaviour of the centrally produced $f_2(1270)$ as a function of the $dP_{T}$ is consistent with what has been observed for other $q\bar{q}$ states.Comment: 6 pages, 6 figures, use file stwol.sty, presented at International High-Energy Physics Euroconference in Quantum Chromodynamics, 2-8 July 1998, Montpellier, France on behalf of the GAMS and WA102 Collaboration

Study of the ηπo\eta\pi^o system in the mass range up to 1200 MeV

The reaction $\pi^-p \to \eta\pi^o n$ has been studied with GAMS-2000 spectrometer in the secondary 38 GeV/c $\pi^-$-beam of the IHEP U-70 accelerator. Partial wave analysis of the reaction has been performed in the $\eta\pi^o$ mass range up to 1200 MeV. The $a_0(980)$-meson is seen as a sharp peak in S-wave. The $t$-dependence of $a_0(980)$ production cross section has been studied. Dominant production of the $a_0(980)$ at a small transfer momentum $t$ confirms the hypothesis of Achasov and Shestakov about significant contribution of the $\rho_2$ exchange ($I^GJ^{PC}=1^+2^{--}$) in the mechanism of $a_0(980)$ meson production in $t$-channel of the reaction.Comment: 4 pages, 3 figures, talk given at HADRON'9

The lightest scalar glueball

Recently performed investigations of meson spectra allow us to determine the resonance structure for the waves $IJ^{PC}=00^{++}$, $10^{++}$, $02^{++}$, $12^{++}$ = $IJ^P= 1/2 0^+$ in the mass region up to 1900 MeV, thus establishing the meson multiplets $1^3P_0q\bar q$ and $2^3P_0q\bar q$. Experimental data demonstrate that there are five scalar/isoscalar states in this mass region. Four of them are $q\bar q$ states, that is, members of the $1^3P_0q\bar q$ and $2^3P_0q\bar q$ nonets, while the fifth state is an extra one not accomodated by $q \bar q$ systematics; it has the properties of the lightest scalar glueball. Analysis of the $00^{++}$-wave performed within the framework of the dispersion relation technique allows us to reconstruct the mixing of a pure gluonium with neighbouring scalar $q \bar q$ states belonging to $1^3P_0q\bar q$ and $2^3P_0q\bar q$ nonets: three scalar mesons share the gluonium state between each other -- those are two comparatively narrow resonances $f_0(1300)$ and $f_0(1500)$ and a broad resonance $f_0(1530^{+90}_{-250})$. The broad state is a descendant of the gluonium, keeping about 40-50% of its component.Comment: 48 pages, LaTeX, 25 PostScript figures, epsfig.sty. Submitted to Russian Journal Uspekhi Fiz. Nauk (Phys-Uspekhi

Meson model for f_0(980) production in peripheral pion-nucleon reactions

The Juelich model for pion-pion-scattering, based on an effective meson-meson Lagrangian is applied to the analysis of the S-wave production amplitudes derived from the BNL E852 experiment pi^- p -> pi^0 pi^0 n for a pion momentum of 18.3 GeV. The unexpected strong dependence of the S-wave partial wave amplitude on the momentum transfer between the proton and neutron in the vicinity of the f_0(980) resonance is explained in our analysis as interference effect between the correlated and uncorrelated pi^0 pi^0 pairs.Comment: 6 pages, 7 figures, formulas added, typos removed, new figure

The two-pion spectra for the reaction \pi^- p -> \pi^0\pi^0 n at 38 GeV/c pion momentum and combined analysis of the GAMS, Crystal Barrel and BNL data

We perform the K-matrix analysis of meson partial waves with IJ^{PC} =00^{++}, 10^{++}, 02^{++}, 12^{++} basing on GAMS data on \pi^-p -> \pi^0\pi^0 n, \eta\eta n, \eta\eta' n together with BNL data on \pi^-p -> K\bar K n and Crystal Barrel data on p\bar p (at rest) -> \pi^0\pi^0\pi^0, \pi^0\eta\eta, \pi^0\pi^0\eta. The positions of the amplitude poles (physical resonances) are determined as well as the positions of the K-matrix poles (bare states) and the values of bare state couplings to two-meson channels. Nonet classification of the determined bare states is discussed.Comment: LaTex, 15 pages and 10 figure

A study of the etapipi channel produced in central pp interactions at 450 GeV/c

The reaction pp -> pf (eta pi pi) ps has been studied at 450 GeV/c. There is clear evidence for an a2(1320)pi decay mode of the eta2(1645) and eta2(1870). In addition, there is evidence for an a0(980)pi$ decay mode of both resonances and an f2(1270)eta decay mode of the eta2(1870). No evidence is found for a JPC = 2++ a2(1320)pi wave.Comment: 15 pages, Latex, 4 Figures Branching ratio a2pi /f2 eta correcte

A study of the centrally produced pi0pi0pi0 channel in pp interactions at 450 GeV/c

The reaction pp -> pf (pi0pi0pi0) ps has been studied at 450 GeV/c. The pi0pi0pi0 effective mass spectrum shows clear eta(547) and pi2(1670) signals. Branching ratios for the eta(547) and pi_2(1670) are given as well as upper limits for the decays of the omega(782), a1(1260) and a2(1320) into 3pi0.Comment: 10 pages, Latex, 4 Figure

A study of the f0(1370), f0(1500), f0(2000) and f2(1950) observed in the centrally produced 4pi final states

The production and decay properties of the f0(1370), f0(1500), f0(2000) and f2(1950) have been studied in central pp interactions at 450 GeV/c. The dPT, phi and |t| distributions of these resonances are presented. For the J = 0 states, the f0(1370) and f0(2000) have similar dPT and phi dependences. These are different to the dPT and phi dependences of the f0(980), f0(1500) and f0(1710). For the J = 2 states the f2(1950) has different dependences to the f2(1270) and f2'(1520). This shows that the dPT and phi dependences are not just J phenomena.Comment: 14 pages, Latex, 4 Figure

A search for charmonium states produced in central pp interactions at 450 GeV/c

A search for centrally produced charmonium states has been presented. There is no significant evidence for any charmonium production. An upper limit of 2 nb is found for the cross section of chic production using the decay chic(1P)-> J/psi gamma.Comment: 10 pages, Latex, 4 Figure

Experimental evidence for a vector-like behaviour of Pomeron exchange

Evidence is presented that the Pomeron act as a non-conserved vector current. A study has been made of the azimuthal angle phi, which is defined as the angle between the pT vectors of the two outgoing protons, in the reaction pp -> pp(X0) for those resonances (X0) which are compatible with being produced by double Pomeron exchange. These distributions have been compared with a model which describes the Pomeron as a non-conserved vector current and a qualitative agreement is found. In addition, when one of the particles exchanged is known to have spin 0, namely pi-Pomeron exchange, the phi distribution is flat.Comment: 13 pages, Latex, 4 Figure