D.Barberis,W .Beusch,F.G.Binon,A.M .Blick,F.E.Close,K.M .Danielsen, A.V.Dolgopolov,S.V.Donskov,B.C.Earl,D.Evans,B.R.French,T.Hino,S.Inaba, A.V.Inyakin,T.Ishida,A.Jacholkowski,T.Jacobsen,G.T Jones,G.V.Khaustov, T.Kinashi,J.B.Kinson,A.Kirk,W .Klem pt,V.Kolosov,A.A.Kondashov, A.A.Lednev,V.Lenti,S.M aljukov,P.M artinengo,I.M inashvili,T.Nakagawa, K.L.Norm an,J.P.Peigneux,S.A.Polovnikov,V.A.Polyakov,V.Rom anovsky, H.Rotscheidt,V.Rum yantsev,N.Russakovich,V.D.Sam oylenko,A.Sem enov,M .Sen e, R.Sen e,P.M .Shagin,H.Shim izu,A.V.Singovsky,A.Sobol,A.Solovjev, M .Stassinaki,J.P.Stroot,V.P.Sugonyaev,K.Takam atsu,G.Tchlatchidze,T.Tsuru, M .Venables,O.VillalobosBaillie,M .F.Votruba,Y.Yasu.

The reaction pp --> p(f)(pi (0)pi (0)pi (0))p(s) has been studied at 450 GeVc. The pi (0)pi (0)pi (0) effective mass spectrum shows clear eta (547) and pi (2)(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), a(1)(1260) and a(2)(1320) into 3 pi (0). (C) 2001 Published by Elsevier Science B.V.

The reactions pp -> pf (X0) ps, where X0 is observed decaying to pi0pi0pi0pi0, pi+pi-pi0pi0 and pi+pi-pi+pi-, have been studied at 450 GeV/c. There is evidence for an a2(1320)pi decay mode of the eta2(1645) and eta2(1870) in the pi+pi-pi0pi0 and pi+pi-pi+pi- final states. The f2(1950) is consistent with being a single resonance with a dominant f2(1270)pipi decay mode. The f0(1370) is found to decay dominantly to rho-rho while the f0(1500) is found to decay to rho-rho and sigma-sigma.

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 chi(c) production using the decay chi(c)(1P) --> J/psi gamma. (C) 2000 Elsevier Science B.V. All rights reserved.

Ž . The reaction ppTMp vv p has been studied at 450 GeVrc and a spin analysis of the vv channel has been performed f s Ž . PC qq for the first time in central production. Evidence is found for the f 1910 in the J s2 wave with spin projection 2 J s2. This is the only state observed in central production with spin projection J s2. Its dP and f dependencies are Z Z T similar to those observed for other glueball candidates. In addition, evidence is found for a state with J s4 consistent Ž . Ž . with the f 2300 . The f 2000 , previously observed in the rr final state, is confirmed. q 2000 Elsevier Science B.V. All 4 0 rights reserved. Ž . E-mail address: andrew.kirk@cern.ch A. Kirk . 0370-2693r00r$ see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0370-2693 00 00622-5 ( ) D. Barberis et al.rPhysics Letters B 484 2000 198–204 199 The vv channel has been studied in several different production mechanisms. In pp interactions the vv final state has been studied by the w x w x NA12 1 and VES 2 collaborations. In both experiments clear signals were observed at 1.6 and 1.9 GeV and were found to have J P C s2, called the Ž . Ž . w x f 1640 and X 1910 3 . In addition, the VES 2 collaboration reported evidence for an vv decay Ž . mode of the f 2050 and, more recently, for a 4 P C qq w x J s4 object in the 2.3 GeV region 4 . In pp annihilations C. Baker et al., using the data from the w x Crystal Barrel experiment 5 , have reported eviŽ . dence for a structure similar to the f 1640 in the 2 vv final state but have shown that this state can be Ž . interpreted as being due to the f 1565 previously 2 w x w x observed in the pp final state 3 . The PDG 3 lists Ž . the X 1910 observed in the vv final state with another J P C s2 resonance with similar mass and width observed in the hh final state. In central production the WA102 experiment did not observe Ž . w x the f 1565 in the pp final state 6 , therefore, the 2 centrally produced vv channel can give information Ž . Ž . on the validity of the f 1565 rf 1640 assignment. 2 2 In addition, in the hh final state of the WA102 w x experiment 7 a peak was observed at 1.9 GeV which was consistent in mass and width with the Ž . X 1910 . A spin analysis showed that this state was consistent with having J P C s1 with spin projection J s1 or J P C s2 with spin projection J s Z Z 2. If the latter hypothesis were true then this was the first time that a state had been observed in central production that was produced with spin projection J s2. Hence, if the states observed in vv and hh Z Ž . P C qq are the same and the X 1910 has J s2 , the Ž . X 1910 should be observed in the J s2 projection Z in the vv final state. In central production, the vv final state was previously observed by the WA76 w x experiment 8 but only 80 events were observed and hence no strong conclusions could be drawn. In this paper, a study is presented of the vv final state formed in the reaction ppTMp vv p 1 Ž . Ž . f s at 450 GeVrc. It represents more than a factor of 60 increase in statistics over previous data on the cenw x trally produced vv final state 8 and, moreover, will present a spin analysis of this channel in central production. The data come from the WA102 experiment which has been performed using the CERN Omega Spectrometer, the layout of which is dew x Ž . scribed in Ref. 9 . Reaction 1 has been isolated using the ppp 0 decay mode of both vs. The reaction ppTMp ppppp p 0 p Ž . f s has been isolated from the sample of events having six outgoing charged tracks and four g s reconstructed in the GAMS-4000 calorimeter, by first imposing the following cuts on the components of < < the missing momentum: missing P -17.0 GeVrc, x < < < < missing P -0.16 GeVrc and missing P -0.12 y z GeVrc, where the x axis is along the beam direction. The two photon mass spectrum, when the mass of the other 2g-pair lies within a band around the p 0 Ž . 0 mass 100–170 MeV , shows a clear p signal with small background. Events containing a fast qqŽ . Ž q. D 1232 were removed if M p p -1.3 GeV, f which left 294 463 centrally produced pp ppp p 0 events. Ž q y 0. Fig. 1a shows a lego plot of M p p p versus Ž q y 0. Ž . M p p p four combinations per event . A clear signal of the vv channel can be observed. Fig. 1b shows the ppp 0 mass spectrum if the other ppp 0 combination is compatible with being an Ž Ž q y 0. . v 0.76FM p p p F0.81 GeV where a clear v signal can be observed. A tight cut has been used around the v signal to increase the signal to background ratio in the selected sample. In order to decrease the background further the parameter l is introduced which describes the v decay on the Dalitz plot and is defined as: < < 2 p =p q y ls 2 3 1 2 2 m ymp ž / 4 9 < < where p =p is proportional to the decay matrix q y element for vTMppp , p is the three momen" tum of the p " in the v rest frame and m is the ppp 0 effective mass squared. Superimposed on Fig. 1b as a shaded histogram is the ppp 0 mass distribution for l)0.3. As can be seen the signal to background ratio in the v region has increased. The vv final state has been selected using the ppp 0 mass cuts described above and by requiring that the l)0.3 for each v candidate. The ( ) D. Barberis et al.rPhysics Letters B 484 2000 198–204 200 Ž . Ž q y 0 . Ž q y 0 . Ž . Ž q y 0 . q y 0 Fig. 1. Selection of the vv final state: a M p p p versus M p p p , b M p p p if the other p p p combination is in Ž Ž q y 0 . . Ž . the v band 0.76FM p p p F0.81 GeV . Superimposed as a shaded histogram is the case for l)0.3. c The vv mass spectrum. Superimposed as a shaded histogram is an estimation of the background contribution. resulting vv mass spectrum is shown in Fig. 1c and consists of 5067 events. As can be seen there is a peak in the 1.9 GeV region. The background below the v signal has several sources including combinatorics and other channels. The combinatorial background is removed, in part, in the selection procedure. The remaining background is approximately 27%. Four methods have been used to determine the effects of this background; studying the side bands around the v signal, studying events that do not balance momentum, studying events that do not pass the l selection cuts and studying events from the pppppp channel. Since the majority of the background is due to other physical Ž . Ž . Ž . channels for example a 1260 a 1260 or v a 1260 1 1 1 production, the two methods that best reproduce the background are the one using events that do not pass the l cut and the other uses events from the pppppp channel. These two methods give a very similar representation of the background. ( ) D. Barberis et al.rPhysics Letters B 484 2000 198–204 201 In the remainder of this paper the method used to determine the background will be the mean of these two methods. Superimposed on the vv mass spectrum in Fig. 1c as a shaded histogram is the estimate of the background. A spin analysis of the centrally produced vv system has been performed using the method dew x scribed in Ref. 10 for the rr final state modified for the vv channel. The z axis is defined by the momentum vector of the exchanged particle with the greatest four-momentum transferred in the vv centre of mass. Assuming that only angular momenta up to 4 contribute, the amplitudes have been calculated Ž . in the spin-orbit LS scheme using spherical harmonics. In order to perform a spin parity analysis the log Ž . likelihood function, L sÝ log P i , is defined by j i j combining the probabilities of all events in 50 MeV vv mass bins from 1.5 to 3.0 GeV. The incoherent sum of various event fractions a is calculated so as j to include more than one wave in the fit, Ls log a P i q 1y a 2 Ž . Ž . Ý Ý Ý j j j ž / ž / i j j Ž . where the term 1yÝ a represents the phase space j j background. The negative log likelihood function Ž . w x yL is then minimised using MINUIT 11 . Coherence between different J P states has been neglected in the fit. Different combinations of waves have been tried and insignificant contributions have been removed from the final fit. It is found necessary to introduce the J P C s2 wave with both J s0 and 2, the J P C s0 wave Z and the J P C s4 wave with J s1. The results of Z the best fit are shown in Fig. 2. The J P C s2 wave with J s2 shows a peak Z at 1.9 GeV. This wave has been fitted using a spin 2 relativistic Breit-Wigner and a linear background and is shown superimposed. The fit gives Ms1897"11 MeV, Gs202 " 32 MeV, parameters consistent Ž . X with those of the X 1910 found from a fit to the hh w x final state 7 . Hence this consistent with the fact that Ž . X the X 1910 has vv and hh decay modes, and we Ž . shall refer to it as the f 1910 hereafter. Correcting 2 for the unseen decay modes and the effects of the X Ž . detector, the branching ratio vvrhh of the f 1910 2 is 2.6 " 0.6. There was no evidence for any wave with J s2 in the hh final state of the WA102 Z w x experiment 12 and hence an upper limit for the X Ž . branching ratio hhrhh of the f 1910 has been 2 Ž . calculated to be 0.2 90% CL . The J P C s2 wave with J s0 shows a broad Z enhancement. Superimposed on the wave is a shaded Ž . histogram representing the f 1640 . As can be seen 2 the J P C s2 wave with J s0 is not compatible Z Ž . with the f 1640 observed by other experiments. 2 This non observation does not contradict the claim Ž . that the f 1640 is an vv decay mode of the 2 Ž . f 1565 since this state is also not observed in 2 central production. The J P C s0 wave shows some activity near threshold and a broad enhancement around 2 GeV. In a previous analysis of the 4p channel, the WA102 experiment observed a similar structure in the J P C s0 rr wave which was identified with the Ž . f 2000 . Superimposed on the wave is a shaded 0 Ž . histogram representing the f 2000 assuming that 0 the branching ratio rrrvv s 3 as expected for a isoscalar resonance. This well represents the wave in the 2 GeV region. The J P C s4 wave with

A partial wave analysis of the centrally produced eta pi(0) and eta pi(-) channels has been performed in pp collisions using an incident beam momentum of 450 GeV/c. Clear a(0)(980) and a(2)(1320) signals have been observed in S and D+ waves respectively. The dP(T), phi and \t\ distributions of these resonances are presented. (C) 2000 Elsevier Science B.V. All rights reserved.

We perform a K-matrix analysis of IJ PC =00++, 10++, 02++, and 12++ meson partial waves using GAMS data on π−p → π0π0n, ηηn, ηη'n that are supplemented with BNL data on π−p → K\(\bar K\)n and Crystal Barrel data on p\(\bar p\) (at rest) → π0π0π0, π0ηη, π0π0η. The positions of the amplitude poles (physical resonances) are determined, together with the positions of the K-matrix poles (bare states) and the values of barestate couplings to two-meson channels. The nonet classification of the bare states found in the present analysis is discussed.

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 x production using the decay c

The reaction π-p → ηπ0n at primary π- meson momenta of 32, 38, and 100 GeV/c has been studied by using the GAMS facilities. A partial-wave analysis has been performed in the effective-mass range 0.77 ≤ Mηπ0

Evidence is presented that the Pomeron acts as a non-conserved vector current. A study has been made of the azimuthal angle phi, which is defined as the angle between the p(T) vectors of the two outgoing protons, in the reaction pp-->pp(X-0) for those resonances (X-0) which are compatible with being produced by double Pomeron exchange. These distributions have been compared with a moder 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. (C) 1999 Elsevier Science B.V. All rights reserved.

The pi(0)pi(0) system produced in charge-exchange pi(-)p interactions at a primary momentum of 100 GeV/c has been studied. The data employed come from the experiment that was performed at the CERN SPS accelerator and which recorded photons from pi(0) decays with the aid of the hodoscopic multiphoton GAMS-4000 spectrometer. A partial-wave analysis of the pi(0)pi(0) system in the mass interval between 0.8 and 3 GeV has been performed with allowance for the S, D, G, and J waves. The S wave has a rather complicated structure, displaying a series of four bumps separated by three dips at about 1, 1.5, and 2 GeV. This suggests the existence of several scalar resonances. The higher waves show clear peaks corresponding to the f(2)(1270), f(4)(2050), and f(6)(2510) mesons, which are produced predominantly via one-pion exchange. The parameters of these mesons and their production cross sections have been determined.

A coupled channel analysis of the centrally produced K q K y and p q p y final states has been performed in pp collisions . at an incident beam momentum of 450 GeVrc. The pole positions and branching ratios to pp and KK of the f 980 , 0

New results on meson spectroscopy that were obtained by the GAMS collaboration over the years 1997 and 1998 are presented. A partial-wave analysis of the pi(0)pi(0) system formed in charge-exchange pi(-)p interaction at a momentum of 100 GeV/c has been performed. The eta eta system produced in the reaction pi(-)p --> eta eta n at a momentum of 38 GeV/c has been studied. The results of a partial-wave analysis of the pi(0)pi(0) system formed in central proton-proton collisions at a momentum of 450 GeV/c have been discussed.

A coupled channel analysis of the centrally produced K + K and + nal states has been performed in pp collisions at an incident beam momentum of 450 GeV/c. The pole positions and branching ratios to and KK of the f0(980), f0(1370), f0(1500) and f0(1710) have been determined. A systematic study of the production properties of all the resonances observed in the + and K + K channels has been performed.

A partial wave analysis of the centrally produced K+K− and KS0KS0 channels has been performed in pp collisions using an incident beam momentum of 450 GeV/c. An unambiguous physical solution has been found in each channel. The striking feature is the observation of peaks in the S-wave corresponding to the f0(1500) and fJ(1710) with J = 0. The D-wave shows evidence for the f2(1270)a2(1320), the f′2(1525) and the f2(2150) but there is no evidence for a statistically significant contribution in the D-wave in the 1.7 GeV mass region.

The reaction pi(-)p --> eta pi(0)n at primary pi(-) meson momenta of 32, 38, and 100 GeV/c has been studied by using the GAMS facilities. A partial-wave analysis has been performed in the effective-mass range 0.77 less than or equal to M-eta pi 0 < 1.82 GeV/c(2). A peak associated with the a(2) meson is clearly seen in the P+-wave. The difference of the D+- and P+-wave phases changes abruptly in the region of the a(2) mass. A significant contribution of the P+ wave is observed at the a(2) mass value and above, but this wave does not show a clear-cut resonance behavior. No significant contribution from exchanges of unnatural spin-parity are observed with the exception of the S-wave contribution in the region of the a(0) mass and the D-0-wave contribution in the region of the a(2) mass.

A partial wave analysis of the centrally produced π0π0 channel has been performed in pp collisions using an incident beam momentum of 450 GeV/c. An unambiguous physical solution has been found. Evidence is found for the f0(980), f0(1300) and f0(1500) in the the S-wave. and the f2(1270) is observed dominantly in the D0−-wave. In addition, there is evidence for a broad enhancement in the D-wave below 1 GeV.