A study has been made of pseudoscalar mesons produced centrally in pp
interactions. The results show that the eta and etaprime appear to have a
similar production mechanism which differs from that of the pi0. The production
properties of the eta and etaprime are not consistent with what is expected
from double Pomeron exchange. In addition the production mechanism for the eta
and etaprime is such that the production cross section are greatest when the
azimuthal angle between the pT vectors of the two protons is 90 degrees.Comment: 11 pages, Latex, 3 Figure

Barberis, D.

Beusch, W.

Binon, F.G.

Blick, A.M.

Close, F.E.

Danielsen, K.M.

Dolgopolov, A.V.

Donskov, S.V.

Earl, B.C.

Evans, D.

French, B.R.

Hino, T.

Inaba, S.

Inyakin, A.V.

Ishida, T.

Jacholkowski, A.

Jacobsen, T.

Jones, G.T.

Khaustov, G.V.

Kinashi, T.

Kinson, J.B.

Kirk, A.

Klempt, W.

Kolosov, V.

Kondashov, A.A.

Lednev, A.A.

Lenti, V.

Maljukov, S.

Martinengo, P.

Minashvili, I.

Myklebost, K.

Nakagawa, T.

Norman, K.L.

Olsen, J.M.

Peigneux, J.P.

Polovnikov, S.A.

Polyakov, V.A.

Romanovsky, V.

Rotscheidt, H.

Rumyantsev, V.

Russakovich, N.

Samoylenko, V.D.

Semenov, A.

Sené, M.

Sené, R.

Shagin, P.M.

Shimizu, H.

Singovsky, A.V.

Sobol, A.

Solovjev, A.

Stassinaki, M.

Stroot, J.P.

Sugonyaev, V.P.

Takamatsu, K.

Tchlatchidze, G.

Tsuru, T.

Venables, M.

Villalobos Baillie, O.

Votruba, M.F.

Yasu, Y.

Physics Letters B

English

arXiv

A study has been made of pseudoscalar mesons produced centrally in pp interactions. The results show that the eta and etaprime appear to have a similar production mechanism which differs from that of the pi0. The production properties of the eta and etaprime are not consistent with what is expected from double Pomeron exchange. In addition the production mechanism for the eta and etaprime is such that the production cross section are greatest when the azimuthal angle between the pT vectors of the two protons is 90 degrees.A study has been made of pseudoscalar mesons produced centrally in pp interactions. The results show that the eta and etaprime appear to have a similar production mechanism which differs from that of the pi0. The production properties of the eta and etaprime are not consistent with what is expected from double Pomeron exchange. In addition the production mechanism for the eta and etaprime is such that the production cross section are greatest when the azimuthal angle between the pT vectors of the two protons is 90 degrees.A study has been made of pseudoscalar mesons produced centrally in pp interactions. The results show that the eta and etaprime appear to have a similar production mechanism which differs from that of the pi0. The production properties of the eta and etaprime are not consistent with what is expected from double Pomeron exchange. In addition the production mechanism for the eta and etaprime is such that the production cross section are greatest when the azimuthal angle between the pT vectors of the two protons is 90 degrees.A study has been made of pseudoscalar mesons produced centrally in pp interactions. The results show that the eta and etaprime appear to have a similar production mechanism which differs from that of the pi0. The production properties of the eta and etaprime are not consistent with what is expected from double Pomeron exchange. In addition the production mechanism for the eta and etaprime is such that the production cross section are greatest when the azimuthal angle between the pT vectors of the two protons is 90 degrees.A study has been made of pseudoscalar mesons produced centrally in pp interactions. The results show that the eta and etaprime appear to have a similar production mechanism which differs from that of the pi0. The production properties of the eta and etaprime are not consistent with what is expected from double Pomeron exchange. In addition the production mechanism for the eta and etaprime is such that the production cross section are greatest when the azimuthal angle between the pT vectors of the two protons is 90 degrees.A study has been made of pseudoscalar mesons produced centrally in pp interactions. The results show that the eta and etaprime appear to have a similar production mechanism which differs from that of the pi0. The production properties of the eta and etaprime are not consistent with what is expected from double Pomeron exchange. In addition the production mechanism for the eta and etaprime is such that the production cross section are greatest when the azimuthal angle between the pT vectors of the two protons is 90 degrees.A study has been made of pseudoscalar mesons produced centrally in pp interactions. The results show that the η and η ′ appear to have a similar production mechanism which differs from that of the π 0 . The production properties of the η and η ′ are not consistent with what is expected from double Pomeron exchange. In addition the production mechanism for the η and η ′ is such that the production cross section are greatest when the azimuthal angle between the p T vectors of the two protons is 90 degrees

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arXiv:hep-ex/9803029v1  30 Mar 199825 March 1998A study of pseudoscalar states produced centrally in ppinteractions at 450 GeV/cThe WA102 CollaborationD.Barberis5, W.Beusch5, F.G.Binon7, A.M.Blick6, F.E.Close4, K.M.Danielsen12,A.V.Dolgopolov6, S.V.Donskov6, B.C.Earl4, D. Evans4, B.R. French5, T.Hino13, S. Inaba9,A.V. Inyakin6, T. Ishida9, A. Jacholkowski5, T. Jacobsen12, G.TJones4, G.V.Khaustov6,T.Kinashi14, J.B.Kinson4, A.Kirk4, W.Klempt5, V.Kolosov6, A.A.Kondashov6,A.A. Lednev6, V. Lenti5, S.Maljukov8, P.Martinengo5, I.Minashvili8, K.Myklebost3,T.Nakagawa13, K.L.Norman4, J.M.Olsen3, J.P. Peigneux1, S.A.Polovnikov6, V.A.Polyakov6,V.Romanovsky8, H.Rotscheidt5, V.Rumyantsev8, N.Russakovich8, V.D. Samoylenko6,A. Semenov8, M. Sene´5, R. Sene´5, P.M. Shagin6, H. Shimizu14, A.V. Singovsky1,6, A. Sobol6,A. Solovjev8, M. Stassinaki2, J.P. Stroot7, V.P. Sugonyaev6, K.Takamatsu10, G.Tchlatchidze8,T.Tsuru9, M.Venables4, O.Villalobos Baillie4, M.F.Votruba4, Y.Yasu9.AbstractA study has been made of pseudoscalar mesons produced centrally in pp interactions. Theresults show that the η and η′ appear to have a similar production mechanism which differsfrom that of the pi0. The production properties of the η and η′ are not consistent with what isexpected from double Pomeron exchange. In addition the production mechanism for the η andη′ is such that the production cross section are greatest when the azimuthal angle between thepT vectors of the two protons is 90 degrees.Submitted to Physics Letters1 LAPP-IN2P3, Annecy, France.2 Athens University, Physics Department, Athens, Greece.3 Bergen University, Bergen, Norway.4 School of Physics and Astronomy, University of Birmingham, Birmingham, U.K.5 CERN - European Organization for Nuclear Research, Geneva, Switzerland.6 IHEP, Protvino, Russia.7 IISN, Belgium.8 JINR, Dubna, Russia.9 High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305, Japan.10 Faculty of Engineering, Miyazaki University, Miyazaki, Japan.11 RCNP, Osaka University, Osaka, Japan.12 Oslo University, Oslo, Norway.13 Faculty of Science, Tohoku University, Aoba-ku, Sendai 980, Japan.14 Faculty of Science, Yamagata University, Yamagata 990, Japan.1The WA102 experiment is designed to study the properties of centrally produced mesons.Reactions of this type are expected to be mediated by double exchange processes, with a mixtureof Pomeron-Pomeron, Reggeon-Pomeron and Reggeon-Reggeon exchange. In order to try tounderstand the nature of the centrally produced mesons it is interesting to try to determinewhich exchange process is producing them. For instance, the Pomeron is thought to be a multi-gluonic object and consequently it has been anticipated that the production of glue rich statesmay be especially favoured in Double Pomeron Exchange (DPE). It has been proposed thatthe η and η′ are strongly connected to glue [1]. Further information on this subject could comefrom studying if the η or η′ are produced by DPE.It has previously been reported that in central production 0−+ states are suppressed relativeto 1++ states [2]. In addition, both the η and η′ signals are suppressed at small four-momentumtransfers where DPE is believed to be dominant [2, 3]. Hence it could be conjectured that 0−+objects do not couple to DPE. This hypothesis has been further tested by measuring the crosssection of the production of the η and η′ as a function of energy [4, 5]. The result shows thatthe cross section for production of these resonances decreases with energy which is inconsistentwith production via DPE which is predicted to give a constant cross section.This paper presents new results from the WA102 experiment on the centrally produced pi0,η and η′ formed in the reactionspp→ pf(pi0 → γγ)ps (1)pp→ pf (η → γγ)ps (2)pp→ pf(η → pi+pi−pi0, pi0 → γγ)ps (3)pp→ pf(η′ → pi+pi−η, η → γγ)ps (4)at 450 GeV/c. The subscripts f and s indicate the fastest and slowest particles in the laboratoryrespectively. The data come from experiment WA102 which has been performed using theCERN Omega Spectrometer. The layout of the Omega Spectrometer used in this run is similarto that described in ref. [6] with the replacement of the OLGA calorimeter by GAMS 4000 [7].Reactions (1)-(4) have been isolated from the sample of events having the required numberof outgoing charged tracks plus two γs reconstructed in the electromagnetic calorimeter1 by firstimposing the following cuts on the components of the missing momentum: |missing Px| < 17.0GeV/c, |missing Py| < 0.16 GeV/c and |missing Pz| < 0.12 GeV/c, where the x axis is alongthe beam direction. A correlation between pulse-height and momentum obtained from a systemof scintillation counters was used to ensure that the slow particle was a proton. Evidence ofproton excitation can be observed in the pfpi0 mass spectrum (i.e. ∆+ or N∗+ production)which has been removed by requiring M(pfpi0) > 2.0 GeV.Fig. 1a) and b) shows the two photon mass spectra in the region of the pi0 and η respectivelyfor reactions 1 and 2. The mass resolution is σ = 14 MeV for the pi0 and σ = 33 MeV for theη. Fig. 1c) shows the pi+pi−pi0 mass spectrum in the region of η for reaction (3) where the pi0is detected decaying to two photons and kinematically fitted to give the pi0 mass. The massresolution is σ = 11 MeV. Fig. 1d) shows the ηpi+pi− mass spectrum in the region of η′ for1The showers associated with the impact of the charged tracks on the calorimeter have been removed fromthe event before the requirement of only two γs was made.2reaction (4) where the η is detected decaying to two photons and kinematically fitted to givethe η mass. The mass resolution is σ = 10 MeV.A Monte Carlo simulation has been performed to calculate the acceptance for each decaymode. The acceptance corrected Feynman x (xF ) distributions are shown in fig. 2a), b) and c)for the pi0, η and η′ respectively for xF ≥ 0.0. A cut of 0.0 ≤ xF ≤ 0.1 has been used to selectcentral events in a region where the acceptance is effectively flat for all three mesons.After acceptance correction the branching ratio of the η to 2γ and pi+pi−pi0 has been calcu-lated to beη → γγη → pi+pi−pi0= 1.60± 0.05± 0.08 (5)which is consistent with the PDG [8] value of 1.69± 0.04. The systematic error is due mainlyto the different trigger efficiencies for the decay of central systems to all photon final statesrelative to final states involving charged particles. Since the background below the η decay topi+pi−pi0 is smaller than in the 2γ decay mode, it is the data from the pi+pi−pi0 decay mode whichwill be used in the following analysis. However, the 2γ decay mode gives consistent results.It has recently been suggested [9, 10] that the central production of pseudoscalars couldbe explained if the production mechanism is through the fusion of two vectors. In particularref. [10] has suggested that γγ fusion may be the dominant mechanism for pseudoscalars incentral production. To test this hypothesis, and provide further information on their productionproperties, the cross sections for the production of pseudoscalar mesons have been calculatedfor the Feynman x interval 0.0 ≤ xF ≤ 0.1 taking into account the unseen decay modes. Theresulting cross sections areσ(pi0) = 17609 ± 210 ± 2400 nbσ(η) = 1295 ± 16 ± 120 nbσ(η′) = 588 ± 18 ± 60 nb.The dominant contribution to the systematic error comes from the uncertainty in the sensitivityof the experiment. These cross sections are several orders of magnitude larger than what wouldbe expected for γγ fusion which we have calculated, using the method described in ref. [11], tobe less than 1 nb in the kinematic window considered.The relative cross sections can be measured more precisely due to the cancellation of commonsystematic errors and areσ(pi0) : σ(η) : σ(η′) = 1 : 0.073± 0.005 : 0.033± 0.002.These ratios are in agreement with σ(pi0) : σ(η) : σ(η′) = 1 : 0.080±0.015 : 0.028±0.009 foundpreviously by the NA12/2 experiment studying the reaction pi−N → pi−NX0 at 300 GeV/cincident beam momentum [12]. It is interesting to note that the NA12/2 experiment foundthat the xF dependence of the pi0, η and η′ was effectively flat in the range 0.0 ≤ xF ≤ 0.3 incontrast to what is observed in this current experiment (see fig. 2a), b) and c)).In previous analyses of other channels it has been observed that when the centrally producedsystem has been analysed as a function of the parameter dPT , which is the difference in thetransverse momentum vectors of the two exchange particles [13], all the undisputed qq states3are suppressed at small dPT . Therefore, a study of the centrally produced pseudoscalar stateshas been performed as a function of dPT . Fig. 2d), e) and f) shows the dPT spectra for the pi0,η and η′ respectively. The dPT spectra for the η and η′ are very similar; however, the pi0 has adifferent spectrum with more events at small dPT . Table 1 gives the fraction of each resonancein three bins of dPT . As can be seen all the states are suppressed at small dPT consistent withwhat has been observed previously for all other qq states [13]. This suppression of pseudoscalarstates at small dPT is consistent with their production through vector vector fusion [9, 10].Fig. 3a), b) and c) shows the four momentum transfered from one of the proton vertices forthe pi0, η and η′ respectively. None of these distributions can be fitted with a single exponential.The η and η′ have a similar distribution while the pi0 is different. It should be noted that thet spectra for the η and η′ are not consistent with what is expected from DPE, namely an e−btbehaviour with b ≈ 6− 8GeV −2 [14]. The t distributions have been fitted to the formdσdt= αe−b1t + βtne−b2t (6)where values of n of 1 or 2 have been tried. Fits with n = 2 were found to give the best fit tothe data. The parameters resulting from the fit are given in table 2. As can be seen the valuesof b1 and b2 are consistent in each case. The main difference is that the pi0 has a larger valueof the ratio α/β.The azimuthal angle (φ) between the pT vectors of the two protons, which is shown infig. 3d), e) and f), shows a very interesting effect. The η and η′ are produced predominantlywhen the angle φ is 90 degrees.In summary, it would appear that the η and η′ have a similar production mechanism whichdiffers from that of the pi0. The t spectra for the η and η′ are not consistent with what is expectedfrom DPE and this fact together with the previous observation that the energy dependence ofthe cross section of the η or η′ is not constant [4, 5] confirms that neither the η nor the η′are produced dominantly by DPE. In addition the production mechanism for the η and η′ issuch that the production cross sections are greatest when the azimuthal angle between the pTvectors of the two protons is 90 degrees.AcknowledgementsThis work is supported, in part, by grants from the British Particle Physics and AstronomyResearch Council, the British Royal Society, the Ministy of Education, Science, Sports andCulture of Japan (grants no. 04044159 and 07044098) and the Russian Foundation for BasicResearch (grant 96-15-96633).4References[1] V.A. Novikov et al.,, Nucl. Phys. B191 (1981) 301;J. Rosner, Phys. Rev. D27 (1983) 1101;S.S. Gershtein, A.A. Likhoded and Yu. D. Prokoshkin, Zeit. Phys. C24 (1984) 305;R. Akhoury and J.-M. Frere, Phys. Lett B220 (1989) 258;P. Ball, J.-M. Frere and M. Tytgat, Phys. Lett B365 (1996) 367.[2] T. Armstrong et al., Zeit. Phys. C52 (1991) 389.[3] T. Armstrong et al., Zeit. Phys. C48 (1990) 213.[4] D. Barberis et al., hep-ex/9801003, To be published in Phys. Lett.[5] F.E. Close and A. Kirk, Zeit. Phys. C76 (1997) 469.[6] F. Antinori et al., Il Nuovo Cimento A107 (1994) 1857.[7] D. Alde et al., Nucl. Phys. B269 (1986) 485.[8] Particle Data Group, Phys Rev. D54 (1996) 1.[9] F.E. Close, hep-ph/9710450.[10] P. Castoldi, R. Escribano and J.-M. Frere, hep-ph/9712387.[11] W. Kilian and O. Nachtmann, hep-ph/9712371.[12] D. Alde et al., Zeit. Phys. C43 (1989) 541.[13] D. Barberis et al., Phys. Lett. B397 (1997) 339.[14] S.N. Ganguli and D.P. Roy, Phys. Rep. 67 (1980) 203.5TablesTable 1: Resonance production as a function of dPT expressed as a percentage of its totalcontribution.dPT≤0.2 GeV 0.2≤dPT≤0.5 GeV dPT≥0.5 GeVpi0 13 ± 1 ± 2 45 ± 1 ± 2 42 ± 1± 4η 6 ± 1± 2 34 ± 1±2 60 ± 1 ± 3η′ 3 ± 1 ± 2 33 ± 1 ± 2 64 ± 1 ± 36Table 2: Parameters from the fit to the t distributionα x103 b1 GeV−2 β x103 b2 GeV−2pi0 128± 9 14.9 ± 0.3 411± 61 12.3 ± 0.4η 2.3 ± 0.3 15 ± 5 215 ±12 11.6 ±0.2η′ 0.3 ± 0.2 15 ± 5 108 ± 8 11.2 ±0.27FiguresFigure 1: The effective mass spectra for the reaction pp→ pfpsX0 with X0 decaying to a), b)γγ, c) pi+pi−pi0 and d) ηpi+pi−.Figure 2: a), b) and c) The xF distribution for the pi0, η and η′ respectively. d), e) and f) ThedPT spectra for the pi0, η and η′ respectively.Figure 3: The four momentum transfer squared (|t|) from one of the proton vertices for thea) pi0, b) η and c) and η′. The azimuthal angle (φ) between the two outgoing protons for thed) pi0, e) η and f) and η′.8Figure 19Figure 210Figure 311

A study of pseudoscalar states produced centrally in pp interactions at 450 GeV/c

A study of pseudoscalar states produced centrally in pp interactions at
  450 GeV/c

A study of pseudoscalar states produced centrally in pp interactions at 450 GeV/c

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