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the mechanism of exclusive production of mesons at high energies became recently a very active field of research ( see e.g. ref . @xcite and references therein ) . central exclusive production processes represent a very promising and novel way to study qcd in hadron - hadron collisions . recently , there is a growing interest in understanding exclusive three - body reactions @xmath6 at high energies , where the meson ( resonance ) @xmath7 is produced in the central rapidity region . in particular , these reactions provide a valuable tool to investigate in detail the properties of resonance states . many of the resonances decay into @xmath8 and/or @xmath9 channels . the representative examples are : @xmath10 and , as we shall emphasis here , @xmath2 . various decay channels can be studied . it is clear that these resonances are seen ( or will be seen ) `` on '' the background of a @xmath8 or @xmath9 continuum . production ( see e.g. ref . @xcite ) . ] the two - pion background to exclusive production of @xmath11 meson was already discussed in ref . the recent works concentrated on the production of @xmath12 mesons ( see e.g. refs . @xcite and references therein ) where the qcd mechanism is similar to the exclusive production of the higgs boson . furthermore , the @xmath13 states are expected to annihilate via two - gluon processes into light mesons and may , therefore , allow the study of glueball production dynamics @xcite .    recently , the cdf collaboration has measured the cross section for exclusive production of @xmath12 mesons in proton - antiproton collisions at the tevatron @xcite , by selecting events with large rapidity gaps separating the centrally produced state from the dissociation products of the incoming protons . in this experiment @xmath12 mesons are identified via decay to the @xmath14 with @xmath15 channel . the experimental invariant mass resolution was not sufficient to distinguish between scalar , axial and tensor @xmath12 . while the branching fractions to this channel for axial and tensor mesons are large @xcite ( @xmath16 and @xmath17 , respectively ) the branching fraction for the scalar meson is very small @xmath18 @xcite . on the other hand , the cross section for exclusive @xmath2 production obtained within the @xmath3-factorization is much bigger than that for @xmath19 and @xmath20 . as a consequence , all @xmath21 mesons give similar contributions @xcite to the @xmath14 decay channel . clearly , the measurement via decay to the @xmath14 channel can not provide cross section for different @xmath12 . could other decay channels be used ? the @xmath2 meson decays into several two - body channels ( e.g. @xmath22 , @xmath23 , @xmath24 ) or four - body hadronic modes ( e.g. @xmath25 , @xmath26 ) . the branching ratios are shown in table  [ tab : hadronic_modes ] . in this paper we analyze a possibility to measure @xmath2 via its decay to @xmath27 channel . the advantage of this channel is that the @xmath27 continuum has been studied recently @xcite and is relatively well known . in addition the axial @xmath19 does not decay to the @xmath22 channel and the branching ratio for the @xmath20 decay into two pions is smaller . a much smaller cross section for @xmath20 production means , in practice , that only @xmath2 will contribute to the signal .    .branching fractions for the @xmath28 two- and four - body hadronic decays , taken from ref . @xcite . [ cols="^,^,^,^",options="header " , ] the main experimental task is to measure the distributions in the @xmath2 rapidity and transverse momentum . can one recover such distributions based on the measured ones in spite of the severe cuts on pion kinematical variables ? in fig . [ fig : ratio ] we show the two - dimensional ratio of the cross sections for the @xmath2 meson in its rapidity and transverse momentum : @xmath29 the numerator includes limitations on @xmath30 and @xmath31 . these distributions provide a fairly precise evaluation of the expected acceptances when experimental cuts are imposed . the experimental data could be corrected by our two - dimensional acceptance function to recover the distributions of interest . it was realized recently that the measurement of exclusive production of @xmath21 via decay in the @xmath14 channel can not give production cross sections for different species of @xmath21 . in this decay channel the contributions of @xmath21 mesons with different spins are similar and experimental resolution is not sufficient to distinguish them .    in the present paper we have analyzed a possibility to measure the exclusive production of @xmath2 meson in the proton-(anti)proton collisions at the lhc , tevatron and rhic via @xmath32 decay channel . since the cross section for exclusive @xmath2 production is much larger than that for @xmath19 and @xmath20 and the branching fraction to the @xmath22 channel for @xmath2 is larger than that for @xmath20 ( @xmath19 does not decay into two pions ) the two - pion channel should provide an useful information about the @xmath2 exclusive production .    we have performed detailed studies of several differential distributions and demonstrated how to impose extra cuts in order to improve the signal - to - background ratio . the two - pion background was calculated in a simple model with parameters adjusted to low energy data . we have shown that relevant measurements at tevatron and lhc are possible . at rhic the signal - to - background ratio is much worse but measurements should be possible as well . imposing cuts distorts the original distributions for @xmath2 in rapidity and transverse momentum . we have demonstrated how to recover the original distributions and presented the correction functions for some typical experimental situations .    in the present paper we have concentrated on @xmath33 channel only . this is mainly due to the relatively good control of the background . measurements of other decay channels , e.g. @xmath23 , are possible as well and will be discussed elsewhere . * acknowledgments * this study was partially supported by the polish grant of mnisw n n202 249235 . r. barbieri , m. caffo , r. gatto and e. remiddi , nucl . b192 * ( 1981 ) 61 ; w. kwong , p.b . mackenzie , r. rosenfeld and j.l . rosner , phys . * d37 * ( 1988 ) 3210 ; m.l . mangano and a. patrelli , b352 * ( 1995 ) 445 .
we consider a measurement of exclusive production of scalar @xmath0 meson in the proton - proton collisions at lhc and rhic and in the proton - antiproton collisions at the tevatron via @xmath1 decay . 
 the corresponding amplitude for exclusive double - diffractive @xmath2 meson production was obtained within the @xmath3-factorization approach including virtualities of active gluons and the corresponding cross section is calculated with unintegrated gluon distribution functions ( ugdfs ) known from the literature . 
 the four - body @xmath4 reaction constitutes an irreducible background to the exclusive @xmath2 meson production . 
 we calculate several differential distributions for @xmath5 process including absorptive corrections . the influence of kinematical cuts on the signal - to - background ratio is investigated . 
 corresponding experimental consequences are discussed .