The first three pomerons...

A model of a three pomeron contribution to high energy elastic pp and scattering is proposed. The data are well described for all momenta ( GeV) and energies ( GeV) (). The model predicts the appearance of two dips in the differential cross-section which will be measured at LHC. The parameters of the pomeron trajectories are . Received: 11 July 2001 / Published online: 20 December 2001     

Hard diffractive quarkonium hadroproduction at high energies

We present a study of heavy quarkonium production in hard diffractive processes by pomeron exchange for Tevatron and LHC energies. The numerical results are computed using a recent experimental determination of the diffractive parton density functions in the pomeron and these are corrected by unitarity corrections through the gap survival probability factor. We give predictions for single as well as central diffractive ratios. These processes are sensitive to the gluon content of the pomeron at small Bjorken variable x and may be particularly useful in studying small-xphysics. They may also be a good place to test the different available mechanisms for quarkonium production at hadron colliders. PACS 13.60.Hb; 12.38.Bx; 12.40.Nn; 13.85.Ni; 14.40.Gx     

Double pomeron exchange in high-energy pp collisions

The double pomeron exchange cross section in high-energy pp collisions is analyzed in detail for different phase-space cuts. The ratio of double pomeron exchange signal to diffraction dissociation background is examined as a function of s. The theoretical predictions are found to be in excellent agreement with the recent results of the experiments at the CERN ISR. The properties of the central cluster as well as the predictions for high energies are discussed.     

Unitarity and the BFKL pomeron

High energy onium-onium scattering is calculated as a function of impact parameter in the one- and two-pomeron exchange approximation. Difficulties with using the multiple scattering series to unitarize single pomeron exchange at high energy are noted. An operator formalism which sums all numbers of pomeron exchange is given. A toy model which has a similar operator structure at high energy as QCD is presented and the S-matrix is evaluated. Estimates of the energies and impact parameters at which blackness occurs in onium-onium scattering are given. It is emphasized that the problem of unitarity in high energy onium-onium scattering can be solved in a purely perturbative context, with a non-running coupling if the onium is heavy enough.     

Associated J/ψ+γ Production Through Double Pomeron Exchange: the Nature of the Pomeron and Hard Diffractive Factorization Breaking

We present a study of associated J/ψ+γ production through double pomeron exchange at energies reached at the Fermilab Tevatron.and CERN LHC based on the Ingelman-Schlein model for hard difiactive scattering and the factorization formalism of nonrelativistic QCD for quarkonia production. We find that the process p+p→p +p + J/ψ+γ + X can be used to probe the gluon content of the pomeron and study the nature of hard difiactive factorization breaking.     

Finite nuclei in the reggeon “toy model”

Hadron–nucleus amplitudes at high energies are studied in the “toy” Regge model in zero transverse dimension for finite nuclei, when the standard series of fan diagrams is converted into a finite sum and loses physical sense at quite low energies. Taking into account all the loop contributions by numerical methods we find a physically meaningful amplitudes at all energies. They practically coincide with the amplitudes for infinite nuclei. A surprising result is that for finite nuclei and small enough triple pomeron coupling the infinite series of fan diagrams describes the amplitude quite well in spite of the fact that in reality the series should be cut and as such deprived of any physical sense at high energies.     

Cluster production and the pomeron in meson-baryon and baryon-baryon collisions

The bare pomeron in models based on duality diagrams is found to contribute very differently at low energies to pp and Kp total cross-sections. A simple quantitative comparison of these cross-sections is found to be consistent with phenomenological cluster production models.     

Unitarisation and black-disk limit at the LHC in the presence of a hard pomeron

Recent models of soft diffraction include a hard pomeron pole besides the usual soft term. Such models violate the black-disk limit around Tevatron energies, so that they need to be supplemented by a unitarisation scheme. Two standard schemes are considered in this Letter, and we show that they lead to an uncertainty at the LHC much larger than previously estimated. We also examine the signature of unitarisation on various small-t observables, the slope in t of the elastic cross section, or the ratio of the real to imaginary parts of the scattering amplitude, and show that the existence of a unitarised hard pomeron in soft scattering may be confirmed by LHC data.     

Proton–proton interaction in constituent quarks model at LHC energies

In this paper we consider soft processes at LHC energies in the framework of the constituent quark model. We show that this rather naive model is able to describe all available soft process data at lower energies and to predict the behavior of the total cross section, the elastic and diffractive cross sections at LHC energy. It turns out that the “input” pomeron that has been used in this approach has parameters that are close to the so called “hard” pomeron with rather large intercept Δ≈0.12 and small value of the slope α^′ _P≈0.08 GeV^-2. We show that the elastic amplitude has a minimum at impact parameter b=0 and a maximum at b≈2 GeV^-1. Such a behavior is the result of overlapping of the parton clouds that belong to the different quarks in the hadron.     

Spin effects in hadron scattering at very high energies

In this paper a spin-dependent diffractive model is studied for πN and NN elastic scattering. We find non-trivial results for spin correlation parameters which persist at high energies and have very distinct features in the dip region. It is stressed that these parameters provide good tests of pomeron factorization.     

Search for glue balls in a pomeron pomeron scattering experiment

The exclusive reactionpp→ppπ⁺ π^? has been studied using the SFM spectrometer at ISR energies of \(\sqrt s = 24\) and 63 GeV. The cross section in the double pomeron exchange region defined by |x _p |>0.9, |y _π |<1 is 28±6, 23(+13, ?6) and 29(+29, ?10)μb, respectively. The ππ mass spectrum is dominated by an 1/m _ππ ² part, as expected for pomeron pomeron scattering. In addition, thef(1, 270) resonance is clearly distinguished. There are no further resonance signals, which could be assigned to glueball candidates expected in the 1,000 MeV region. Compared to photon photon scattering, the ratio of continuum tof-resonance production cross sections is significantly larger in pomeron pomeron scattering.     

The bootstrap condition for many reggeized gluons and the photon structure function at lowx andN c����

The bootstrap condition is generalized ton reggeized gluons. As a result it is demonstrated that the intercept generated byn reggeized gluons cannot be lower than the one forn=2. Arguments are presented that in the limitN _c???? the bootstrap condition reduces then gluon chain with interacting neighbours to a single BFKL pomeron. In this limit the contribution fromn gluons leading at high energies corresponds ton/2 non-interacting BFKL pomerons (then/2 pomeron cut). The sum overn leads to a unitary??*?? amplitude of the eikonal form.     

The bootstrap condition for many reggeized gluons and the photon structure function at lowx andN c→∞

The bootstrap condition is generalized ton reggeized gluons. As a result it is demonstrated that the intercept generated byn reggeized gluons cannot be lower than the one forn=2. Arguments are presented that in the limitN _c→∞ the bootstrap condition reduces then gluon chain with interacting neighbours to a single BFKL pomeron. In this limit the contribution fromn gluons leading at high energies corresponds ton/2 non-interacting BFKL pomerons (then/2 pomeron cut). The sum overn leads to a unitaryγ*γ amplitude of the eikonal form.     

Particle production at high energies in the Cardy pomeron model

Particle production at very high energies inhh, hA andAB collisions is studied in the framework of the pomeron model with a strong self-interaction proposed by Cardy. It is shown that the interaction between pomerons substancially damps the production rate one nuclei, the multiplicities forhA collisions becomingA-independent.     

Probing the structure of the pomeron

We suggest that the pseudo-rapidity cut dependence of diffractive deep-inelastic scattering events at HERA may provide a sensitive test of models of diffraction. A comparison with the experimental cross section shows that the Donnachie-Landshoff model and a simple two-gluon exchange model of the pomeron model are disfavoured. However a model with a direct coupling of the pomeron to quarks is viable for a harder quark–pomeron form factor, as is a model based on the leading-twist operator contribution. We also consider a direct-coupling scalar pomeron model. We comment on the implications of these results for the determination of the partonic structure of the pomeron. Received: 5 March 1999 / Published online: 3 August 1999     

A new interpretation of the absorption mechanism for high energy scattering

We propose a new s-channel absorption mechanism for high energy processes. A possible small dimensionless physical quantity naturally emerges. Consequently, the proposed s-channel equation can accommodate, at present energies, an elastic amplitude dominated by a simple factorizable bare pomeron pole, as in the t-channel perturbative expansion of the Gribov's Reggeon calculus in the strong coupling limit.     

Triple pomeron vertex in the limit N_c\rightarrow\infty

In the hard pomeron theory with the number of colours the diffractive amplitude obtained in [3] is compared with the results found for in [1] and in the dipole approach in [5]. It is shown that the double pomeron exchange contribution can be substituted by an equivalent triple pomeron interaction term. After such a substitution the triple pomeron vertices in [1,3,5] essentially coincide. It is demonstrated that, in any form, the triple pomeron vertex is conformal invariant. It is also shown that higher order densities in the dipole approach do not involve 1 to k pomeron verteces with but are rather given by a set of pomeron fan diagrams with only a triple pomeron coupling. Received: 11 December 1997 / Revised version: 6 February 1998 / Published online: 7 August 1998