Inclusive Double-Pomeron Exchange at the Fermilab Tevatron p¯p Collider (original) (raw)
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Physics Letters B, 1998
The reaction γγ → J/ΨJ/Ψ is discussed assuming dominance of the QCD BFKL pomeron exchange. We give prediction for the cross-section of this process for LEP2 and TESLA energies. We solve the BFKL equation in the non-forward configuration taking into account dominant non-leading effects which come from the requirement that the virtuality of the exchanged gluons along the gluon ladder is controlled by their transverse momentum squared. We compare our results with those corresponding to the simple two gluon exchange mechanism and with the BFKL pomeron exchange in the leading logarithmic approximation. The BFKL effects are found to generate a steeper t-dependence than the two gluon exchange. The cross-section is found to increase with increasing CM energy W as (W 2) 2λ. The parameter λ is slowly varying with W and takes the values λ ∼ 0.23 − 0.28. The magnitude of the total cross-section for the process γγ → J/ΨJ/Ψ is found to increase from 4 to 26 pb within the energy range accessible at LEP2.
Physics Letters B - PHYS LETT B, 2010
We evaluate within the LO DGLAP approximation the dependence on energy of the cross section of the photo(electro)production of vector meson V (V=J/ψ,…) in the hard elastic processes off a parton γ∗+g→V+g as the function of momentum transfer t=(qγ−pV)2. We demonstrate that in the limit −t⩾mV2+Q2 the cross section does not contain double logarithmic terms in any order of the DGLAP approximation leading to the energy independent cross section. Thus the energy dependence of cross section γ∗+p→J/ψ+rapidity gap+X is governed at large t by the gluon distribution within a proton, i.e. it is unambiguously predicted within the DGLAP approximation including the stronger WγN dependence at larger −t. This prediction explains recent HERA data. The calculations which follow perturbative Pomeron logic predict opposite trend of a weaker WγN dependence at larger t. We explain that at the HERA energies double logarithmic terms characteristic for DGLAP approximation dominate in the hard processes as th...
Large rapidity gap reactions on nuclei: breakdown of QCD factorization
Nuclear Physics B - Proceedings Supplements, 2005
The relative production rate of high-pT hadrons in deuteron-gold and proton-proton collisions measured at forward rapidities in the BRAHMS experiment is found to be suppressed. Observing other reactions, one may notice that any reaction (forward production of light hadron, Drell-Yan process, heavy avor production, etc.) expose the same property: the cross section at large xF is suppressed by nuclei. Although it is tempting to interpret this e ect as a result of coherence, or color glass condensate, it takes place even at low energies. We demonstrate here that there is a suppression mechanism common for all reactions which can be understood as Sudakov suppression or as a reduced survival probability of a large rapidity gap process in nuclei. This is con rmed by calculations, which provide a good description for all the reactions under consideration.
Generalized parton distributions and rapidity gap survival in exclusive diffractive pp scattering
Physical Review D, 2007
We propose a new approach to the problem of rapidity gap survival (RGS) in the production of high-mass systems (H = dijet, heavy quarkonium, Higgs boson) in double-gap exclusive diffractive pp scattering, pp → p + (gap) + H + (gap) + p. It is based on the idea that hard and soft interactions proceed over widely different time-and distance scales and are thus approximately independent. The high-mass system is produced in a hard scattering process with exchange of two gluons between the protons. Its amplitude is calculable in terms of the gluon generalized parton distributions (GPDs) in the protons, which can be measured in J/ψ production in exclusive ep scattering. The hard scattering process is modified by soft spectator interactions, which we calculate in a model-independent way in terms of the pp elastic scattering amplitude. Contributions from inelastic intermediate states are suppressed. A simple geometric picture of the interplay of hard and soft interactions in diffraction is obtained. The onset of the black-disk limit in pp scattering at TeV energies strongly suppresses diffraction at small impact parameters and is the main factor in determining the RGS probability. Correlations between hard and soft interactions (e.g. due to scattering from the long-range pion field of the proton, or due to possible short-range transverse correlations between partons) further decrease the RGS probability. We also investigate the dependence of the diffractive cross section on the transverse momenta of the final-state protons ("diffraction pattern"). By measuring this dependence one can perform detailed tests of the interplay of hard and soft interactions, and even extract information about the gluon GPD in the proton. Such studies appear to be feasible with the planned forward detectors at the LHC.
Hard diffraction from parton rescattering in QCD
Physical Review D, 2005
We analyze the QCD dynamics of diffractive deep inelastic scattering. The presence of a rapidity gap between the target and diffractive system requires that the target remnant emerges in a color singlet state, which we show is made possible by the soft rescattering of the struck quark. This rescattering is described by the path-ordered exponential (Wilson line) in the expression for the parton distribution function of the target. The multiple scattering of the struck parton via instantaneous interactions in the target generates dominantly imaginary diffractive amplitudes, giving rise to an 'effective pomeron' exchange. The pomeron is not an intrinsic part of the proton but a dynamical effect of the interaction. This picture also applies to diffraction in hadron-initiated processes. Due to the different color environment the rescattering is different in virtual photonand hadron-induced processes, explaining the observed non-universality of diffractive parton distributions. This framework provides a theoretical basis for the phenomenologically successful Soft Color Interaction model which includes rescattering effects and thus generates a variety of final states with rapidity gaps. We discuss developments of the SCI model to account for the color coherence features of the underlying subprocesses.