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Double diffractive Higgs production at $pp$ (or $\bar{p}p$) colliders continues to attract attention as a potential signal in the search for the boson. We present improved perturbative QCD estimates of the event rates for both the exclusive and inclusive double diffractive Higgs processes, paying particular attention to the survival probability of the rapidity gaps. We find that the major uncertainty is in the prediction for the survival probability associated with soft rescattering. We show that an analogous process, the double diffractive production of a pair of jets with large values of $E_T$, has an event rate which makes it accessible at the Tevatron. Observation of this process can therefore be used as a luminosity monitor for two- gluon exchange processes, such as the production of a Higgs boson with rapidity gaps on either side.Comment: 20 pages LaTex + 3 figure

Abstract:The singlet contribution to the g 1 (x, Q 2 ) structure function is calculated in the double-logarithmic approximation of perturbative QCD in the region x ≪ 1. Double logarithmic contributions of the type (α s ln 2 (1/x)) k which are not included in the GLAP evolution equations are shown to give a power-like rise at small-x which is much stronger than the extrapolation of the GLAP expressions. The dominant contribution is due to the gluons which, in contrast to the unpolarized case, mix with the fermions also in the region x ≪ 1. The two main reasons why the small-x behavior of the double logarithmic approximation is so much stronger than the usual GLAP evolution are: the larger kinematical region of integration (in particular, no ordering in transverse momentum) and the contributions from non-ladder diagrams.

We show that high energy hadronic reactions which contain a rapidity gap and a hard subprocess have a specific dependence on the kinematic variables, which results in a characteristic behaviour of the survival probability of the gap. We incorporate this mechanism in a two-channel eikonal model to make an essentially parameter-free estimate of diffractive dijet production at the Tevatron, given the diffractive structure functions measured at HERA. The estimates are in surprising agreement with the measurements of the CDF collaboration. We briefly discuss the application of the model to other hard processes with rapidity gaps.Comment: 18 pages, 5 figures, Late

We compare the W W and pomeron-pomeron fusion mechanisms for the doublediffractive production of a Higgs boson. We determine the suppression of the 'rapidity gap' pomeron-pomeron fusion events due to QCD radiative effects. In particular we use leading log techniques to estimate the cross sections for both exclusive and inclusive double-diffractive Higgs production at LHC energies. The same approach can be applied to the double-diffractive central production of large E T dijets. These two processes provide one of the most justified applications of various aspects of leading logarithm QCD techniques.

The singlet contribution to the g 1 (x, Q 2 ) structure function is calculated in the double-logarithmic approximation of perturbative QCD in the region x ≪ 1. Double logarithmic contributions of the type (α s ln 2 (1/x)) k which are not included in the GLAP evolution equations are shown to give a power-like rise at small-x which is much stronger than the extrapolation of the GLAP expressions. The dominant contribution is due to the gluons which, in contrast to the unpolarized case, mix with the fermions also in the region x ≪ 1. The two main reasons why the small-x behavior of the double logarithmic approximation is so much stronger than the usual GLAP evolution are: the larger kinematical region of integration (in particular, no ordering in transverse momentum) and the contributions from non-ladder diagrams.

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