We study the double-diffractive production of various heavy systems (e.g. Higgs, dijet, tt and SUSY particles) at LHC and Tevatron collider energies. In each case we compute the probability that the rapidity gaps, which occur on either side of the produced system, survive the effects of soft rescattering and QCD bremsstrahlung effects. We calculate both the luminosity for different production mechanisms, and a wide variety of subprocess cross sections. The results allow numerical predictions to be readily made for the cross sections of all these processes at the LHC and the Tevatron collider. For example, we predict that the cross section for the exclusive double-diffractive production of a 120 GeV Higgs boson at the LHC is about 3 fb, and that the QCD background in the bb decay mode is about 4 times smaller than the Higgs signal if the experimental missing-mass resolution is 1 GeV. For completeness we also discuss production via γγ or W W fusion.

E the !& decade jet physics h s bee. i&~sive!y .?-.died zt ete-afid hadro~ic colliders. With the start of LEP activity a wealth of new data has become available (see, for example, [l]). They show that the global features of hadronic jets systems (multiplicities, angular patterns of particle flows, inclusive energy spectra etc), calcnlated at the parton level, agree very well with the measured ones. This convincingly demonstrates the dominant role of the perturbative (PT) phase of jet evolution and strongly supports the hypothesis of local parton-hadron duality (LPHD) [Zj 31; Such a local duality is naturally connected with the 'preconfinement' properties [4] of the QCD cascades. Together with the modified leading logarithmic approximation (MLLA)

We present a formalism for high energy soft processes, mediated by Pomerons, which embodies pion-loop insertions in the Pomeron trajectory, rescattering effects via a twochannel eikonal and high-mass diffractive dissociation. It describes all the main features of the data throughout the ISR to Tevatron energy interval. We give predictions for soft diffractive phenomena at the LHC energy, and we calculate the different survival probabilities of rapidity gaps which occur in various diffractive processes.

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

In this review we discuss the analytical perturbative approach, based on perturbative QCD and local parton hadron duality (LPHD), and its application to multiparticle production in jets in the semisoft region. Analytical formulae are presented for various observables within the accuracy of the modified leading logarithmic approximation (MLLA), i.e. with terms of relative order [Formula: see text] taken into account systematically, and in some cases with even higher accuracy. These predictions are confronted with existing experimental data. Many details of the perturbative approach to multiple hadroproduction have been consolidated in recent years, and the overall picture is remarkably healthy. The prospects of future studies of the semisoft jet physics are also discussed.