We consider exclusive double diffractive production of scalar χ_c(0^+), axial-vector χ_c(1^+) and tensor χ_c(2^+) charmonia in proton-(anti)proton collisions at different energies. The corresponding amplitudes for these processes are derived within the k_t-factorisation approach and the corresponding cross section is calculated with different unintegrated gluon distribution functions (UGDFs) known from the literature. We compare exclusive production of all charmonium states χ_c(0^+), χ_c(1^+) and χ_c(2^+) including branching fraction for radiative J/Ψ+ γdecay channel. Corresponding experimental consequences are discussed.
We discuss the different models of central diffractive production of the Higgs boson at the Tevatron and the LHC. We also describe how the models can be tested using diffractive production data being taken at the Tevatron. We finally discuss the advantages of using diffractive events to reconstruct the mass of the Higgs boson especially at the LHC.
We review the diffractive measurements made by the CDF and DØ collaborations during Run I at the Tevatron and summarize the detector upgrades relevant for the Run II diffractive physics program.
Improved possibilities to find the Higgs boson in diffractive events, having less hadronic activity, depend on whether the cross section is large enough. Based on the soft color interaction models that successfully describe diffractive hard scattering at HERA and the Tevatron, we find that only a few diffractive Higgs events may be produced at the Tevatron, but we predict a substantial rate at the LHC.
We use the POMWIG Monte Carlo generator to predict the cross-sections for double diffractive higgs and di-photon production at the Tevatron and LHC. We find that the higgs production cross-section is too small to be observable at Tevatron energies, and even at the LHC observation would be difficult. Double diffractive di-photon production, however, should be observable within one year of Tevatron Run II.
Measurements of soft and hard diffractive processes have been performed at the Tevatron p-pbar collider during the past decade. Diffractive events are studied by means of identification of one or more rapidity gaps and/or a leading antiproton. Here, results are discussed within the Tevatron data and compared to those obtained at the HERA ep collider. The traditional ``pomeron'' is described within the framework of QCD and the issues discussed include pomeron structure, diffractive cross section factorization, and universality of rapidity gap formation. Exclusive dijet and low-mass state produc…
We make a brief presentation of the soft colour interactions models, the Soft Colour Interaction and the Generalised Area Law, and summarise the results when they are applied to p-pbar scattering. The models give a good description of the Tevatron data on production of W, bottom and jets in diffractive events, as well as jets with two rapidity gaps, alternatively leading particles. We also give predictions for diffractive J/psi production and discuss diffractive Higgs production at the Tevatron and LHC.
Experimental results in diffractive processes are summarized and a few notable characteristics described in terms of Quantum Chromodynamics. Exclusive dijet production is used to establish a benchmark for future experiments in the quest for diffractive Higgs production at the Large Hadron Collider. Using new data from the Tevatron and dedicated diffractive triggers, no excess over a smooth falling distribution for exclusive dijet events could be found. Stringent upper limits on the exclusive dijet production cross section are presented. The quark/gluon composition of dijet final states is used…
We discuss the observed scaling of the small-x diffractive and total deep-inelastic structure functions at HERA. We argue that the parton interpretation of Buchmüller and Hebecker can be understood within QCD as the appearance of the Pomeron in a Super-Critical phase. In diffractive hard scattering, the Pomeron appears as reggeized gluon exchange in a color-compensating background field. The formalism can also be applied to diffractive $W$ production at the Tevatron. If the scaling is a true asymptotic property then it should anticipate the appearance of a further massive sector of QCD and ass…
The single diffractive production of the standard model Higgs boson is computed using the diffractive factorization formalism, taking into account a parametrization for the Pomeron structure function provided by the H1 Collaboration. We compute the cross sections at next-to-leading order accuracy for the gluon fusion process, which includes QCD and electroweak corrections. The gap survival probability ($<\!|S|^2\!>$) is also introduced to account for the rescattering corrections due to spectator particles present in the interaction, and to this end we compare two different models for the survi…
We present predictions for the diffractive production of $χ$ mesons in the central rapidity region usually covered by collider detectors. The predicted cross sections are based on the Bialas-Landshoff formalism for both exclusive and inclusive production and makes use of the DPEMC Monte-Carlo simulation adapted with kinematics appropriate for small-mass diffractive production. We compare generator-level results with a CDF measurement for exclusive $χ$ production, and study background and other scenarios including the contribution of inclusive $χ$ production. The results agree with the Tevatron…
The 1994 data published by the H1 collaboration are compared with models based on Regge phenomenology. The $x_{\PO}$ dependence of the data can be described in a model based on the exchange of a dominant diffractive (pomeron) trajectory with additional sub-leading reggeon contributions. The dynamics of the Pomeron structure is studied within the framework of perturbative QCD and new parton distributions are obtained. These parton distributions will allow a direct test of factorisation breaking at Tevatron.
We give predictions for diffractive heavy flavour production at the Tevatron and the LHC in leading--order approximation. In the framework of these studies we use three different models for the partonic structure of the Pomeron recently proposed by Stirling and Kunszt. These Pomeron models are, despite being fitted to the same diffractive deep inelastic HERA data, very different in their parton content and taken together provide a powerful tool to probe the structure of the Pomeron. All models satisfy GLAP evolution and show a significant $Q^2$ dependence. We give numerical predictions for sin…
We evaluate, in a model-independent way, the signal-to-background ratio for Higgs -> b bbar detection in exclusive double-diffractive events at the Tevatron and the LHC. For the missing-mass approach to be able to identify the Higgs boson, it will be necessary to use a central jet detector and to tag b quark jets. The signal is predicted to be very small at the Tevatron, but observable at the LHC. However we note that the background, that is double-diffractive dijet production, may serve as a unique gluon factory. We also give estimates for the double-diffractive production of chi_c and chi_b …
We have studied events with a high-x_F antiproton and two central jets with E_T>7 GeV in CDF, in p+p_bar collisions at sqrt(s) = 1800 GeV. From the di-jet kinematics we derive the diffractive structure function of the antiproton. We also find an excess of events with a rapidity gap at least 3.5 units wide in the proton direction, which we interpret as di-jet production in double pomeron exchange events. We find non-factorization between our single diffractive results and (a) diffraction in ep at HERA (b) double pomeron exchange.
The most important consequence of Pomeron being a pole is the factorization property. However, due to Pomeron intercept being greater than 1, the extrapolated single diffraction dissociation cross section based on a classical triple-Pomeron formula is too large leading to a potential unitarity violation at Tevatron energies. It is our desire here to point out that the "flavoring" of Pomeron plays the dominant role in resolving this apparent "paradox".
The diffractive production of vector bosons at the Tevatron is studied. We take a hard pomeron flux and use the H1 parton density functions extracted from their measurement of F_2^{D(3)}. To this we add a reggeon exchange contribution. We find that the ratio of diffractive to non-diffractive W boson production is in good agreement with the CDF data. We note that the poorly understood reggeon contribution might be as large as the pomeron contribution in the kinematic range of the data. We also note that our pomeron exchange contribution is much smaller than earlier predictions due to our use of…
We show that the cross section of the diffractive production of $b \bar b$ can be described as the sum of two contributions: the first is proportional to the probability of finding a small size $b \bar b$ color dipole in the fast hadron wave function before the interaction with a target, while the second is the $b \bar b$-production after or during the interaction with the target. The formulae are presented as well as the discussion of the interralation between these two contributions and the Ingelman- Schlein and coherent diffraction mechanisms. The main precdition is that the coherent diffra…
Central exclusive production (CEP) processes in high-energy hadron collisions offer a very promising framework for studying both novel aspects of QCD and new physics signals. We report on the results of a theoretical study of the CEP of heavy quarkonia (chi and eta) at the Tevatron, RHIC and LHC. These processes provide important information on the physics of bound states and can probe the current ideas and methods of QCD, such as effective field theories and lattice QCD.
The CDF Forward Detector upgrade project was designed to enhance the capabilities for diffractive physics at the Tevatron. It consists of a Roman Pot spectrometer to detect leading antiprotons, a set of counters near and around the beam-pipe to reject the non-diffractive event contamination to the data sample, and two Miniplug calorimeters to measure the event energy flow in the very forward rapidity region. In the novel design of the Miniplugs, a lead/liquid-scintillator is read out by wave-length shifting fibers arranged in a flexible tower geometry and relatively short depth allows calorime…
Recent results on diffraction at HERA, from the H1 and ZEUS Collaborations, and at Tevatron, from the CDF and D0 Collaborations, are reviewed. The measurement of the diffractive structure function at HERA is presented, and the pomeron structure function is extracted from QCD fits. Diffractive dijet production is given as an example analysis of the diffractive final state. These analysis are consistent with a leading gluon partonic structure for the pomeron. Hard single diffraction, double diffraction and double pomeron exchange processes are studied at the Tevatron and complement the studies p…
The process of soft diffractive dissociation in hadronic collisions is discussed in the framework of the Miettinen-Pumplin model. A good description of the data in the ISR-Tevatron energy range is found. Predictions for the total, elastic and single diffractive cross sections for the LHC are also presented. The total cross section is expected to be 15% smaller than that given by Donnachie and Landshoff in the model with soft pomeron. The diffractive cross section remains constant in the Tevatron-LHC energy range.
An improved understanding of nonperturbative QCD can be obtained by the recently developed soft color interaction models. Their essence is the variation of color string-field topologies, giving a unified description of final states in high energy interactions, e.g., diffractive and nondiffractive events in ep and ppbar. Here we present a detailed study of such models (the soft color interaction model and the generalized area law model) applied to ppbar, considering also the general problem of the underlying event including beam particle remnants. With models tuned to HERA ep data, we find a go…
We study the double-diffractive production of various heavy systems (e.g. Higgs, dijet, t tbar 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 collid…
We briefly present the soft colour interaction models which are successful in reproducing a multitude of diffractive hard scattering data, and give predictions for diffractive Higgs production at the Tevatron and LHC. Only a few diffractive Higgs events may be produced at the Tevatron, but we predict a substantial rate at the LHC.
We quantify the rate and the signal-to-background ratio for Higgs --> b anti-b detection in double-diffractive events at the Tevatron and the LHC. The signal is predicted to be very small at the Tevatron, but observable at the LHC. We show that the double-diffractive dijet production may serve as a unique gluon factory. This process can be used also as a Pomeron-Pomeron luminosity monitor.
Diffractive production of the Higgs boson at hadron colliders is discussed in the light of the observed rate of hard diffractive dijet events at the Tevatron. The Higgs predictions of models successful for dijets are compared. LHC seems promising for a diffractive light Higgs boson and its mass determination. Hard diffractive dijets, diphotons and dileptons at the Tevatron (Run II) will be necessary to remove the remaining large uncertainties on cross-sections and signals.
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 two-channel 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.
In the prospect of diffractive Higgs production at the LHC collider, we give an extensive study of Higgs boson, dijet, diphoton and dilepton production at hadronic colliders via diffraction at both hadron vertices. Our model, based on non factorizable Pomeron exchange, describes well the observed dijet rate observed at Tevatron Run I. Taking the absolute normalization from data, our predictions are given for diffractive processes at Tevatron and LHC. Stringent tests of our model and of its parameters using data being taken now at Tevatron Run II are suggested. These measurements will also allo…
We compute the cross section for exclusive double-diffractive gamma-gamma production at the Tevatron, $p{\bar p} \to p + γγ+ {\bar p}$, and the LHC. We evaluate both the gluon-gluon and quark-antiquark t-channel exchange contributions to the process. The observation of exclusive gamma-gamma production at the Tevatron will provide a check on the model predictions, and offer an opportunity to confirm the expectations for exclusive double-diffractive Higgs production at the LHC.
We extract diffractive parton densities from diffractive, deep inelastic (DIS) ep data from the ZEUS experiment. Then we use these fits to predict the diffractive production of jets and of W's and Z's in p\bar p collisions at the Tevatron. Although the DIS data require a hard quark density in the pomeron, we find fairly low rates for the Tevatron processes (a few percent of the inclusive cross section). This results from the combined effects of Q^{2} evolution and of a normalization of the parton densities to the data. The calculated rates for W production are generally consistent with the pre…
Results from a phenomenological analysis of dijet and W hard diffractive hadroproduction at Fermilab Tevatron energies are reported. The theoretical framework employed here is a modified version of the Ingelman-Schlein approach which includes DGLAP-evolved structure functions. Different from what has been achieved by the DESY ep HERA reactions, a reasonable overall description of such diffractive hadron processes is obtained only when a complex, quark-rich Pomeron structure function is employed in the calculation.
We present the first NLO QCD analysis of single-diffractive dijet production in proton-antiproton collisions. By comparing the ratio of single- and non-diffractive cross sections to data from the Tevatron, the rapidity-gap survival probability is determined as a function of the momentum fraction of the parton in the antiproton. Assuming Regge factorization, this probability can be interpreted as a suppression factor for the diffractive structure function measured in deep-inelastic scattering at HERA. In contrast to the observations for photoproduction, the suppression factor in proton-antiprot…
Central production cross-sections of hard dijets with 2,1 or 0 rapidity gap at Tevatron are analyzed in terms of diffractive (``a la Good-Walker'') and non diffractive fluctuations of the incident particles. The observed large factorization breaking and the unexpected high value of the 2 to 1 gap cross-section ratio are explained in terms of scattering with and between the incident particles.
We perform a NLO QCD analysis of single-diffractive dijet production in proton-antiproton collisions. By comparing the ratio of single- and non-diffractive cross sections to data from the Tevatron, the rapidity-gap survival probability is determined as a function of the momentum fraction of the parton in the antiproton. Assuming Regge factorization, this probability can be interpreted as a suppression factor for the diffractive structure function measured in deep-inelastic scattering at HERA. In contrast to the observations for photoproduction, the suppression factor in proton-antiproton colli…
Exclusive dijet production at the Tevatron can be used as a benchmark to establish predictions on exclusive diffractive Higgs production, a process with a much smaller cross section. Exclusive dijet production in Double Pomeron Exchange processes, including diffractive Higgs production with measurements at the Tevatron and predictions for the Large Hadron Collider are presented. Using new data from the Tevatron and dedicated diffractive triggers, no excess over a smooth falling distribution for exclusive dijet events could be found. Upper limits on the exclusive dijet production cross section …
Models based on soft colour exchanges to rearrange colour strings in the final state provide a general framework for both diffractive and non-diffractive events in ep and hadron-hadron collisions. We study two such models and find that they can reproduce rapidity gap data from both HERA and the Tevatron. We also discuss the influence of parton cascades and multiple interactions on the results.
Results on diffractive particle interactions from the Fermilab Tevatron pbar-p collider are placed in perspective through a QCD inspired phenomenological approach, which exploits scaling and factorization properties observed in data. The results discussed are those obtained by the CDF Collaboration from a comprehensive set of single, double, and multigap soft and hard diffraction processes studied during the twenty year period since 1985, when the CDF diffractive program was proposed and the first Blois Workshop was held.
We extract diffractive parton densities from data on diffractive deep inelastic scattering (DIS) and on diffractive photoproduction of jets. We explore the results of several ansaetze for the functional form of the parton densities. Then we use the fitted parton densities to predict the diffractive production of jets and of W's and Z's in p-pbar collisions at the Tevatron. To fit the photoproduction data requires a large gluon density in the Pomeron. The predictions for the Tevatron cross sections are substantially higher than data; this signals a breakdown of hard-scattering factorization in …
We present a study of diffractive associated jpsi + gamma production at the Fermilab Tevatron and LHC based on the Ingelman-Schlein model for hard diffractive scattering and the factorization formalism of NRQCD for quarkonia production. We find that this process (p + pbar to p + jpsi + gamma + X) can be used to probe the gluon content of the Pomeron and test the assumption of diffractive hard scattering factorization. Using the renormalized Pomeron flux factor D simeq 0.11 (0.052), the single diffractive jpsi + gamma production cross section at 4<P_T< 10 GeV, -1<eta<1 region is found to be of …
Hadronic processes in which hard diffractive production takes place have been observed and analyzed in collider experiments for several years. The experimental rates of diffractive W's and dijets measured at the Tevatron and the cross sections of diffractively produced dijets recently obtained at the HERA experiment are the object of this analysis. We use the Pomeron structure function obtained from the HERA data by two different approaches to calculate the rates and cross sections for these processes. The comparison of theoretical predictions with the measured values reveals some discrepancie…
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_…
Models for soft color interactions have been successful in describing and predicting diffractive hard scattering processes in ep collisions at DESY HERA and ppbar at the Fermilab Tevatron. Here we present new comparisons of the model to recent diffractive dijet data, also showing good agreement. The topical issue of diffractive Higgs production at the Tevatron and LHC hadron colliders is further investigated. For H->gamma gamma the irreducible background of prompt photon pairs from qqbar->gamma gamma and gg->gamma gamma is always dominating, implying that higher branching ratio decay modes of …
The forward photoproduction amplitude for gamma p to Upsilon p is calculated in a pQCD k_t-factorization approach with an unintegrated gluon distribution constrained by inclusive deep-inelastic structure functions. The total cross section for diffractive Upsilons is compared with a recent HERA data. We also discuss the 2S/1S ratio in diffractive Upsilon-production. The amplitude is used to predict the cross section for exclusive Upsilon production in hadronic reactions. Differential distributions for the exclusive p pbar to p Upsilon pbar process are calculated for Tevatron energies. We also s…
In this talk, given at "RunII QCD and weak boson WS", we give the highest of reasonable estimates for the value of cross section of the double Pomeron Higgs meson production and suggest a new mechanism for heavy quark diffractive production which will dominate at the Tevatron energies.
We explore the diffractive interaction of a proton with an anti-proton which results in centrally produced dijets. This process has been recently studied at the Tevatron. We make predictions within an Ingelman-Schlein approach and compare them to the recent data presented by the CDF collaboration. Earlier calculations resulted in theoretical cross-sections which are much larger than those observed by CDF. We find that, after consideration of hadronisation effects and the parton shower, and using parton density functions extracted from diffractive deep inelastic scattering at HERA, it is possib…
Virtual photons have both the transverse and longitudinal polarization. In the inclusive DIS the impact of longitudinal photons, quantified by R=sigmaL/\igmaT sim 0.2, is marginal, but in diffractive DIS with excitation of small mass hadronic states or exclusive diffraction into vector mesons, QCD predicts R >> 1 in agreement with the experiment. After a brief review of the modern status of QCD theory of diffractive vector meson production I argue that longitudinally polarized gluons give rise to a large longitudinal polarization of the prompt JPsi and Psiprim observed at the Tevatron.
We use a Monte Carlo implementation of recently developped models of exclusive diffractive $W$, top, Higgs and stop productions to assess the sensitivity of the LHC experiments.
We present and discuss two different topics where Tevatron and HERA data can be compared directly. A method allowing for a direct comparison of data with theoretical predictions is proposed for forward jet production at HERA. An application to the determination of the effective Pomeron intercept in the BFKL-LO parametrization from $dσ/dx$ data at HERA leads to a good fit with a significantly high effective intercept, $α_P= 1.43 \pm 0.025 (stat.) \pm 0.025 (syst.)$. It is less than the value of the pomeron intercept using dijets with large rapidity intervals obtained at Tevatron. In a second pa…
The interest in the study of diffractive meson production is discussed. The description of diffraction within Regge phenomenology is presented, and the QCD-based understanding of diffractive processes is given. Central production is reviewed, and the corresponding main results from the COMPASS experiment and from the experiments at the ISR, RHIC, TEVATRON and LHC collider are summarised.
We describe new QCD fits to diffractive proton structure functions measured at HERA, and we use these parton densities to predict the shape of the dijet mass fraction at the Tevatron and look for the existence of exclusive events in the dijet channel.
We present predictions for the diffractive production of heavy quarks in deep-inelastic scattering and hadron-hadron collisions and for double diffractive dijet production in hadron-hadron collisions. With the assumption of hard scattering factorization, the predictions are made using diffractive parton densities that we have previously fitted to HERA data. Comparisons of our predictions with preliminary data from HERA and the Tevatron indicate that factorization is obeyed in diffractive DIS but fails in hadron-induced processes.
We study diffractive hard dijet production, with one or two rapidity gaps, at high energies. We emphasize that both hard and Regge factorization are broken in these processes. We show that a multi-Pomeron-exchange model for screening effects gives a specific pattern for the breakdown of factorization, which is in good agreement with diffractive dijet data collected at the Tevatron.
Experimental rates of W and dijets diffractively produced at the Tevatron Collider have recently become available. We use parametrizations of the pomeron structure function obtained from HERA data by two different schemes to compare theoretical expectations with the measured rates.
Central diffractive production of heavy states (massive dijets, Higgs boson) is studied in the exclusive mode using a new Hybrid Pomeron Model (HPM). Built from Hybrid Pomerons defined by the combination of one hard and one soft color exchanges, the model describes well the centrally produced diffractive dijet data at the Tevatron. Predictions for the Higgs boson and dijet exclusive production at the LHC are presented.
We calculate several differential distributions for exclusive double diffractive $χ_c(0^{++})$ production in proton-antiproton collisions at the Tevatron and in proton-proton collisions at RHIC and LHC in terms of unintegrated gluon distributions (UGDFs) within the $k_t$-factorisation approach. The uncertainties of the Khoze-Martin-Ryskin approach are discussed in detail. The $g^* g^* \to χ_c(0^{++})$ transition vertex is calculated as a function of gluon virtualities applying the standard pNRQCD technique. The off-shell effects are discussed and quantified. They lead to a reduction of the cro…
We use a Monte Carlo implementation of recently developped models of inclusive and exclusive diffractive $W$, top, Higgs and stop productions to assess the sensitivity of the LHC experiments. We also discuss how the Tevatron experiments could test the models and measure the gluon density in the pomeron, which is needed to make precise predictions at the LHC.
We compute the hard diffractive hadroproduction of bosons W at high energies using Regge factorization and taking into account multiple Pomeron exchange corrections. The ratio of diffractive to non-diffractive W production agrees with the current Tevatron data and a prediction for the LHC is presented.
We review the results of measurements on soft and hard diffractive processes performed by the CDF Collaboration at the Fermilab Tevatron pbar-p collider in run I and place them in perspective by internal comparisons, as well as by comparisons with results obtained at the HERA e-p collider and with theoretical expectations.
The most important consequence of Pomeron being a pole is the factorization property. However, due to Pomeron intercept being greater than 1, the extrapolated single diffraction dissociation cross section based on a classical triple-Pomeron formula is too large leading to a potential unitarity violation at Tevatron energies, which has been referred to as "Dino's paradox". We review our resolution which involves a proper implementation of final-state screening correction, with "flavoring" for Pomeron as the primary dynamical mechanism for setting the relevant energy scale. In this approach, fac…
