R. M. Godbole, A. Grau, G. Pancheri, Y. N. Srivastava
We calculate the probability of large rapidity gaps in high energy hadronic collisions using a model based on QCD mini-jets and soft gluon emission down into the infrared region. Comparing with other models we find a remarkable agreement among most predictions.
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In this talk, given at "RunII QCD and weak boson WS", we report on calculations of the survival probability of the large rapidity gap (LRG) processes and its energy behaviour.
We summarize the discussions on the value of the survival probabilities of large rapidity gap (LRG) processes at Durham WS'98.
We study the probability for no jets with transverse momenta above a given cut to be found in the rapidity region between two high pT jets with a large rapidity separation. Our investigation uses the parton shower event generator DEDUCTOR with color beyond the leading-color-plus approximation included perturbatively.
We discuss recent calculations of the survival probability of the large rapidity gaps in exclusive processes of the type pp --> p+A+p at high energies. Absorptive or screening effects are important, and one consequence is that the total cross section at the LHC is predicted to be only about 90 mb.
We apply the phenomenological Reggeon field theory framework to investigate rapidity gap survival (RGS) probability for diffractive dijet production in proton-proton collisions. In particular, we study in some detail rapidity gap suppression due to elastic rescatterings of intermediate partons in the underlying parton cascades, described by enhanced (Pomeron-Pomeron interaction) diagrams. We demonstrate that such contributions play a subdominant role, compared to the usual, so-called "eikonal", rapidity gap suppression due to elastic rescatterings of constituent partons of the colliding proton…
The energy dependence for the survival probability of large rapidity gaps (LRG) $< \mid S \mid^2 >$, is calculated in an Eikonal model assuming a Gaussian opacity. The parameters determining $< \mid S \mid^2 >$ are evaluated directly from experimental data, without further recourse to models. We find that $< \mid S \mid^2 >$ decreases with increasing energy, in line with recent results for LRG dijet production at the Tevatron.
We summarize how the approach to the black-disk regime (BDR) of strong interactions at TeV energies influences rapidity gap survival in exclusive hard diffraction pp -> p + H + p (H = dijet, Qbar-Q, Higgs). Employing a recently developed partonic description of such processes, we discuss (a) the suppression of diffraction at small impact parameters by soft spectator interactions in the BDR; (b) further suppression by inelastic interactions of hard spectator partons in the BDR; (c) correlations between hard and soft interactions. Hard spectator interactions substantially reduce the rapidity gap…
We summarize our understanding of the dynamical mechanisms governing rapidity gap survival in central exclusive diffraction, pp -> p + H + p (H = high-mass system), and discuss the uncertainties in present estimates of the survival probability. The main suppression of diffractive scattering is due to inelastic soft spectator interactions at small pp impact parameters and can be described in a mean-field approximation (independent hard and soft interactions). Moderate extra suppression results from fluctuations of the partonic configurations of the colliding protons. At LHC energies absorptive …
Our presentation centers on the consequences of s-channel unitarity, manifested by soft re-scatterings of the spectator partons in a high energy diffractive process, focusing on the calculations of gap survival probabilities. Our emphasis is on recent estimates relevant to exclusive diffractive Higgs production at the LHC. To this end, we critically re-examine the comparison of the theoretical estimates of large rapidity gap hard di-jets with the measured data, and remark on the difficulties in the interpretation of HERA hard di-jet photoproduction.
The values and energy dependence for the survival probability $< \mid S\mid^2 >$ of large rapidity gaps (LRG) are calculated in a three channel model. This model includes single and double diffractive production, as well as elastic rescattering. It is shown that $< \mid S \mid^2 >$ decreases with increasing energy, in line with recent results for LRG dijet production at the Tevatron. This is in spite of the weak dependence on energy of the ratio $ (σ_{el}+ σ_{SD})/σ_{tot}$.
We summarize how the approach to the black--disk regime (BDR) of strong interactions at TeV energies influences rapidity gap survival in exclusive hard diffraction pp--> p + H + p (H =dijet, \bar Q Q, Higgs). Employing a recently developed partonic description of such processes, we discuss (a) the suppression of diffraction at small impact parameters by soft spectator interactions in the BDR; (b) further suppression by inelastic interactions of hard spectator partons in the BDR; (c) effects of correlations between hard and soft interactions, as suggested by various models of proton structure (…
Observations of rare processes containing large rapidity gaps at high energy colliders may be exceptionally informative. However the cross sections of these events are small in comparison with that for the inclusive processes since there is a large probability that the gaps may be filled by secondary particles arising from additional soft interactions or from gluon radiation. Here we review the calculations of the probability that the gaps survive population by particles from these effects for a wide range of different processes.
The theory of the perturbative pomeron, due to Lipatov and collaborators, is used to compute the probability of observing parton-parton elastic scattering and rapidity gaps between jets in hadron collisions at Tevatron energies.
The theory of the perturbative pomeron, due to Lipatov and collaborators, is used to compute the probability of observing parton-parton elastic scattering and rapidity gaps between jets in hadron collisions at SSC and LHC energies.
The theory of the perturbative pomeron, due to Lipatov and collaborators, is used to compute the probability of observing parton-parton elastic scattering and rapidity gaps between jets in hadron collisions at very high energies.
We discuss an application of dynamical multi-parton interaction model, tuned to measurements of underlying event topology, for a description of destroying rapidity gaps in the jet-gap-jet processes at the LHC. We concentrate on the dynamical origin of the mechanism of destroying the rapidity gap. The cross section for jet-gap-jet is calculated within LL BFKL approximation. We discuss the topology of final states without and with the MPI effects. We discuss some examples of selected kinematical situations (fixed jet rapidities and transverse momenta) as distributions averaged over the dynamics …
Using an eikonal analysis, we simultaneously fit a QCD-inspired parameterization of all accelerator data on forward proton-proton and antiproton-proton scattering amplitudes, together with cosmic ray data (using Glauber theory), to predict proton-air and proton-proton cross sections at energies near \sqrt s \approx 30 TeV. The p-air cosmic ray measurements greatly reduce the errors in the high energy proton-proton and proton-air cross section predictions--in turn, greatly reducing the errors in the fit parameters. From this analysis, we can then compute the survival probability of rapidity gap…
In this talk I consider the formation of a rapidity gap in hadron production between two jets.
We consider photon-initiated events with large rapidity gaps in proton-proton collisions, where one or both protons may break up. We formulate a modified photon PDF that accounts for the specific experimental rapidity gap veto, and demonstrate how the soft survival probability for these gaps may be implemented consistently. Finally, we present some phenomenological results for the two-photon induced production of lepton and $W$ boson pairs.
In this talk we review the models describing the hard diffractive production of jets or more generally high-mass states in presence of rapidity gaps in hadron-hadron and lepton-hadron collisions. By rapidity gaps we mean regions on the lego plot in (pseudo)-rapidity and azimuthal angle where no hadrons are produced, between the jet(s) and an elastically scattered hadron (single hard diffraction) or between two jets (double hard diffraction).
When rapidity gaps in high-$p_T$ dijet events are identified by energy flow in the central region, they may be calculated from factorized cross sections in perturbative QCD, up to corrections that behave as inverse powers of the central region energy. Although power-suppressed corrections may be important, a perturbative calculation of dijet rapidity gaps in ${\rm p}\bar{\rm p}$ scattering successfully reproduces the overall features observed at the Tevatron. In this formulation, the average color content of the hard scattering is well-defined. We find that hard dijet rapidity gaps in quark-an…
In this paper we discuss the example of one rapidity gap process: the inclusive cross sections of the leading neutrons in deep inelastic scattering with protons (DIS). The equations for this process are proposed and solved, giving the example of theoretical calculation of the survival probability for one rapidity gap processes. It turns out that the value of the survival probability is small and it decreases with energy
We show that the hadroproduction of a pair of jets with large transverse energy in the central region bounded by rapidity gaps is an ideal process to see important double logarithmic QCD suppression effects. We compute the cross sections for both exclusive and inclusive double-diffractive dijet production at Tevatron and LHC energies for a range of rapidity configurations.
The survival probability of large rapidity gaps in pp collisions is calculated for several different eikonal models of the Gaussian form. Results obtained for models based on partonic interactions are quite similar. The Regge-pole model predicts a higher value of $ < \vert S \vert^{2} > $ .
New results are presented for total ${\rm pp}/ {\rm \bar p p}$ cross-sections, in the framework of our QCD based model (GGPS). This is an improved eikonal mini-jet model, where soft gluon radiation tames the fast energy rise normally present in mini-jet models. We discuss the variability in our predictions and provide a handy parametrization of our results for the LHC. We find that our model predictions span the range $σ_{tot}^{LHC}=100 ^{+10}_{-13} mb$. While this matches nicely with the range of most other models, it does not agree with recent ones which include a "hard" Pomeron, even though…
We present a new mechanism for the creation of large rapidity gaps in DIS events at HERA. Soft colour interactions between perturbatively produced partons and colour-charges in the proton remnant, modifies the colour structure for hadronization giving colour singlet systems that are well separated in rapidity. An explicit model is presented that, although the detailed results depend on the initial state parton emission, can describe both the observed rapidity gaps and, in addition, the forward energy flow in an inclusive event sample.
In this paper we present a self consistent theoretical approach for the calculation of the Survival Probability for central dijet production . These calculations are performed in a model of high energy soft interactions based on two ingredients:(i) the results of N=4 SYM, which at the moment is the only theory that is able to deal with a large coupling constant; and (ii) the required matching with high energy QCD. Assuming, in accordance with these prerequisites, that soft Pomeron intercept is rather large and the slope of the Pomeron trajectory is equal to zero, we derive analytical formulae …
We study central Z-boson production accompanied by rapidity gaps on either side as a way to gauge Higgs weak boson fusion production at the LHC. We analyse the backgrounds for the bb-decay mode and show that these can be substantially reduced. Special attention is paid to the evaluation of the gap survival factor, which is the major source of theoretical uncertainty in the rate of H and Z central production events with rapidity gaps.
Multiparton interactions modify the high energy hadronic cross section to produce minijets with a rapidity gap in the distribution of secondaries. At Tevatron energy the correction to the single scattering term is large for transverse momenta smaller than 6 GeV.
We show that soft color rearrangement of final states can account for the appearance of rapidity gaps between jets. In the color evaporation model the probability to form a gap is simply determined by the color multiplicity of the final state. This model has no free parameters and reproduces all data obtained by the ZEUS, H1, D0, and CDF collaborations.
The recently discovered correspondence between the distribution of rapidity gaps in electron-nucleus diffractive processes and the statistics of the height of genealogical trees in branching random walks is reviewed. In addition, a new comparison of numerical solutions of exact equations for diffraction on the one hand, and for ancestry on the other hand, both established in the framework of the color dipole model, is presented.
Soft colour exchange models give a unified description of both diffractive and non-diffractive events, such that e-p and p-pbar collider data with and without rapidity gaps are well reproduced. We show that these models also describe the new Tevatron data on diffraction based on observed leading antiprotons, which provide new information on how to treat the beam particle remnant in the Monte Carlo model.
I examine the phenomenology of particle multiplicity distributions, with special emphasis on the low multiplicities that are a background in the study of rapidity gaps. In particular, I analyze the multiplicity distribution in a rapidity interval between two jets, using the HERWIG QCD simulation with some necessary modifications. The distribution is not of the negative binomial form, and displays an anomalous enhancement at zero multiplicity. Some useful mathematical tools for working with multiplicity distributions are presented. It is demonstrated that ignoring particles with pt<0.2 has theo…
The use of rapidity gaps is proposed as a measure of the spatial pattern of an event. When the event multiplicity is low, the gaps between neighboring particles carry far more information about an event than multiplicity spikes, which may occur very rarely. Two moments of the gap distrubiton are suggested for characterizing an event. The fluctuations of those moments from event to event are then quantified by an entropy-like measure, which serves to describe erraticity. We use ECOMB to simulate the exclusive rapidity distribution of each event, from which the erraticity measures are calculated…
The success of recently proposed models for describing rapidity-gap events in DIS at HERA, in terms additional colour exchange between the struck system and the proton remnant in boson-gluon fusion events, are found to rely heavily on the absence or artificial suppression of perturbative gluon emission in the forward region. A model without such suppression is presented, which cannot describe the rapidity-gap events without a pomeron-inspired mechanism.
We introduce soft colour interactions as a novel mechanism to understand the observed events with large rapidity gaps in $ep$ collisions at HERA. Colour exchanges between produced partons and colour-charges in the proton remnant modifies the colour structure for hadronization, such that colour singlet systems may appear well separated in rapidity. Our explicit model show characteristics of diffractive scattering, although no explicit pomeron dynamics have been introduced, and for non-gap events an increased forward energy flow gives agreement with data.
A simple semiquantitative picture of diffractive electroproduction is described. Although the diffractive component of $F_2$ is approximately independent of $Q^2$ and $W^2$, this mechanism is "soft," i.e. it depends upon large-distance physics and is not readily describable within perturbative QCD.
We calculate the probability for rapidity gaps in the parton cascade for different approximations within the perturbative QCD and compare the results with recent measurements. The aim is to find out whether the dual connection between the parton and hadron final states -- observed so far in various inclusive measurements -- holds as well for the extreme kinematic configurations with colour sources separated by large rapidity gaps. A description of the data is possible indeed choosing the parameters of the cascade in the range suggested by recent analyses of the energy spectra (the $k_\perp$ cu…
We have searched for high Pt (>40 GeV/c) jet events in ppbar collisions at the Fermilab TEVATRON (S**1/2 = 1800 GeV/c2) which have large pseudo-rapidity differences between the jets and are consistent with zero particle production from the underlying event. Preliminary analysis indicates that a significant fraction of these events with "voids" are present. (3 pages of plain text, 7 Figures available on request from the author)
We study central Z-boson production accompanied by rapidity gaps on either side as a way to gauge Higgs weak boson fusion production at the LHC. We analyse the possible backgrounds for the bb-decay mode and show that these can be substantially reduced. Special attention is paid to the evaluation of the gap survival factor, which is the major source of theoretical uncertainty in the rate of H, Z and W central production events with rapidity gaps.
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 ha…
A model for the production of large rapidity gaps being implemented in the Monte Carlo event generator PHOJET is discussed. In this model, high-mass diffraction dissociation exhibits properties similar to hadron production in non-diffractive hadronic collisions at high energies. Hard diffraction is described using leading-order QCD matrix elements together with a parton distribution function for the pomeron and pomeron-flux factorization. Since this factorization is imposed on Born graph level only, unitarity corrections lead to a non-factorizing flux function. Rapidity gaps between jets are o…
We derive the probability for rapidity gaps in a parton cascade and investigate the dual connection with hadronic final states. A good description of observations in e+e- annihilations is obtained by perturbative QCD calculations in MLLA using previously determined parameters (QCD scale Λand k_T-cut-off Q_0) and applying the parton hadron duality picture. Further predictions are derived; especially, for gaps between jets at variable resolution we predict a strong variation of gap probabilities for small parameters y_{cut} -> 0 in the transition from jets to hadrons. Large gaps between partons …
We calculate the probability that the rapidity gaps in diffractive processes survive both eikonal and enhanced rescattering. We present arguments that enhanced rescattering, which violates soft-hard factorization, is not very strong. Accounting for NLO effects, there is no reason to expect that the black disc regime is reached at the LHC. We discuss the predictions for the survival of the rapidity gaps for exclusive Higgs production at the LHC.
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.
High energy hadronic interactions can produce a final state characterized by minijets separated by a large gap in the rapidity distribution of the produced secondary particles. We discuss the process by keeping into account the possibility of having multiple parton collisions in the hadronic interaction. At Tevatron energy the correction to the single scattering term induced by the presence of multiparton interactions is large for transverse momenta smaller than 6 GeV.
An excess of events with a rapidity gap between jets, over what would be expected from non-diffractive processes, has been observed at HERA. A process based on a perturbative QCD calculation of colour singlet exchange has been added to HERWIG. With this addition, HERWIG is able to describe the number of events with a gap between jets over the number without a gap. This gap fraction is predicted to rise at large rapidity intervals between jets which would only be visible if the detector coverage were increased.
Large Rapidity Gaps in proton-nucleus interaction
本文分析CMS质子-铅碰撞大快度间隔事件截面，指出光子诱导的质子解离截面接近实验值，质疑坡密子贡献在数据中缺失的原因。
Diffractive deep inelastic scattering at HERA and diffractive W and jet production at the Tevatron are well described by soft colour exchange models. Their essence is the variation of colour string-field topologies giving both gap and no-gap events, with a smooth transition and thereby a unified description of all final states.
We point out that an unorthodox way to describe the production of rapidity gaps in deep inelastic scattering, recently proposed by Buchmüller and Hebecker, suggests a description of the production of heavy quark bound states which is in agreement with data. The approach questions the conventional treatment of the color quantum number in perturbative QCD.
We discuss rapidity-gap events between two jets produced at high momentum transfer in $p$ $\bar{p}$ scattering, from the point of view of the soft energy flow into the interjet region. We define a gap cross section and, in perturbative QCD (pQCD), resum all the leading logarithms in the soft intermediate energy. We show that the numerical result from our cross section reproduces the shape of the D0 and CDF \cite{D0,CDF,D0fig} experimental data.
The possibility of distinguishing between two higgs production mechanisms, W fusion and gluon fusion, is investigated using the Monte Carlo event generator PYTHIA. It is shown that, considering the designed CM energy and luminosity for the LHC, it is not possible to distinguish between the two higgs production processes as, for a given integrated luminosity, they lead to the same number of events containing a rapidity gap.
We argue that the probability of gap survival in dijet production in $γp$ scattering as measured by ZEUS may be due to the color transparency phenomenon and suggest ways to test this hypothesis in the future $γp$ and $γA$ processes.
We show that the `orthogonal' characteristics of the observed rapidity gaps and large forward energy flows in deep inelastic scattering at HERA, can be described within a single framework. Our Monte Carlo model is based on perturbative QCD matrix elements and parton showers together with Lund string model hadronization, but has in addition a new mechanism for soft colour interactions which modifies the perturbative colour structure and thereby the hadronization. Effects of perturbative multiparton emission are investigated and the non-perturbative treatment of the proton remnant is discussed a…
We discuss a formalism in which high-$p_T$ dijet rapidity gaps are identified by energy flow in the interjet region. When the gap energy, $Q_{\rm gap}$, is sufficiently large, the cross section may be computed from standard factorization theorems. For $p_T\gg Q_T\ggΛ_{\rm QCD}$, this is a two-scale perturbative problem, in which we may resum logarithms of $Q_{\rm gap}/p_T$. The cross section computed as a function of $Q_{\rm gap}$ reproduces many of the features of the Tevatron dijet gap data. The factorized cross section gives meaning to the color content of the hard scattering.
Rapidity gaps between two hard jets at the Tevatron have been interpreted as being due to the exchange of two gluons which are in an overall color-singlet state. We show that this simple picture involves unitarity violating amplitudes. Unitarizing the gluon exchange amplitude leads to qualitatively different predictions for the fraction of $t$-channel color singlet exchange events in forward $qq$, $qg$ or $gg$ scattering, which better fit Tevatron data.
We compute the survival probability $<|S|^{2}>$ of large rapidity gaps (LRG) in a QCD based eikonal model with a dynamical gluon mass, where this dynamical infrared mass scale represents the onset of nonperturbative contributions to the diffractive hadron-hadron scattering. Since rapidity gaps can occur in the case of Higgs boson production via fusion of electroweak bosons, we focus on $WW\to H$ fusion processes and show that the resulting $<|S|^{2}>$ decreases with the increase of the energy of the incoming hadrons, in line with the available experimental data for LRG. We obtain $<|S|^{2} > =…
Nubmer of physically interesting processes is charachterized by the rapidity gaps. In reality, this gaps is filled by uderlying events with high (more than 0.75 for higgs) probability. In this paper we purpose a way to detect this shadowed events with aim to raise the number of rare events.
By defining dijet rapidity gap events according to interjet energy flow, we treat the photoproduction cross section of two high transverse momentum jets with a large intermediate rapidity region as a factorizable quantity in perturbative QCD. We show that logarithms of soft gluon energy in the interjet region can be resummed to all orders in perturbation theory. The resummed cross section depends on the eigenvalues of a set of soft anomalous dimension matrices, specific to each underlying partonic process, and on the decomposition of the scattering according to the possible patterns of hard co…
We calculate the cross section for $p p \to W^{+} W^-$ in the recently developed $k_{\rm T}$-factorisation approach, including transverse momenta of the virtual photons. We focus on processes with single and double proton dissociation. First we discuss the gap survival on the parton level as due to the emission of extra jet. Both the role of valence and sea contributions is discussed. The hadronisation of proton remnants is performed with {PYTHIA 8} string fragmentation model, assuming a simple quark-diquark model for proton. Highly excited remnant systems hadronise producing particles that ca…
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