Exclusive diffractive Higgs production at the LHC
We use a Monte Carlo implementation of recently developped models of double diffractive Higgs production to assess the sensitivity of the LHC experiments.
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arXiv subjects
C. Royon
Publications and source records attributed to C. Royon.
Sensitivity to the Standard Model Higgs Boson in Exclusive Double Diffraction
We use a Monte Carlo implementation of recently developed models of double diffraction to assess the sensitivity of the LHC experiments to Standard Model Higgs bosons produced in exclusive double diffraction. The signal is difficult to extract, due to experimental limitations related to the first level trigger, and to contamination by inclusive double diffractive background. Assuming the above difficulties can be overcome, the expected signal-to-background ratio is presented as a function of the experimental resolution on the missing mass. Injecting a missing mass resolution of 2 GeV, a signal-to-background ratio of about 0.5 is obtained; a resolution of 1 GeV brings a signal to background ratio of 1. This result is lower than previous estimates, and the discrepancy is explained.
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Popping out the Higgs boson off vacuum at Tevatron and LHC
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 allow to discriminate between various models and finally to give precise predictions on diffractive Higgs boson production cross-section at the LHC.
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Diffractive Higgs boson production at Tevatron and LHC: an experimental review
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.
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Hard diffraction and the nature of the Pomeron
We ask the question whether the quark and gluon distributions in the Pomeron obtained from QCD fits to hard diffraction processes at HERA can be dynamically generated from a state made of ``valence-like'' gluons and sea quarks as input. By a method combining backward Q^2-evolution for data exploration and forward Q^2-evolution for a best fit determination, we find that the diffractive structure functions published by the H1 collaboration at HERA can be described by a simple ``valence-like'' input at an initial scale of order mu^2 ~ 2.3-2.7 GeV^2. The parton number sum rules at the initial scale mu^2 for the H1 fit gives 2.1\pm .1\pm .1 and .13\pm .01 \pm .02 for gluon and sea quarks respectively, corresponding to an initial Pomeron state made of (almost) only two gluons. It has flat gluon density leading to a plausible interpretation in terms of a gluonium state.
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Discussion session on diffractive Higgs production
This note summarizes the discussion session on diffractive Higgs production at the DIS2002 workshop.
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The Diffractive Interactions Working Group Summary
Diffractive interactions represent a lively domain of investigations, as confirmed by the progresses reported during the conference. We summarize the diffractive interactions session and put the new experimental data (section 1), developments in modeling diffraction (section 2) and the theoretical relations with Quantum Chromodynamics (section 3) in perspective.
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Higgs boson production via Double Pomeron Exchange at the LHC
We study Higgs boson production via Double Pomeron Exchange allowing for the presence of Pomeron remnants. We estimate the number of events produced at the LHC collider, as a function of the Higgs boson mass and its decay channel. The model which successfully describes the high mass dijet spectrum observed at Tevatron (run I) is used to predict rates of events with tagged protons for the acceptance range of the CMS/Totem experiments. Sizeable cross-sections and encouraging event selection signals are found, demonstrating especially for smaller Higgs boson masses the importance to study the diffractive channels. Tagging of the Pomeron remnants can be exploited to achieve a good resolution on the Higgs boson mass for inclusive diffractive events, by optimizing an intermediary analysis between higher cross-sections of the fully {\it inclusive} mode (all Pomeron remnants) and cleaner signals of the {\it exclusive} mode (without Pomeron remnants).
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Inclusive Higgs boson and dijet production via Double Pomeron exchange
We evaluate Higgs boson and dijet cross-sections at the Tevatron collider via Double Pomeron exchange when accompanying particles in the central region are taken into account. Such {\it inclusive} processes, normalized to the observed dijet rate observed at run I, noticeably increase the predictions for tagged (anti)protons in the run II with respect to {\it exclusive} ones, with the potentiality of Higgs boson detection.
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QCD analysis of the diffractive structure function F_2^{D(3)}
The proton diffractive structure function $F_2^{D(3)}$ measured in the H1 and ZEUS experiments at HERA is analyzed in terms of both Regge phenomenology and perturbative QCD evolution. A new method determines the values of the Regge intercepts in ``hard'' diffraction, confirming a higher value of the Pomeron intercept than for soft physics. The data are well described by a QCD analysis in which point-like parton distributions, evolving according to the DGLAP equations, are assigned to the leading and sub-leading Regge exchanges. The gluon distributions are found to be quite different for H1 and ZEUS. A {\it global fit} analysis, where a higher twist component is taken from models, allows us to use data in the whole available range in diffractive mass and gives a stable answer for the leading twist contribution. We give sets of quark and gluon parton distributions for the Pomeron, and predictions for the charm and the longitudinal proton diffractive structure function from the QCD fit. An extrapolation to the Tevatron range is compared with CDF data on single diffraction. Conclusions on factorization breaking depend critically whether H1 (strong violation) or ZEUS (compatibility at low $β$) fits are taken into account.
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Single superpartner production at Tevatron Run II
We study the single productions of supersymmetric particles at Tevatron Run II which occur in the $2 \to 2-body$ processes involving R-parity violating couplings of type $ł'_{ijk} L_i Q_j D_k^c$. We focus on the single gaugino productions which receive contributions from the resonant slepton productions. We first calculate the amplitudes of the single gaugino productions. Then we perform analyses of the single gaugino productions based on the three charged leptons and like sign dilepton signatures. These analyses allow to probe supersymmetric particles masses beyond the present experimental limits, and many of the $ł'_{ijk}$ coupling constants down to values smaller than the low-energy bounds. Finally, we show that the studies of the single gaugino productions offer the opportunity to reconstruct the $\tilde χ^0_1$, $\tilde χ^{\pm}_1$, $\tilde ν_L$ and $\tilde l^{\pm}_L$ masses with a good accuracy in a model independent way.
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QCD analysis of the diffractive structure functions measured at HERA and factorisation breaking at 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.
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Pomeron intercepts at colliders
A method allowing for a direct comparison of data with theoretical predictions is proposed for forward jet production at HERA and Mueller-Navelet jets at Tevatron and LHC. An application to the determination of the effective Pomeron intercept in the BFKL-LO parametrization from d sigma/dx data at HERA leads to a good fit with a significantly higher effective intercept, $α_P= 1.43 \pm 0.025 (stat.) \pm 0.025 (syst.),$ than for proton (total and diffractive) structure functions. It is however less than the value of the pomeron intercept using dijets with large rapidity intervals obtained at Tevatron. We also evaluate the rapidity veto contribution to the higher order BFKL corrections. We suggest to measure the dependence of the dijet cross-sections as a function of the jet transverse energies as a signal for BFKL pomeron at LHC.
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A new determination of the Pomeron intercept in hard processes
A method allowing for a direct comparison of data with theoretical predictions is proposed for forward jet production at HERA. It avoids the reconstruction of multi-parton contributions by expressing the experimental data directly as correction factors on the QCD forward jet cross-section. An application to the determination of the effective Pomeron intercept in the BFKL-LO parametrization from dsigma/dx data at HERA leads to a good fit with a significantly higher effective intercept, alpha_P = 1.43 \pm 0.025(stat.) \pm >.025(syst.), than for proton (total and diffractive) structure functions. It is however less than the value of the Pomeron intercept using dijets with large rapidity intervals obtained at Tevatron. We also evaluate the rapidity veto contribution to the higher order BFKL corrections. The method can be extended to other theoretical inputs.
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Resonant sneutrino production at Tevatron Run II
We consider the single chargino production at Tevatron $p \bar p \to \tilde ν_i \to \tilde χ^{\pm}_1 l_i^{\mp}$ as induced by the resonant sneutrino production via a dominant \RPV coupling of type $ł'_{ijk} L_i Q_j D_k^c$. Within a supergravity model, we study the three leptons final state. The comparison with the expected background demonstrate that this signature allows to extend the sensitivity on the \susyq mass spectrum beyond the present LEP limits and to probe the relevant \RPV coupling down to values one order of magnitude smaller than the most stringent low energy indirect bounds. The trilepton signal offers also the opportunity to reconstruct the neutralino mass in a model independent way with good accuracy.
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BFKL signatures at a linear collider
The BFKL dynamics can be successfully tested at the future high energy $e^+e^-$ linear collider. The total $γ^*γ^*$ cross-section is calculated in the Leading Log QCD dipole picture of BFKL dynamics, and compared with the one from 2-gluon exchange. The rapidity dependence of the cross-section remains a powerful tool to increase the ratio between the BFKL and the 2-gluon cross-sections and is more sensitive to BFKL effects, even in the presence of higher order corrections. Other potential signals like diffractive $J/ Ψ$ and 'forward' jet productions will also be discussed.
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A phenomenological study of BFKL evolution
The QCD dipole picture allows to build an unified theoretical description -based on BFKL dynamics- of the total and diffractive nucleon structure functions measured at HERA. We use a four parameter fit to describe the 1994 H1 proton structure function $F_{2}$ data in the low x, moderate $Q^{2}$ range. The diffractive dissociation processes are discussed within the same framework, and a 6 parameter fit of the 1994 H1 diffractive structure function data is performed. The BFKL dynamics can also be successfully tested at the $e^+e^-$ collider LEP and a future high energy linear collider. The total $γ^*γ^*$ cross-section is calculated in the Leading Order QCD dipole picture of BFKL dynamics, and compared with the one from 2-gluon exchange. Next to Leading order corrections to the BFKL evolution have been determined phenomenologically, and are found to give very large corrections to the BFKL cross-section, leading to a reduced sensitivity for observing BFKL effects. The Y dependence of the cross-section remains a powerful tool to increase the ratio between the BFKL and the 2-gluon cross-sections and is more sensitive to BFKL effects, even in the presence of large higher order corrections.
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$γ^*γ^*$ total cross-section in the dipole picture of BFKL dynamics
The total $γ^*γ^*$ cross-section is derived in the Leading Order QCD dipole picture of BFKL dynamics, and compared with the one from 2-gluon exchange. The Double Leading Logarithm approximation of the DGLAP cross-section is found to be small in the phase space studied. Cross sections are calculated for realistic data samples at the $e^+e^-$ collider LEP and a future high energy linear collider. Next to Leading order corrections to the BFKL evolution have been determined phenomenologically, and are found to give very large corrections to the BFKL cross-section, leading to a reduced sensitivity for observing BFKL.
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