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F. Boudjema

Publications and source records attributed to F. Boudjema.

85 records · Page 5Linked to original sources
arXiv1997

Aspects of W Physics at the Linear Collider

It is argued that the next linear colliders can serve as W factories that may be exploited for precision tests on the properties of the massive gauge bosons. The connection between the probing of the symmetry breaking sector and precise measurement of the self-couplings of the weak vector bosons is stressed. The discussion relies much on the impact of the present low-energy data, especially LEP1. These have restricted some paths that lead to the exploration of the scalar sector through the investigation of the so-called anomalous couplings of the W's and suggest a hierarchy in the classification of these parameters. The limits we expect to set on these couplings at the different modes of the linear colliders are reviewed and compared with those one obtains at the LHC. The conclusion is that the first phase of a linear collider running at 500 GeV and the LHC are complementary. Some important issues concerning radiative corrections and backgrounds that need further studies in order that one conducts high precision analyses at high energies are discussed.

hep-ph↗
arXiv1997

Semi-leptonic four-fermion final states in polarised γγreactions: Exact results vs an improved narrow width approximation

We calculate the process $γγ\rightarrow e^- \barν_e u \bar{d}$ with the full set of Feynman diagrams. We consider different implementations of the $W$ width and different combinations of the photon polarisations. The results of an improved narrow width approximation based on $γγ\rightarrow W^+ W^-$ with full spin-correlations that takes into account different angular cuts as well as cuts on the invariant masses are compared to those of the complete calculation.

hep-ph↗
arXiv1997

Effects of Non-Standard Tri-linear Couplings in Photon-Photon Collisions: I. $γγ\to W^+ W^-$

The effect of anomalous couplings in $γγ\to W^+ W^-$ is studied for different energies of the $γγ$ mode of the next linear collider. The analysis based on the maximum likelihood method exploits the variables in the four-fermion semi-leptonic final state. Polarised differential cross sections based on the complete set of diagrams for these channels with the inclusion of anomalous couplings are used and compared to an approximation based on $γγ\to W^+ W^-$ with full spin correlations. To critically compare these results with those obtained in $e^+ e^-$ we perform an analysis based on the complete calculation of the four-fermion semi-leptonic final state. The anomalous couplings that we consider are derived from the next-to-leading order operators in the non-linear realisation of symmetry breaking.

hep-ph↗
arXiv1996

New Physics with three-photon events at LEP

The effect of the most general \z3gt vertex in the reaction $e^+e^- \ra 3γ$ is studied with a particular attention to LEP searches. We give exact analytical expressions including realistic cuts for the signal and present a detailed analysis based on a Monte Carlo that includes the effect of the irreducible $3γ$ QED cross section. As special applications we discuss the effect of heavy scalars, fermions and gauge bosons and comment on the ``monopole" connection.

hep-ph↗
arXiv1996

Anomalous Couplings and Chiral Lagrangians: An Update

We present an update of the limits expected for anomalous gauge boson couplings in the language of chiral Lagrangian operators at the LHC and the Linear Collider. Both, the $e^+e^-$ and the $γγ$ mode of the Linear Collider are analyzed. With a 500~GeV $e^+e^-$ collider, and an integrated luminosity of 50~--~80~fb$^{-1}$, one reaches the domain of precision measurements.

hep-ph↗
arXiv1995

Inverse Neutrinoless Double Beta Decay Revisited

We critically reexamine the prospects for the observation of the $ΔL=2$ lepton-number-violating process $\eeWW$ using the $e^-e^-$ option of a high-energy $e^+e^-$ collider (NLC). We find that, except in the most contrived scenarios, constraints from neutrinoless double beta decay render the process unobservable at an NLC of $\sqrt{s}<2$ TeV. Other $ΔL=2$ processes such as $\ggllww$, $\egnllw$, $\eennll$ ($\ell=μ,τ$), and $\egeww$, which use various options of the NLC, require a $\sqrt{s}$ of at least 4 TeV for observability.

hep-ph↗
arXiv1995

Double Higgs Production at the Linear Colliders and the Probing of the Higgs Self-Coupling

We study double Higgs production in the $e^+ e^-$ and $γγ$ modes of the linear collider. It is also shown how one can probe the scalar potential in these reactions. We discuss the effective longitudinal $W$ approximation in $γγ$ processes and the $W_L W_L$ luminosities in the two modes of a high-energy linear collider. A generalised non-linear gauge-fixing condition, which is particularly useful for tree-level calculations of electroweak processes for the laser induced collider, is presented. Its connection with the background-field approach to gauge fixing is given.

hep-ph↗
arXiv1995

Threshold Behaviour in Gauge Boson Pair Production at LEP 2

We discuss the form of the amplitude for gauge boson pair production at or near threshold.We show that in the case of W-pair production at LEP2 near threshold only one anomalous electromagnetic coupling can contribute. This anomalous coupling is CP violating and contributes to the electric dipole moment of the $W$. Since this coupling is likely to be small, it is important to look for ZZgamma couplings in Zgamma production. These couplings are not suppressed at the W-threshold.

hep-ph↗
arXiv1994

Extracting the Intermediate-Mass Higgs Resonance at Photon-Photon Colliders

We address the problem of how to extract the signal of a Higgs within the intermediate mass range at a photon-photon collider that has a wide energy spectrum. All backgrounds from two-jets production are included: direct, so-called resolved and twice-resolved as well as single $Z$ and $W$ production. Uncertainties in the evaluation of the QCD-initiated processes such as the choice of structure function and the issue of radiative corrections are discussed. We consider various combinations of the polarizations and invariant mass resolutions as well as jet-tagging strategies with different efficiencies. The analysis is based on an automatized technique that, given a specific detector and machine configuration, returns the optimal set of cuts corresponding to the best significance one may hope to achieve for each particular Higgs mass. We find that at a photon machine obtained from a 500GeV \epm\ linear collider with $\int\!{\cal L}=10$~fb$^{-1}$ it will be possible to extract a Higgs signal in the range 110--140~GeV, while with the same luminosity, a 350~GeV option not only extends the discovery limit down to 90~GeV but gives much better significance levels.

hep-ph↗
arXiv1994

Electroweak Physics Issues at a High Energy Photon Collider

The main attractions of studying the bosonic sector of the electroweak standard model and its extensions at a future high energy photon collider are reviewed. A presentation of the laser scheme for obtaining such a collider is given where we emphasize the importance of polarised \gag spectra. The need for {\em measuring} the differential luminosities is stressed. We show that, in a large variety of processes, the yield of weak vector bosons is much higher than at the \epm mode but unfortunately, the cross sections are dominated by the transverse modes. Investigation of the physics related to the symmetry breaking sector both in $W$ and $Z$ pair production is given and contrasted with what we expect to obtain in the \epm mode and at the LHC. We reassess the issue of whether an intermediate-mass Higgs can be observed as a resonance when we have a broad spectrum that allows the simultaneous study of a host of electroweak phenomena. This investigation includes the important background of the so-called ``resolved" photon. We analyse the important issues of the mass resolution, the $b$ tagging efficiencies, and the polarisation of the beams at two typical \epm energies: 300GeV and 500GeV. New efficient cuts are found to suppress the background. The importance of $WWH$ production at $\sim$1TeV is emphasized and contrasted with other Higgs production mechanisms at both \epm and $eγ$. Finally, we examine the interesting problem of the longitudinal $W$ ($W_L$) content of the photon. A new set of polarised structure functions for the $W_L$ inside the photon is proposed. We test the validity of the ensuing effective $W$ approximation in the \ggwwht process.

hep-ph↗
arXiv1993

{\Large{\bf Higgs or Neutral Vector Boson Production with a $W$ Pair in {\LARGE $γγ$} Collisions}}

Exploiting the fact that $W$ pair production in high-energy $γγ$ collisions is very large, we use this process to trigger Higgs, $Z$ or photon radiation. We find that there are sizeable rising cross-sections for triple bosons production. At energies about $1TeV$ the new mechanism for Higgs production becomes very competitive with the dominant Higgs production processes in $e^+e^-$ and $e γ$ reactions. The effect of different polarized photon spectra obtained through back-scattered laser light on the electron beam of a linear collider is investigated . We give a special attention to the search of the intermediate mass Higgs in $WWH$ production and discuss how to effectively suppress the backgrounds.

hep-ph↗
arXiv1993

Higgs Production in Association with a Vector Boson Pair at Future e+ e- Colliders

We study Higgs boson production in association with a pair of electroweak vector bosons ($WW,ZZ,Zγ$) at future $\epem$ colliders in the framework of the Standard Model. Total cross sections and distributions for the intermediate-mass Higgs are presented, with special emphasis on the Next Linear Collider (NLC) case operating at a centre-of-mass energy $\sqrt{s} \simeq 500$ GeV, where the cross sections turn out to be more favourable than in larger-$\sqrt{s}$ collisions. We find that with an integrated luminosity of 20 fb$^{-1}$ there is a sizeable event rate for the $HWW$ and $HZγ$ (with a high $p_T^γ$) channels, while a larger integrated luminosity is needed to study the $HZZ$ production. We take into account various backgrounds, notably top-pair and triple vector-boson production, and show ways to significantly reduce their effects.

hep-ph↗