Showing papers by "Georges Azuelos published in 2002"
TL;DR: A search for pair-produced doubly charged Higgs bosons has been performed using data samples corresponding to an integrated luminosity of about 614 pb−1 collected with the OPAL detector at LEP at centre-of-mass energies between 189 GeV and 209 GeV as discussed by the authors.
48 citations
TL;DR: In this paper, a lower bound of 96.9 GeV was obtained if the mass difference between the scalar bottom quark and the lightest neutralino is larger than 10 GeV.
44 citations
TL;DR: In this paper, a two-Higgs-Doublet model (2HDM) search for a light Higgs boson in the mass range of 4-12 GeV has been performed in the Yukawa process, where the number of observed events is in good agreement with the expected background.
Abstract: Within a Two-Higgs-Doublet Model (2HDM) a search for a light Higgs boson in the mass range of 4–12 GeV has been performed in the Yukawa process \(\mathrme^+ \mathrme^-\rightarrow \mathrm{b}\bar{\mathrm{b}}\mathrm{A}/\mathrm{h}\rightarrow\mathrm{b} \bar{\mathrm{b}}\tau^+\tau^-\), using the data collected by the OPAL detector at LEP between 1992 and 1995 in \(\mathrme^+ \mathrme^-\) collisions at about 91 GeV centre-of-mass energy. A likelihood selection is applied to separate background and signal. The number of observed events is in good agreement with the expected background. Within a CP-conserving 2HDM type II model the cross-section for Yukawa production depends on \(\xi^{\mathrm{A}}_d=|\tan\beta|\) and \(\xi^{\mathrm{h}}_d=|\sin\alpha/\cos\beta|\) for the production of the CP-odd A and the CP-even h, respectively, where \(\tan\beta\) is the ratio of the vacuum expectation values of the Higgs doublets and \(\alpha\) is the mixing angle between the neutral CP-even Higgs bosons. From our data 95% C.L. upper limits are derived for \(\xi^{\mathrm{A}}_d\) within the range of 8.5 to 13.6 and for \(\xi^{\mathrm{h}}_d\) between 8.2 to 13.7, depending on the mass of the Higgs boson, assuming a branching fraction into \(\tau^+\tau^-\) of 100%. An interpretation of the limits within a 2HDM type II model with Standard Model particle content is given. These results impose constraints on several models that have been proposed to explain the recent BNL measurement of the muon anomalous magnetic moment.
33 citations
TL;DR: In this paper, the interaction of virtual photons is investigated using the reaction of virtual hadrons based on data taken by the OPAL experiment at the center-of-mass energies of the virtual photons.
Abstract: The interaction of virtual photons is investigated using the reaction ${\rm e^+e^-} \rightarrow{\rm e^+e^-}$
hadrons based on data taken by the OPAL experiment at ${\rm e^+e^-}$
centre-of-mass energies $\sqrt{s_{\rm ee}}=189-209$
GeV, for $W>5$
GeV and at an average $Q^{2}$
of 17.9 GeV
$^2$
. The measured cross-sections are compared to predictions of the Quark Parton Model (QPM), to the Leading Order QCD Monte Carlo model PHOJET, to the NLO prediction for the reaction ${\rm e^+e^-}\rightarrow{\rm e^+e^-} q\bar{q}$
, and to BFKL calculations. PHOJET, NLO ${\rm e^+e^-}\rightarrow{\rm e^+e^-} q\bar{q}$
, and QPM describe the data reasonably well, whereas the cross-section predicted by a Leading Order BFKL calculation is too large.
31 citations
Posted Content•
TL;DR: The report of the Higgs working group for the Workshop ''Physics at TeV Colliders'' as mentioned in this paper, Les Houches, France, 21 May - 1 June 2001, contains 7 separate sections: A. Theoretical Developments B. Higgs Searches at the Tevatron C. Experimental Observation of an invisible Higgs Boson at LHC D. Search for the Standard Model Higgs boson using Vector Boson Fusion at the LHC E. Study of the MSSM channel $A/H \to \tau \tAU$ at
Abstract: Report of the Higgs working group for the Workshop `Physics at TeV Colliders', Les Houches, France, 21 May - 1 June 2001. It contains 7 separate sections: A. Theoretical Developments B. Higgs Searches at the Tevatron C. Experimental Observation of an invisible Higgs Boson at LHC D. Search for the Standard Model Higgs Boson using Vector Boson Fusion at the LHC E. Study of the MSSM channel $A/H \to \tau \tau$ at the LHC F. Searching for Higgs Bosons in $t\bar t H$ Production G. Studies of Charged Higgs Boson Signals for the Tevatron and the LHC.
29 citations
Université de Montréal1, University of California, Berkeley2, Stanford University3, Brown University4, University of Florida5, CERN6, Institute on Taxation and Economic Policy7, University of Upper Alsace8, University of Cambridge9, University of Southampton10, University of Milano-Bicocca11, University of Bonn12, Russian Academy of Sciences13, Durham University14, Lawrence Berkeley National Laboratory15, University of Chicago16, University of Paris-Sud17, Indian Institute of Science18, University of Warsaw19, University of Montpellier20, Fermilab21, North Eastern Hill University22, University of Sheffield23
21 citations
08 Aug 2002
TL;DR: In this paper, theoretical aspects of physics beyond the Standard Model at hadron colliders are discussed, focusing on those issues that most immediately impact the projects pursued as part of the BSM group at this meeting.
Abstract: Various theoretical aspects of physics beyond the Standard Model at hadron colliders are discussed. Our focus will be on those issues that most immediately impact the projects pursued as part of the BSM group at this meeting.
19 citations
TL;DR: In this article, the b quark forward-backward asymmetry has been measured using hadronic Z0 decays collected by the OPAL experiment at LEP, and the results, corrected to the quark level, are: A FB b =0.0582±0.0012 at s =89.50 GeV, A FB c =0 0.0977±0.0018 at s=91.26 GeV, A FB dc b = 0 0.1221± 0.
18 citations
TL;DR: A search for charged excited leptons decaying into a lepton and a photon has been performed using approximately 680 pb−1 of e+e− collision data collected by the OPAL detector at LEP at centre-of-mass energies between 183 and 209 GeV as discussed by the authors.
18 citations
TL;DR: In this paper, the hadronic structure function of the photon was measured as a function of Bjorken x and of photon virtuality Q² using deep-inelastic scattering data taken by the OPAL detector at LEP at e⁺e⁻ center-of-mass energies from 183 to 209 GeV.
TL;DR: The impact of possible LHC upgrades on the physics capabilities of the ATLAS detector is discussed in this article, where an increase in the luminosity by a factor of 10 is considered.
Abstract: The impact of possible LHC upgrades on the physics capabilities of the ATLAS detector is discussed. As a benchmark, an increase in the luminosity by a factor of 10 is considered. For comparison, the doubling of the LHC energy is also explored. Both upgrades significantly enhance the physics capabilities of ATLAS. Measured in terms of the mass reach for new particles, the energy upgrade is more powerful. However, in cases where the effect of an upgrade is to increase the precision of measurements as a result of larger data samples, the luminosity upgrade can be at least as powerful. The pile-up of minimum bias events at higher luminosity could limit the physics performance of ATLAS in areas where tagging of forward jets is needed.
TL;DR: In this article, the particle multiplicities of two-and three-jet events from the reaction e\(+\)e\(^-\)-rightarrow hadrons are measured for Z\(−)-decays to light quark (uds) flavors.
Abstract: The charged particle multiplicities of two- and three-jet events from the reaction e\(^+\)e\(^-\)\(\rightarrow\) Z\(^0\rightarrow hadrons\) are measured for Z\(^0\) decays to light quark (uds) flavors. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jets are extracted over a range of jet energies from about 11 to 30 GeV. We find consistency between these results and direct measurements of unbiased gluon jet multiplicity from \(\Upsilon\) and Z\(^0\) decays. The unbiased gluon jet data including the direct measurements are compared to corresponding results for quark jets. We perform fits based on analytic expressions for particle multiplicity in jets to determine the ratio \(r\equiv\mathrm{N}_{g}/\mathrm{N}_{q}\) of multiplicities between gluon and quark jets as a function of energy. We also determine the ratio of slopes, \(r^{(1)}\equiv(\mathrm{d}\mathrm{N}_{g} /\mathrm{d}y) /(\mathrm{d}\mathrm{N}_{q} /\mathrm{d}y)\), and of curvatures, \(r^{(2)}\equiv(\mathrm{d}^2\mathrm{N}_{g} /\mathrm{d}y^2) /(\mathrm{d}^2\mathrm{N}_{q} /\mathrm{d}y^2)\), where y specifies the energy scale. At 30 GeV, we find \(r=1.422\pm0.051,r^{(1)}=1.761\pm0.071\) and \(r^{(2)}=1.98\pm0.13\), where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement with theoretical predictions. In addition, we use the measurements of the energy dependence of \({\mathrm{N}}_{g}\) and \({\mathrm{N}}_{q}\) to determine an effective value of the ratio of QCD color factors, \(C_{\mathrm A}/C_{\mathrm F}\). Our result, \(C_{\mathrm A}/C_{\mathrm F}=2.23\pm0.14 \)(total), is consistent with the QCD value of 2.25.
TL;DR: In this paper, the production of charm quarks was studied in deepinelastic electron-photon scattering using data recorded by the OPAL detector at LEP at nominal e+e− centre-of-mass energies from 183 to 209GeV.
TL;DR: In this paper, a search for first generation scalar and vector leptoquarks as well as for squarks in R-parity violating SUSY models with the direct decay of the $\tilde{\mbox{q}}$ into Standard Model particles has been performed using collisions collected with the OPAL detector at LEP at an integrated luminosity of about 160 pb.
Abstract: A search for first generation scalar and vector leptoquarks (LQ) as well as for squarks (
$\tilde{\mbox{q}}$
) in R-parity violating SUSY models with the direct decay of the $\tilde{\mbox{q}}$
into Standard Model particles has been performed using e
$^+$
e
$^-$
collisions collected with the OPAL detector at LEP at an e
$^+$
e
$^-$
centre-of-mass energy $\sqrt{s_{\rm ee}}$
of 189 GeV. The data correspond to an integrated luminosity of about 160 pb
$^{-1}$
. The dominant process for this search is $\mbox{eq}\to\LQ/\tilde{\mbox{q}}\to\mbox{eq},
u\mbox{q}$
, where a photon, which has been radiated by one of the beam electrons, serves as a source of quarks. The numbers of selected events found in the two decay channels are in agreement with the expectations from Standard Model processes. This result allows to set lower limits at the 95% confidence level on the mass of first generation scalar and vector leptoquarks, and of squarks in R-parity violating SUSY models. For Yukawa couplings $\lambda$
to fermions larger than $\sqrt{4\pi\alpha_{\rm em}}$
, the mass limits range from 121 GeV
$/c^2$
to $175$
GeV
$/c^2$
(
$149$
GeV
$/c^2$
to $188$
GeV
$/c^2$
) depending on the branching ratio $\beta$
of the scalar (vector) leptoquark state. Furthermore, limits are set on the Yukawa couplings $\lambda$
for leptoquarks and $\lambda'_{1jk}$
for squarks, and on $\beta$
as a function of the scalar leptoquark/squark mass.
TL;DR: In this paper, a search is performed for production of short-lived particles in e(+)e(-) --> XY, with X --> gammagamma and Y --> f (f) over bar, for scalar X and scalar or vector Y.
TL;DR: In this paper, the mean charged particle multiplicities separately for b b, c c and light quark (u u, d d, s s ) initiated events produced in e + e − annihilations at LEP were measured with OPAL detector at eleven different energies above the Z 0 peak.
TL;DR: In this paper, the branching ratio of orbitally-excited B mesons decaying into the decay π(X) was measured using a sample of more than 570, 000 inclusively reconstructed b mesons from about 4 million hadronic decays recorded by the OPAL detector.
Abstract: From about 4 million hadronic \(\rm Z^0\) decays recorded by the OPAL detector on and near to the \(\rm Z^0\) resonance, we select a sample of more than 570 000 inclusively reconstructed B mesons. Orbitally-excited mesons \({\rm B}^*_J\) are reconstructed using \({\rm B}\pi^\pm\) combinations. Independently, \({\rm B}^*\) mesons are reconstructed using the decay ${\rm B}^*\rightarrow{\rm B}{\gamma}\(. The selected \){\rm B}^*$ candidates are used to obtain samples enriched or depleted in the decay \({\rm B}^*_J \rightarrow{\rm B}^* \pi^{\pm}(X)\), where (X) refers to decay modes with or without additional accompanying decay particles. From the number of signal candidates in the \({\rm B}\pi^\pm\) mass spectra of these two samples, we perform the first measurement of the branching ratio of orbitally-excited B mesons decaying into \({\rm B}^*\pi(X)\):
TL;DR: In this article, the impact on the physics capabilities of the ATLAS detector of possible LHC upgrades is discussed, and an increase in the luminosity by a factor of ten is considered.
Abstract: The impact on the physics capabilities of the ATLAS detector of possible LHC upgrades is discussed. As a benchmark, an increase in the luminosity by a factor of ten is considered. For comparison, a doubling of the LHC energy is also explored. Both upgrades significantly enhance the physics capabilities of ATLAS. As measured in terms of the mass reach for new particles, the energy upgrade is more powerful. However, in cases where the effect of an upgrade is to increase the precision of measurements as a result of the larger data samples, the luminosity upgrade can be at least as powerful. The pile-up of minimum bias events at higher luminosity could limit the physics performance of ATLAS in areas where tagging of forward jets is needed.
TL;DR: In this article, searches for first generation scalar and vector leptoquarks, and for squarks in R-parity violating SUSY models with the direct decay of the squark into Standard Model particles, have been performed using e+e− collisions collected with the OPAL detector at LEP at e−e− centre-of-mass energies between 189 and 209 GeV.
TL;DR: In this article, the authors used the OPAL detector at LEP at a center of mass energy of 189 GeV to measure the cross-section of the branching ratio of the Z/γ decaying into hadrons.
Abstract: The process \(e^+ e^- \to e^+ e^- Z/\gamma^*\) is studied with the OPAL detector at LEP at a centre of mass energy of \(\sqrt{s}\) = 189 GeV. The cross-section times the branching ratio of the Z/\(\gamma^*\) decaying into hadrons is measured within Lorentz invariant kinematic limits to be \((1.2 \pm 0.3 \pm 0.1)\) pb for invariant masses of the hadronic system between 5 GeV and 60 GeV and \((0.7 \pm 0.2 \pm 0.1)\) pb for hadronic masses above 60 GeV. The differential cross-sections of the Mandelstam variables \(\hat{s}, \hat{t}\), and \(\hatu\) are measured and compared with the predictions from the Monte Carlo generators grc4f and PYTHIA. From this, based on a factorisation ansatz, the total and differential cross-sections for the subprocess \({\rm e} \gamma\to{\rm e Z}/\gamma^*\) are derived.
Posted Content•
TL;DR: The report of the "Beyond the Standard Model" working group for the Workshop 'Physics at TeV Colliders', Les Houches, France, 21 May - 1 June 2001 as discussed by the authors, consists of 18 separate parts:
Abstract: Report of the "Beyond the Standard Model" working group for the Workshop `Physics at TeV Colliders', Les Houches, France, 21 May - 1 June 2001. It consists of 18 separate parts:
1. Preface;
2. Theoretical Discussion;
3. Numerical Calculation of the mSUGRA and Higgs Spectrum;
4. Theoretical Uncertainties in Sparticle Mass Predictions;
5. High Mass Supersymmetry with High Energy Hadron Colliders;
6. SUSY with Heavy Scalars at LHC;
7. Inclusive Study of MSSM in CMS;
8. Establishing a No-Lose Theorem for NMSSM Higgs Boson Discovery at the LHC;
9. Effects of Supersymmetric Phases on Higgs Production in Association with Squark Pairs in the Minimal Supersymmetric Standard Model;
10. Study of the Lepton Flavour Violating Decays of Charged Fermions in SUSY GUTs;
11. Interactions of the Goldstino Supermultiplet with Standard Model Fields;
12. Attempts at Explaining the NuTeV Observation of Di-Muon Events;
13. Kaluza-Klein States of the Standard Model Gauge Bosons: Constraints From High Energy Experiments;
14. Kaluza-Klein Excitations of Gauge Bosons in the ATLAS Detector;
15. Search for the Randall Sundrum Radion Using the ATLAS Detector;
16. Radion Mixing Effects on the Properties of the Standard Model Higgs Boson;
17. Probing Universal Extra Dimensions at Present and Future Colliders;
18. Black Hole Production at Future Colliders.
TL;DR: In this article, the OPAL detector at LEP at center-of-mass energies from 183-GeV to 209 -GeV was used to obtain four-fermion final states q q e + e − and q q μ + μ − from neutral current interactions in e+e− collisions.
Journal Article•
TL;DR: In this article, the authors proposed a preselection requirement that the energy deposited had to be less than 5, 2 and 5 GeV in each side of the SW, FD and GC detectors to reduce the background from two-photon processes.