A search is made for charged Higgs bosons predicted by Two-Higgs-Doublet extensions of the Standard Model (2HDM) using electron-positron collision data collected by the OPAL experiment at
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\begin{document}$\sqrt{s}=189\mbox{--}209\ \mbox{GeV}$\end{document}
, corresponding to an integrated luminosity of approximately 600 pb
−1
. Charged Higgs bosons are assumed to be pair-produced and to decay into
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\begin{document}$\mathrm{q} \bar{\mathrm{q}}$\end{document}
,
τν
τ
or AW
±
. No signal is observed. Model-independent limits on the charged Higgs-boson production cross section are derived by combining these results with previous searches at lower energies. Under the assumption
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\begin{document}$\mathrm{BR} (\mathrm{H}^{\pm} \to \tau\nu_{\tau}) + \mathrm{BR} (\mathrm{H}^{\pm} \to \mathrm{q} \bar{\mathrm{q}}) = 1$\end{document}
, motivated by general 2HDM type II models, excluded areas on the
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\begin{document}$m_{\mathrm{H}^{\pm}} , \mathrm{BR} (\mathrm {H}^{\pm} \to \tau\nu_{\tau})$\end{document}
plane are presented and charged Higgs bosons are excluded up to a mass of 76.3 GeV at 95 % confidence level, independent of the branching ratio BR(H
±
→
τν
τ
). A scan of the 2HDM type I model parameter space is performed and limits on the Higgs-boson masses
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\begin{document}$m_{\mathrm{H}^{\pm}}$\end{document}
and
m
A
are presented for different choices of tan
β
.
A search is performed for Higgs bosons decaying into invisible final states, produced in association with a Z0 boson in e+e− collisions at energies between 183 and 209 GeV. The search is based on ...data samples collected by the OPAL detector at LEP corresponding to an integrated luminosity of about 660 pb−1. The analysis aims to select events containing the hadronic decay products of the Z0 boson and large missing momentum, as expected from Higgs boson decay into a pair of stable weakly interacting neutral particles, such as the lightest neutralino in the Minimal Supersymmetric Standard Model. The same analysis is applied to a search for nearly invisible Higgs boson cascade decays into stable weakly interacting neutral particles. No excess over the expected background from Standard Model processes is observed. Limits on the production of invisibly decaying Higgs bosons produced in association with a Z0 boson are derived. Assuming a branching ratio BR(h0→invisible)=1, a lower limit of 108.2 GeV is placed on the Higgs boson mass at the 95% confidence level. Limits on the production of nearly invisibly decaying Higgs bosons are also obtained.
Inclusive jet production (e+e−→e+e−+jet+X) is studied in collisions of quasi-real photons radiated by the LEP beams at e+e− centre-of-mass energies see from 189 to 209 GeV. Jets are reconstructed ...using the k⊥ jet algorithm. The inclusive differential cross-section is measured as a function of the jet transverse momentum, pTjet, in the range 5<pTjet<40 GeV for pseudo-rapidities, ηjet, in the range −1.5<ηjet<1.5. The results are compared to predictions of perturbative QCD in next-to-leading order in the strong coupling constant.
Hadronic events produced in e+e- collisions by the LEP collider and recorded by the OPAL detector were used to form distributions based on the number of reconstructed jets. The data were collected ...between 1995 and 2000 and correspond to energies of 91 GeV, 130-136 GeV and 161-209 GeV. The jet rates were determined using four different jet-finding algorithms (Cone, JADE, Durham and Cambridge). The differential two-jet rate and the average jet rate with the Durham and Cambridge algorithms were used to measure in the LEP energy range by fitting an expression in which calculations were matched to a NLLA prediction and fitted to the data. Combining the measurements at different centre-of-mass energies, the value of () was determined to beαS(MZ) = 0.1177 ± 0.0006 (stat.) ± 0.0012 (expt.) ± 0.0010 (had.) ± 0.0032 (theo.).
Test results of a fully projective lead/scintillating-fiber calorimeter
Nuclear instruments and methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment/Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/1994
Journal Article
A classification problem in high energy physics has been solved on simulated data using a simple multilayer perceptron comprising binary units which was trained with the CHIR algorithm. The unstable ...training of such a network on a nonseparable set has been overcome by selecting those weight vectors with good performance while providing a flexible choice of the two types of classification errors. Specific features of the problem have been exploited in order to simplify and optimize the solution which has been compared to the popular backpropagation algorithm and found to perform on a similar level. Additional aspects of this work are the use of the CHIR algorithm on continuous input and incorporating the classic idea of a phi-machine in a multilayer perceptron.
Thin, high gain wire chambers for electromagnetic presampling in OPAL
Nuclear instruments and methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment/Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/1990
Journal Article
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