Search for the Standard Model Higgs Boson in e+e- Collisions at sqrt(s) = 192-209 GeV
The OPAL collaboration, G. Abbiendi
TL;DR
This paper presents a Higgs boson search in e+e− collisions at sqrt(s) ≈ 192–209 GeV with the OPAL detector, focusing on Higgs-strahlung e+e− → HZ with H decaying to bb or ττ across multiple final states. A multichannel analysis employing preselection, b-tagging, and mass reconstruction via kinematic fits, combined with a likelihood-based CLs statistical framework, yields a 95% CL lower bound on the SM Higgs mass of 109.7 GeV, with a small local excess near 107 GeV that is not statistically significant. The data show only mild preference for a 115 GeV Higgs but remain compatible with the background hypothesis; the results underscore the value of combining LEP experiments to improve sensitivity. Overall, the work extends Higgs mass constraints and informs future Higgs searches by detailing channel-specific selections, discriminants, and the CLs methodology.
Abstract
A search for the Standard Model Higgs boson has been performed with the OPAL detector at LEP based on the full data sample collected at sqrt(s) = 192-209 GeV in 1999 and 2000, corresponding to an integrated luminosity of approximately 426 pb-1. The data are examined for their consistency with the background-only hypothesis and various Higgs boson mass hypotheses. A lower bound of 109.7 GeV is obtained on the Higgs boson mass at the 95% confidence level. At higher masses, the data are consistent with both the background and the signal-plus-background hypotheses.