Search for the Standard Model Higgs Boson at LEP
G. Abbiendi
TL;DR
The paper reports a combined search for the Standard Model Higgs boson using data from the four LEP experiments collected at 189–209 GeV. A likelihood-ratio framework compares background to signal-plus-background across possible Higgs masses, incorporating multiple final states and systematic uncertainties. The analysis sets a 95% CL lower bound on the Higgs mass of 114.4 GeV/$c^2$ and provides upper bounds on the HZZ coupling under various decay scenarios, with only mild, statistically insignificant excesses observed near 115 GeV/$c^2$. The results demonstrate LEP’s extended sensitivity and place important constraints on Higgs properties ahead of the LHC era.
Abstract
The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have collected a total of 2461 pb-1 of e+e- collision data at centre-of-mass energies between 189 and 209 GeV. The data are used to search for the Standard Model Higgs boson. The search results of the four collaborations are combined and examined in a likelihood test for their consistency with two hypotheses: the background hypothesis and the signal plus background hypothesis. The corresponding confidences have been computed as functions of the hypothetical Higgs boson mass. A lower bound of 114.4 GeV/c2 is established, at the 95% confidence level, on the mass of the Standard Model Higgs boson. The LEP data are also used to set upper bounds on the HZZ coupling for various assumptions concerning the decay of the Higgs boson.