Searches for Invisible Higgs bosons: Preliminary combined results using LEP data collected at energies up to 209 GeV
ALEPH Collaboration, DELPHI Collaboration, L3 Collaboration, OPAL Collaboration, the LEP Higgs Working Group
TL;DR
The paper tackles the search for a neutral CP-even Higgs boson decaying invisibly by combining LEP data from four experiments collected up to 209 GeV. It merges 2000 data with prior runs, predicting signals and backgrounds with the HZHA model and interpolating across energies while using the CLs framework for statistical interpretation. The analysis focuses on Higgs-strahlung final states with Z decays to jets or leptons, exploiting acoplanar jet and lepton topologies; no excess over the Standard Model is found. Consequently, it establishes a 95% confidence level lower bound on the invisible Higgs mass of $m_H > 114.4~\mathrm{GeV}/c^2$, tightening constraints on invisible decay scenarios and illustrating the power of a combined LEP Higgs search. The work demonstrates the viability of cross-experiment data combination to probe non-standard Higgs decays and informs future collider searches.
Abstract
In the year 2000 the four LEP experiments have collected data at energies between 200 and 209 GeV, for approximately 868 pb-1 integrated luminosity. The LEP working group for Higgs boson searches has combined these data with earlier data sets collected at lower centre-of-mass energies to search for a neutral CP-even Higgs boson, produced at the Standard Model rate, decaying into "invisible" particles. No statistically significant excess has been observed when compared to the Standard Model background prediction, and assuming that the Higgs boson decays only into such states a lower bound has been set on its mass at 95% confidence level of 114.4 GeV.