Search for the standard model Higgs boson in e+e- collisions at √s=161-172 GeV

This paper describes a search for the Standard Model Higgs boson using data from e(+)e(-) collisions collected at center-of-mass energies of 161, 170 and 172 GeV by the OPAL detector at LEP. The data collected at these energies correspond to integrated luminosities of 10.0, 1.0 and 9.4 pb(-1), respectively. The search is sensitive to the main final states from the process in which the Higgs boson is produced in association with a fermion anti-fermion pair, namely four jets, two jets with missing energy. and two jets produced together with a pair of electron, muon or tau leptons. One candidate event is observed, in agreement with the Standard Model background expectation. In combination with previous OPAL searches at center-of-mass Energies close to the Z(0) resonance and the revised previous OPAL searches at 161 GeV, we derive a lower limit of 69.4 GeV for the mass of the Standard Model Higgs boson at the 95% confidence level.