G. Alexander et al., SEARCH FOR NEUTRAL HIGGS BOSONS IN Z(0) DECAYS USING THE OPAL DETECTOR AT LEP, Zeitschrift fur Physik. C, Particles and fields, 73(2), 1997, pp. 189-199
A search for neutral Higgs bosons has been performed using the full sa
mple of Z(0) decays collected by the OPAL detector at LEP up to 1995.
The data were taken at centre-of-mass energies between 88 GeV and 95 G
eV and correspond to an integrated luminosity of approximately 160 pb(
-1). The present search addresses the processes Z(0) --> H(0)Z and h(
0)Z, where H-0 is the Higgs boson predicted by the Standard Model and
h(0) the lightest neutral scalar Higgs boson predicted in the framewo
rk of the Minimal Supersymmetric Standard Model. For the virtual Z(0)
boson, Z, the following decay channels are considered: Z* --> nu<(nu)
over bar>, e(+)e(-) and mu(+)mu(-). Two candidate events have been fou
nd in the nu<(nu)over bar>H-0 channel and one in the mu(+)mu(-) H-0 ch
annel. Combined with earlier searches, the present search excludes the
SM Higgs boson, at the 95% confidence level (CL), from the mass range
below 59.6 GeV. In the framework of the Minimal Supersymmetric Standa
rd Model, allowing a wide range of variation for most relevant model p
arameters, a 95% CL lower limit of 44.3 GeV is obtained for the mass o
f the h(0) boson. Combined with earlier direct searches for the Higgs
boson pair production process Z(0) --> h(0)A(0) and with measurements
of the Z(0) line shape, a 95% CL lower limit of 23.5 GeV is obtained f
or the mass of the pseudoscalar Higgs boson A(0), assuming tan beta gr
eater than or equal to 1.