Experimental Constraints on the Higgs Mass

Established measurements of the Z boson mass at LEP and the top quark mass at the Tevatron now allow predictions of the Higgs mass from precise measurements of the weak mixing angle, the W mass and the Z width.

Higgs' Mass Plot by Technique.  The yellow region is excluded  by direct searches for the Higgs by the LEP experiments. The curves represent probability distributions for what the Higgs mass should be based on several different experimental techniques.  The minimum of the curves is the most likely Higgs mass and where the curves intersect the 95% CL or 99% CL lines indicate that the Higgs mass should be below that intersection point with 95% or 99% confidence, respectively. SLD's result is shown in red.  The CERN result using leptonic asymmetries is shown in blue. Combined results from W mass measurements at CERN and Fermilab are shown in green.  The black band labeled 'Other' includes LEP measurements of G_Z, s_had⁰, and R_l, LEP/SLD measurements of R_b and R_c, SLD measurements of A_b and A_c, and NuTeV's measurement of R^-.  All these techniques are self-consistent and prefer a light Higgs mass.  But the CERN result from the hadronic measurement of the weak mixing angle, which uses the forward-backward asymmetry in decays of the Z⁰ to b quarks (shown in magenta), favors a much heavier Higgs.   (This plot is made using Da_had(M_Z²)=0.02738 +/- 0.00020.)

Higgs' Mass Plot comparing the LEP A_FB^b measurement with the rest of the world's data..  Combining all the world's data, but excluding the LEP A_FB^b result, yields the curve shown in red and determines that the Higgs should be lighter than 190 GeV at 99% CL.  The magenta curve shows the forward-backward b-quark asymmetry result from LEP.  In this case, one finds that the Higgs should be heavier than 190 GeV at 99% CL!    (This plot is made using Da_had(M_Z²)=0.02738 +/- 0.00020.)