Particle Physics Booklet - Particle Data Group - Lawrence Berkeley ...

180 10. Electroweak model and constraints on new physics
Therefore, observables (other than Rb) which favor mt values higher
than the Tevatron range favor lower values of MH. MW has additional
MH dependence through Δ�rW which is not coupled to m2 t effects. The
strongest individual pulls toward smaller MH are from MW and A0 LR ,
while A (0,b)
FB favors higher values. The difference in χ2 for the global fit is
Δχ2 = χ2 (MH = 300 GeV) − χ2 min ≈ 25. Hence, the data favor a small
value of MH, as in supersymmetric extensions of the SM. The central
value of the global fit result, MH =90 +27
−22 GeV, is below the direct lower
bound, MH ≥ 114.4 GeV (95% CL) [161].
The 90% central confidence range from all precision data is
55 GeV ≤ MH ≤ 135 GeV. (10.36)
Including the results of the direct searches at LEP 2 [161] and the
Tevatron [219] as extra contributions to the likelihood function drives
the 95% upper limit to MH ≤ 147 GeV. As two further refinements, we
account for (i) theoretical uncertainties from uncalculated higher order
contributions by allowing the T parameter (see next subsection) subject
to the constraint T =0± 0.02, (ii) the MH dependence of the correlation
matrix which gives slightly more weight to lower Higgs masses [220]. The
resulting limits at 95 (90, 99)% CL are, respectively,
MH ≤ 149 (145, 194) GeV. (10.37)
10.7. Constraints on new physics
A number of authors [226–231] have considered the general effects on
neutral-current and Z and W boson observables of various types of heavy
(i.e., Mnew ≫ M Z) physics which contribute to the W and Z self-energies
but which do not have any direct coupling to the ordinary fermions. In
addition to non-degenerate multiplets, which break the vector part of weak
SU(2), these include heavy degenerate multiplets of chiral fermions which
break the axial generators. These effects can be described, for example,
by the so-called T and S parameters, respectively, where the latter is
typically rather large in Technicolor theories.
T
1.25
1.00
0.75
0.50
0.25
0.00
-0.25
-0.50
-0.75
Γ Z , σ had , R l , R q
asymmetries
M W
ν scattering
e scattering
APV
all: M = 117 GeV
H
all: M = 340 GeV
H
all: M = 1000 GeV
H
-1.00
-1.5 -1.25 -1 -0.75 -0.5 -0.25 0 0.25
S
0.5 0.75 1 1.25 1.5 1.75 2
Figure 10.1: 1 σ constraints (39.35%) on S and T from various
inputs combined with MZ. S and T represent the contributions of
new physics only.
Further discussion and all references may be found in the full Review.