68
G. Altarelli and S. Forte
Table 3.2 Standard Model fits of electroweak data [8]
Fit
1
2
3
Measurements
m W
m t
m t , m W
m t (GeV)
178.9
+12
−9
170.9 ± 1.8
171.3 ± 1.7
m H (GeV)
145
+240
−81
99
+52
−35
76
+34
−24
log [m H (GeV)]
2.16 ± +0.39
2.00 ± 0.19
1.88 ± 0.16
α s (m Z )
0.1190 ± 0.0028
0.1189 ± 0.0027
0.1185 ± 0.0026
m W (MeV)
80385 ± 19
80360 ± 20
80374 ± 15
All fits use the Z pole results and
(5)
had (m 2
Z ) as listed in Table 3.1. In addition, the measurements
listed on top of each column are included as well. The fitted W mass is also shown [8] (the directly
measured value is m W = 80398 ± 25 MeV)
the input from the direct search result). This is quite encouraging for the ongoing
search for the Higgs particle. More general, if the Higgs couplings are removed
from the Lagrangian the resulting theory is non renormalizable. A cutoff must
be introduced. In the quantum corrections log m H is then replaced by log plus
a constant. The precise determination of the associated finite terms would be lost
(that is, the value of the mass in the denominator in the argument of the logarithm).
A heavy Higgs would need some unfortunate accident: the finite terms, different in
the new theory from those of the SM, should by chance compensate for the heavy
Higgs in a few key parameters of the radiative corrections (mainly 1 and 3 , see,
for example, [49]). Alternatively, additional new physics, for example in the form
of effective contact terms added to the minimal SM lagrangian, should accidentally
do the compensation, which again needs some sort of conspiracy.
To the list of precision tests of the SM one should add the results on low
energy tests obtained from neutrino and antineutrino deep inelastic scattering
(NuTeV [52]), parity violation in Cs atoms (APV [53]) and the recent measurement
of the parity-violating asymmetry in Moller scattering [54] (see Chap. 6). When
these experimental results are compared with the SM predictions the agreement
is good except for the NuTeV result that shows a deviation by three standard
deviations. The NuTeV measurement is quoted as a measurement of sin
2 θ W =
1 − m 2
W /m 2
Z from the ratio of neutral to charged current deep inelastic crosssections from ν μ and ¯
ν μ using the Fermilab beams. But it has been argued and it
is now generally accepted that the NuTeV anomaly probably simply arises from an
underestimation of the theoretical uncertainty in the QCD analysis needed to extract
sin
2 θ W . In fact, the lowest order QCD parton formalism on which the analysis has
been based is too crude to match the experimental accuracy.
When confronted with these results, on the whole the SM performs rather well,
so that it is fair to say that no clear indication for new physics emerges from the
data. However, as already mentioned, one problem is that the two most precise
measurements of sin
2 θ eff from A LR and A
b
FB differ by about 3σ s. In general, there
appears to be a discrepancy between sin
2 θ eff measured from leptonic asymmetries
((sin
2 θ eff ) l ) and from hadronic asymmetries ((sin
2 θ eff ) h ). In fact, the result from
G. Altarelli and S. Forte
Table 3.2 Standard Model fits of electroweak data [8]
Fit
1
2
3
Measurements
m W
m t
m t , m W
m t (GeV)
178.9
+12
−9
170.9 ± 1.8
171.3 ± 1.7
m H (GeV)
145
+240
−81
99
+52
−35
76
+34
−24
log [m H (GeV)]
2.16 ± +0.39
2.00 ± 0.19
1.88 ± 0.16
α s (m Z )
0.1190 ± 0.0028
0.1189 ± 0.0027
0.1185 ± 0.0026
m W (MeV)
80385 ± 19
80360 ± 20
80374 ± 15
All fits use the Z pole results and
(5)
had (m 2
Z ) as listed in Table 3.1. In addition, the measurements
listed on top of each column are included as well. The fitted W mass is also shown [8] (the directly
measured value is m W = 80398 ± 25 MeV)
the input from the direct search result). This is quite encouraging for the ongoing
search for the Higgs particle. More general, if the Higgs couplings are removed
from the Lagrangian the resulting theory is non renormalizable. A cutoff must
be introduced. In the quantum corrections log m H is then replaced by log plus
a constant. The precise determination of the associated finite terms would be lost
(that is, the value of the mass in the denominator in the argument of the logarithm).
A heavy Higgs would need some unfortunate accident: the finite terms, different in
the new theory from those of the SM, should by chance compensate for the heavy
Higgs in a few key parameters of the radiative corrections (mainly 1 and 3 , see,
for example, [49]). Alternatively, additional new physics, for example in the form
of effective contact terms added to the minimal SM lagrangian, should accidentally
do the compensation, which again needs some sort of conspiracy.
To the list of precision tests of the SM one should add the results on low
energy tests obtained from neutrino and antineutrino deep inelastic scattering
(NuTeV [52]), parity violation in Cs atoms (APV [53]) and the recent measurement
of the parity-violating asymmetry in Moller scattering [54] (see Chap. 6). When
these experimental results are compared with the SM predictions the agreement
is good except for the NuTeV result that shows a deviation by three standard
deviations. The NuTeV measurement is quoted as a measurement of sin
2 θ W =
1 − m 2
W /m 2
Z from the ratio of neutral to charged current deep inelastic crosssections from ν μ and ¯
ν μ using the Fermilab beams. But it has been argued and it
is now generally accepted that the NuTeV anomaly probably simply arises from an
underestimation of the theoretical uncertainty in the QCD analysis needed to extract
sin
2 θ W . In fact, the lowest order QCD parton formalism on which the analysis has
been based is too crude to match the experimental accuracy.
When confronted with these results, on the whole the SM performs rather well,
so that it is fair to say that no clear indication for new physics emerges from the
data. However, as already mentioned, one problem is that the two most precise
measurements of sin
2 θ eff from A LR and A
b
FB differ by about 3σ s. In general, there
appears to be a discrepancy between sin
2 θ eff measured from leptonic asymmetries
((sin
2 θ eff ) l ) and from hadronic asymmetries ((sin
2 θ eff ) h ). In fact, the result from