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HAL Id: in2p3-00009825

http://hal.in2p3.fr/in2p3-00009825

Submitted on 2 Aug 2001

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The global fit to electroweak data

B. Pietrzyk

To cite this version:

B. Pietrzyk. The global fit to electroweak data. International conference on high-energy physics 30

ICHEP, Jul 2000, Osaka, Japan. pp.710-713. �in2p3-00009825�

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LAPP-EXP 2000-06 September 2000

The global t to Electroweak data

B. PIETRZYK

LAPP, IN2P3-CNRS, Chemin de Bellevue, BP110, F-74941, Annecy-le-Vieux

abstract

The global t to electroweak data is given. The Standard model is in a good shape and is consistent. The new BES measurements of

Rhad

are used in the determination of the hadronic contribution to the running of

. Using these measurements, data still prefer low m

H

, but less low.

Talk given at the XXXth Int. Conf. on High Energy Physics, ICHEP 2000,

July 27 - August 2, 2000, Osaka, Japan

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For Publisher’s use

THE GLOBAL FIT TO ELECTROWEAK DATA

B. PIETRZYK

LAPP, IN2P3, ch. de Bellevue, 74941 Annecy-le-Vieux Cedex, France.

E-mail: pietrzyk@lapp.in2p3.fr

The global fit to electroweak data is given. The Standard model is in a good shape and is consistent.

The new BES measurements ofRhad are used in the determination of the hadronic contribution to the running ofα. Using these measurements, data still prefer low mH, but less low.

0 2 4 6

10 102 103

mH[GeV]

∆χ2

Excluded Preliminary

∆αhad =

∆α(5)

0.02804±0.00065 0.02755±0.00046

theory uncertainty

Figure 1. ∆χ2distribution of the Standard Model fit results as a function of the Higgs mass mH. Official fit results are shown by the solid line, the dotted line rep- resents fits results with the ∆α(5)had(s) obtained here.

Beautiful experimental results have been presented in this session. These results are used in the global fit to electroweak data in which the validity of the Standard Model (SM) is assumed. In this fit the consistency of the Standard Model is tested. The value of the Higgs mass is extracted from the mea- surements of radiative corrections.

Figure 1 shows the ∆χ2 distribution of the fit results. The central value of the Higgs mass is

mH = 60+52−29GeV

The one-sided 95%CL (90% two-sided) upper limit on mH is 165 GeV.

This value was 66.5±+60−33in Moriond in spring 2000, so the change is small. The largest

Measurement Pull Pull

-3 -2 -1 0 1 2 3

-3 -2 -1 0 1 2 3 mZ [GeV]

mZ [GeV] 91.1875 ± 0.0021 .05 ΓZ [GeV]

ΓZ [GeV] 2.4952 ± 0.0023 -.42 σhadr [nb]

σ0 41.540 ± 0.037 1.62 Rl

Rl 20.767 ± 0.025 1.07 Afb

A0,l 0.01714 ± 0.00095 .75 Ae

Ae 0.1498 ± 0.0048 .38 Aτ

Aτ 0.1439 ± 0.0042 -.97 sin2θeff

sin2θlept 0.2321 ± 0.0010 .70 mW [GeV]

mW [GeV] 80.427 ± 0.046 .55 Rb

Rb 0.21653 ± 0.00069 1.09 Rc

Rc 0.1709 ± 0.0034 -.40 Afb

A0,b 0.0990 ± 0.0020 -2.38 Afb

A0,c 0.0689 ± 0.0035 -1.51 Ab

Ab 0.922 ± 0.023 -.55 Ac

Ac 0.631 ± 0.026 -1.43 sin2θeff

sin2θlept 0.23098 ± 0.00026 -1.61 sin2θW

sin2θW 0.2255 ± 0.0021 1.20 mW [GeV]

mW [GeV] 80.452 ± 0.062 .81 mt [GeV]

mt [GeV] 174.3 ± 5.1 -.01

∆αhad(mZ)

∆α(5) 0.02804 ± 0.00065 -.29

Osaka 2000

Figure 2. Input values to the fit and the pulls.

contribution to the change comes from the change in the value of mW. In this analysis the most advanced fitting programs ZFIT- TER and TOPAZ0 are used. The band around the solid line represents theoreti- cal uncertainties obtained by comparison of results of two fitting programs, and also by varying the different implementations of higher order corrections in these programs in order to estimate the size of the remaining even higher order terms. The shadowed re- gion is excluded by direct searches.

Input values to the fit and the pulls are shown in figure 2. The χ2/d.o.f. is 21/15, giving a reasonable probability of 12%. The only pull above 2 comes from the A0,bf b mea- surement. The pull of the ALRmeasurement

osaka00˙article: submitted to World Scientificon September 13, 2000 1

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0 0.5 1 1.5 2 2.5 3 3.5 Log(Mhiggs(GeV))

Figure 3. The results of the Higgs mass fit to different measurements.

is 1.6.

The results of the Higgs mass fit to differ- ent measurements is shown in figure 3. A rea- sonable distribution of the results of these fits around the central value is observed. Three measurements A0,lF B, ALR and mW give cen- tral value of mH of about 30 GeV.

The numerical values of fit results are given in reference1.

Very good consistency of the Standard Model is observed in figures 4, 5, 6 by com- paring fit results with the direct measure- ments.

Figure 7 shows the fit results and the Standard Model predictions in the MW, Γl plane. The Standard Model prediction is also shown when radiative corrections are re- stricted to the running of αalone. The gen- uinely electroweak radiative corrections are clearly seen. These corrections, from mea- surements of which the Higgs mass value is obtained, depend also strongly on the top contribution.

Thus, in order to determine the central value and the error of the Higgs mass one has to knowprecisely the central values and the uncertainties on α and mt. The strong

*

140 160 180 200

102 103

140 160 180 200

1.5 2 2.5 3

mHiggs[GeV] mTop[GeV]

1 σ ZFITTER 68 %C.L.

1 σ TOPAZ0 EXCLUDED BY DIR

ECT SEARCHES

mtop=174.3±5.1 GeV

PREL. Summer 2000 (no direct mtop)

Figure 4. Consistency of the SM.

80.3 80.4 80.5

102 103

80.3 80.4 80.5

1.5 2 2.5 3

mHiggs[GeV] mW[GeV]

EXCLUDED BY DIR

ECT SEARCHES

mW=80.434±0.037 GeV

1 σ ZFITTER 68%C.L.

1 σ TOPAZ0

PREL. Summer 2000 (no direct mW)

Figure 5. Consistency of the SM.

140 160 180

80.2 80.4

mW[ GeV ] mTop[ GeV ]

indirect measurements (no direct mW, mtop)

direct measurements mHig

gs

=1 T eV

mHig gs=300 G

eV

mHig gs=110 G

eV 68 %C.L.

PREL. summer 2000

Figure 6. Consistency of the SM.

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For Publisher’s use

83.6 83.8 84 84.2

80 80.2 80.4 80.6

∆α

Preliminary 68% CL

MW [GeV] Γl [MeV]

mt= 174.3 ± 5.1 GeV mH= 113...1000 GeV

mt

mH

Figure 7. The fit results and the Standard Model pre- dictions in the MW, Γlplane.

2.5 5 7.5

102

2.5 5 7.5

2 2.5

mHiggs[GeV500]

∆χ2 ∆χ2 ∆χ2 ∆χ2

EXCLUDED BY D IR

ECT SEARCHES PREL. Summer 2000

standard

∆α

∆α,∆t

t

Figure 8. The dependence of the fit results on the variation of central values ofαand mt.

dependence of the fit results on the variation of central values ofαand mtis shown in fig- ure 8. The central value of α−1 is changed by 0.09 (1σ), and the central value of mtby 5.1 GeV (1σ) in the direction which increases the value of mH in the fit output.

αis running :

α(s) = α(0)

1αl(s)α(5)had(s)αtop(s) The contribution of the leptonic loops ∆αl(s) is precisely known2. The contribution of quark loops is obtained by integrating the Rhad distribution measured in e+e annihi-

Figure 9. The results ofRhadmeasurements with 85 preliminary and 6 published points of BES.

lation.

Re Πγγ(s) =α s 3π P

4m2π

Rhad(s) s(s−s)ds The BES collaboration reported3 at this conference the newpreliminary measure- ments of Rhad in the c.m.s region 2-5 GeV.

The 85 preliminary points together with the 6 published ones (figure 9) are used in a very preliminary update of the results of calcula- tions in reference4. The value of

α(5)had(s) = 0.02755±0.00046 is obtained corresponding to α−1= 128.945±0.060.

The central value is changed by 0.7σin com- parison with the published4 value of 0.0280

±0.0007.

The values ofRhadmeasured by BES are generally lower than the earlier data used in the previous analysis both in the lowenergy region (figure 10) and in the charmonium re- gion. The solid line in figure 10, used in the

α(5)had(s) analysis, is nowcloser to the per- turbative QCD prediction5 (figure 10).

osaka00˙article: submitted to World Scientificon September 13, 2000 3

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Figure 10. The results ofRhadmeasurements in the low e+ec.m.s. energy region.

Fits of the Higgs mass to different chan- nels are repeated using the newvalue of α (figure 11). The central values of different measurements are shifted to the higher val- ues and those of A0,lF B, ALRand mW give the

χ2 minima at 40-50 GeV.

The change in the ∆χ2distribution using the newvalue of ∆α(5)had(s) is shown by the dotted line in figure 1. The ∆χ2 minimum moves to about 88 GeV and the one-sided 95%CL upper limit moves to 210 GeV.

In conclusion :

the Standard Model is still in good shape

the Standard Model is consistent

the most significant changes are : BES R measurements, not yet in-

cluded in the official fit results mW from LEP

Z lineshape is nowfinal, but pre- liminary numbers were already very good

the data prefer a lowHiggs mass official fit resultsmH = 60+52−29GeV,

mH<165 GeV

using BES R measurements, the data still prefer lowmH, but less low

0 0.5 1 1.5 2 2.5 3 3.5

Log(Mhiggs(GeV))

Figure 11. The results of the Higgs mass fit to dif- ferent measurements using the value of ∆α(5)had(s) ob- tained here.

thanks to :

Gunter Quast with his ZF package, Zheng- guo Zhao and his BES team, LEPP EWWG with Martin Gruenewald and Bob Clare, LEP Collaborations and Helmut Burkhardt.

References

1. http://alephwww.cern.ch/˜pietrzyk/fit- osaka00.ps; the small difference between numbers presented in Osaka and given here are explained there.

2. M. Steinhauser,

Phys. Lett. B429(1998)158.

3. Z. Zhao,Measurements of R at 2-5 GeV, this proceedings.

4. H. Burkhardt and B. Pietrzyk, Phys. Lett. B356(1995)398.

5. M. Davier and A. H¨ocker, Phys. LettB419(1998)419.

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