LEP EW WG Plots for the Winter 2005 Conferences

Latest corrections and/or modifications 18-APR-2005.

You can find here the plots that have been produced for the Winter 2005 conferences. Most results are final, such as the Z-pole measurements from SLD and at LEP, while the LEP-2 results (such as mass and width of the W boson) are still preliminary. Note that essentially the full set of plots will be made available, including those that have data that hasn't changed, so that "one-stop shopping" can be done.

Changes:

Compared to summer 2004, the (not-yet quite) final Z-pole heavy-flavour combination is available, using final measurements and including the revised correction to go from the measured asymmetry to the pole asymmetry calculated using the latest ZITTER version 6.41. Since version 6.40, ZFITTER includes complete two-loop calculations for MW, leading three-loop rho caluclations, and fermionic two-loop calculations for sin2teff.

Attention:
Since winter 2004, the global SM fits now use only high-Q2 results from LEP, SLC and the Tevatron (together with the hadronic vacuum polarisation). This disentangles the numerical Higgs-mass constraint and limit from the issue of the high chi2 caused by the low-Q2 NuTeV measurement which, however, has only a small influence on the fitted Higgs mass. Based on these high-Q2 analyses, predictions for low-Q2 measurements such as atomic parity violation in cesium (APV), parity violation in Moller scattering (e-e-), and neutrino-nucleon scattering (NuTeV) are derived.

Answers to FAQs on plots presented below:

For plots showing generic SM predictions in form of arrows or areas, the following parametric variations are used: dal5had = 0.02761(36), alpha_s = 0.118(3), MZ = 91187.5(2.1) MeV, M_top = 178.0(4.3) GeV, M_Higgs = 300+700-186 GeV (lower limit of 114 GeV as given by the direct search). The arrows are pointing in the direction of increasing parameter values!
Afb_q and R_q[=GZ_q/GZ_had] bar-chart plots for heavy quark flavours comparing ADLOS results:
- In contrast to previous versions of these plots for older conferences, all numerical values as well as all dots with error bars are so-called pole quantities, eg, Afb0q, and in particular corrected to exactly the same set of values for other parameters. When applicable, the measurements at the off-peak energy are transported to the peak and included in the results.
- Thus the results shown are directly comparable, among themselves as well as with the average, but do not neccessarily correspond digit-by-digit to the numerical values found in the individual experimental publications.
Light-quark effective couplings plot:
- In this analysis, the hadronic Z-decay partial width is no longer an independent parameter but is calculated as:
  GZ_had = GZ_dd+GZ_uu+GZ_ss+GZ_cc+GZ_bb.
- Since there are not sufficiently many different light-quark flavour pseudo-observables measured to disentangle u, d and s quarks completely, an assumption is made in the extraction of pseudo-observables, such as partial widths or effective coupling constants, for light quarks: quark universality is imposed for the two down-type light-quark flavours, so that s=d for all pseudo-observables relating to s and d quarks.
- For the light-quark contours (u and d=s), a second solution exists, mirroring the contour curves at the origin, (gvq,gaq) <->(-gvq,-gaq). The light-quark measurements are also invariant under the exchange gvq<->gaq, leading to contours symmetric with respect to the diagonal (gvq=gaq). To resolve these ambiguity, one needs to measure the CM energy dependence of the asymmetry (which is done only for the heavy quarks b and c).
- The allowed area for neutrinos, assuming three generations of neutrinos with identical vector couplings and identical axial-vector couplings, is bounded by circles centred at the origin since the invisible partial width constrains the sum of the squares of the effective couplings only. The ring is so thin that it appears as a single line in the plot.
Epsilon-parameter contour
- Based on a fit varying alpha(dal5had), alpha_s, MZ, and the four epsilon_123b parameters
- Data set consists of all measurements except Gamma_W, M_top and sin2theta from NUTEV due to its explicit M_top/M_Higgs dependence (M_top/M_Higgs cannot be expressed in terms of the four epsilon parameters). APV is also not included, as additional model assumptions are needed to express APV in terms of the epsilon parameters.
STU-parameter contour
- Based on a fit varying alpha(dal5had), alpha_s, MZ, and the three STgamma_b parameters
- U=0 fixed throughout
- Data set consists of all measurements except Gamma_W, M_top and sin2theta from NUTEV due to its explicit M_top/M_Higgs dependence (M_top/M_Higgs cannot be expressed in terms of the four STUgamma_b parameters). APV is also not included, as additional model assumptions are needed to express APV in terms of the STUgamma_b parameters.
- The additional bands correspond to +-1sigma bands for the alpha_s independent quantities GZ_lepton, MW and sin2teff (in order of increasing slope dT/dS). GZ_lepton instead of GZ_tot is chosen because the latter depends in addition on alpha_s and the former exhibits a more extreme (ie, flatter) slope. All other fit parameters are fixed.
- The MSM reference values (STUgamma_b=0) are dal5had=0.02761, alpha_s=0.118, MZ=91.1875 GeV, M_top=175 GeV, M_Higgs=150 GeV
Higgs constraint from each measurement:
- For each observable, the corresponding constraint on the Higgs mass is determined in a full MSM fit to the measurement result of this observable, constraining dal5had=0.02761+-0.00036, alpha_s=0.118+-0.003, MZ = 91.1875+-0.0021 GeV and M_top=178.0+-4.3 GeV.
- For Higgs masses larger than about 1 TeV, the MSM and its formulae used do not make too much sense, so that part of the Higgs mass regime is cut of as it should not be taken quantitatively.
- The vertical green band denotes the overall constraint on the Higgs mass derived from the fit to all data.
- The vertical black line denotes the limit on the Higgs mass obtained from the direct search at LEP-2.
- The effects of real Higgs-strahlung, Z*+H, is not taken into account, neither in the experimental analyses (such as Higgs-mass dependent efficiencies for various Z*H decay channels) nor in the calculation of MSM predictions (increased Z decay widths). Thus quantitative conclusions from individual observables are uncertain in the low Higgs-mass regime.
SM parameter sensitivity of each observable
- This normalised sensitivity is calculated as follows: Within the SM, the partial derivative of the observable calculation w.r.t. the SM parameter in question is calculated, and then divided by the measurement error of the observable and multiplied by the error of the SM parameter. Values and errors for the SM parameters for this calculation are: dal5had=0.02761+-0.00036, alpha_s=0.118+-0.003, MZ=91.1875+-0.0021 GeV, M_top=178.0+-4.3 GeV, M_H=150 GeV and error on logM_H=0.2.