LEP EW WG Plots for the Winter 2004 Conferences

Latest modification April 23rd, 2004.

You can find here the plots that have been produced for the Winter 2004 conferences. Some plots may show up here in a couple of slightly different presentations, depending on who has made the plot. They all use the same data. Many results and plots are still based on preliminary results.

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.

Compared to summer 2003, besides a very small change in M_W/G_W (using the latest Tevatron Run-I combination to combine with LEP-2), the only change occurs in M_top (new Run-I combination yielding M_top = 178.0+-4.3 GeV). Hence all SM fits and plots showing SM expectations change (the heavy-flavor bar-chart plots are not updated for the new SM expectation).

Attention:
The global SM fits now use only high-Q2 results from LEP, SLC and the Tevatron (together with the hadronic vacuum polarisation). Based on these 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(2), 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+-0.002, 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.