Comprehensive analysis of data pertaining to the weak neutral current and the intermediate-vector-boson masses

Abstract

The results of a comprehensive analysis of existing data on the weak neutral current and the W and Z masses are presented. The principal results are the following. (a) There is no evidence for any deviation from the standard model. (b) A global fit to all data yields sin 0~= 1 -Mgr /Mz =0.230+0.0048, where this error and all others given here include full statistical, systematic, and theoretical uncertainties (computed assuming three fermion families, m, & 100 GeV, and MH & 1 TeV). (c) Allowing p=M~/(Mz cos'0~) as well as sin'0~to vary one obtains sin 0~=0.229+0.0064 and p =0.998+0.0086. This implies 90%%uo-confidence-level (C.L.) upper limits of 0.047 and 0.081 for the vacuum expectation values (relative to those of Higgs doublets) for Higgs triplets with weak hypercharge of 0 and +1, respectively. (d) The parameter6~=drhs (1 -Ar)/sin'0, which is a measure of the radiative corrections relating deepinelastic neutrino scattering, the 8' and Z masses, and muon decay, is determined to be 0. 112+0.037. This is consistent with the value 5~--0. 106 expected for m, =45 GeV and MH --100 GeV and establishes the existence of radiative corrections at the 3o. level. (e) The radiative corrections are sensitive to isospin breaking associated with a large m, . Assuming no deviation from the standard model, consistency of the various reactions requires m«180 GeV at 90%%uo C.L. for M& & 100 GeV, with a slightly weaker limit for larger MH. Similar results hold for the mass splittings between fourth-generation quarks or leptons. (f) Most of the parameters in modelindependent fits to vq, ve, eq, and e+e processes are now determined uniquely and precisely. (g) Limits are given on the masses and mixing angles of additional Z bosons expected in popular models. For theoretically expected coupling constants one finds that the neutral-current constraints are usually more stringent than the direct-production limits from the CERN SppS collider, but nevertheless masses as low as 120 -300 GeV are typically allowed. (h) The implications of these results for grand unification are discussed. sin 0~is )2.5 standard deviations above the prediction of minimal SU(5) and similar models for all m, . It is closer to the prediction of simple supersymmetric grand unified theories but is still somewhat low. (i) The dominant theoretical uncertainty (the charm-quark threshold in deep-inelastic charged-current scattering) is considered in some detail.

Physics implications of precision electroweak experiments

“…Alberto has played a unique and indispensable role in the development and testing of the standard model and of renormalizable gauge field theories. My one major collaboration with Alberto [3] was one of the most pleasant of my career. Happy birthday Alberto!…”

“…It was found that ordinary SU (5) was excluded (consistent with the non-observation of proton decay), but that the supersymmetric extension was allowed, i.e., that the data was "consistent with SUSY GUTS and perhaps even the first harbinger of supersymmetry" [3].…”

“…The third generation of experiments [3,4] began in the 1980's, and continues with WNC experiments even to the present. They were typically of order 1-5% precision.…”

Search for gauge extensions of the MSSM at the LHC

“…Sleptons in the intermediate states couple to gauginos and leptons via the modes listed in Table I. Thus, when the LSP is dominated by bino (which is what happens in most of the parameter space [6]), a prime signature of a Uð1Þ 0 extension of the MSSM is the reduction of purely hadronic events originating from the decays (22) and a corresponding enhancement of the leptonic events via the decays (25) and (26). While the rates of these decays and the depletion in the number of purely hadronic events depend on the masses and couplings of the intermediate sparticles in the cascades, the leptonic final states stemming from the right-handed squarks should offer sufficiently clean signatures to establish the existence of a Uð1Þ 0 extension at the LHC.…”

“…or tetraleptons (26) in the final state. Sleptons in the intermediate states couple to gauginos and leptons via the modes listed in Table I.…”