Perspectives in High-energy Physics

A personal view of current prospectives in particle physics is presented, inspired by the contributions to this meeting. Particular emphasis is laid in precision tests of the Standard Model and the search for the Higgs boson, on probes of CP violation, on speculations about possible physics beyond the Standard Model, on neutrino masses and oscillations, on the quest for supersymmetry, on opportunities @ future accelerators, and on the ultimate phenomenological challenge offered by the quest for a Theory of Everything. CERN-TH/2000-129 hep-ph/0007161 1. The Standard Model The Standard Model continued to rule accelerator experiments during 1999, even as the heroic efforts of the CERN accelerator engineeers pushed the LEP centre-of-mass energy to 202 GeV, and briefly to 204 GeV. There were no surprises in fermion-pair production or in the bread-and-butter reaction of LEP2, e+e− → W+W−. Both the γW+W− and Z0W+W− triple-gauge-boson vertices are there, as seen in Fig. 1, with magnitudes close to the Standard Model values [1, 2]. Looking into the final states, there are no confirmed interferences in (W → q̄q)⊗ (W− → q̄q) final states, due to either colour rearrangement or Bose-Einstein correlations: the difference between the W mass measured in purely hadronic and other final states is 15 ± 55 MeV [3]. Combining all the LEP measurements, one finds [1] mW = 80.401± 0.048 GeV (LEP), (1.1) contributing with the hadron colliders (MW = 80.448± 0.062 GeV) to a global average mW = 80.419± 0.038 GeV (world). (1.2) This error is now comparable with the value estimated indirectly from precision electroweak meaFigure 1: The Standard Model rules OK: measurements of σ(ee → WW) at LEP 2 agree with theory, demonstrating the existence of the expected γWW and ZWW vertices [1]. surements: mW = 80.382± 0.026 GeV, provides new, independent evidence for a light Higgs boson, and begins to impact significantly the radiativecorrection estimate [1] mH = 77 +69 −39 GeV (1.3) SILAFAE III, Cartagena de Indias, Colombia, April 2-8, 2000 John Ellis when αem(mZ) −1 = 128.878± 0.090 is assumed (or log(MH/GeV) = 1.96 +0.21 −0.23 if the estimate 128.905±0.036, with the error reduced by theory, is assumed). The Higgs boson probably weighs less than 200 GeV. The plan is to raise the LEP energy as high as possible during 2000, with the primary aim of searching for the Higgs boson. An integrated luminosity of 50/pb per experiment at 206 GeV would increase the sensitivity of the Higgs reach from the current lower limit of 107.9 GeV [4, 5] to about 114 GeV [6]. A small numerical increase, but in the most interesting range, also from the point of view of supersymmetry [7]. The LEP energies attained so far range up to 208.7 GeV, with a total luminosity (so far) of 109 pb−1 at an average energy above 205 GeV. It seems that the target sensitivity to mH = 114 GeV is well within reach. At the time of writing, the current sensitivity is to mH ∼ 113.4 GeV, and the latest update may be obtained from [8]. Then, in Autumn 1999, LEP must be shut down and dismantled to make way for the LHC excavations and installation. It will be the end of an era of precision electroweak measurements. The search for the Higgs boson will then pass to Fermilab, where the Tevatron has a chance of exploring higher Higgs masses if it gathers more than 10 fb−1 of luminosity, as seen in Fig. 2 [10].