Higgs Physics: from LEP to a Future Linear Collider

New preliminary combined results from the LEP experiments on searches for the Higgs boson beyond the Standard Model are presented. The new determination of the top quark mass at the Tevatron in 2004 influences the interpretations of the LEP results in both, the Standard Model, and the Minimal Supersymmetric extension of the Standard Model. Higgs boson physics will also be a major research area at the future Linear Collider. A review including new preliminary results on the potential for precision measurements is given. Presented at the XVIIIth International Workshop on High Energy Physics and Quantum Field Theory (QFTHEP), 2004, St. Petersburg, Russia; and at the Xth Workshop on Nuclear Physics, WONP’2005, Havana, Cuba. Higgs Physics: from LEP to a Future Linear Collider André Sopczak Lancaster University, UK. E-mail: [email protected] Abstract New preliminary combined results from the LEP experiments on searches for the Higgs boson beyond the Standard Model are presented. The new determination of the top quark mass at the Tevatron in 2004 influences the interpretations of the LEP results in both, the Standard Model, and the Minimal Supersymmetric extension of the Standard Model. Higgs boson physics will also be a major research area at the future Linear Collider. A review including new preliminary results on the potential for precision measurements is given. The LEP experiments took data between August 1989 and November 2000 at center-of-mass energies first around the Z resonance (LEP-1) and from 1996 up to 209 GeV (LEP-2). In 2000 most data was taken around 206 GeV. The LEP accelerator operated very successfully and a total luminosity of L = 2461 pb was accumulated at LEP-2 energies. Data-taking ended on 3 November 2000, although some data excess was observed in searches for the Standard Model (SM) Higgs boson with 115 GeV mass. In the following sections, these aspects are addressed: 1) SM candidates and mass limits; 2) coupling limits; 3) the Minimal Supersymmetric extension of the SM (MSSM): dedicated searches, three-neutral-Higgs-boson hypothesis, benchmark and general scan mass limits; 4) CP-violating models; 5) invisible Higgs boson decays; 6) neutral Higgs bosons in the general two-doublet Higgs model; 7) Yukawa Higgs boson processes bb̄h and bb̄A; 8) singly-charged Higgs bosons; 9) doubly-charged Higgs bosons; 10) fermiophobic Higgs boson decays h→WW,ZZ, γγ; 11) uniform and stealthy Higgs boson scenarios; 12) summary of LEP limits; 13) the International Linear Collider (ILC); 14) SM Higgs physics; 15) beyond the SM. While the results from Standard Model Higgs boson searches are final [1], the results of searches in extended models are mostly preliminary [2]. Limits are given at 95% CL. The Linear Collider aspects are based on Refs. [3, 4]. 1 SM Candidates and Mass Limits From precision electro-weak measurements, the Higgs boson of the SM has a stringent upper mass limit as shown in Fig. 1 (left plot). The preferred value for the SM Higgs boson mass is 114 GeV. This value increased due to the new top mass measurements [5] and it is now very close to mass limit from direct searches. Including both the experimental and the theoretical uncertainties, the mass of the SM Higgs boson is lower than about 260 GeV (one-sided 95% upper CL). The figure shows also the reconstructed mass of the Higgs boson candidates for a 115 GeV Higgs boson hypothesis. In addition, the observed SM Higgs boson mass limit and the expected limit for a background-only hypothesis are shown.