Complete LEP Data: Status of Higgs Boson Searches

The LEP experiments completed data-taking in November 2000. New preliminary combined results of the four LEP experiments ALEPH, DELPHI, L3 and OPAL are presented for various Higgs boson searches.Comment: 9 pages, 12 figures. Proc. Third Int.Conference on Non-Accelerator New Physics, NANP-01, Moscow, 200

A General MSSM Parameter Scan

The excluded tan(beta) range and Higgs boson mass regions in the framework of the Minimal Supersymmetric extension of the Standard Model (MSSM) depend on several parameters. The Higgs boson masses, cross-sections and branching fractions have been determined including two-loop diagrammatic calculations. The limits obtained with a more general scan over the parameter space of the MSSM are compared with those in the so-called benchmark scenario. The combination of the searches for Higgs particles in the 1999 data collected by the DELPHI collaboration at center-of-mass energies between 191.6 and 201.7 GeV allows stringent limits to be set in combination with previous DELPHI results. In addition, an interpretation in the framework of the general MSSM scan of the 2000 LEP data at the hightest energies between 201.7 and 209.0 GeV is given. We show that the current data for the HZ and hA production can be comfortably accommodated in the MSSM.Comment: 3 pages, 3 figure

A Comparison of Mixed-Higgs Scenarios In the NMSSM and the MSSM

We study scenarios in the minimal and next-to minimal supersymmetric models in which the lightest CP-even Higgs boson can have mass below the 114 GeV standard model LEP limit by virtue of reduced ZZ coupling due to substantial mixing among the Higgs bosons. We pay particular attention to the size of corrections from superpartners needed for these scenarios to be viable and point to boundary conditions at large scales which lead to these scenarios while at the same time keeping electroweak fine tuning modest in size. We find that naturalness of electroweak symmetry breaking in the mixed-Higgs scenarios of both models points to the same region of soft supersymmetry breaking terms, namely those leading to large mixing in the stop sector at the electroweak scale, especially if we also require that the lightest CP-even Higgs explains the Higgs-like LEP events at about 98 GeV.Comment: 14 pages, 19 figure

Limits on Extensions of the Minimal Standard Model from Combined LEP Lineshape Data

The high statistics of the combined LEP lineshape data are used to derive constraints on hypothetical extensions of the Minimal Standard Model. The data comprises about eight million visible Z decays, recorded between 1989 and 1993. This letter gives limits for simple tests on models which predict additional Z boson decays or modified Z-couplings. As an application the two-doublet Higgs model is considered.Comment: 8 pages, 1 figure, PS fil

Comparison of Higgs Boson Mass and Width Determination of the LHC and a Linear Collider

Two important properties of a Higgs boson are its mass and width. They may distinguish the Standard Model (SM) Higgs boson from Higgs bosons of extended models. We show results from a direct mass and width reconstruction for a Higgs boson mass range from 120 to 340 GeV. The mass and width have been reconstructed from the H --> ZZstar --> mu+mu-mu+mu- reaction in an LHC simulation of the CMS detector. The determined mass accuracy has been compared with that obtained from studies for a linear collider (LC). The mass precision from the latter studies is derived by scaling previous LC simulation results according to the expected event rates. For the Higgs boson width we compare a direct determination with indirect methods and find good complementarity.Comment: 4 pages, 4 figure

The NMSSM Solution to the Fine-Tuning Problem, Precision Electroweak Constraints and the Largest LEP Higgs Event Excess

We present an extended study of how the Next to Minimal Supersymmetric Model easily avoids fine-tuning in electroweak symmetry breaking for a SM-like light Higgs with mass in the vicinity of 100\gev, as beautifully consistent with precision electroweak data, while escaping LEP constraints due to the dominance of $h\to aa$ decays with $m_a<2m_b$ so that a\to \tauptaum or jets. The residual $\sim 10$ branching ratio for h\to b\anti b explains perfectly the well-known LEP excess at \mh\sim 100\gev. Details of model parameter correlations and requirements are discussed as a function $\tan(\beta)$. Comparisons of fine-tuning in the NMSSM to that in the MSSM are presented. We also discuss fine-tuning associated with scenarios in which the $a$ is essentially pure singlet, has mass m_a>30\gev, and decays primarily to \gam\gam leading to an h\to aa\to 4\gam Higgs signal.Comment: 26 pages, 37 figures, published version with minor text and reference improvement

Dark Matter and Collider Phenomenology with two light Supersymmetric Higgs Bosons

Recently, it has been pointed out that two different excesses of events observed at LEP could be interpreted as the CP-even Higgs bosons of the MSSM with masses of approximately 98 and 114 GeV. If this is the case, the entire MSSM Higgs sector is required to be light. In this article, we explore such a scenario in detail. We constrain the Higgs and supersymmetric spectrum using $B$ physics constraints as well as the magnetic moment of the muon. We then point out the implications for neutralino dark matter -- next generation direct detection experiments will be sensitive to all MSSM models with such a Higgs sector. Finally, we find that all models outside of a very narrow corridor of the parameter space have a charged Higgs boson which will be observed at the LHC. In those exceptional models which do not contain an observable charged Higgs, a light top squark will always be seen at the LHC, and likely at the Tevatron.Comment: 12 pages, 18 figure

Study of Scalar Top Quarks in the Neutralino and Chargino Decay Channel

The scalar top discovery potential has been studied with a full-statistics background simulation at sqrt(s)=500 GeV and L = 500 fb-1 for the TESLA project. The beam polarization is very important to measure the scalar top mixing angle and to determine its mass. The latest estimation of the beam polarization parameters is applied. This study includes e+ polarization, which improves the sensitivity. For a 180 GeV scalar top at minimum production cross section, we obtain delta(m) = 0.8 GeV and delta(cosT) = 0.008 in the neutralino decay channel, and delta(m) = 0.5 GeV and delta(cosT) = 0.004 in the chargino decay channel.Comment: 4 pages, 6 figures, Proc. LCWS Chicago, November 200