Supersymmetric particle searches at LEP

Searches for supersymmetric particles performed at LEP 1 and LEP 2 are reviewed. Using the MSSM with R-parity conservation as a reference model, the various analyses are briefly described, and the results are presented in terms of mass and coupling limits. Further implications of these results are discussed, including lower limits on the mass of a neutralino LSP, assuming the MSSM with GUT relations. Less conventional scenarii, among which those involving R-parity violation, are also investigated.Comment: 23 pages, Latex, 15 figures included, to appear in ``Perspectives on Supersymmetry'', World Scientific Publishing Company, Gordon L. Kane edito

Searches beyond the standard model at high-energy colliders

Recent searches for physics beyond the standard model at high-energy colliders are reviewed, with emphasis on supersymmetry, additional space dimensions, extra gauge bosons, leptoquarks, and model-independent searches. The results reported are based on data samples of up to 0.5 and 2.5 fb-1 collected at HERA and at the Tevatron, respectively.Comment: Plenary talk at ICHEP08, Philadelphia, USA, July 2008. 10 pages, LaTeX, 16 ps and eps figures. ICHEP08 header added in v

L'héritage des collisionneurs LEP et TeVatron

Les quinze dernières années du précédent millénaire ont donné lieu, grâce à l'avènement de trois projets majeurs en Physique des Hautes énergies, à une moisson de résultats permettant une meilleure compréhension des mécanismes régissant l'évolution de l'Univers. Le LEP et le SLC, d'une part, et le TeVatron, d'autre part, ont recueilli pendant plus d'une décennie les fruits des collisions électron-positon et proton-antiproton avec une énergie et une précision jamais atteintes auparavant. Nous nous concentrerons ici sur la finesse et la portée fondamentale de ces mesures de précision, et nous concluerons par les signes avant-coureurs de probables futures découvertes

Search for charginos nearly mass-degenerate with the lightest neutralino e+e−e^+e^- collisions up to s\sqrt{s} = 209GeV

Search for chargino nearly mass-degenerate with the lightest neutralino is performed with the data collected at a centre-of-mass energy from 189 to 209~GeV by the ALEPH detector at LEP. The analysis uses the detection of an isolated and energetic initial state radiation photon, produced in association with the chargino pair, whose decay products have small visible energy. No evidence of signal is found and lower limits on the chargino mass of 91 and 89~GeV/$c^2$ at 95\% confidence level are derived, for large scalar masses, in gaugino and in higgsino region respectively

Higgs limits in the MSSM: beyond the benchmark

Up to now, the ALEPH limits on the MSSM neutral Higgs boson masses have been reported for specific sets of model parameters corresponding to the so-called minimal and maximal mixing configurations. An investigation of the robustness of these results is performed by means of a scan of the parameter space in which more than 30 million sets of m_0, m_1/2, mu, A_t, m_A and tan(beta) values are probed. In the low tan(beta) regime, the m_h limit obtained in the cases of minimal and maximal mixing is found to remain valid for 99.991341f the parameter sets explored. In the case of large tan(beta), and considering the limit on m_h + m_A, this fraction reduces to 99.

Muonium-Antimuonium Oscillations in an extended Minimal Supersymmetric Standard Model with right-handed neutrinos

The electron and muon number violating muonium-antimuonium oscillation process in an extended Minimal Supersymmetric Standard Model is investigated. The Minimal Supersymmetric Standard Model is modified by the inclusion of three right-handed neutrino superfields. While the model allows the neutrino mass terms to mix among the different generations, the sneutrino and slepton mass terms have only intra-generation lepton number violation but not inter-generation lepton number mixing. So doing, the muonium-antimuonium conversion can then be used to constrain those model parameters which avoid further constraint from the $\mu\to e\gamma$ decay bounds. For a wide range of parameter values, the contributions to the muonium-antimuonium oscillation time scale are at least two orders of magnitude below the sensivity of current experiments. However, if the ratio of the two Higgs field VEVs, $\tan\beta$, is very small, there is a limited possibility that the contributions are large enough for the present experimental limit to provide an inequality relating $\tan\beta$ with the light neutrino mass scale $m_\nu$ which is generated by see-saw mechanism. The resultant lower bound on $\tan\beta$ as a function of $m_\nu$ is more stringent than the analogous bounds arising from the muon and electron anomalous magnetic moments as computed using this model.Comment: 29 pages, 7 figures, 3 tables, Late

Fitting the Phenomenological MSSM

We perform a global Bayesian fit of the phenomenological minimal supersymmetric standard model (pMSSM) to current indirect collider and dark matter data. The pMSSM contains the most relevant 25 weak-scale MSSM parameters, which are simultaneously fit using `nested sampling' Monte Carlo techniques in more than 15 years of CPU time. We calculate the Bayesian evidence for the pMSSM and constrain its parameters and observables in the context of two widely different, but reasonable, priors to determine which inferences are robust. We make inferences about sparticle masses, the sign of the $\mu$ parameter, the amount of fine tuning, dark matter properties and the prospects for direct dark matter detection without assuming a restrictive high-scale supersymmetry breaking model. We find the inferred lightest CP-even Higgs boson mass as an example of an approximately prior independent observable. This analysis constitutes the first statistically convergent pMSSM global fit to all current data.Comment: Added references, paragraph on fine-tunin