Precision analysis of the lightest MSSM Higgs boson at future colliders

We investigate the sensitivity of observables measurable in e ⁺e^-, γγ and μ⁺μ^- collisions for distinguishing the properties of the light neutral C℘-even. Higgs boson in the minimal supersymmetric extension of the Standard Model (MSSM) from those of a Standard Model (SM) Higgs boson with the same mass. We explore first the available parameter space in the constrained MSSM (CMSSM), with universal soft supersymmetry-breaking parameters, incorporating the most recent direct limits on sparticle and Higgs masses, the indirect constraints from b → sγ and gu - 2, and the cosmological relic density Ω_χh². We calculate the products of the expected CMSSM Higgs production cross sections and decay branching ratios σ × B normalized by the corresponding values expected for those of a SM Higgs boson of the same mass. The results are compared with the precisions expected at each collider, and allow for a direct comparison of the different channels. The measurements in the Higgs sector are found to provide important consistency tests of the CMSSM. We then generalize our analysis to the case of a non-universal Higgs model (NUHM), where the values of M_A and μ are independent parameters. We explore in particular the sensitivity to M _A, finding that measurements at e⁺e^-, γγ and μ⁺μ^- colliders could yield indirect constraints on its value, up to M_A ∼ 1200 GeV. We discuss the potential of these measurements for distinguishing between the CMSSM and the NUHM, probing in this way the assumption of universality.