Determining tanβ with Neutral and Charged Higgs Bosons at a Future e^+e^- Linear Collider

The ratio of neutral Higgs field vacuum expectation values, tan(beta), is one of the most important parameters to determine in either the Minimal Supersymmetric Standard Model (MSSM) or a general type-II Two-Higgs Doublet Model (2HDM). Assuming an energy and integrated luminosity of sqrts=500 GeV and L=2000 fb-1 at a future linear collider (LC), we show that a very accurate determination of tan(beta) will be possible for low and high tan(beta) values by measuring the production rates of Higgs bosons and reconstructing Higgs boson decays. In particular, based on a TESLA simulation, and assuming no other light Higgs bosons and 100<=mA<=200 GeV, we find that the rate for the process e+e- --> bbA --> bbbb provides a good determination of tan(beta) at high tan(beta). In the MSSM Higgs sector, in the sample case of mA = 200 GeV, we find that the rates for e+e- --> bbA+bbH --> bbbb and for e+e- --> HA --> bbbb provide a good determination of tan(beta) at high and low tan(beta), respectively. We also show that the direct measurement of the average total widths of the H and A in e+e- --> HA --> bbbb events provides an excellent determination of tan(beta) at large values. In addition, the charged Higgs boson process e+e- --> H+H- --> tbtb has been studied. The sensitivity to tan(beta) at the LHC obtained directly from heavy Higgs boson production is briefly compared to the LC results.