Establishing a No-Lose Theorem for NMSSM Higgs Boson Discovery at the LHC

We scan the parameter space of the NMSSM for the observability of at least one Higgs boson at the LHC with 300 fb integrated luminosity, taking the present LEP2 constraints into account. We restrict the scan to those regions of parameter space for which Higgs boson decays to other Higgs bosons and/or supersymmetric particles are kinematically forbidden. We find that if WW -fusion detection modes for a light Higgs boson are not taken into account, then there are still significant regions in the scanned portion of the NMSSM parameter space where no Higgs boson can be observed at the 5σ level, despite the recent improvements in ATLAS and CMS procedures and techniques and even if we combine all non-fusion discovery channels. However, if the WW -fusion detection modes are included using the current theoretical study estimates, then we find that for all scanned points at least one of the NMSSM Higgs bosons will be detected. If the estimated 300 fb significances for ATLAS and CMS are combined, one can also achieve 5σ signals after combining just the non-WW -fusion channels signals. We present the parameters of several particularly difficult points, and discuss the complementary roles played by different modes. We conclude that the LHC will discover at least one NMSSM Higgs boson unless there are large branching ratios for decays to SUSY particles and/or to other Higgs bosons. LPT Orsay 01-100 UCD-01-13 RAL-TR-2001-035 IPPP/01/45 hep-ph/0111179 October, 2001 Unité Mixte de Recherche CNRS UMR 8627