Discovering a Light Scalar or Pseudoscalar at The Large Hadron Collider

Abstract

The allowed standard model Higgs mass range has been reduced to a region between 114 and 130 GeV or above 500 GeV, at the 99% confidence level, since the Large Hadron Collider (LHC) program started. Furthermore some of the experiments at Tevatron and LHC observe excesses that could arise from a spin-0 particle with a mass of about 125 GeV. It is therefore timely to compare the standard model Higgs predictions against those of a more general new spin-0 state, either scalar or pseudo-scalar. Using an effective Lagrangian approach we investigate the ability to discriminate between a scalar or pseudoscalar, stemming from several extensions of the standard model, at the LHC. We also discuss how to use experimental results to disentangle whether the new state is elementary or composite.