Discovering a Light Scalar or Pseudoscalar at The Large Hadron Collider

TL;DR

This paper explores how to distinguish a potential new spin-0 particle, either scalar or pseudoscalar, at the LHC, using an effective Lagrangian approach to compare predictions and analyze experimental data.

Contribution

It introduces a method to differentiate scalar from pseudoscalar states and assess their elementary or composite nature using LHC data and effective field theory.

Findings

Discrimination between scalar and pseudoscalar states is feasible with current LHC data.

Effective Lagrangian approach helps interpret experimental excesses around 125 GeV.

Strategies to identify the nature of the new state as elementary or composite are proposed.

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.