# Light Scalars with EFT couplings¶

Andy Buckley, Jon Butterworth, Louie Corpe, Sylvain Fichet, Linda Finco, Suzanne Gascon-Shotkin, David Grellscheid, Gregory Moreau, Peter Richardson, Graeme Watt, David Yallup, Song Zhang

See:
• Sensitivity of current (and future?) LHC measurements to a new light scalar particle in the 2017 Les Houches proceedings [109] for a description of the model and the motivation.

• Some discussion and updated results in [120]

• More updates, where the model is used as the first demonstrator for the use of both correlation information and theory information, in the Les Houches 2019 proceedings [110], which is where the heatmaps below come from.

The key features of the model are the addition of a light scalar particle $$\phi$$ which may be odd or even under CP. The parameters are then the mass $$M_\phi$$ and the couplings to SM particles, which are taken to be effective couplings governed by some set of scales $$\Lambda_i$$ for each class of SM particle $$i$$. For the CP-odd case, all scales are set to very high values except for those to $$W, B$$, which are set equal to each other and scanned over a range. For the CP-even case, the scale associated with the coupling to the Higgs is also set equal to this value and scanned over.

The sensitivities derived from multiple measured distributions are combined into heatmaps which delineate exclusion regions and contours in the parameter space of $$\Lambda$$and $$M_{\phi}$$.

CP-odd Light Scalar Model

Heatmap and contour for all available data as of Rivet 2.7.x, without using correlation info or theory.

CP-even Light Scalar Model

Heatmap and contour for all available data as of Rivet 3.1.x, Contur 1.0.x, without using correlation info or theory.

And using information about correlations between the systematic uncertainties:

And using SM theory calculations instead of data as the background

For a discussion of the differences, see Contur update in [110]

Note that after the first study was was completed, we became aware of a closely related and comparable study by A. Mariotti et al [174] which reaches some similar conclusions.

The model files are available in the NSCPO, NSCPE directories here