# Les Houches 2017 work on models with Light Scalars¶

See the contribution “Sensitivity of current (and future?) LHC measurements to a new light scalar particle” in the 2017 Les Houches proceedings [97] for a description of the model and the motivation. Some updated results are also discussed in [105]. The key features are the addition of a light scalar particle $$\phi$$ which may be odd or even under CP. The key parameters are the 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 (measurements from 7, 8 and 13 TeV runs in Rivet 2.6.1)

Heatmaps for CP-even Scalar Model

Heatmap and contour for all available data (measurements from 7, 8 and 13 TeV runs in Rivet 2.6.1)

## CP odd, $$M_\phi = 10$$ GeV, $$\Lambda = 3.5$$ TeV¶

Plots 1

The most powerful exclusion in the 8 TeV data comes from the $$\gamma + E_T^{\rm miss}$$ channel, specifically the $$E_T^\gamma$$ differential cross section for events with no jets, in this paper.

There is also some exclusion from the $$\tau$$ distribution in the $$H \rightarrow \gamma\gamma$$ paper - see below for more on that.

Also once the 7 TeV data are included, the inclusive and diphotons cover this point on their own.

## CP odd, $$M_\phi = 20$$ GeV, $$\Lambda = 3.5$$ TeV¶

Plots 2

Another low mass, moderate coupling point. Chosen because for this one, diphoton measurements give the most powerful exclusion for the 8 TeV data set (although $$\gamma + E_T^{\rm miss}$$ still contributes, and once 7 TeV are included, the photon measurement would rule this point out too). The inclusive diphotons would contribute at low $$M_{\gamma\gamma}$$, because the 20 GeV mass of the $$\phi$$ now sneaks into the measurement at the bottom of the range, but the most sensitive plot in the diphoton category (and thus the one chosen by Contur) is again from the Higgs paper, this time $$p_T^{\gamma\gamma}$$. This may be surprising because the Higgs measurement has a mass window cut at $$105 < M^{\gamma\gamma} < 160$$ GeV, much higher than $$M_\phi$$. The contribution to the Higgs fiducial phase space seems to be coming from $$q\bar{q} \rightarrow \phi \gamma$$ events, where the additional photon pairs with one of the $$\phi$$ decay products. This interesting but should probably not be taken face value because it is not clear how such a contribution would impact on the continuum in the fits used to extract the $$H \rightarrow \gamma\gamma$$ cross section.

## CP odd, $$M_\phi = 80$$ GeV, $$\Lambda = 7.5$$ TeV¶

Plots 3

This point is chosen to look at the higher end of the $$M_\phi$$ range, where the sensitivity is greater, and so we look at a high $$\Lambda$$ value. Again the sensitivity is driven by this paper, but now it is the $$\gamma\gamma + E_T^{\rm miss}$$ cross section that does the work.

And again once the 7 TeV data are included, the inclusive and diphotons cover this point on their own.

Explanation of Contur plot format

Note that after this work was completed, we became aware of a closely related and comparable study by A. Mariotti et al [218] which reaches some similar conclusions.

J. M. Butterworth, S. Fichet, L. Finco, S. Gascon-Shotkin, D. Grellscheid, G. Moreau, P. Richardson, D. Yallup, S. Zhang