Reweighing the Evidence for a Light Higgs Boson in Dileptonic $W$ Boson Decays

We reconsider observables for discovering and measuring the mass of a Higgs boson via its dileptonic decays $h\to W{W}^{(*)}\to \ell \nu \ell \nu$. We define an observable generalizing the transverse mass that takes into account the fact that one of the intermediate $W$ bosons is likely to be on shell. We compare this new variable with existing ones and argue that it gives a significant improvement for discovery in the region $m_h<2m_W$.

Figure 1

Simulation of $h\to WW$ signal (for $m_h\in \{130,160,200\}\mathrm{GeV}$) for the variables $m_T^{\mathrm{true}}$ (top), $m_T^{\star }$ (middle), and $m_T^{\mathrm{bound}}$ (bottom). The shading gives the shape of the dominant $WW$ background. It should be noted that a logarithmic $y$-axis scale (and displaced $x$ axis) has been used when plotting $m_T^{\mathrm{bound}}$.

Figure 2

Higgs boson discovery potential as a function of $m_h$, using only $m_T^{\mathrm{true}}$ (dotted lines, shaded area) or $m_T^{\star }$ (solid lines, open area). The center of each band indicates the difference in log-likelihood between models with and without a Higgs boson contribution. Lower values correspond to better discovery potential. The half-width of the each band gives the root-mean-squared over 50 trial samples. The integrated luminosity simulated is $10{\mathrm{fb}}^{-1}$.