SUSY Higgs at the LHC: Large stop mixing effects and associated production

TL;DR

The paper addresses how large stop mixing in the MSSM affects the lightest Higgs boson at the LHC, showing that reductions in the inclusive $pp \rightarrow h \rightarrow \gamma\gamma$ channel can be offset by enhanced associated production ($Wh$, $Zh$, $t\bar{t}h$) and by Higgs production via stop decays. It develops a detailed treatment of the $\tilde{t}_1\tilde{t}_1 h$ vertex, recalculates $pp \rightarrow \tilde{t}_1\tilde{t}_1 h$ production, and explores the role of the heavier stop via $\tilde{t}_2 \rightarrow \tilde{t}_1 h,A,H$, including decays to the pseudoscalar $A$ and the possibility of $A\rightarrow Zh$ cascades. The analysis spans several $\tan\beta$ values and $M_A$ regimes, highlighting that large mixing can either enhance or suppress various channels, but overall provides more robust Higgs discovery prospects than in no-mixing scenarios. The work also assesses constraints from $m_h$, $\Delta\rho$, and CCB, and emphasizes that stop-induced Higgs production channels can compensate for inclusive-rate declines, especially when $\tilde{t}_1$ is light and mixing is large. Collectively, the results suggest new, experimentally promising Higgs search pathways at the LHC driven by stop-sector dynamics, including sizable cross sections for $pp \rightarrow \tilde{t}_1\tilde{t}_1 h$ and cascade processes like $pp \rightarrow \tilde{t}_2\tilde{t}_2 \rightarrow \tilde{t}_2\tilde{t}_1 h$.

Abstract

We revisit the effect of the large stop mixing on the decay and production of the lightest SUSY Higgs at the LHC. We stress that whenever the inclusive 2-photon signature is substantially reduced, associated production, $Wh$ and $t\bar t h$, with the subsequent decay of the Higgs into photons is enhanced and becomes an even more important discovery channel. We also point out that these reductions in the inclusive channel do not occur for the smallest Higgs mass where the significance is known to be lowest. We show that in such scenarios the Higgs can be produced in the decay of the heaviest stop. For not too heavy masses of the pseudo-scalar Higgs where the inclusive channel is even further reduced, we show that large stop mixing also allows the production of the pseudo-scalar Higgs through stop decays. These large mixing scenarios therefore offer much better prospects than previously thought. As a by-product we have recalculated stop1-stop1-h production at the LHC and give a first evaluation of stop1-stop1-Z.

Figures (24)

• Figure 1: Variation of $R_{gg\gamma\gamma}$ with $M_A$, for $\tan \beta=2.5$ (full) and $\tan \beta=10$ (dotted)
• Figure 2: a) $R_{gg\gamma\gamma}$ vs $M_h$ as $M_A$ varies from 200GeV to 1000GeV for different values of $\tan \beta$. $\mu=-180$GeV. The lowest values of $R_{gg\gamma\gamma}$ and $R_{\gamma\gamma}$ correspond to $M_A=200$GeV. b) $R_{gg\gamma\gamma}$ vs $R_{\gamma\gamma}$.
• Figure 3: Variation of $R_{gg\gamma\gamma}$ vs $R_{W\gamma\gamma}$-$R_{t\bar{t} \gamma\gamma}$ with $200\le M_A \le 1000$GeV and $\tan \beta=2.5 (full),10 (dotted)$.
• Figure 4: $\tilde{t}_1 \tilde{t}_1 h$ at the LHC as a function of $m_{\tilde{t}_1}$ and for a range of SUSY Higgs masses. The $\tilde{t}_1 \tilde{t}_1 h$ vertex is set in the limit of large $M_A$ with no mixing and no D-term, see text of how to normalise it when the SUSY parameters are fixed. Also shown is $\tilde{t}_1 \tilde{t}_1 Z$. For the latter the vertex has been computed with $\cos^2 \theta_{\tilde{t}}=1/2$, i.e. maximal mixing. For other values of the mixing, rescale by using the vertex $(\cos^2 \theta_{\tilde{t}}/2 -2/3 s_W^2)$. We have taken the CTEQ4 structure function with a scale set at the invariant mass of the subprocess.
• Figure 5: As in Figure \ref{['t1t1h_mt1']} but as function of the Higgs mass. The $t \bar{t} h$ is also shown for comparison for the same set of structure functions and by only taking into account the gluon gluon processes. For the latter including the small quark initiated process, our results agree with Higgs_xsections_update. Also shown is $t \bar{t} Z$.