Are There Hints of Light Stops in Recent Higgs Search Results?

TL;DR

This study performs a global fit of Higgs search results from the LHC and Tevatron, allowing loop-induced widths to deviate from Standard Model values. The data prefer an enhanced $\Gamma_{h\to\gamma\gamma}$ and a suppressed $\Gamma_{h\to gg}$, which significantly improves the fit over the SM; no strong evidence is found for modifications of tree-level widths. The authors show that such a pattern can be produced by new charged-colored particles, with a notably attractive realization being a light, highly mixed stop in supersymmetry, parameterized by $R_t \equiv y_t/y_t^{\rm SM}$. They find that $m_{\tilde t_1} \lesssim 300$ GeV and $A_t \gtrsim 2$ TeV can accommodate the favored region, while metastability and current stop searches leave the scenario viable but tightly constrained. These results motivate future high-statistics Higgs measurements to confirm or refute the presence of new, TeV-scale colored states influencing Higgs loop processes.

Abstract

The recent discovery at the LHC by the CMS and ATLAS collaborations of the Higgs boson presents, at long last, direct probes of the mechanism for electroweak symmetry breaking. While it is clear from the observations that the new particle plays some role in this process, it is not yet apparent whether the couplings and widths of the observed particle match those predicted by the Standard Model. In this paper, we perform a global fit of the Higgs results from the LHC and Tevatron. While these results could be subject to as-yet-unknown systematics, we find that the data are significantly better fit by a Higgs with a suppressed width to gluon-gluon and an enhanced width to gamma gamma, relative to the predictions of the Standard Model. After considering a variety of new physics scenarios which could potenially modify these widths, we find that the most promising possibility is the addition of a new colored, charged particle, with a large coupling to the Higgs. Of particular interest is a light, and highly mixed, stop, which we show can provide the required alterations to the combination of gg and gamma gamma widths.

Figures (5)

• Figure 1: The observed rates in various Higgs search channels at the LHC and Tevatron, compared to those predicted from a 125 GeV Standard Model Higgs boson. The Standard Model Higgs boson provides a somewhat poor global fit ($\chi^2=19.67$, over 17-1 degrees-of-freedom). If the Higgs' decay widths to gluons and photons are modified to their best fit values (0.66 and 2.5 times the Standard Model values, respectively), the global fit improves significantly to $\chi^2=9.77$, over 17-3 degrees-of-freedom.
• Figure 2: The 68%, 95% and 99% confidence level contours of the global fit to the data summarized in Fig. \ref{['data']}, allowing the decay widths of the Higgs to photons and gluons to vary while keeping all others fixed. We have also fixed the mass of the Higgs to 125 GeV. The best fit point (shown as a cross) yields an overall $\chi^2$ of 9.77, over 17-3 degrees-of-freedom. In contrast, the Standard Model case, located at (1,1) in this figure, yields $\chi^2=19.67$, and at face value appears to be disfavored over the best-fit case at the 99% confidence level.
• Figure 3: The 68%, 95% and 99% confidence level contours of the global fit to the data (as shown in Fig. \ref{['fitwidth']}), compared to the range of decay widths of the Higgs that can result from the addition of new charged particles, or new charged and colored particles (top partners, defined as particles with Higgs coupling, charge, and color equal to that of the top quark).
• Figure 4: The quality of the global fit as a function of the parameter $R_t \equiv y_t/y^{\rm SM}_t$. The miniumum near $R_t = -0.85$ (corresponding to the point marked by a star on Fig. \ref{['contours']}) provides a significantly better fit to the data than the Standard Model case.
• Figure 5: $R_t$ as a function of the mass of the lightest stop, for several values of $A_t$. Here, we have assumed that $A_t \gg \mu \cot \beta$ and $m_{Q_3}=m_{U_3}$. The shaded horizontal band represents the range of $R_t$ that is favored by the global fit, as shown in Fig. \ref{['Rt']}. For values of $A_t \mathrel{\hbox{$>$$\sim$}} 2$ TeV and $m_{\tilde{t}_1} \mathrel{\hbox{$<$$\sim$}} 300$ GeV, the favored range of $R_t$ can be accommodated.