HiggsSignals: Confronting arbitrary Higgs sectors with measurements at the Tevatron and the LHC

TL;DR

Higgs-Signals provides a public, Fortran-based framework to test arbitrary Higgs sectors against Tevatron and LHC data by computing a chi^2 from Higgs signal strengths and masses. It implements two complementary tests—the peak-centered and mass-centered chi^2—and allows their simultaneous use to maximize information for models with multiple Higgs bosons. The approach integrates HiggsBounds inputs, models production/decay rates, and treats uncertainties and correlations within a Gaussian framework, with validation against ATLAS/CMS results and demonstrations in SM-like, MSSM, and global coupling contexts. The authors discuss practical limitations, notably incomplete channel efficiencies and correlated systematics, and advocate using Higgs-Signals alongside Higgs-Bounds for robust Higgs-sector constraints and global fits.

Abstract

HiggsSignals is a Fortran90 computer code that allows to test the compatibility of Higgs sector predictions against Higgs rates and masses measured at the LHC or the Tevatron. Arbitrary models with any number of Higgs bosons can be investigated using a model-independent input scheme based on HiggsBounds. The test is based on the calculation of a chi-squared measure from the predictions and the measured Higgs rates and masses, with the ability of fully taking into account systematics and correlations for the signal rate predictions, luminosity and Higgs mass predictions. It features two complementary methods for the test. First, the peak-centered method, in which each observable is defined by a Higgs signal rate measured at a specific hypothetical Higgs mass, corresponding to a tentative Higgs signal. Second, the mass-centered method, where the test is evaluated by comparing the signal rate measurement to the theory prediction at the Higgs mass predicted by the model. The program allows for the simultaneous use of both methods, which is useful in testing models with multiple Higgs bosons. The code automatically combines the signal rates of multiple Higgs bosons if their signals cannot be resolved by the experimental analysis. We compare results obtained with HiggsSignals to official ATLAS and CMS results for various examples of Higgs property determinations and find very good agreement. A few examples of HiggsSignals applications are provided, going beyond the scenarios investigated by the LHC collaborations. For models with more than one Higgs boson we recommend to use HiggsSignals and HiggsBounds in parallel to exploit the full constraining power of Higgs search exclusion limits and the measurements of the signal seen at around 125.5 GeV.

Figures (16)

• Figure 1: Measured signal strength modifiers by ATLAS in the search for $H\to ZZ^{(*)}\to 4\ell$ATLAS-CONF-2013-013 (a), and the best fit rates (in all currently investigated Higgs decay channels) for a Higgs signal at $m_H=125.7\,\, \mathrm{GeV}$ according to CMS CMS-PAS-HIG-13-005 (b).
• Figure 2: Overview of the Higgs signal rate and mass measurements (status shortly after the Moriond conference 2013) from ATLAS ATLAS-CONF-2012-091ATLAS-CONF-2012-160ATLAS-CONF-2012-161ATLAS-CONF-2012-170ATLAS-CONF-2013-012ATLAS-CONF-2013-013ATLAS-CONF-2013-030ATLAS-CONF-2013-034Aad:2013wqa, CMS CMS-PAS-HIG-11-024*CMS-PAS-HIG-12-042CMS-PAS-HIG-12-015CMS-PAS-HIG-12-039CMS-PAS-HIG-12-044CMS-PAS-HIG-12-045CMS-PAS-HIG-13-001CMS-PAS-HIG-13-002CMS-PAS-HIG-13-003CMS-PAS-HIG-13-004CMS-PAS-HIG-13-005Chatrchyan:2013yea and the Tevatron experiments CDF Aaltonen:2013ipa and DØ Abazov:2013zea, as they are implemented in Higgs-Signals-1.0.0 as peak observables. The left panel shows the Higgs mass value for which the signal strength was measured. A value with error bars indicates that the mass value is treated as a Higgs mass observable in the peak-centered $\chi^2$ method, whereas a gray asterisk only serves as an indication of the Higgs mass value, which was assumed in the rate measurement. This value does not enter directly the total $\chi^2$. For some LHC analyses, measurements for both the $7\,\, \mathrm{TeV}$ and $8\,\, \mathrm{TeV}$ data exist, shown in blue and red, respectively. If the measurement is based on the combined $7/8\,\, \mathrm{TeV}$ dataset, we treat it as an $8\,\, \mathrm{TeV}$ measurement only. For the $H\to\gamma\gamma$ analyses from ATLAS and CMS, the special tagged categories were implemented as separate peak observables, including their efficiencies, but collected together in assignment groups. In total there are 4 Higgs mass observables and 63 Higgs signal rate observables. This data is used for the performance scans in Fig. \ref{['Fig:SM']} and the example applications in Sect. \ref{['sect:Combinedfits']}.
• Figure 3: Total $\chi^2$ distribution obtained by the peak-centered $\chi^2$ method for a SM Higgs boson with mass $m_H$ obtained from the 63 peak observables (status: April 2013) shown in Fig. \ref{['Fig:peakobservables']}. In (a, b), the total $\chi^2$ is evaluated without taking into account the correlations among the systematic uncertainties, whereas they are fully included in (c, d). In (a, c) no theoretical mass uncertainty $\Delta m$ is assumed (like in the SM) whereas in (b, d) we set $\Delta m=2\,\, \mathrm{GeV}$. For each setting, we show the total $\chi^2$ obtained for all three parametrizations of the theoretical Higgs mass uncertainty: box (solid red), Gaussian (dashed green) and box+Gaussian (dotted blue) pdf. For each case, we also give the total number of peak observables, which have been assigned with the Higgs boson, depicted by the corresponding faint lines.
• Figure 4: Reconstruction of the combined best-fit signal strength from the results of the individual dataset / channels with the mass-centered $\chi^2$ method (a, b). For comparison, we give the official ATLAS results in (c, d).
• Figure 5: Results from a simultaneous fit to the Higgs mass and signal strength using the experimental data from the ATLAS searches $H\to\gamma\gamma$ATLAS-CONF-2012-168, $H\to WW^{(*)}\to \ell\nu\ell\nu$ATLAS-CONF-2013-030 and $H\to ZZ^{(*)}\to 4\ell$ATLAS-CONF-2013-013. The corresponding results from ATLAS are overlaid as faintly colored contours.