Abstract

The properties of the observed Higgs boson with mass around 125 GeV can be affected in a variety of ways by new physics beyond the Standard Model (SM). The wealth of experimental results, targeting the different combinations for the production and decay of a Higgs boson, makes it a non-trivial task to assess the compatibility of a non-SM-like Higgs boson with all available results. In this paper we present Lilith, a new public tool for constraining new physics from signal strength measurements performed at the LHC and the Tevatron. Lilith is a Python library that can also be used in C and C++/ROOT programs. The Higgs likelihood is based on experimental results stored in an easily extensible XML database, and is evaluated from the user input, given in XML format in terms of reduced couplings or signal strengths. The results of Lilith can be used to constrain a wide class of new physics scenarios.

Highlights

  • Lilith is a library written in Python that can be used in any Python script as well as in C and C++/ROOT codes, and for which we provide a command-line interface

  • The user input can be given in terms of reduced couplings or signal strengths for one or multiple Higgs states, and it is specified in an XML format

  • The signal strength framework used by the ATLAS and CMS Collaborations is based on the general form of Eq (2), on the assumption that new physics results only in the scaling of Standard Model (SM) Higgs processes

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Summary

Signal strength measurements

Thanks to the excellent operation of the LHC and to the wealth of accessible final states for a 125 GeV SM-like Higgs boson, the properties of the observed Higgs boson have been measured with unforeseeable precision by the ATLAS and CMS Collaborations already during Run I of the LHC at 7–8 TeV center-of-mass energy [4,5]. The signal strength framework used by the ATLAS and CMS Collaborations is based on the general form of Eq (2), on the assumption that new physics results only in the scaling of SM Higgs processes This makes it possible to combine the information from various Higgs searches and assess the compatibility of given scalings of SM production and/or decay processes from a global fit to the Higgs data. This framework is very powerful as it can be used to constrain a wide variety of new physics models Combining the results from several Higgs searches is non-trivial and deserves scrutiny

Event categories versus unfolded production and decay modes
Statistical procedure
Parametrization of new physics
Scaling factors and reduced couplings
CP-violating admixtures
Getting started
The Lilith API
Command-line interface
Experimental input
XML format
User model input
XML format for signal strengths
XML format for reduced couplings
Output
Validation
Reconstruction of the experimental likelihoods
Comparison to Higgs coupling fits from ATLAS and CMS
Examples of applications
Reduced coupling determination
Higgs constraints on superpartners of the tau lepton
Prospects for Run II of the LHC
Conclusions
Full Text
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