Higgs physics

After the discovery of the standard model-like Higgs boson in 2012, the question of how many Higgs bosons exist in nature has become one of the biggest questions in particle physics. The search for charged Higgs bosons has the potential to either find new Higgs bosons or constrain theoretical models by setting limits on H⁺production.

During 2013-2015, the HIP team has been playing a leading role in searching for charged Higgs bosons at the CMS experiment. The team has been responsible for the analysis of the most sensitive decay channel: H⁺ -> tau nu in a fully hadronic final state. Compared to other H⁺ decay channels, the fully hadronic final state allows the separation of the potential H⁺ signal from background events through the reconstruction of the transverse mass.
Furthermore, model-independent limits without assumption on H⁺ branching fractions can be obtained in this decay channel. This decay channel allows also the use of tau helicity correlations to suppress the largest backgrounds.

The analysis on the fully hadronic final state with 20 fb^-1 of data recorded at sqrt(s)=8 TeV was approved in 2014 (CMS Physics analysis summary HIG-14-020) and reported for the first time at the Charged14 conference. A paper targetting JHEP and consisting of the combination of four different H⁺ searches is in the final stages in the collaboration review process before being submitted to the journal. The obtained result is compatible with standard model predictions and consequently limits on the H⁺ production are placed. Our analysis dominates the sensitivity in the combination and gives a more sensitive limit than the respective ATLAS analysis up to m_H⁺ = 400 GeV. Furthermore, our analysis is able to rule out H⁺ below m_H⁺ = 155 GeV in minimal supersymmetric (MSSM) benchmark models. The MSSM scenario where the discovered boson is the heavy scalar is completely ruled out by our result.

The main tasks and impact by the team during 2013-2015 were:

Design and efficiency measurement of the dedicated tau+missing E_Ttrigger. The results were used also by two other unrelated analysis groups.
Development of novel selection methods based on angular correlations to improve analysis sensitivity.
Development of the embedding of a simulated tau decay which replaces a genuine muon for the data-driven measurement of the genuine tau background. This pioneering work in CMS enables obtaining model-independent limits on the H⁺ production. The method is usable also in other unrelated searches, such as W’ searches.
Participation in the LHC Higgs Cross Section Working Group, charged Higgs boson subgroup CMS contact from HIP in 2010-2013.
Leading role in statistical combination of the results of four different CMS H⁺ searches.
Close collaboration with the CMS tau group; including validation of tau algorithm development.
Development of a new data-driven measurement for the mis-identified tau background for run II.
Preparation of analysis code for run II.

During the years 2016-2018 the search for charged Higgs bosons will be one of the most interesting Higgs boson searches at CMS, since the new collected data allows the H⁺ to be found or excluded in a large part of so far uncovered parameter space. The H⁺ -> tau nu in a fully hadronic final state will remain the most sensitive H⁺ search channel in a large part of the parameter space.

Recent publications:

CMS-PAS-HIG-14-020 (2014): sqrt(s) = 8 TeV preliminary results with 20 fb^-1 of data
CMS-PAS-HIG-12-052 (2012): sqrt(s) = 7 TeV preliminary results with 2-5 fb^-1 of data
JHEP 1207 (2012) 143 : sqrt(s) = 7 TeV results in combination with leptonic final states with 2 fb^-1 of data
CMS-PAS-HIG-11-008 (2011): sqrt(s) = 7 TeV preliminary results with 1 fb^-1 of data