Search for a lighter neutral custodial fiveplet scalar in the Georgi-Machacek model

Many researches from both theoretical and experimental perspectives have been performed to search for a new Higgs Boson that is lighter than the 125 GeV Higgs boson, which was discovered at the LHC in 2012. In this study, we explore the possibility of constraining a lighter neutral custodial fiveplet scalar H-5(0) in the Georgi-Machacek (GM) model using the latest results of the search for a lighter Higgs boson decaying into two photons from LHC data. The custodial-singlet mass eigenstate h or H is considered to be the LHC observed 125 GeV Higgs boson. A new set of constrained parameters that is favoured by low-mass H-5(0) is proposed to generate events efficiently. The production of H-5(0) from a scan based on the constrained parameters is compared to the latest results of the search for a lighter Higgs boson decaying into two photons by the CMS Collaboration after applying theoretical constraints from the GM model and constraints from all existing relevant experimental measurements, including the recent results of the Higgs boson searches by the LHC. Numerical analyses of the surviving GM parameter space are performed. The tendencies and correlations of the GM input parameters from phenomenological studies are summarized. In addition, the discovery potential of the other interesting decay channels of this low-mass neutral custodial fiveplet scalar are discussed.