LHC Evidence Of A 126 GeV Higgs Boson From H ! With Three And Four Generations
Department of Physics and Center for Theoretical Sciences, National Taiwan University, Taipei, TaiwanSearches for Higgs boson at the LHC have excluded standard model (SM) Higgs boson mass inthe range between 127 GeV to 600 GeV. With a fourth generation, the excluded range is wider. Toclose the windows between 114 GeV to 127 GeV, the mode H → γγ plays an important role. Thereare evidences that the Higgs boson mass is about 126 GeV from LHC data. H → γγ can occurat one loop level in the SM. In the SM with three generations (SM3), the dominant contributionis from W boson with some cancellation from top quark in the loop. With SM4, the large massof the fourth generation quarks and charged lepton cancel the W boson contribution signiﬁcantly,the decay width is suppressed by a factorin the range of 0.25 ∼ 0.55 for the fourth generation massin the range of 500 to 1000 GeV. This reduction factor makes σ(pp → HX)Br(H → γγ) for SM4comparable to that for SM3 for Higgs boson mass in the window allowed mentioned earlier. UsingH → γγ alone, therefore, it is diﬃcult at present to distinguish whether the Higgs boson is fromSM3 or SM4. We also comments on some other detection channels.