Status of the fourth fermion generation before ICHEP2012: Higgs data and electroweak precision observables

Eberhardt, Otto; Menzel, Andreas; Nierste, Ulrich; Wiebusch, Martin; Lenz, Alexander

doi:10.1103/PhysRevD.86.074014

Article
Report number	arXiv:1207.0438 ; TTP12-023 ; CERN-PH-TH-2012-182 ; TTP12-023 ; CERN-PH-TH-2012-182
Title	Status of the fourth fermion generation before ICHEP2012: Higgs data and electroweak precision observables
Author(s)	Eberhardt, Otto (KIT, Karlsruhe, TTP) ; Lenz, Alexander (CERN) ; Menzel, Andreas (Humboldt U., Berlin) ; Nierste, Ulrich (KIT, Karlsruhe, TTP) ; Wiebusch, Martin (KIT, Karlsruhe, TTP)
Publication	2012
Imprint	03 Jul 2012
Number of pages	5
Note	new introductory paragraph, few clarifying sentences and references added, journal version
In:	Phys. Rev. D 86 (2012) 074014
DOI	10.1103/PhysRevD.86.074014
Subject category	Particle Physics - Phenomenology
Abstract	We perform a global fit of the parameters of the Standard Model with a sequential fourth generation (SM4) to LHC and Tevatron Higgs data and electroweak precision data. We find that the minimal chi-square value of the SM4 is larger than that of the Standard Model with three generations (SM3) by 8 units. We then perform several likelihood ratio tests which compare the the performance of the SM4 and SM3 at describing the measured data. Since the SM3 and SM4 are not nested (i.e. the SM3 can not be considered as a special case of the SM4 with some parameters fixed) the usual analytical formulae for p-values in likelihood ratio tests do not hold. We thus apply a new method to compute these p-values. For a Higgs mass of 126.5 GeV we find that the SM4 is excluded at 3.1 sigma.
Copyright/License	Preprint: © 2012-2024 CERN (License: CC-BY-3.0)

$Minimum $\chi^2$ values for a fixed neutrino mass as a function of $m_{\nu_4}$. The blue (red) lines show the results from the combined analysis of EWPOs and Higgs signal strengths with (without) the $H\to\tau\tau$ channel. The solid and dashed lines correspond to the SM4 and SM3, respectively.$ $The minimum $\chi^2$ value of the SM3 as a function of the Higgs mass $m_H$. The solid line shows the results of the combined analysis of signal strengths and EWPOs. For the dashed line only the signal strengths were included in the fit.$ $The minimum $\chi^2$ value of the SM4 as a function of the Higgs mass $m_H$. The solid line shows the results of the combined analysis of signal strengths and EWPOs. For the dashed line only the signal strengths were included in the fit.$ Show more plots

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