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Impact of a Higgs boson at a mass of 126 GeV on the standard model with three and four fermion generations.

Eberhardt, Otto and Herbert, Geoffrey and Lacker, Heiko and Lenz, Alexander and Menzel, Andreas and Nierste, Ulrich and Wiebusch, Martin (2012) 'Impact of a Higgs boson at a mass of 126 GeV on the standard model with three and four fermion generations.', Physical review letters., 109 (24). p. 241802.


We perform a comprehensive statistical analysis of the standard model (SM) with three and four generations using the latest Higgs search results from LHC and Tevatron, the electroweak precision observables measured at LEP and SLD, and the latest determinations of MW, mt, and αs. For the three-generation case we analyze the tensions in the electroweak fit by removing individual observables from the fit and comparing their predicted values with the measured ones. In particular, we discuss the impact of the Higgs search results on the deviations of the electroweak precision observables from their best-fit values. Our indirect prediction of the top mass is mt=175.7+3.0−2.2  GeV at 68.3% C.L., which is in good agreement with the direct measurement. We also plot the preferred area in the MW-mt plane. The best-fit Higgs boson mass is 126.0 GeV. For the case of the SM with a perturbative sequential fourth fermion generation (SM4) we discuss the deviations of the Higgs signal strengths from their best-fit values. The H→γγ signal strength now disagrees with its best-fit SM4 value at more than 4σ. We perform a likelihood-ratio test to compare the SM and SM4 and show that the SM4 is excluded at 5.3σ. Without the Tevatron data on H→bb¯ the significance drops to 4.8σ.

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Publisher statement:Reprinted with permission from the American Physical Society: Otto Eberhardt, Geoffrey Herbert, Heiko Lacker, Alexander Lenz, Andreas Menzel, Ulrich Nierste, and Martin Wiebusch (2012) Impact of a Higgs boson at a mass of 126 GeV on the standard model with three and four fermion generations. Physical Review Letters, 109, 24, 241802 © 2012 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.
Date accepted:No date available
Date deposited:18 July 2014
Date of first online publication:December 2012
Date first made open access:No date available

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