Simultaneous Extraction of the Fermi constant and PMNS matrix elements in the presence of a fourth generation

Abstract

Several recent studies performed on constraints of a fourth generation of quarks and leptons suffer from the ad-hoc assumption that 3 x 3 unitarity holds for the first three generations in the neutrino sector. Only under this assumption one is able to determine the Fermi constant G_F from the muon lifetime measurement with the claimed precision of G_F = 1.16637 (1) x 10^-5 GeV^-2. We study how well G_F can be extracted within the framework of four generations from leptonic and radiative mu and tau decays, as well as from K_l3 decays and leptonic decays of charged pions, and we discuss the role of lepton universality tests in this context. We emphasize that constraints on a fourth generation from quark and lepton flavour observables and from electroweak precision observables can only be obtained in a consistent way if these three sectors are considered simultaneously. In the combined fit to leptonic and radiative mu and tau decays, K_l3 decays and leptonic decays of charged pions we find a p-value of 2.6% for the fourth generation matrix element |U_{e 4}|=0 of the neutrino mixing matrix.

19 pages, 3 figures with 16 subfigures, references and text added refering to earlier related work, figures and text in discussion section added, results and conclusions unchanged

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• Implications of gauge-mediated supersymmetry breaking with vector-like quarks and a ~125 GeV Higgs boson
• Test of Lepton Flavour Universality in K+ --> l+nu Decays
• Status of the fourth fermion generation before ICHEP2012: Higgs data and electroweak precision observables
• Closing in on a perturbative fourth generation
• Model-independent extraction of $|V_{tq}|$ matrix elements from top-quark measurements at hadron colliders
• Large mass splittings for fourth generation fermions allowed by LHC Higgs exclusion
• Electroweak Precision Observables within a Fourth Generation Model with General Flavour Structure
• Fourth Generation Majorana Neutrinos
• Status of the Fourth Generation - A Brief Summary of B3SM-III Workshop in Four Parts
• Neutrino Masses and a Fourth Generation of Fermions
• $\mu -e$ Conversion With Four Generations
• Neutrino masses from new generations
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• Pair Production of New Heavy Leptons with $U(1{)}^{\prime }$ Charge at Linear Colliders
• Bounds on fourth generation induced Lepton Flavour Violating double insertions in Supersymmetry
• Rare Kaon Decay Experiments at CERN
• Higgs Mass Constraints on a Fourth Family: Upper and Lower Limits on CKM Mixing
• Flavour physics with a 4th generation