Leptonic-decay-constant ratio fK+/fπ+ from lattice QCD with physical light quarks

Bazavov, A. et al. (2013) Leptonic-decay-constant ratio fK+/fπ+ from lattice QCD with physical light quarks. Physical Review Letters, 110(17), p. 172003. (doi: 10.1103/PhysRevLett.110.172003) (PMID:23679710)

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Publisher's URL: http://dx.doi.org/10.1103/PhysRevLett.110.172003


A calculation of the ratio of leptonic decay constants fK+/fπ+ makes possible a precise determination of the ratio of Cabibbo-Kobayashi-Maskawa (CKM) matrix elements |Vus|/|Vud| in the standard model, and places a stringent constraint on the scale of new physics that would lead to deviations from unitarity in the first row of the CKM matrix. We compute fK+/fπ+ numerically in unquenched lattice QCD using gauge-field ensembles recently generated that include four flavors of dynamical quarks: up, down, strange, and charm. We analyze data at four lattice spacings a≈0.06, 0.09, 0.12, and 0.15 fm with simulated pion masses down to the physical value 135 MeV. We obtain fK+/fπ+=1.1947(26)(37), where the errors are statistical and total systematic, respectively. This is our first physics result from our Nf=2+1+1 ensembles, and the first calculation of fK+/fπ+ from lattice-QCD simulations at the physical point. Our result is the most precise lattice-QCD determination of fK+/fπ+, with an error comparable to the current world average. When combined with experimental measurements of the leptonic branching fractions, it leads to a precise determination of |Vus|/|Vud|=0.2309(9)(4) where the errors are theoretical and experimental, respectively.

Item Type:Articles
Glasgow Author(s) Enlighten ID:DeTar, Professor Carleton and Foley, Dr Justin
Authors: Bazavov, A., Bernard, C., DeTar, C., Foley, J., Freeman, W., Gottlieb, S., Heller, U.M., Hetrick, J.E., Kim, J., Laiho, J., Levkova, L., Lightman, M., Osborn, J., Qiu, S., Sugar, R.L., Toussaint, D., Van de Water, R.S., and Zhou, R.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Physical Review Letters
Publisher:American Physical Society
ISSN (Online):1079-7114

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
481951Investigations in Quantum Chromodynamics and Physics Beyond the Standard ModelChristine DaviesScience & Technologies Facilities Council (STFC)ST/G00059X/1P&A - PHYSICS & ASTRONOMY
573721Phenomenology from Lattice QCD and Collider PhysicsChristine DaviesScience & Technologies Facilities Council (STFC)ST/J000442/1P&A - PHYSICS & ASTRONOMY