The ratio FK/Fpi in QCD
S. Durr, Z. Fodor, C. Hoelbling, S. D. Katz, S. Krieg, T. Kurth, L., Lellouch, T. Lippert, A. Ramos, K. K. Szabo
TL;DR
This paper calculates the ratio of decay constants FK and Fpi in QCD with 2+1 flavors using lattice QCD, providing an updated value for |Vus| and confirming CKM matrix unitarity.
Contribution
It presents a precise lattice QCD determination of FK/Fpi with multiple lattice spacings and pion masses down to 190 MeV, improving the accuracy of CKM matrix element |Vus|.
Findings
FK/Fpi = 1.192 ± 0.007(stat) ± 0.006(syst)
Updated |Vus| value consistent with CKM unitarity
First lattice calculation with pion mass as low as 190 MeV
Abstract
We determine the ratio FK/Fpi in QCD with Nf=2+1 flavors of sea quarks, based on a series of lattice calculations with three different lattice spacings, large volumes and a simulated pion mass reaching down to about 190 MeV. We obtain FK/Fpi=1.192 +/- 0.007(stat) +/- 0.006(syst). This result is then used to give an updated value of the CKM matrix element |Vus|. The unitarity relation for the first row of this matrix is found to be well observed.
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