### Abstract

A calculation of the ratio of leptonic decay constants f_{K} ^{+}/f_{π}^{+} makes possible a precise determination of the ratio of Cabibbo-Kobayashi-Maskawa (CKM) matrix elements |V _{us}|/|V_{ud}| 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 f_{K} ^{+}/f_{π}^{+} 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 f_{K}^{+}/f _{π}^{+}=1.1947(26)(37), where the errors are statistical and total systematic, respectively. This is our first physics result from our N_{f}=2+1+1 ensembles, and the first calculation of f_{K} ^{+}/f_{π}^{+} from lattice-QCD simulations at the physical point. Our result is the most precise lattice-QCD determination of f_{K}^{+}/f_{π}^{+}, 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 |V _{us}|/|V_{ud}|=0.2309(9)(4) where the errors are theoretical and experimental, respectively.

Original language | English (US) |
---|---|

Article number | 172003 |

Journal | Physical Review Letters |

Volume | 110 |

Issue number | 17 |

DOIs | |

State | Published - Apr 26 2013 |

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### ASJC Scopus subject areas

- Physics and Astronomy(all)

### Cite this

_{K}

^{+}/f

_{π}

^{+}from lattice QCD with physical light quarks.

*Physical Review Letters*,

*110*(17), [172003]. https://doi.org/10.1103/PhysRevLett.110.172003

**Leptonic-decay-constant ratio f _{K}^{+}/f _{π}^{+} from lattice QCD with physical light quarks.** / Bazavov, A.; Bernard, C.; Detar, C.; Foley, J.; Freeman, W.; Gottlieb, Steven; Heller, U. M.; Hetrick, J. E.; Kim, J.; Laiho, J.; Levkova, L.; Lightman, M.; Osborn, J.; Qiu, S.; Sugar, R. L.; Toussaint, William D; Van De Water, R. S.; Zhou, R.

Research output: Contribution to journal › Article

_{K}

^{+}/f

_{π}

^{+}from lattice QCD with physical light quarks',

*Physical Review Letters*, vol. 110, no. 17, 172003. https://doi.org/10.1103/PhysRevLett.110.172003

_{K}

^{+}/f

_{π}

^{+}from lattice QCD with physical light quarks. Physical Review Letters. 2013 Apr 26;110(17). 172003. https://doi.org/10.1103/PhysRevLett.110.172003

}

TY - JOUR

T1 - Leptonic-decay-constant ratio fK+/f π+ from lattice QCD with physical light quarks

AU - Bazavov, A.

AU - Bernard, C.

AU - Detar, C.

AU - Foley, J.

AU - Freeman, W.

AU - Gottlieb, Steven

AU - Heller, U. M.

AU - Hetrick, J. E.

AU - Kim, J.

AU - Laiho, J.

AU - Levkova, L.

AU - Lightman, M.

AU - Osborn, J.

AU - Qiu, S.

AU - Sugar, R. L.

AU - Toussaint, William D

AU - Van De Water, R. S.

AU - Zhou, R.

PY - 2013/4/26

Y1 - 2013/4/26

N2 - 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 |V us|/|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+/f π+=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 |V us|/|Vud|=0.2309(9)(4) where the errors are theoretical and experimental, respectively.

AB - 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 |V us|/|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+/f π+=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 |V us|/|Vud|=0.2309(9)(4) where the errors are theoretical and experimental, respectively.

UR - http://www.scopus.com/inward/record.url?scp=84876967881&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84876967881&partnerID=8YFLogxK

U2 - 10.1103/PhysRevLett.110.172003

DO - 10.1103/PhysRevLett.110.172003

M3 - Article

AN - SCOPUS:84876967881

VL - 110

JO - Physical Review Letters

JF - Physical Review Letters

SN - 0031-9007

IS - 17

M1 - 172003

ER -