# 36th Annual International Symposium on Lattice Field Theory

Jul 22 – 28, 2018
Kellogg Hotel and Conference Center
EST timezone

## The $K_{\ell 3}$ form factor from four-flavor lattice QCD and $|V_{us}|$

Jul 25, 2018, 2:00 PM
20m
103 (Kellogg Hotel and Conference Center)

### 103

#### Kellogg Hotel and Conference Center

219 S Harrison Rd, East Lansing, MI 48824
Parallel Weak Decays and Matrix Elements

### Speaker

Prof. Aida El-Khadra (University of Illinois at Urbana-Champaign)

### Description

Using HISQ $N_f=2+1+1$ MILC ensembles at five different lattice spacings, including four ensembles with physical quark masses, we perform the most precise computation to date of the $K\to\pi\ell\nu$ vector form factor at zero momentum transfer. This is the first calculation that includes the dominant finite-volume effects, as calculated in chiral perturbation theory at next-to-leading order. Our result for the form factor provides a direct determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{us}|$, when combined with the corresponding experimental average. For the first time, the resulting theory error on $|V_{us}|$ is commensurate with the experimental uncertainty. We find that this determination of $|V_{us}|$ is in tension at the $2-2.6\sigma$ level both with determinations from leptonic decays and with the unitarity of the CKM matrix.

### Primary authors

Prof. Aida El-Khadra (University of Illinois at Urbana-Champaign) Prof. Claude Bernard (Washington University) Dr Elvira Gamiz (University of Granada)

### Co-authors

Dr Alexei Bazavov (Michigan State University) Dr Andreas Kronfeld (Fermilab) Carleton DeTar (University of Utah) Prof. Doug Toussaint (University of Arizona) Dr Elizabeth Freeland (School of the Art Institute of Chicago) Prof. Ethan Neil (University of Colorado, Boulder) Dr James Simone (Fermilab) Dr Javad Komijani (University of Glasgow) John Laiho (Syracuse University) Paul Mackenzie (Fermilab) Robert Sugar (University of California, Santa Barbara) Dr Ruth Van de Water (Fermilab) Steven Gottlieb (Indiana Univ.) Dr Urs Heller (American Physical Society)

 Slides