# Precision Computation of fK/fπ from Staggered 2+1+1 Flavor Simulations

Principal Investigator: Stephan Duerr, Wuppertal University and IAS/JSC at Forschungszentrum Jülich
HPC Platform: JUQUEEN of JSC
Date Published: October 2013
JSC Project ID: hwu07

Project “Precision computation of fK/fπ from staggered 2+1+1 flavor simulations“ aims at a precision test of the first-row unitarity relation of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. To this end, a team of scientists of the University of Wuppertal and Forschungszentrum Jülich under leadership of Dr. Stephan Duerr computes the ratio fK/fπ of the leptonic decay constants of the kaon and the pion. The computation is from first principles, by solving the relevant equations of motion in the underlying fundamental theory, known as quantum chromodynamics'' (QCD). Once the result is in hand, the scientists use it to obtain a precise value of the CKM element |Vus| based on |Vud| which is known very accurately. By combining this with the known element |Vub| the scientists can test whether the relation

|Vud|2 + |Vus|2 + |Vub|2 = 1

holds within errors. Any deviation would signal the presence of new physics in the aforementioned leptonic decays.