We present an unquenched Nf=2 lattice computation of the BK parameter which controls K0−Kˉ0 oscillations. A partially quenched setup is employed with two maximally twisted dynamical (sea) light Wilson quarks, and valence quarks of both the maximally twisted and the Osterwalder--Seiler variety. Suitable combinations of these two kinds of valence quarks lead to a lattice definition of the BK parameter which is both multiplicatively renormalizable and O(a) improved. Employing the non-perturbative RI-MOM scheme, in the continuum limit and at the physical value of the pion mass we get BKRGI=0.729±0.030, a number well in line with the existing quenched and unquenched determinations.
@article{arxiv.1009.5606,
title = {BK-parameter from Nf = 2 twisted mass lattice QCD},
author = {ETM Collaboration and M. Constantinou and P. Dimopoulos and R. Frezzotti and K. Jansen and V. Gimenez and V. Lubicz and F. Mescia and H. Panagopoulos and M. Papinutto and G. C. Rossi and S. Simula and A. Skouroupathis and F. Stylianou and A. Vladikas},
journal= {arXiv preprint arXiv:1009.5606},
year = {2011}
}
Comments
Accepted for publication in Phys. Rev. D; systematic error discussion slightly modified; total uncertainty estimate on the BK result unchanged; 42 pages, 25 figures