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Physical Review D 83 (2011) 014505
BK-parameter from Nf = 2 twisted mass lattice QCD
M. Constantinou, P. Dimopoulos, R. Frezzotti, K. Jansen1, V. Gimenez, V. Lubicz, F. Mescia, H. Panagopoulos, M. Papinutto2, G.C. Rossi, S. Simula, A. Skouroupathis, F. Stylianou, A. Vladikas
ETM Collaboration(s)

We present an unquenched $N_f=2$ lattice computation of the $B_{K}$ parameter which controls $K^0-\bar K^0$ 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 $B_{K}$ 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 $B^{\rm RGI}_K=0.729\pm 0.030$, a number well in line with the existing quenched and unquenched determinations.
1 :  DESY - Deutsches Elektronen-Synchrotron [Zeuthen]
2 :  LPSC - Laboratoire de Physique Subatomique et de Cosmologie
Physique/Physique des Hautes Energies - Réseau

Physique/Physique des Hautes Energies - Phénoménologie
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