Precision computation of the kaon bag parameter

S. Dürr, Z. Fodor, C. Hoelbling, S. D. Katz, S. Krieg, T. Kurth, L. Lellouch, T. Lippert, C. McNeile, A. Portelli, K. K. Szabó

Research output: Contribution to journalArticlepeer-review

80 Scopus citations


Indirect CP violation in K→ππ decays plays a central role in constraining the flavor structure of the Standard Model (SM) and in the search for new physics. For many years the leading uncertainty in the SM prediction of this phenomenon was the one associated with the nonperturbative strong interaction dynamics in this process. Here we present a fully controlled lattice QCD calculation of these effects, which are described by the neutral kaon mixing parameter BK. We use a two step HEX smeared clover-improved Wilson action, with four lattice spacings from a≈0.054 fm to a≈0.093 fm and pion masses at and even below the physical value. Nonperturbative renormalization is performed in the RI-MOM scheme, where we find that operator mixing induced by chiral symmetry breaking is very small. Using fully nonperturbative continuum running, we obtain our main result BKRI(3.5 GeV)=0.531(6)stat(2)sys. A perturbative 2-loop conversion yields BKMS-NDR(2 GeV)=0.564(6)stat(3)sys(6)PT and B̂K=0.773(8)stat(3)sys(8)PT, which is in good agreement with current results from fits to experimental data.

Original languageEnglish (US)
Pages (from-to)477-481
Number of pages5
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Issue number5
StatePublished - Nov 24 2011

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics


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