A high-statistics lattice calculation of λ1 and λ2 in the B-meson Original Research Article

We present a high-statistics lattice calculation of the kinetic energy −λ1/2mb of the heavy quark inside the B-meson and of the chromo-magnetic term A2, related to the B∗−B mass splitting, performed in the HQET Our results have been obtained from a numerical simulation based on 600 gauge field configurations generated at β = 6.0, on a lattice volume 243 × 40 and using, for the meson correlators, the results obtained with the SW-Clover O(a) improved lattice action for the light quarks. For the kinetic energy we found −λ1 = 〈B|h̄(iD)2h|B〉/(2MB) = −(0.09 ± 0.14) GeV2, which is interesting for phenomenological applications. We also found λ2 = 0.07 ± 0.01 GeV2, corresponding to MB∗2 − MB2 = 4λ2 = 0.280 ± 0.060 GeV2, which is about one half of the experimental value. The origin of the discrepancy with the experimental number needs to be clarified.