An improved measurement of direct CP violation parameters in B± → J/ψK± and B± → J/ψπ± decays

We present a measurement of the direct CP-violating charge asymmetry in B-+/- mesons decaying to J/psi K-+/- and J/psi pi(+/-) where J/psi decays to mu(+)mu(-), using 10.4 fb(-1) of proton-antiproton collisions collected by the D0 detector during Run II at the Fermilab Tevatron Collider. A difference in the yield of B- and B+ mesons in these decays is found by fitting to the difference between their reconstructed invariant mass distributions resulting in asymmetries of A(J/psi K) = [0.59 +/- 0.36] %, which is the most precise measurement to date, and A(J/psi pi) = [-4.2 +/- 4.8] %. Both measurements are consistent with standard model predictions. These measurements are combined with all previous measurements to form new world averages of A(J/psi K) and A(J/psi pi).