An improved measurement of direct CP violation parameters in B^pm -> J/psi K^pm and B^pm -> J/psi pi^pm decays

Abstract

We present a measurement of the direct CP-violating charge asymmetry in B^pm mesons decaying to J/psi K^pm and J/psi pi^pm 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 ajpk =[ 0.59 \pm 0.36 ]%, which is the most precise measurement to date, and ajppi= [ -4.2 \pm 4.8 ]%.Both measurements are consistent with standard model predictions. These measurements are combined with all previous measurements to form new world averages of \ajpk\ and \ajppi .