We measure the masses of $b$ hadrons in exclusively reconstructed final states containing a $J/\psi\to\mu^-\mu^+$ decay using $\rm 220 pb^{ -1}$ of data collected by the CDF II experiment. We find: m(B^+) = 5279.10 \pm 0.41_{ (stat.)} \pm 0.36_{ (sys.)} MeVcc, m(B^0) = 5279.63 \pm 0.53_{ (stat.)} \pm 0.33_{ (sys.)} MeVcc, m(B^0_s) = 5366.01 \pm 0.73_{ (stat.)} \pm 0.33_{ (sys.)} MeVcc, m(\Lambda^0_b) = 5619.7 \pm 1.2_{ (stat.)} \pm 1.2_{ (sys.)} MeVcc. m(B^+) - m(B^0) = -0.53 \pm 0.67_{ (stat.)} \pm 0.14_{ (sys.)} MeVcc, m(B^0_s) - m(B^0) = 86.38 \pm 0.90_{ (stat.)} \pm 0.06_{ (sys.)} MeVcc m(\Lambda^0_b) - m(B^0) = 339.2 \pm 1.4_{ (stat.)} \pm 0.1_{ (sys.)} MeVcc. The measurements of the $B^0_s$, $\Lambda^0_b$ mass, $m(B^0_s)-m(B^0)$ and $m(\Lambda^0_b)-m(B^0)$ mass difference are of better precision than the current world averages.
Categories: hep-ex