  We present a new measurement of the $B^+$ meson differential cross section
$d\sigma/d p_T$ at $\sqrt{s}=1960$ GeV. The data correspond to an integrated
luminosity of 739pb$^{-1}$ collected with the upgraded CDF detector (CDF II) at
the Fermilab Tevatron collider. $B^+$ candidates are reconstructed through the
decay $B^+ \to J/\psi K^+$, with $J/\psi \to \mu^+ \mu^-$. The integrated cross
section for producing $B^+$ mesons with $p_T \geq 6$ GeV/c and $|y| \leq 1$ is
measured to be $2.78 \pm 0.24 \mu$b
