Measurement of b-hadron production fractions in 7 TeV centre-of-mass energy pp collisions

This report describes the determination of $b$ quark fragmentation into bottom hadrons in proton-proton collisions at a centre-of-mass energy of 7 TeV. We study the ratios of strange $B$ meson to light $B$ meson production [$f_s/(f_u+f_d)$] and $\Lambda_b$ baryon to light $B$ meson production [$f_{\Lambda_b}/(f_u+f_d)$] as a function of the charmed hadron-muon system transverse momentum $p_t$ and of the $b$-hadron pseudo-rapidity $\eta$, for $p_t$ between 0 and 14 GeV and $\eta$ between 2 and 5. We find that [$f_s/(f_u+f_d)$] is independent of $p_t$ and $\eta$, and we determine [$f_s/(f_u+f_d)$] = 0.134$\pm$0.004$^{+0.011}_{-0.010}$, where the first error is statistical and the second systematic. The corresponding ratio [$f_{\Lambda_b}/(f_u+f_d)$] is found to be dependent upon the transverse momentum of the charm hadron-$\mu$ pair. Thus we quote $[f_{\Lambda_b}/(f_u+f_d)]=(0.404\pm 0.017 (stat) \pm 0.027 (sys) \pm 0.105 (Br) )\times[1 -(0.031 \pm 0.004\pm 0.003)\times p_t {\rm (GeV)}]$, where the errors on the scale factor are statistical, systematic, and $Br$ reflects an absolute scale uncertainty due to the poorly known branching fraction ${\cal B}(\Lambda_c\to pK\pi)$