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Abstract
The ratio of the Λb(0) baryon lifetime to that of the B(0) meson is measured using 1.0 fb(-1) of integrated luminosity in 7 TeV center-of-mass energy pp collisions at the LHC. The Λb(0) baryon is observed for the first time in the decay mode Λb(0)→J/ψpK-, while the B(0) meson decay used is the well known B(0)→J/ψπ+ K- mode, where the π+ K- mass is consistent with that of the K(*0)(892) meson. The ratio of lifetimes is measured to be 0.976±0.012±0.006, in agreement with theoretical expectations based on the heavy quark expansion. Using previous determinations of the B(0) meson lifetime, the Λb(0) lifetime is found to be 1.482±0.018±0.012 ps. In both cases, the first uncertainty is statistical and the second systematic.
Highlights
Background model pK helicityAcceptance function B"0 lifetime ÁÁÁ Total 0.2 (b) Yield ratio 0.1 t [ps]FIG. 5. (a) Decay J=c pKÀ shown as circles, atinmdeB"d0is!tribJu=tcioKn"sÃ0fðo8r92ÃÞ0bd!ecays shown as squares
Ratio of the decay time acceptances between Ã0b ! J=c pKÀ and B"0 ! J=c K" Ã0ð892Þ decays obtained from simulation
For most entries the error bars are smaller than the points. (b) Yield ratio of Ã0b ! J=c pKÀ to B"0 ! J=c K" Ã0ð892Þ events fitted as a function of decay time
Summary
We determine the event yields in both decay modes by fitting the invariant mass distributions in 16 bins of decay time, each bin 0.4 ps wide, using the same signal and. Fit to the invariant mass spectrum of J=c þKÀ combinations with þKÀ invariant mass within Æ100 MeV of the K" Ã0 mass. The B"0 signal is shown by the solid (magenta) curve, the combinatorial background by the dotted (black) line, the B"0s ! J=c þKÀ signal by the dashed (red) curve, and the total by the solid (blue) curve. Ratio of the decay time acceptances between Ã0b ! J=c K" Ã0ð892Þ decays obtained from simulation. The solid (blue) line shows the result of the linear fit
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