Precision measurement of the mass and lifetime of the $\hat{I}{ž}_b^0$ baryon

Abstract

Using a proton-proton collision data sample corresponding to an integrated luminosity of 3 fb${}^{-1}$ collected by LHCb at center-of-mass energies of 7 and 8 TeV, about 3800 $\hat{I}{ž}_b^0\to \hat{I}{ž}_c^{+}\ddot{I}{€}^{-}$, $\hat{I}{ž}_c^{+}\to p{K}^{-}\ddot{I}{€}^{+}$ signal decays are reconstructed. From this sample, the first measurement of the $\hat{I}{ž}_b^0$ baryon lifetime is made, relative to that of the $\hat{I}{›}_b^0$ baryon. The mass differences $M(\hat{I}{ž}_b^0)-M(\hat{I}{›}_b^0)$ and $M(\hat{I}{ž}_c^{+})-M(\hat{I}{›}_c^{+})$ are also measured with precision more than four times better than the current world averages. The resulting values are $\frac{\ddot{I}{„}_{\hat{I}{ž}_b^0}}{\ddot{I}{„}_{\hat{I}{›}_b^0}}=1.006\pm 0.018\pm 0.010$, $M(\hat{I}{ž}_b^0)-M(\hat{I}{›}_b^0)=172.44\pm 0.39\pm 0.17MeV/c^2$, $M(\hat{I}{ž}_c^{+})-M(\hat{I}{›}_c^{+})=181.51\pm 0.14\pm 0.10MeV/c^2$, where the first uncertainty is statistical and the second is systematic. The relative rate of $\hat{I}{ž}_b^0$ to $\hat{I}{›}_b^0$ baryon production is measured to be $\frac{f_{\hat{I}{ž}_b^0}}{f_{\hat{I}{›}_b^0}}\frac{\mathcal{B}(\hat{\mathcal{I}}{ž}_b^0\to \hat{\mathcal{I}}{ž}_c^{+}\ddot{\mathcal{I}}{€}^{-})}{\mathcal{B}(\hat{\mathcal{I}}{›}_b^0\to \hat{\mathcal{I}}{›}_c^{+}\ddot{\mathcal{I}}{€}^{-})}\frac{\mathcal{B}(\hat{\mathcal{I}}{ž}_c^{+}\to p{\mathcal{K}}^{-}\ddot{\mathcal{I}}{€}^{+})}{\mathcal{B}(\hat{\mathcal{I}}{›}_c^{+}\to p{\mathcal{K}}^{-}\ddot{\mathcal{I}}{€}^{+})}=(1.88\pm 0.04\pm 0.03)\times 10^{-2}$, where the first factor is the ratio of fragmentation fractions, $b\to \hat{I}{ž}_b^0$ relative to $b\to \hat{I}{›}_b^0$. Relative production rates as functions of transverse momentum and pseudorapidity are also presented.

7 pages, 4 figures