Measurement of the $\hat{I}{\cdot }_c(1S)$ production cross-section in proton-proton collisions via the decay $\hat{I}{\cdot }_c(1S)\to p\bar{p}$

Abstract

The production of the $\hat{I}{\cdot }_c(1S)$ state in proton-proton collisions is probed via its decay to the $p\bar{p}$ final state with the LHCb detector, in the rapidity range $2.0<y<4.5$ and in the meson transverse-momentum range $p_T>6.5$ GeV/c. The cross-section for prompt production of $\hat{I}{\cdot }_c(1S)$ mesons relative to the prompt $J/\ddot{I}ˆ$ cross-section is measured, for the first time, to be $\ddot{I}{ƒ}_{\hat{I}{\cdot }_c(1S)}/\ddot{I}{ƒ}_{J/\ddot{I}ˆ}=1.74\pm 0.29\pm 0.28\pm 0.18_B$ at a centre-of-mass energy $\sqrt{s}=7$ TeV using data corresponding to an integrated luminosity of 0.7 fb${}^{-1}$, and $\ddot{I}{ƒ}_{\hat{I}{\cdot }_c(1S)}/\ddot{I}{ƒ}_{J/\ddot{I}ˆ}=1.60\pm 0.29\pm 0.25\pm 0.17_B$ at $\sqrt{s}=8$ TeV using 2.0 fb${}^{-1}$. The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the $\hat{I}{\cdot }_c(1S)$ and $J/\ddot{I}ˆ$ decays to the $p\bar{p}$ final state. In addition, the inclusive branching fraction of $b$-hadron decays into $\hat{I}{\cdot }_c(1S)$ mesons is measured, for the first time, to be $B(b\to \hat{I}{\cdot }_{c}X)=(4.88\pm 0.64\pm 0.29\pm 0.67_B)\times 10^{-3}$, where the third uncertainty includes also the uncertainty on the $J/\ddot{I}ˆ$ inclusive branching fraction from $b$-hadron decays. The difference between the $J/\ddot{I}ˆ$ and $\hat{I}{\cdot }_c(1S)$ meson masses is determined to be $114.7\pm 1.5\pm 0.1$ MeV/c${}^2$.

20 pages, 3 figures