Measurement of the differential branching fraction of the decay $\Lambda_b^0\rightarrow\Lambda\mu^+\mu^-$

TL;DR

This paper measures the differential branching fraction of the decay Lambda_b^0 to Lambda mu+ mu- as a function of q^2, observing a significant signal above the J/psi mass region and setting upper limits at lower q^2.

Contribution

First measurement of the differential branching fraction of Lambda_b^0 to Lambda mu+ mu- across q^2, providing new experimental data for this decay mode.

Findings

Significant signal observed above J/psi mass region.

Branching fraction measured as (0.96±0.16(stat)±0.13(syst)±0.21(norm))×10^{-6}.

Upper limits set at low q^2 regions.

Abstract

The differential branching fraction of the decay $\Lambda_b^0\rightarrow\Lambda\mu^+\mu^-$ is measured as a function of the square of the dimuon invariant mass, $q^2$. A yield of $78\pm12$ $\Lambda_b^0\rightarrow\Lambda\mu^+\mu^-$ decays is observed using data, corresponding to an integrated luminosity of 1.0\,fb$^{-1}$, collected by the LHCb experiment at a centre-of-mass energy of 7\,TeV. A significant signal is found in the $q^2$ region above the square of the $J/\psi$ mass, while at lower-$q^2$ values upper limits are set on the differential branching fraction. Integrating the differential branching fraction over $q^2$, while excluding the $J/\psi$ and $\psi(2S)$ regions, gives a branching fraction of $\BF($\Lambda_b^0\rightarrow\Lambda\mu^+\mu^-$)=(0.96\pm 0.16\stat\pm 0.13\syst\pm 0.21 (\mathrm{norm}))\times 10^{-6}$, where the uncertainties are statistical, systematic and due to the normalisation mode, $$\Lambda_b^0\rightarrow J/psi\Lambda$, respectively.