Differential branching fraction and angular analysis of Λ(formula presented.)decays

Abstract

Abstract: The differential branching fraction of the rare decay Λb0 → Λμ+μ− is measured as a function of q2, the square of the dimuon invariant mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb−1, collected by the LHCb experiment. Evidence of signal is observed in the q2 region below the square of the J/ψ mass. Integrating over 15 < q2< 20 GeV2/c4 the differential branching fraction is measured asdℬ(formula presented.)±0.03±0.27×10−7GeV2/c4−1,$$ \mathrm{d}\mathrm{\mathcal{B}}\left({\varLambda}_b^0\to \varLambda {\mu}^{+}{\mu}^{-}\right)/d{q}^2=\left({1.18}_{-0.08}^{+0.09}\pm 0.03\pm 0.27\right)\times {10}^{-7}{\left({\mathrm{GeV}}^2/{c}^4\right)}^{-1}, $$where the uncertainties are statistical, systematic and due to the normalisation mode, Λb0 → J/ψΛ, respectively. In the q2 intervals where the signal is observed, angular distributions are studied and the forward-backward asymmetries in the dimuon (AFBℓ) and hadron (AFBh) systems are measured for the first time. In the range 15 < q2< 20 GeV2/c4 they are found to be(formula presented.)=−0.29±0.07stat±0.03syst.$$ \begin{array}{l}{A}_{\mathrm{FB}}^{\ell }=-0.05\pm 0.09\left(\mathrm{stat}\right)\pm 0.03\left(\mathrm{syst}\right)\;\mathrm{and}\hfill \\ {}{A}_{\mathrm{FB}}^h=-0.29\pm 0.07\left(\mathrm{stat}\right)\pm 0.03\left(\mathrm{syst}\right).\hfill \end{array} $$[Figure not available: see fulltext.]