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The differential branching fraction of the rare decay Λ b 0  → Λμ + μ − is measured as a function of q 2, 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 q 2 region below the square of the J/ψ mass. Integrating over 15 < q 2 < 20 GeV2 /c 4 the differential branching fraction is measured as $$ \mathrm{d}\mathrm{\mathcal{B}}\left({\varLambda}_b^0\to \varLambda {\mu}^{+}{\mu}^{-}\right)/d{q}^2=\left({1.18}_{-0.08}^{+0.09}\pm 0.03\pm 0.27\right)\times {10}^{-7}{\left({\mathrm{GeV}}^2/{c}^4\right)}^{-1}, $$ d ℬ Λ b 0 → Λ μ + μ − / d q 2 = 1.18 − 0.08 + 0.09 ± 0.03 ± 0.27 × 10 − 7 GeV 2 / c 4 − 1 , where the uncertainties are statistical, systematic and due to the normalisation mode, Λ b 0  → J/ψΛ, respectively. In the q 2 intervals where the signal is observed, angular distributions are studied and the forward-backward asymmetries in the dimuon (A FB ℓ ) and hadron (A FB h ) systems are measured for the first time. In the range 15 < q 2 < 20 GeV2 /c 4 they are found to be $$ \begin{array}{l}{A}_{\mathrm{FB}}^{\ell }=-0.05\pm 0.09\left(\mathrm{stat}\right)\pm 0.03\left(\mathrm{syst}\right)\;\mathrm{and}\hfill \\ {}{A}_{\mathrm{FB}}^h=-0.29\pm 0.07\left(\mathrm{stat}\right)\pm 0.03\left(\mathrm{syst}\right).\hfill \end{array} $$ A F B ℓ = − 0.05 ± 0.09 stat ± 0.03 syst and A F B h = − 0.29 ± 0.07 stat ± 0.03 syst .

The production of J/ψ and Υ mesons in pp collisions at √ s = 8 TeV is studied with the LHCb detector. The J/ψ and Υ mesons are reconstructed in the µ + µ − decay mode and the signal yields are determined with a fit to the µ + µ − invariant mass distributions. The analysis is performed in the rapidity range 2.0 < y < 4.5 and transverse momentum range 0 < p T < 14 (15) GeV/c of the J/ψ (Υ ) mesons. The J/ψ and Υ production crosssections and the fraction of J/ψ mesons from b-hadron decays are measured as a function of the meson p T and y. The LHCb collaboration 27 IntroductionSuccessfully describing heavy quarkonium production is a long-standing problem in QCD. An effective field theory, non-relativistic QCD (NRQCD) [1,2], provides the foundation for much of the current theoretical work. According to NRQCD, the production of heavy quarkonium factorises into two steps: a heavy quark-antiquark pair is first created at short distances and subsequently evolves non-perturbatively into quarkonium at long distances. The NRQCD calculations depend on the colour-singlet (CS) and colour-octet (CO) matrix elements, which account for the probability of a heavy quark-antiquark pair in a particular colour state to evolve into a heavy quarkonium state. The CS model (CSM) [3,4], which provides a leading-order description of quarkonium production, was initially used to describe experimental data. However, it underestimates the observed cross-section for single J/ψ production at high transverse momentum (p T ) at the Tevatron [5]. To resolve this discrepancy, the CO mechanism was introduced [6]. The corresponding matrix elements were determined from the high-p T data, as the CO cross-section decreases more slowly with p T than that predicted by CS. More recent higher-order calculations [7][8][9][10] close the gap between the CS predictions and the experimental data [11], reducing the need for large CO contributions.

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π − are reconstructed using data, corresponding to an integrated luminosity of 3.0 fb −1 , collected by the LHCb detector. The inclusive CP asymmetries of these modes are measured to bewhere the first uncertainty is statistical, the second systematic, and the third is due to the CP asymmetry of the B AE → J=ψK AE reference mode. The distributions of these asymmetries are also studied as functions of position in the Dalitz plot and suggest contributions from rescattering and resonance interference processes.