A measurement of the ratio of the branching fractions of the B(+) → K(+)μ(+)μ(-) and B(+) → K(+)e(+)e(-) decays is presented using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb(-1), recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. The value of the ratio of branching fractions for the dilepton invariant mass squared range 1 < q(2) < 6 GeV(2)/c(4) is measured to be 0.745(-0.074)(+0.090)(stat) ± 0.036(syst). This value is the most precise measurement of the ratio of branching fractions to date and is compatible with the standard model prediction within 2.6 standard deviations.

The isospin asymmetries of B → Kµ + µ − and B → K * µ + µ − decays and the partial branching fractions of the B 0 → K 0 µ + µ − , B + → K + µ + µ − and B + → K * + µ + µ − decays are measured as functions of the dimuon mass squared, q 2 . The data used correspond to an integrated luminosity of 3 fb −1 from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions favour lower values than their respective theoretical predictions, however they are all individually consistent with the Standard Model.

Resonant structures in B^{0}→ψ^{'}π^{-}K^{+} decays are analyzed by performing a four-dimensional fit of the decay amplitude, using pp collision data corresponding to 3  fb^{-1} collected with the LHCb detector. The data cannot be described with K^{+}π^{-} resonances alone, which is confirmed with a model-independent approach. A highly significant Z(4430)^{-}→ψ^{'}π^{-} component is required, thus confirming the existence of this state. The observed evolution of the Z(4430)^{-} amplitude with the ψ^{'}π^{-} mass establishes the resonant nature of this particle. The mass and width measurements are substantially improved. The spin parity is determined unambiguously to be 1^{+}.

The production of J/ψ mesons with rapidity 1.5 < y < 4.0 or −5.0 < y < −2.5 and transverse momentum p T < 14 GeV/c is studied with the LHCb detector in proton-lead collisions at a nucleon-nucleon centre-of-mass energy √ s N N = 5 TeV. The J/ψ mesons are reconstructed using the dimuon decay mode. The analysis is based on a data sample corresponding to an integrated luminosity of about 1.6 nb −1 . For the first time the nuclear modification factor and forward-backward production ratio are determined separately for prompt J/ψ mesons and J/ψ from b-hadron decays. Clear suppression of prompt J/ψ production with respect to proton-proton collisions at large rapidity is observed, while the production of J/ψ from b-hadron decays is less suppressed. These results show good agreement with available theoretical predictions. The measurement shows that cold nuclear matter effects are important for interpretations of the related quark-gluon plasma signatures in heavy-ion collisions.Keywords: Relativistic heavy ion physics, Quarkonium, Heavy quark production, Heavy Ions, Particle and resonance production A Results in tables 13The LHCb collaboration 19 IntroductionThe suppression of heavy quarkonia production with respect to proton-proton (pp) collisions [1] is one of the most distinctive signatures of the formation of quark-gluon plasma, a hot nuclear medium created in ultrarelativistic heavy-ion collisions. However, the suppression of heavy quarkonia and light hadron production with respect to pp collisions can also take place in proton-nucleus (pA) collisions, where a quark-gluon plasma is not expected to be created and only cold nuclear matter effects, such as nuclear absorption, parton shadowing and parton energy loss in initial and final states occur [2][3][4][5][6][7][8]. The study of pA collisions is important to disentangle the effects of quark-gluon plasma from cold nuclear matter, and to provide essential input to the understanding of nucleus-nucleus collisions. Nuclear effects are usually characterised by the nuclear modification factor, defined as the production cross-section of a given particle in pA collisions divided by that in pp collisions and the number of colliding nucleons in the nucleus (given by the atomic number A),where y is the rapidity of the particle in the nucleon-nucleon centre-of-mass frame, p T is the transverse momentum of the particle, and √ s NN is the nucleon-nucleon centre-of-mass energy. The suppression of heavy quarkonia and light hadron production with respect to pp collisions at large rapidity has been observed in pA collisions [9, 10] and in deuterongold collisions [11][12][13], but has not been studied in proton-lead (pPb) collisions at the TeV -1 - JHEP02(2014)072scale. Previous experiments [9][10][11][12][13] have also shown evidence that the production crosssection of J/ψ mesons or light hadrons in the forward region (positive rapidity) of pA or deuteron-gold collisions differs from that in the backward region (negative rapidity), where "forward" and "backward" are define...

A search for heavy Majorana neutrinos produced in the B- → π+ μ- μ- decay mode is performed using 3  fb(-1) of integrated luminosity collected with the LHCb detector in pp collisions at center-of-mass energies of 7 and 8 TeV at the LHC. Neutrinos with masses in the range 250 to 5000 MeV and lifetimes from zero to 1000 ps are probed. In the absence of a signal, upper limits are set on the branching fraction B(B- → π+ μ- μ-) as functions of neutrino mass and lifetime. These limits are on the order of 10(-9) for short neutrino lifetimes of 1 ps or less. Limits are also set on the coupling between the muon and a possible fourth-generation neutrino.