The ratio of branching fractions R(D^{*-})≡B(B^{0}→D^{*-}τ^{+}ν_{τ})/B(B^{0}→D^{*-}μ^{+}ν_{μ}) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3  fb^{-1}. For the first time, R(D^{*-}) is determined using the τ-lepton decays with three charged pions in the final state. The B^{0}→D^{*-}τ^{+}ν_{τ} yield is normalized to that of the B^{0}→D^{*-}π^{+}π^{-}π^{+} mode, providing a measurement of B(B^{0}→D^{*-}τ^{+}ν_{τ})/B(B^{0}→D^{*-}π^{+}π^{-}π^{+})=1.97±0.13±0.18, where the first uncertainty is statistical and the second systematic. The value of B(B^{0}→D^{*-}τ^{+}ν_{τ})=(1.42±0.094±0.129±0.054)% is obtained, where the third uncertainty is due to the limited knowledge of the branching fraction of the normalization mode. Using the well-measured branching fraction of the B^{0}→D^{*-}μ^{+}ν_{μ} decay, a value of R(D^{*-})=0.291±0.019±0.026±0.013 is established, where the third uncertainty is due to the limited knowledge of the branching fractions of the normalization and B^{0}→D^{*-}μ^{+}ν_{μ} modes. This measurement is in agreement with the standard model prediction and with previous results.

The first full amplitude analysis of B þ → J=ψϕK þ with J=ψ → μ þ μ − , ϕ → K þ K − decays is performed with a data sample of 3 fb −1 of pp collision data collected at ffiffi ffi s p ¼ 7 and 8 TeV with the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into ϕK þ , and four J=ψϕ structures are observed, each with significance over 5 standard deviations. The quantum numbers of these structures are determined with significance of at least 4 standard deviations. The lightest has mass consistent with, but width much larger than, previous measurements of the claimed Xð4140Þ state. DOI: 10.1103/PhysRevLett.118.022003 There has been a great deal of experimental and theoretical interest in J=ψϕ mass structures in B þ → J=ψϕK þ decays 1 since the CDF Collaboration presented 3.8σ evidence for a near-threshold Xð4140Þ mass peak, with width Γ¼11.7MeV [1].2 Much larger widths are expected for charmonium states at this mass because of open flavor decay channels [2], which should also make the kinematically suppressed X → J=ψϕ decays undetectable. Therefore, it has been suggested that the Xð4140Þ peak could be a molecular state [3][4][5][6][7][8][9], a tetraquark state [10][11][12][13][14], a hybrid state [15,16] or a rescattering effect [17,18]. Subsequent measurements resulted in the confusing experimental situation summarized in Table I In an unpublished update to their analysis [26], the CDF Collaboration presented 3.1σ evidence for a second relatively narrow J=ψϕ mass peak near 4274 MeV. A second peak was also observed by the CMS Collaboration at a mass which is higher by 3.2 standard deviations, but its statistical significance was not determined [23]. The Belle Collaboration obtained 3.2σ evidence for a narrow (Γ ¼ 13 þ18 −9 AE 4 MeV) J=ψϕ peak at 4350.6 þ4.6 −5.1 AE 0.7 MeV in two-photon collisions, which implies J PC ¼ 0 þþ or 2 þþ , and found no signal for Xð4140Þ [27].The Xð4140Þ and Xð4274Þ states are the only known candidates for four-quark systems that contain neither of the light u and d quarks. Their confirmation, and determination of their quantum numbers, would allow new insights into the binding mechanisms present in multiquark systems, and help improve understanding of QCD in the nonperturbative regime.The data sample used in this work corresponds to an integrated luminosity of 3 fb −1 collected with the LHCb detector in pp collisions at center-of-mass energies 7 and 8 TeV. The LHCb detector is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, described in detail in Refs. [28,29]. Thanks to the larger signal yield, corresponding to 4289 AE 151 reconstructed B þ → J=ψϕK þ decays, the roughly uniform efficiency and the relatively low background across the entire J=ψϕ mass range, this data sample offers the best sensitivity to date, not only to probe for the previously claimed J=ψϕ structures, but also to inspect the high mass region for the first time. All previous analyses were based on naive J=ψϕ mass (m J=ψϕ ) fits, with...

The first full amplitude analysis of B þ → J=ψϕK þ with J=ψ → μ þ μ − , ϕ → K þ K − decays is performed with a data sample of 3 fb −1 of pp collision data collected at ffiffi ffi s p ¼ 7 and 8 TeV with the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into ϕK þ , and four J=ψϕ structures are observed, each with significance over 5 standard deviations. The quantum numbers of these structures are determined with significance of at least 4 standard deviations. The lightest has mass consistent with, but width much larger than, previous measurements of the claimed Xð4140Þ state. The model includes significant contributions from a number of expected kaon excitations, including the first observation of the K Ã ð1680Þ þ → ϕK þ transition.

An angular analysis of the decay J/ψ→μ+μ− is performed to measure the polarization of prompt J/ψ mesons produced in pp collisions at . The dataset corresponds to an integrated luminosity of 0.37 fb−1 collected with the LHCb detector. The measurement is presented as a function of transverse momentum, pT, and rapidity, y, of the J/ψ meson, in the kinematic region 2

The first measurement of the lifetime of the doubly charmed baryon Ξ_{cc}^{++} is presented, with the signal reconstructed in the final state Λ_{c}^{+}K^{-}π^{+}π^{+}. The data sample used corresponds to an integrated luminosity of 1.7  fb^{-1}, collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV. The Ξ_{cc}^{++} lifetime is measured to be 0.256_{-0.022}^{+0.024}(stat)±0.014(syst)  ps.