RESUMEN
A measurement is reported of the ratio of branching fractions R(J/ψ)=B(B_{c}^{+}âJ/ψτ^{+}ν_{τ})/B(B_{c}^{+}âJ/ψµ^{+}ν_{µ}), where the τ^{+} lepton is identified in the decay mode τ^{+}âµ^{+}ν_{µ}ν[over ¯]_{τ}. This analysis uses a sample of proton-proton collision data corresponding to 3.0 fb^{-1} of integrated luminosity recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. A signal is found for the decay B_{c}^{+}âJ/ψτ^{+}ν_{τ} at a significance of 3 standard deviations corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be R(J/ψ)=0.71±0.17(stat)±0.18(syst). This result lies within 2 standard deviations above the range of central values currently predicted by the standard model.
RESUMEN
The time-integrated untagged Dalitz plot of the three-body hadronic charmless decay B[over ¯]^{0}âK_{S}^{0}π^{+}π^{-} is studied using a pp collision data sample recorded with the LHCb detector, corresponding to an integrated luminosity of 3.0 fb^{-1}. The decay amplitude is described with an isobar model. Relative contributions of the isobar amplitudes to the B[over ¯]^{0}âK_{S}^{0}π^{+}π^{-} decay branching fraction and CP asymmetries of the flavor-specific amplitudes are measured. The CP asymmetry between the conjugate B[over ¯]^{0}âK^{*}(892)^{-}π^{+} and B^{0}âK^{*}(892)^{+}π^{-} decay rates is determined to be -0.308±0.062.
RESUMEN
Searches are performed for both promptlike and long-lived dark photons, A^{'}, produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using A^{'}âµ^{+}µ^{-} decays and a data sample corresponding to an integrated luminosity of 1.6 fb^{-1} collected with the LHCb detector. The promptlike A^{'} search covers the mass range from near the dimuon threshold up to 70 GeV, while the long-lived A^{'} search is restricted to the low-mass region 214
RESUMEN
The ratio of branching fractions R(D^{*-})≡B(B^{0}âD^{*-}τ^{+}ν_{τ})/B(B^{0}âD^{*-}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}âD^{*-}τ^{+}ν_{τ} yield is normalized to that of the B^{0}âD^{*-}π^{+}π^{-}π^{+} mode, providing a measurement of B(B^{0}âD^{*-}τ^{+}ν_{τ})/B(B^{0}âD^{*-}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}âD^{*-}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}âD^{*-}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}âD^{*-}µ^{+}ν_{µ} modes. This measurement is in agreement with the standard model prediction and with previous results.
RESUMEN
A search for the rare decay Σ^{+}âpµ^{+}µ^{-} is performed using pp collision data recorded by the LHCb experiment at center-of-mass energies sqrt[s]=7 and 8 TeV, corresponding to an integrated luminosity of 3 fb^{-1}. An excess of events is observed with respect to the background expectation, with a signal significance of 4.1 standard deviations. No significant structure is observed in the dimuon invariant mass distribution, in contrast with a previous result from the HyperCP experiment. The measured Σ^{+}âpµ^{+}µ^{-} branching fraction is (2.2_{-1.3}^{+1.8})×10^{-8}, where statistical and systematic uncertainties are included, which is consistent with the standard model prediction.
RESUMEN
Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb^{-1}, recorded by the LHCb detector at center-of-mass energies of 7 and 8 TeV, the B_{c}^{+}âD^{0}K^{+} decay is observed with a statistical significance of 5.1 standard deviations. By normalizing to B^{+}âD[over ¯]^{0}π^{+} decays, a measurement of the branching fraction multiplied by the production rates for B_{c}^{+} relative to B^{+} mesons in the LHCb acceptance is obtained, R_{D^{0}K}=(f_{c}/f_{u})×B(B_{c}^{+}âD^{0}K^{+})=(9.3_{-2.5}^{+2.8}±0.6)×10^{-7}, where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first B_{c}^{+} decay of this nature to be observed.
RESUMEN
A search for the B^{0}âK^{+}K^{-} decay is performed using pp-collision data collected by LHCb. The data set corresponds to integrated luminosities of 1.0 and 2.0 fb^{-1} at center-of-mass energies of 7 and 8 TeV, respectively. This decay is observed for the first time, with a significance of more than 5 standard deviations. The analysis also results in an improved measurement of the branching fraction for the B_{s}^{0}âπ^{+}π^{-} decay. The measured branching fractions are B(B^{0}âK^{+}K^{-})=(7.80±1.27±0.81±0.21)×10^{-8} and B(B_{s}^{0}âπ^{+}π^{-})=(6.91±0.54±0.63±0.19±0.40)×10^{-7}. The first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the B^{0}âK^{+}π^{-} branching fraction used as a normalization. For the B_{s}^{0} mode, the fourth accounts for the uncertainty on the ratio of the probabilities for b quarks to hadronize into B_{s}^{0} and B^{0} mesons.
RESUMEN
The Ξ_{c}^{+}K^{-} mass spectrum is studied with a sample of pp collision data corresponding to an integrated luminosity of 3.3 fb^{-1}, collected by the LHCb experiment. The Ξ_{c}^{+} is reconstructed in the decay mode pK^{-}π^{+}. Five new, narrow excited Ω_{c}^{0} states are observed: the Ω_{c}(3000)^{0}, Ω_{c}(3050)^{0}, Ω_{c}(3066)^{0}, Ω_{c}(3090)^{0}, and Ω_{c}(3119)^{0}. Measurements of their masses and widths are reported.
RESUMEN
A search for the rare decays B_{s}^{0}âµ^{+}µ^{-} and B^{0}âµ^{+}µ^{-} is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4 fb^{-1}. An excess of B_{s}^{0}âµ^{+}µ^{-} decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be B(B_{s}^{0}âµ^{+}µ^{-})=(3.0±0.6_{-0.2}^{+0.3})×10^{-9}, where the first uncertainty is statistical and the second systematic. The first measurement of the B_{s}^{0}âµ^{+}µ^{-} effective lifetime, τ(B_{s}^{0}âµ^{+}µ^{-})=2.04±0.44±0.05 ps, is reported. No significant excess of B^{0}âµ^{+}µ^{-} decays is found, and a 95% confidence level upper limit, B(B^{0}âµ^{+}µ^{-})<3.4×10^{-10}, is determined. All results are in agreement with the standard model expectations.
RESUMEN
The production of J/ψ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the J/ψ meson, z(J/ψ)≡p_{T}(J/ψ)/p_{T}(jet), is measured using jets with p_{T}(jet)>20 GeV in the pseudorapidity range 2.5<η(jet)<4.0. The observed z(J/ψ) distribution for J/ψ mesons produced in b-hadron decays is consistent with expectations. However, the results for prompt J/ψ production do not agree with predictions based on fixed-order nonrelativistic QCD. This is the first measurement of the p_{T} fraction carried by prompt J/ψ mesons in jets at any experiment.
RESUMEN
A search for the rare decays B_{s}^{0}âτ^{+}τ^{-} and B^{0}âτ^{+}τ^{-} is performed using proton-proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3 fb^{-1} collected in 2011 and 2012. The τ leptons are reconstructed through the decay τ^{-}âπ^{-}π^{+}π^{-}ν_{τ}. Assuming no contribution from B^{0}âτ^{+}τ^{-} decays, an upper limit is set on the branching fraction B(B_{s}^{0}âτ^{+}τ^{-})<6.8×10^{-3} at the 95% confidence level. If instead no contribution from B_{s}^{0}âτ^{+}τ^{-} decays is assumed, the limit is B(B^{0}âτ^{+}τ^{-})<2.1×10^{-3} at the 95% confidence level. These results correspond to the first direct limit on B(B_{s}^{0}âτ^{+}τ^{-}) and the world's best limit on B(B^{0}âτ^{+}τ^{-}).
RESUMEN
Asymmetries in the time-dependent rates of D^{0}âK^{+}K^{-} and D^{0}âπ^{+}π^{-} decays are measured in a pp collision data sample collected with the LHCb detector during LHC Run 1, corresponding to an integrated luminosity of 3 fb^{-1}. The asymmetries in effective decay widths between D^{0} and D[over ¯]^{0} decays, sensitive to indirect CP violation, are measured to be A_{Γ}(K^{+}K^{-})=(-0.30±0.32±0.10)×10^{-3} and A_{Γ}(π^{+}π^{-})=(0.46±0.58±0.12)×10^{-3}, where the first uncertainty is statistical and the second systematic. These measurements show no evidence for CP violation and improve on the precision of the previous best measurements by nearly a factor of two.
RESUMEN
We report the first observation of a baryonic B_{s}^{0} decay, B_{s}^{0}âpΛ[over ¯]K^{-}, using proton-proton collision data recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb^{-1}. The branching fraction is measured to be B(B_{s}^{0}âpΛ[over ¯]K^{-})+B(B_{s}^{0}âp[over ¯]ΛK^{+})=[5.46±0.61±0.57±0.50(B)±0.32(f_{s}/f_{d})]×10^{-6}, where the first uncertainty is statistical and the second systematic, the third uncertainty accounts for the experimental uncertainty on the branching fraction of the B^{0}âpΛ[over ¯]π^{-} decay used for normalization, and the fourth uncertainty relates to the knowledge of the ratio of b-quark hadronization probabilities f_{s}/f_{d}.
RESUMEN
The first observation of the decay of a B^{0} meson to a purely baryonic final state, B^{0}âpp[over ¯], is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3.0 fb^{-1}. The branching fraction is determined to be B(B^{0}âpp[over ¯])=(1.25±0.27±0.18)×10^{-8}, where the first uncertainty is statistical and the second systematic. The decay mode B^{0}âpp[over ¯] is the rarest decay of the B^{0} meson observed to date. The decay B_{s}^{0}âpp[over ¯] is also investigated. No signal is seen and the upper limit B(B_{s}^{0}âpp[over ¯])<1.5×10^{-8} at 90% confidence level is set on the branching fraction.
RESUMEN
The decays χ_{c1}âJ/ψµ^{+}µ^{-} and χ_{c2}âJ/ψµ^{+}µ^{-} are observed and used to study the resonance parameters of the χ_{c1} and χ_{c2} mesons. The masses of these states are measured to be m(χ_{c1})=3510.71±0.04(stat)±0.09(syst) MeV and m(χ_{c2})=3556.10±0.06(stat)±0.11(syst) MeV, where the knowledge of the momentum scale for charged particles dominates the systematic uncertainty. The momentum-scale uncertainties largely cancel in the mass difference m(χ_{c2})-m(χ_{c1})=45.39±0.07(stat)±0.03(syst) MeV. The natural width of the χ_{c2} meson is measured to be Γ(χ_{c2})=2.10±0.20(stat)±0.02(syst) MeV. These results are in good agreement with and have comparable precision to the current world averages.
RESUMEN
A search for baryon-number violating Ξ_{b}^{0} oscillations is performed with a sample of pp collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb^{-1}. The baryon number at the moment of production is identified by requiring that the Ξ_{b}^{0} come from the decay of a resonance Ξ_{b}^{*-}âΞ_{b}^{0}π^{-} or Ξ_{b}^{'-}âΞ_{b}^{0}π^{-}, and the baryon number at the moment of decay is identified from the final state using the decays Ξ_{b}^{0}âΞ_{c}^{+}π^{-},Ξ_{c}^{+}âpK^{-}π^{+}. No evidence of baryon-number violation is found, and an upper limit at the 95% confidence level is set on the oscillation rate of ω<0.08 ps^{-1}, where ω is the associated angular frequency.
RESUMEN
The first observation of the D^{0}âπ^{+}π^{-}µ^{+}µ^{-} and D^{0}âK^{+}K^{-}µ^{+}µ^{-} decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8 TeV, and corresponding to 2 fb^{-1} of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay D^{0}âK^{-}π^{+}[µ^{+}µ^{-}]_{ρ^{0}/ω}, where the two muons are consistent with coming from the decay of a ρ^{0} or ω meson. The results are B(D^{0}âπ^{+}π^{-}µ^{+}µ^{-})=(9.64±0.48±0.51±0.97)×10^{-7} and B(D^{0}âK^{+}K^{-}µ^{+}µ^{-})=(1.54±0.27±0.09±0.16)×10^{-7}, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated.
RESUMEN
The first full amplitude analysis of B^{+}âJ/ψÏK^{+} with J/ψâµ^{+}µ^{-}, ÏâK^{+}K^{-} decays is performed with a data sample of 3 fb^{-1} of pp collision data collected at sqrt[s]=7 and 8 TeV with the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into ÏK^{+}, and four J/ψÏ 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 X(4140) state.
RESUMEN
The polarization of photons produced in radiative B_{s}^{0} decays is studied for the first time. The data are recorded by the LHCb experiment in pp collisions corresponding to an integrated luminosity of 3 fb^{-1} at center-of-mass energies of 7 and 8 TeV. A time-dependent analysis of the B_{s}^{0}âÏγ decay rate is conducted to determine the parameter A^{Δ}, which is related to the ratio of right- over left-handed photon polarization amplitudes in bâsγ transitions. A value of A^{Δ}=-0.98_{-0.52}^{+0.46}_{-0.20}^{+0.23} is measured. This result is consistent with the standard model prediction within 2 standard deviations.
RESUMEN
Decays of the Ξ_{b}^{-} and Ω_{b}^{-} baryons to the charmless final states ph^{-}h^{'-}, where h^{(')} denotes a kaon or pion, are searched for with the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at center-of-mass energies sqrt[s]=7 and 8 TeV, corresponding to an integrated luminosity of 3 fb^{-1}. The decay Ξ_{b}^{-}âpK^{-}K^{-} is observed with a significance of 8.7 standard deviations, and evidence at the level of 3.4 standard deviations is found for the Ξ_{b}^{-}âpK^{-}π^{-} decay. Results are reported, relative to the B^{-}âK^{+}K^{-}K^{-} normalization channel, for the products of branching fractions and b-hadron production fractions. The branching fractions of Ξ_{b}^{-}âpK^{-}π^{-} and Ξ_{b}^{-}âpπ^{-}π^{-} relative to Ξ_{b}^{-}âpK^{-}K^{-} decays are also measured.