526 research outputs found

    Observation of the Bc+→J/ψπ+π0 decay

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    The first observation of the Bc+→J/ψπ+π0 decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the Bc+→J/ψπ+ channel is measured to be (Formula presented.) where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for B+ → J/ψK*+ and Bc+→J/ψπ+ decays, which are used to determine the π0 detection efficiency. The π+π0 mass spectrum is found to be consistent with the dominance of an intermediate ρ+ contribution in accordance with a model based on QCD factorisation

    Measurement of the branching fraction of B0→ J/ψπ0 decays

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    The ratio of branching fractions between B0 → J/ψπ0 and B+ → J/ψK*+ decays is measured with proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. The measured value is (Formula presented.) where the first uncertainty is statistical and the second is systematic. The branching fraction for B0 → J/ψπ0 decays is determined using the branching fraction of the normalisation channel, resulting in (Formula presented.) where the last uncertainty corresponds to that of the external input. This result is consistent with the current world average value and competitive with the most precise single measurement to date

    Measurement of associated J/ψ-ψ(2S) production cross-section in pp collisions at √s = 13TeV

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    The cross-section of associated J/ψ-ψ(2S) production in proton-proton collisions at a centre-of-mass energy of √s = 13TeV is measured using a data sample corresponding to an integrated luminosity of 4.2 fb−1, collected by the LHCb experiment. The measurement is performed for both J/ψ and ψ(2S) mesons having transverse momentum pT< 14 GeV/c and rapidity 2.0 < y < 4.5, assuming negligible polarisation of the J/ψ and ψ(2S) mesons. The production cross-section is measured to be 4.5 ± 0.7 ± 0.3 nb, where the first uncertainty is statistical and the second systematic. The differential cross-sections are measured as functions of several kinematic variables of the J/ψ-ψ(2S) candidates. The results are combined with a measurement of J/ψ-J/ψ production, giving a cross-section ratio between J/ψ-ψ(2S) and J/ψ-J/ψ production of 0.274 ± 0.044 ± 0.008, where the first uncertainty is statistical and the second systematic

    Study of the rare decay J/ψ → μ+μ−μ+μ−

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    The rare electromagnetic J/ψ → μ+μ−μ+μ− decay is observed with a significance greatly exceeding the discovery threshold, using proton-proton collision data collected by the LHCb experiment during 2016–2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb−1. The rate of this decay is measured relative to that of the J/ψ → μ+μ− mode. Using the QED model for the four-muon decay in the efficiency estimation, its branching fraction is determined to be (Formula presented.) where the uncertainties are statistical, systematic and due to the uncertainty on the branching fraction of the J/ψ → μ+μ− decay

    A Study of the Cryoscopic Method of Molecular Weight Determination Using Camphur as the Solvent

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    There has probably been no solvent used by organic chemists to a greater extent as a means of finding the molecular weight of newly prepared compounds by the cryoscopic method than camphor. The establishment of the numerical value of the molal freezing point depression constant for this substance is of considerable importance. Of the several values found in the literature for this constant, the one most widely accepted is that of 39.7, as found by Rast. Many of the values found by other investigators are in disagreement with this value; outstanding ones being those of Jounieaux, 49.6; Efremov, 48.7; and Durand, 49.7; as listed by Meldrum, Saxer, and Jones. |These last three mentioned investigators have shown in their paper that the value of the depression constant for camphor is dependent upon the concentration of the solvent; cast's value of 39.7 holding true for solutions within certain concentration limits. |It is the purpose of this study to investigate the molal freezing point depression constant for camphor, keeping in mind the limitations of concentration as shown by Meldrum, Saxer, and Jones. Data will be given concerning the evaluation of the constant, procedure, and method modification noted. Comparison of the data of this author to the data of Meldrum, Saxer, and Jones will be made by means of tables and graphs.ProQuest Traditional Publishing Optio

    Observation of the Bc+ → J/ψπ+π0 decay

    No full text
    The first observation of the Bc+→J/ψπ+π0 decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the Bc+→J/ψπ+ channel is measured to beBBc+→J/ψπ+π0BBc+→J/ψπ+=2.80±0.15±0.11±0.16, where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for B+ → J/ψK*+ and Bc+→J/ψπ+ decays, which are used to determine the π0 detection efficiency. The π+π0 mass spectrum is found to be consistent with the dominance of an intermediate ρ+ contribution in accordance with a model based on QCD factorisation

    Fraction of χc Decays in Prompt J/ψ Production Measured in pPb Collisions at √SNN=8.16 TeV

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    The fraction of χc1 and χc2 decays in the prompt J/ψ yield, Fχc→J/ψ=σχc→J/ψ/σJ/ψ, is measured by the LHCb detector in pPb collisions at sNN=8.16 TeV. The study covers the forward (1.5<4.0) and backward (-5.0<-2.5) rapidity regions, where y∗ is the J/ψ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of 13.6±0.3 and 20.8±0.5 nb-1, respectively. The result is presented as a function of the J/ψ transverse momentum pT,J/ψ in the range

    Observation of Exotic J/ψφ Resonant Structure in Diffractive Processes in Proton-Proton Collisions

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    The first study of J/ψφ production in diffractive processes in proton-proton collisions is presented. The study is based on an LHCb dataset recorded at center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5 fb-1. The data disfavor a nonresonant J/ψφ production but are consistent with a resonant model including several resonant states observed previously only in B+→J/ψφK+ decays. The χc0(4500) state is observed with a significance over 6σ and the χc1(4274) is confirmed with a significance of more than 4σ

    Fraction of χc\chi_c decays in prompt J/ψJ/\psi production measured in pPb collisions at sNN=8.16\sqrt{s_{NN}}=8.16 TeV

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    The fraction of χc1\chi_{c1} and χc2\chi_{c2} decays in the prompt J/ψJ/\psi yield, Fχc=σχcJ/ψ/σJ/ψF_{\chi c}=\sigma_{\chi_c \to J/\psi}/\sigma_{J/\psi}, is measured by the LHCb detector in pPb collisions at sNN=8.16\sqrt{s_{NN}}=8.16 TeV. The study covers the forward (1.5<y<4.01.5<y^*<4.0) and backward (5.0<y<2.5-5.0<y^*<-2.5) rapidity regions, where yy^* is the J/ψJ/\psi rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of 13.6 ±\pm 0.3 nb1^{-1} and 20.8 ±\pm 0.5 nb1^{-1}, respectively. The result is presented as a function of the J/ψJ/\psi transverse momentum pT,J/ψp_{T,J/\psi} in the range 1<pT,J/ψ<20<p_{T, J/\psi}<20 GeV/cc. The FχcF_{\chi c} fraction at forward rapidity is compatible with the LHCb measurement performed in pppp collisions at s=7\sqrt{s}=7 TeV, whereas the result at backward rapidity is 2.4 σ\sigma larger than in the forward region for 1<pT,J/ψ<31<p_{T, J/\psi}<3 GeV/cc. The increase of FχcF_{\chi c} at low pT,J/ψp_{T, J/\psi} at backward rapidity is compatible with the suppression of the ψ\psi(2S) contribution to the prompt J/ψJ/\psi yield. The lack of in-medium dissociation of χc\chi_c states observed in this study sets an upper limit of 180 MeV on the free energy available in these pPb collisions to dissociate or inhibit charmonium state formation.Comment: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-028.html (LHCb public pages

    First measurements of the branching fractions of J/ψ → Ξ0Λ¯K0S+c.c., J/ψ →Ξ0Σ¯0K0S+c.c., and J/ψ → Ξ0Σ¯−K++c.c.

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    By analyzing(10087 ± 44)x 106 J/ψ events collected with the BESIII detector at the BEPCII, the decays J/ψ → Ξ0Λ¯K0S+c.c., J/ψ →Ξ0Σ¯0K0S+c.c., J/ψ → Ξ0Σ¯−K++c.c. and are observed for the first time. Their branching fractions are determined to be B(J/ψ → Ξ0Λ¯K0S+c.c.) = (3.76 ± 0.14 ± 0.23)x10-5, B(J/ψ →Ξ0Σ¯0K0S+c.c.) = (2.24 ± 0.32 ± 0.31)x10-5, and B(J/ψ → Ξ0Σ¯−K++c.c.) = (5.64 ± 0.17 ± 0.28)x10-5, where the first uncertainties are statistical and the second systematic.LPHE-L
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