1,103 research outputs found

    Observation of an Excited Bc+ State

    Get PDF
    Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc∗(2S31)+ state reconstructed without the low-energy photon from the Bc∗(1S31)+→Bc+γ decay following Bc∗(2S31)+→Bc∗(1S31)+π+π-. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date

    Observation of the Decay Λ0b→Λ+cτ−¯ν

    Get PDF
    The first observation of the semileptonic b-baryon decay Λb0→Λc+τ-ν¯τ, with a significance of 6.1σ, is reported using a data sample corresponding to 3 fb-1 of integrated luminosity, collected by the LHCb experiment at center-of-mass energies of 7 and 8 TeV at the LHC. The τ- lepton is reconstructed in the hadronic decay to three charged pions. The ratio K=B(Λb0→Λc+τ-ν¯τ)/B(Λb0→Λc+π-π+π-) is measured to be 2.46±0.27±0.40, where the first uncertainty is statistical and the second systematic. The branching fraction B(Λb0→Λc+τ-ν¯τ)=(1.50±0.16±0.25±0.23)% is obtained, where the third uncertainty is from the external branching fraction of the normalization channel Λb0→Λc+π-π+π-. The ratio of semileptonic branching fractions R(Λc+)B(Λb0→Λc+τ-ν¯τ)/B(Λb0→Λc+μ-ν¯μ) is derived to be 0.242±0.026±0.040±0.059, where the external branching fraction uncertainty from the channel Λb0→Λc+μ-ν¯μ contributes to the last term. This result is in agreement with the standard model prediction

    Measurement of the photon polarization in ΛbΛγ\Lambda_b \to \Lambda \gamma decays

    Get PDF
    The photon polarization in bsγb \to s \gamma transitions is measured for the first time in radiative b-baryon decays exploiting the unique spin structure of ΛbΛγ\Lambda_b \to \Lambda \gamma decays. A data sample corresponding to an integrated luminosity of 6  fb16\;fb^{-1} collected by the LHCb experiment in pppp collisions at a center-of-mass energy of 13  TeV13\;TeV is used. The photon polarization is measured to be αγ=0.820.260.13+0.17+0.04\alpha_{\gamma}= 0.82^{\,+\,0.17\,+\,0.04}_{\,-\,0.26\,-\,0.13}, where the first uncertainty is statistical and the second systematic. This result is in agreement with the Standard Model prediction and previous measurements in b-meson decays. Charge-parity breaking effects are studied for the first time in this observable and found to be consistent with CPCP symmetry.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-2021-030.html (LHCb public pages

    Searches for rare Bs0 and B 0 decays into four muons

    Get PDF
    Searches for rare Bs0 and B0 decays into four muons are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. Direct decays and decays via light scalar and J/ψ resonances are considered. No evidence for the six decays searched for is found and upper limits at the 95% confidence level on their branching fractions ranging between 1.8 × 10−10 and 2.6 × 10−9 are set. [Figure not available: see fulltext.

    Search for CP\textit{CP} violation in the phase space of D0KS0K±πD^{0} \rightarrow K_{S}^{0} K^{\pm} \pi^{\mp} decays with the energy test

    Get PDF
    A search for CP\textit{CP} violation in D0KS0K+πD^{0} \rightarrow K_{S}^{0} K^{+} \pi^{-} and D0KS0Kπ+D^{0} \rightarrow K_{S}^{0} K^{-} \pi^{+} decays is reported. The search is performed using an unbinned model-independent method known as the energy test that probes local CP\textit{CP} violation in the phase space of the decays. The data analysed correspond to an integrated luminosity of 5.4 5.4~fb1^{-1} collected in proton-proton collisions by the LHCb experiment at a centre-of-mass energy of s=13\sqrt{s}=13~TeV, amounting to approximately 950000 and 620000 signal candidates for the D0KS0Kπ+D^{0} \rightarrow K_{S}^{0} K^{-} \pi^{+} and D0KS0K+πD^{0} \rightarrow K_{S}^{0} K^{+} \pi^{-} modes, respectively. The method is validated using D0Kπ+ππ+D^{0} \rightarrow K^{-} \pi^{+} \pi^{-} \pi^{+} and D0KS0π+πD^{0} \rightarrow K_{S}^{0} \pi^{+} \pi^{-} decays, where CP\textit{CP}-violating effects are expected to be negligible, and using background-enhanced regions of the signal decays. The results are consistent with CP\textit{CP} symmetry in both the D0KS0Kπ+D^{0} \rightarrow K_{S}^{0} K^{-} \pi^{+} and the D0KS0K+πD^{0} \rightarrow K_{S}^{0} K^{+} \pi^{-} decays, with pp-values for the hypothesis of no CP\textit{CP} violation of 70% and 66%, respectively.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-019.html (LHCb public pages

    Studies of η\eta and η\eta' production in pppp and ppPb collisions

    Full text link
    The production of η\eta and η\eta' mesons is studied in proton-proton and proton-lead collisions collected with the LHCb detector. Proton-proton collisions are studied at center-of-mass energies of 5.025.02 and 13 TeV13~{\rm TeV}, and proton-lead collisions are studied at a center-of-mass energy per nucleon of 8.16 TeV8.16~{\rm TeV}. The studies are performed in center-of-mass rapidity regions 2.5<yc.m.<3.52.5<y_{\rm c.m.}<3.5 (forward rapidity) and 4.0<yc.m.<3.0-4.0<y_{\rm c.m.}<-3.0 (backward rapidity) defined relative to the proton beam direction. The η\eta and η\eta' production cross sections are measured differentially as a function of transverse momentum for 1.5<pT<10 GeV1.5<p_{\rm T}<10~{\rm GeV} and 3<pT<10 GeV3<p_{\rm T}<10~{\rm GeV}, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for η\eta and η\eta' mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of η\eta mesons are also used to calculate η/π0\eta/\pi^0 cross section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass-dependent nuclear effects in heavy-ion collisions, as well as η\eta and η\eta' meson fragmentation.Comment: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/Publications/p/LHCb-PAPER-2023-030.html (LHCb public pages

    Amplitude analysis of the Λb0→pK−γ decay

    Get PDF
    The resonant structure of the radiative decay Λb0→pK−γ in the region of proton-kaon invariant-mass up to 2.5 GeV/c2 is studied using proton-proton collision data recorded at centre-of-mass energies of 7, 8, and 13 TeV collected with the LHCb detector, corresponding to a total integrated luminosity of 9 fb−1. Results are given in terms of fit and interference fractions between the different components contributing to this final state. Only Λ resonances decaying to pK− are found to be relevant, where the largest contributions stem from the Λ(1520), Λ(1600), Λ(1800), and Λ(1890) states

    Observation of strangeness enhancement with charmed mesons in high-multiplicity pPbp\mathrm{Pb} collisions at sNN=8.16\sqrt {s_{\mathrm{NN}}}=8.16\,TeV

    Full text link
    The production of prompt Ds+D^+_{s} and D+D^+ mesons is measured by the LHCb experiment in proton-lead (pPbp\mathrm{Pb}) collisions in both 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 at a nucleon-nucleon center-of-mass energy of sNN=8.16\sqrt {s_{\mathrm{NN}}}=8.16\,TeV. The nuclear modification factors of both Ds+D^+_{s} and D+D^+ mesons are determined as a function of transverse momentum, pTp_{\mathrm{T}}, and rapidity. In addition, the Ds+D^+_{s} to D+D^+ cross-section ratio is measured as a function of the charged particle multiplicity in the event. An enhanced Ds+D^+_{s} to D+D^+ production in high-multiplicity events is observed for the whole measured pTp_{\mathrm{T}} range, in particular at low pTp_{\mathrm{T}} and backward rapidity, where the significance exceeds six standard deviations. This constitutes the first observation of strangeness enhancement in charm quark hadronization in high-multiplicity pPbp\mathrm{Pb} collisions. The results are also qualitatively consistent with the presence of quark coalescence as an additional charm quark hadronization mechanism in high-multiplicity proton-lead collisions.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-2023-021.html (LHCb public pages

    Observation of Two New Excited Ξb0 States Decaying to Λb0 K-π+

    Get PDF
    Two narrow resonant states are observed in the Λb0K-π+ mass spectrum using a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 6 fb-1. The minimal quark content of the Λb0K-π+ system indicates that these are excited Ξb0 baryons. The masses of the Ξb(6327)0 and Ξb(6333)0 states are m[Ξb(6327)0]=6327.28-0.21+0.23±0.12±0.24 and m[Ξb(6333)0]=6332.69-0.18+0.17±0.03±0.22 MeV, respectively, with a mass splitting of Δm=5.41-0.27+0.26±0.12 MeV, where the uncertainties are statistical, systematic, and due to the Λb0 mass measurement. The measured natural widths of these states are consistent with zero, with upper limits of Γ[Ξb(6327)0]&lt;2.20(2.56) and Γ[Ξb(6333)0]&lt;1.60(1.92) MeV at a 90% (95%) credibility level. The significance of the two-peak hypothesis is larger than nine (five) Gaussian standard deviations compared to the no-peak (one-peak) hypothesis. The masses, widths, and resonant structure of the new states are in good agreement with the expectations for a doublet of 1D Ξb0 resonances
    corecore