Abstract The ratio of production cross-sections of ψ(2S) over J/ψ mesons as a function of charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy s $$ \sqrt{s} $$ = 13 ...TeV is measured with a data sample collected by the LHCb detector, corresponding to an integrated luminosity of 658 pb −1. The ratio is measured for both prompt and non-prompt ψ(2S) and J/ψ mesons. When there is an overlap between the rapidity ranges over which multiplicity and charmonia production are measured, a multiplicity-dependent modification of the ratio is observed for prompt mesons. No significant multiplicity dependence is found when the ranges do not overlap. For non-prompt production, the ψ(2S)-to-J/ψ production ratio is roughly independent of multiplicity, irrespective of the rapidity range over which the multiplicity is measured. The results are compared to predictions of the co-mover model and agree well except in the low multiplicity region. The ratio of production cross-sections of ψ(2S) over J/ψ mesons are cross-checked with other measurements in di-lepton channels and found to be compatible.
Abstract Measurements of the branching fraction ratio B ϕ → μ + μ − / B ϕ → e + e − $$ \mathcal{B}\left(\phi \to {\mu}^{+}{\mu}^{-}\right)/\mathcal{B}\left(\phi \to {e}^{+}{e}^{-}\right) $$ with D s ...+ → π + ϕ $$ {D}_s^{+}\to {\pi}^{+}\phi $$ and D + → π + ϕ decays, denoted R ϕπ s $$ {R}_{\phi \pi}^s $$ and R ϕπ d $$ {R}_{\phi \pi}^d $$ , are presented. The analysis is performed using a dataset corresponding to an integrated luminosity of 5.4 fb −1 of pp collision data collected with the LHCb experiment. The branching fractions are normalised with respect to the B + → K + J/ψ(→ e + e − ) and B + → K + J/ψ(→ μ + μ − ) decay modes. The combination of the results yields R ϕπ = 1.022 ± 0.012 stat ± 0.048 syst . $$ {R}_{\phi \pi}=1.022\pm 0.012\left(\textrm{stat}\right)\pm 0.048\left(\textrm{syst}\right). $$ The result is compatible with previous measurements of the ϕ → ℓ + ℓ − branching fractions and predictions based on the Standard Model.
Abstract A measurement of CP-violating observables associated with the interference of B 0 → D 0 K ⋆(892)0 and B 0 → D ¯ 0 K ⋆ 892 0 $$ {B}^0\to {\overline{D}}^0{K}^{\star }{(892)}^0 $$ decay ...amplitudes is performed in the D 0 → K ∓ π ± (π + π − ), D 0 → π + π − (π + π − ), and D 0 → K + K − final states using data collected by the LHCb experiment corresponding to an integrated luminosity of 9 fb −1. CP-violating observables related to the interference of B s 0 → D 0 K ¯ ⋆ 892 0 $$ {B}_s^0\to {D}^0{\overline{K}}^{\star }{(892)}^0 $$ and B s 0 → D ¯ 0 K ¯ ⋆ 892 0 $$ {B}_s^0\to {\overline{D}}^0{\overline{K}}^{\star }{(892)}^0 $$ are also measured, but no evidence for interference is found. The B 0 observables are used to constrain the parameter space of the CKM angle γ and the hadronic parameters r B 0 DK ⋆ $$ {r}_{B^0}^{DK\star } $$ and δ B 0 DK ⋆ $$ {\delta}_{B^0}^{DK\star } $$ with inputs from other measurements. In a combined analysis, these measurements allow for four solutions in the parameter space, only one of which is consistent with the world average.
Abstract The ratio of branching fractions between B 0 → J/ψπ 0 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 B B 0 → J / ψ π 0 B B + → J / ψ K ∗ + = 1.153 ± 0.053 ± 0.048 × 10 − 2 , $$ \frac{{\mathcal{B}}_{B^0\to J/\psi {\pi}^0}}{{\mathcal{B}}_{B^{+}\to J/\psi {K}^{\ast +}}}=\left(1.153\pm 0.053\pm 0.048\right)\times {10}^{-2}, $$ where the first uncertainty is statistical and the second is systematic. The branching fraction for B 0 → J/ψπ 0 decays is determined using the branching fraction of the normalisation channel, resulting in B B 0 → J / ψ π 0 = 1.670 ± 0.077 ± 0.069 ± 0.095 × 10 − 5 , $$ {\mathcal{B}}_{B^0\to J/\psi {\pi}^0}=\left(1.670\pm 0.077\pm 0.069\pm 0.095\right)\times {10}^{-5}, $$ 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.
Abstract The first observation of the B c + → J / ψ π + π 0 $$ {B}_c^{+}\to J/\psi {\pi}^{+}{\pi}^0 $$ 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 B c + → J / ψ π + $$ {B}_c^{+}\to J/\psi {\pi}^{+} $$ channel is measured to be B B c + → J / ψ π + π 0 B B c + → J / ψ π + = 2.80 ± 0.15 ± 0.11 ± 0.16 , $$ \frac{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}{\pi}^0}}{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}}}=2.80\pm 0.15\pm 0.11\pm 0.16, $$ 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 B c + → J / ψ π + $$ {B}_c^{+}\to J/\psi {\pi}^{+} $$ decays, which are used to determine the π 0 detection efficiency. The π + π 0 mass spectrum is found to be consistent with the dominance of an intermediate ρ + contribution in accordance with a model based on QCD factorisation.
Abstract The production of ψ(2S) mesons in proton-lead collisions at a centre-of-mass energy per nucleon pair of s NN $$ \sqrt{s_{\textrm{NN}}} $$ = 8.16 TeV is studied with the LHCb detector using ...data corresponding to an integrated luminosity of 34 nb −1. The prompt and nonprompt ψ(2S) production cross-sections and the ratio of the ψ(2S) to J/ψ cross-section are measured as a function of the meson transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame, together with forward-to-backward ratios and nuclear modification factors. The production of prompt ψ(2S) is observed to be more suppressed compared to pp collisions than the prompt J/ψ production, while the nonprompt productions have similar suppression factors.
Abstract A search for CP violation in D 0 → K S 0 K + π − $$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ and D 0 → K S 0 K − π + $$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ decays is reported. The search is ...performed using an unbinned model-independent method known as the energy test that probes local CP violation in the phase space of the decays. The data analysed correspond to an integrated luminosity of 5.4 fb −1 collected in proton-proton collisions by the LHCb experiment at a centre-of-mass energy of s $$ \sqrt{s} $$ = 13 TeV, amounting to approximately 950 thousand and 620 thousand signal candidates for the D 0 → K S 0 K − π + $$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ and D 0 → K S 0 K + π − $$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ modes, respectively. The method is validated using D 0 → K − π + π − π + and D 0 → K S 0 π + π − $$ {D}^0\to {K}_S^0{\pi}^{+}{\pi}^{-} $$ decays, where CP-violating effects are expected to be negligible, and using background-enhanced regions of the signal decays. The results are consistent with CP symmetry in both the D 0 → K S 0 K − π + $$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ and the D 0 → K S 0 K + π − $$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ decays, with p-values for the hypothesis of no CP violation of 70% and 66%, respectively.
Abstract The first measurement of the Z boson production cross-section at centre-of-mass energy s $$ \sqrt{s} $$ = 5.02 TeV in the forward region is reported, using pp collision data collected by the ...LHCb experiment in year 2017, corresponding to an integrated luminosity of 100 ± 2 pb −1. The production cross-section is measured for final-state muons in the pseudorapidity range 2.0 < η < 4.5 with transverse momentum p T > 20 GeV/c. The integrated cross-section is determined to be σ Z → μ + μ − = 39.6 ± 0.7 stat ± 0.6 syst ± 0.8 lumi pb $$ {\sigma}_{Z\to \mu +\mu -}=39.6\pm 0.7\left(\textrm{stat}\right)\pm 0.6\left(\textrm{syst}\right)\pm 0.8\left(\textrm{lumi}\right)\textrm{pb} $$ for the di-muon invariant mass in the range 60 < M μμ < 120 GeV/c 2. This result and the differential cross-section results are in good agreement with theoretical predictions at next-to-next-to-leading order in the strong coupling constant. Based on a previous LHCb measurement of the Z boson production cross-section in pPb collisions at s NN $$ \sqrt{s_{NN}} $$ = 5.02 TeV, the nuclear modification factor R pPb is measured for the first time at this energy. The measured values are 1.2 − 0.3 + 0.5 $$ {1.2}_{-0.3}^{+0.5} $$ (stat) ± 0.1(syst) in the forward region (1.53 < y μ ∗ $$ {y}_{\mu}^{\ast } $$ < 4.03) and 3.6 − 0.9 + 1.6 $$ {3.6}_{-0.9}^{+1.6} $$ (stat) ± 0.2(syst) in the backward region (−4.97 < y μ ∗ $$ {y}_{\mu}^{\ast } $$ < −2.47), where y μ ∗ $$ {y}_{\mu}^{\ast } $$ represents the muon rapidity in the centre-of-mass frame.
Abstract The production cross-section of J/ψ pairs in proton-proton collisions at a centre-of-mass energy of s $$ \sqrt{s} $$ = 13 TeV 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 with both J/ψ mesons in the transverse momentum range 0 < p T < 14 GeV/c and rapidity range 2.0 < y < 4.5. The cross-section of this process is measured to be 16.36 ± 0.28 (stat) ± 0.88 (syst) nb. The contributions from single-parton scattering and double-parton scattering are separated based on the dependence of the cross-section on the absolute rapidity difference ∆y between the two J/ψ mesons. The effective cross-section of double-parton scattering is measured to be σ eff = 13.1 ± 1.8 (stat) ± 2.3 (syst) mb. The distribution of the azimuthal angle ϕ CS of one of the J/ψ mesons in the Collins-Soper frame and the p T-spectrum of the J/ψ pairs are also measured for the study of the gluon transverse-momentum dependent distributions inside protons. The extracted values of ⟨cos 2ϕ CS⟩ and ⟨cos 4ϕ CS⟩ are consistent with zero, but the presence of azimuthal asymmetry at a few percent level is allowed.
Abstract The production of prompt D + and D s + $$ {D}_s^{+} $$ mesons is studied in proton-lead collisions at a centre-of-mass energy of s NN $$ \sqrt{s_{NN}} $$ = 5.02 TeV. The data sample ...corresponding to an integrated luminosity of (1.58 ± 0.02)nb −1 is collected by the LHCb experiment at the LHC. The differential production cross-sections are measured using D + and D s + $$ {D}_s^{+} $$ candidates with transverse momentum in the range of 0 < p T < 14 GeV/c and rapidities in the ranges of 1.5 < y ∗ < 4.0 and –5.0 < y ∗ < –2.5 in the nucleon-nucleon centre-of-mass system. For both particles, the nuclear modification factor and the forward-backward production ratio are determined. These results are compared with theoretical models that include initial-state nuclear effects. In addition, measurements of the cross-section ratios between D +, D s + $$ {D}_s^{+} $$ and D 0 mesons are presented, providing a baseline for studying the charm hadronization in lead-lead collisions at LHC energies.
