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 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 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 A study of B c + → χ c π + $$ {B}_c^{+}\to {\chi}_c{\pi}^{+} $$ decays is reported using proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8, ...and 13 TeV, corresponding to an integrated luminosity of 9 fb −1. The decay B c + → χ c 2 π + $$ {B}_c^{+}\to {\chi}_{c2}{\pi}^{+} $$ is observed for the first time, with a significance exceeding seven standard deviations. The relative branching fraction with respect to the B c + → J / ψ π + $$ {B}_c^{+}\to J/\psi {\pi}^{+} $$ decay is measured to be B B c + → χ c 2 π + B B c + → J / ψ π + = 0.37 ± 0.06 ± 0.02 ± 0.01 , $$ \frac{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c2}{\pi}^{+}}}{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}}}=0.37\pm 0.06\pm 0.02\pm 0.01, $$ where the first uncertainty is statistical, the second is systematic, and the third is due to the knowledge of the χ c2 → J/ψγ branching fraction. No significant B c + → χ c 1 π + $$ {B}_c^{+}\to {\chi}_{c1}{\pi}^{+} $$ signal is observed and an upper limit for the relative branching fraction for the B c + → χ c 1 π + $$ {B}_c^{+}\to {\chi}_{c1}{\pi}^{+} $$ and B c + → χ c 2 π + $$ {B}_c^{+}\to {\chi}_{c2}{\pi}^{+} $$ decays of B B c + → χ c 1 π + B B c + → χ c 2 π + = < 0.49 $$ \frac{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c1}{\pi}^{+}}}{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c2}{\pi}^{+}}}=<0.49 $$ is set at the 90% confidence level.
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 A measurement of CP-violating observables in B ± → D * K ± and B ± → D *π± decays is made where the photon or neutral pion from the D * → Dγ or D * → Dπ0 decay is not reconstructed. The D ...meson is reconstructed in the self-conjugate decay modes, D → K S 0 $$ {K}_S^0 $$ π+π− or D → K S 0 $$ {K}_S^0 $$ K + K −. The distribution of signal yields in the D decay phase space is analysed in a model-independent way. The measurement uses a data sample collected in proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of approximately 9 fb −1. The B ± → D * K ± and B ± → D *π± CP-violating observables are interpreted in terms of hadronic parameters and the CKM angle γ, resulting in a measurement of γ = ( 92 − 17 + 21 $$ {92}_{-17}^{+21} $$ ) ° . The total uncertainty includes the statistical and systematic uncertainties, and the uncertainty due to external strong-phase inputs.
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 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.
Abstract This paper reports the observation of the decays B s 0 $$ {B}_{(s)}^0 $$ → D s1(2536)∓ K ± using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated ...luminosity of 9 fb −1. The branching fractions of these decays are measured relative to the normalisation channel B 0 → D ¯ $$ \overline{D} $$ 0 K + K − . The D s1(2536) − meson is reconstructed in the D ¯ $$ \overline{D} $$ *(2007)0 K − decay channel and the products of branching fractions are measured to be B B s 0 → D s 1 2536 ∓ K ± × B D s 1 2536 − → D ¯ ∗ 2007 0 K − = 2.49 ± 0.11 ± 0.12 ± 0.25 ± 0.06 × 10 − 5 , B B 0 → D s 1 2536 ∓ K ± × B D s 1 2536 − → D ¯ ∗ 2007 0 K − = 0.510 ± 0.021 ± 0.036 ± 0.050 × 10 − 5 . $$ {\displaystyle \begin{array}{c}\mathcal{B}\left({B}_s^0\to {D}_{s1}{(2536)}^{\mp }{K}^{\pm}\right)\times \mathcal{B}\left({D}_{s1}{(2536)}^{-}\to {\overline{D}}^{\ast }{(2007)}^0{K}^{-}\right)\\ {}=\left(2.49\pm 0.11\pm 0.12\pm 0.25\pm 0.06\right)\times {10}^{-5},\\ {}\mathcal{B}\left({B}^0\to {D}_{s1}{(2536)}^{\mp }{K}^{\pm}\right)\times \mathcal{B}\left({D}_{s1}{(2536)}^{-}\to {\overline{D}}^{\ast }{(2007)}^0{K}^{-}\right)\\ {}=\left(0.510\pm 0.021\pm 0.036\pm 0.050\right)\times {10}^{-5}.\end{array}} $$ The first uncertainty is statistical, the second systematic, and the third arises from the uncertainty of the branching fraction of the B 0 → D ¯ $$ \overline{D} $$ 0 K + K − normalisation channel. The last uncertainty in the B s 0 $$ {B}_s^0 $$ result is due to the limited knowledge of the fragmentation fraction ratio, f s /f d . The significance for the B s 0 $$ {B}_s^0 $$ and B 0 signals is larger than 10 σ. The ratio of the helicity amplitudes which governs the angular distribution of the D s1(2536) − → D ¯ $$ \overline{D} $$ *(2007)0 K − decay is determined from the data. The ratio of the S- and D-wave amplitudes is found to be 1.11 ± 0.15 ± 0.06 and the phase difference between them 0.70 ± 0.09 ± 0.04 rad, where the first uncertainty is statistical and the second systematic.
