Measurement of fs/fuf_s / f_u Variation with Proton-Proton Collision Energy and BB-Meson Kinematics

International audienceThe ratio of the Bs0 and B+ fragmentation fractions fs and fu is studied with Bs0→J/ψϕ and B+→J/ψK+ decays using data collected by the LHCb experiment in proton-proton collisions at 7, 8, and 13 TeV center-of-mass energies. The analysis is performed in bins of B-meson momentum, longitudinal momentum, transverse momentum, pseudorapidity, and rapidity. The fragmentation-fraction ratio fs/fu is observed to depend on the B-meson transverse momentum with a significance of 6.0σ. This dependency is driven by the 13 TeV sample (8.7σ), while the results for the other collision energies are not significant when considered separately. Furthermore, the results show a 4.8σ evidence for an increase of fs/fu as a function of collision energy

Measurement of the branching fraction of the decay Bs0→KS0KS0B_s^0\to K_S^0 K_S^0

International audienceA measurement of the branching fraction of the decay Bs0→KS0KS0 is performed using proton–proton collision data corresponding to an integrated luminosity of 5  fb-1 collected by the LHCb experiment between 2011 and 2016. The branching fraction is determined to be B(Bs0→KS0KS0)=[8.3±1.6(stat)±0.9(syst)±0.8(norm)±0.3(fs/fd)]×10-6, where the first uncertainty is statistical, the second is systematic, and the third and fourth are due to uncertainties on the branching fraction of the normalization mode B0→ϕKS0 and the ratio of hadronization fractions fs/fd. This is the most precise measurement of this branching fraction to date. Furthermore, a measurement of the branching fraction of the decay B0→KS0KS0 is performed relative to that of the Bs0→KS0KS0 channel, and is found to be B(B0→KS0KS0)B(Bs0→KS0KS0)=[7.5±3.1(stat)±0.5(syst)±0.3(fs/fd)]×10-2

Test of lepton universality with Λb0→pK−ℓ+ℓ− {\Lambda}_b^0\to {pK}^{-}{\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-} decays

International audienceThe ratio of branching fractions of the decays ${\Lambda}_b^0$ → pK$^{−}$e$^{+}$e$^{−}$ and ${\Lambda}_b^0$ → pK$^{−}$μ$^{+}$μ$^{−}$,${R}_{pK}^{-1}$, is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4.7 fb$^{−1}$ recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range 0.1 < q$^{2}$< 6.0 GeV$^{2}$/c$^{4}$ and the pK$^{−}$ mass range m(pK$^{−}$) < 2600 MeV/c$^{2}$, the ratio of branching fractions is measured to be ${R}_{pK}^{-1}={1.17}_{-0.16}^{+0.18}\pm 0.07$, where the first uncertainty is statistical and the second systematic. This is the first test of lepton universality with b baryons and the first observation of the decay ${\Lambda}_b^0$ → pK$^{−}$e$^{+}$e$^{−}$.[graphic not available: see fulltext

Precision measurement of the Ξcc++\Xi_{cc}^{++} mass

International audienceA measurement of the ${\varXi}_{cc}^{++}$ mass is performed using data collected by the LHCb experiment between 2016 and 2018 in pp collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.6 fb$^{−1}$. The ${\varXi}_{cc}^{++}$ candidates are reconstructed via the decay modes ${\varXi}_{cc}^{++}\to {\varLambda}_c^{+}{K}^{-}{\pi}^{+}{\pi}^{+}$ and ${\varXi}_{cc}^{++}\to {\varXi}_c^{+}{\pi}^{+}$. The result, 3621.55 ± 0.23 (stat) ± 0.30 (syst) MeV/c$^{2}$, is the most precise measurement of the ${\varXi}_{cc}^{++}$ mass to date.[graphic not available: see fulltext

Measurement of the Λb0→J/ψΛ\Lambda^0_b\rightarrow J/\psi\Lambda angular distribution and the Λb0\Lambda^0_b polarisation in pppp collisions

International audienceThis paper presents an analysis of the ${\Lambda}_b^0$→ J/ψΛ angular distribution and the transverse production polarisation of ${\Lambda}_b^0$ baryons in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The measurements are performed using data corresponding to an integrated luminosity of 4.9 fb$^{−1}$, collected with the LHCb experiment. The polarisation is determined in a fiducial region of ${\Lambda}_b^0$ transverse momentum and pseudorapidity of 1 < p$_{T}$< 20 GeV/c and 2 < η < 5, respectively. The data are consistent with ${\Lambda}_b^0$ baryons being produced unpolarised in this region. The parity-violating asymmetry parameter of the Λ → pπ$^{−}$ decay is also determined from the data and its value is found to be consistent with a recent measurement by the BES III collaboration.[graphic not available: see fulltext

Search for the doubly charmed baryon Ξcc+\Xi_{cc}^+

International audienceA search for the doubly charmed baryon $\Xi_{cc}^+$ is performed through its decay to the $\Lambda_c^ + {K^ -}{\pi ^ +}$ final state, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV. The data correspond to a total integrated luminosity of 9 fb$^{−1}$. No significant signal is observed in the mass range from 3.4 to 3.8 GeV/c$^{2}$. Upper limits are set at 95% credibility level on the ratio of the $\Xi_{cc}^+$ production cross-section times the branching fraction to that of $\Lambda_c^ +$ and $\Xi_{cc}^{+ +}$ baryons. The limits are determined as functions of the $\Xi_{cc}^+$ mass for different lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15 GeV/c

Constraints on the KS0→μ+μ−K^0_S \rightarrow \mu^+ \mu^- Branching Fraction

International audienceA search for the decay KS0→μ+μ- is performed using proton-proton collision data, corresponding to an integrated luminosity of 5.6  fb-1 and collected with the LHCb experiment during 2016, 2017, and 2018 at a center-of-mass energy of 13 TeV. The observed signal yield is consistent with zero, yielding an upper limit of B(KS0→μ+μ-)<2.2×10-10 at 90% C.L.. The limit reduces to B(KS0→μ+μ-)<2.1×10-10 at 90% C.L. once combined with the result from data taken in 2011 and 2012

Precision measurement of the Bc+B_{c}^{+} meson mass

International audienceA precision measurement of the ${B}_c^{+}$ meson mass is performed using proton- proton collision data collected with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 9.0 fb$^{−1}$. The ${B}_c^{+}$ mesons are reconstructed via the decays ${B}_c^{+}$→ J/ψπ$^{+}$, ${B}_c^{+}$→ J/ψπ$^{+}$π$^{−}$π$^{+}$, ${B}_c^{+}\to J/\psi p\overline{p}{\pi}^{+}$, ${B}_c^{+}\to J/\psi {D}_s^{+}$, ${B}_c^{+}$→ J/ψ D$^{0}$K$^{+}$ and ${B}_c^{+}\to {B}_s^0{\pi}^{+}$. Combining the results of the individual decay channels, the ${B}_c^{+}$ mass is measured to be 6274.47 ± 0.27 (stat) ± 0.17 (syst) MeV/c$^{2}$. This is the most precise measurement of the ${B}_c^{+}$ mass to date. The difference between the ${B}_c^{+}$ and ${B}_s^0$ meson masses is measured to be 907.75 ± 0.37 (stat) ± 0.27 (syst) MeV/c.[graphic not available: see fulltext

Search for the lepton flavour violating decay B+→K+μ−τ+B^+ \rightarrow K^+ \mu^- \tau^+ using Bs2∗0B_{s2}^{*0} decays

International audienceA search is presented for the lepton flavour violating decay B$^{+}$ → K$^{+}$μ$^{−}$τ$^{+}$ using a sample of proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9 fb$^{−1}$. The τ leptons are selected inclusively, primarily via decays with a single charged particle. The four-momentum of the τ lepton is determined by using B$^{+}$ mesons from ${B}_{s2}^{\ast 0}\to {B}^{+}{K}^{-}$ decays. No significant excess is observed, and an upper limit is set on the branching fractionℬ(B$^{+}$ → K$^{+}$μ$^{−}$τ$^{+}$) < 3.9 × 10$^{−5}$ at 90 %  confidence level.The obtained limit is comparable to the world-best limit.[graphic not available: see fulltext