Multidifferential study of identified charged hadron distributions in ZZ-tagged jets in proton-proton collisions at s=\sqrt{s}=13 TeV

Jet fragmentation functions are measured for the first time in proton-proton collisions for charged pions, kaons, and protons within jets recoiling against a $Z$ boson. The charged-hadron distributions are studied longitudinally and transversely to the jet direction for jets with transverse momentum 20 $< p_{\textrm{T}} < 100$ GeV and in the pseudorapidity range $2.5 < \eta < 4$. The data sample was collected with the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.64 fb$^{-1}$. Triple differential distributions as a function of the hadron longitudinal momentum fraction, hadron transverse momentum, and jet transverse momentum are also measured for the first time. This helps constrain transverse-momentum-dependent fragmentation functions. Differences in the shapes and magnitudes of the measured distributions for the different hadron species provide insights into the hadronization process for jets predominantly initiated by light quarks.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-2022-013.html (LHCb public pages

Study of the B−→Λc+Λˉc−K−B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-} decay

The decay $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ is studied in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV using data corresponding to an integrated luminosity of 5 $\mathrm{fb}^{-1}$ collected by the LHCb experiment. In the $\Lambda_{c}^+ K^{-}$ system, the $\Xi_{c}(2930)^{0}$ state observed at the BaBar and Belle experiments is resolved into two narrower states, $\Xi_{c}(2923)^{0}$ and $\Xi_{c}(2939)^{0}$, whose masses and widths are measured to be $$m(\Xi_{c}(2923)^{0}) = 2924.5 \pm 0.4 \pm 1.1 \,\mathrm{MeV}, \\ m(\Xi_{c}(2939)^{0}) = 2938.5 \pm 0.9 \pm 2.3 \,\mathrm{MeV}, \\ \Gamma(\Xi_{c}(2923)^{0}) = \phantom{000}4.8 \pm 0.9 \pm 1.5 \,\mathrm{MeV},\\ \Gamma(\Xi_{c}(2939)^{0}) = \phantom{00}11.0 \pm 1.9 \pm 7.5 \,\mathrm{MeV},$$ where the first uncertainties are statistical and the second systematic. The results are consistent with a previous LHCb measurement using a prompt $\Lambda_{c}^{+} K^{-}$ sample. Evidence of a new $\Xi_{c}(2880)^{0}$ state is found with a local significance of $3.8\,\sigma$, whose mass and width are measured to be $2881.8 \pm 3.1 \pm 8.5\,\mathrm{MeV}$ and $12.4 \pm 5.3 \pm 5.8 \,\mathrm{MeV}$, respectively. In addition, evidence of a new decay mode $\Xi_{c}(2790)^{0} \to \Lambda_{c}^{+} K^{-}$ is found with a significance of $3.7\,\sigma$. The relative branching fraction of $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ with respect to the $B^{-} \to D^{+} D^{-} K^{-}$ decay is measured to be $2.36 \pm 0.11 \pm 0.22 \pm 0.25$, where the first uncertainty is statistical, the second systematic and the third originates from the branching fractions of charm hadron decays.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-028.html (LHCb public pages

Measurement of the ratios of branching fractions R(D∗)\mathcal{R}(D^{*}) and R(D0)\mathcal{R}(D^{0})

The ratios of branching fractions $\mathcal{R}(D^{*})\equiv\mathcal{B}(\bar{B}\to D^{*}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(\bar{B}\to D^{*}\mu^{-}\bar{\nu}_{\mu})$ and $\mathcal{R}(D^{0})\equiv\mathcal{B}(B^{-}\to D^{0}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(B^{-}\to D^{0}\mu^{-}\bar{\nu}_{\mu})$ are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb${ }^{-1}$ of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode $\tau^{-}\to\mu^{-}\nu_{\tau}\bar{\nu}_{\mu}$. The measured values are $\mathcal{R}(D^{*})=0.281\pm0.018\pm0.024$ and $\mathcal{R}(D^{0})=0.441\pm0.060\pm0.066$, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is $\rho=-0.43$. Results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the Standard Model.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb public pages

Testing Lepton Flavor Universality with the B^0 -> K*0 tau+ tau- decay at the LHCb experiment

International audienc

Search for rare B decays with τ in the final state at LHCb and Belle II

International audienc

Recherche de la désintégration rare B0 -> K*0 tau+ tau- avec l'expérience LHCb

A search for the rare B0 -> K*0 tau+ tau- decay is performed using 9/fb of proton-proton collision data collected at the LHCb experiment at CERN. The decay is reconstructed using two final states: the fully hadronic one, in which both tau leptons decay in the tau- -> pi- pi+ pi- (pi0) nu channel, and the mixed hadronic-leptonic, in which one tau decays in the aforementioned channel and the other in the tau- -> mu- nu nu channel. The measure of the branching ratio is performed relatively to that of the normalization mode B0 -> D- (-> pi- K+ pi-) Ds+ (-> K+ K- pi+). The full event selection makes use of Boosted Decision Trees (BDT) based on kinematic and isolation variables in order to reduce the amount of background. A binned maximum likelihood fit on the output of a BDT classifier is performed to extract the number of signal events in the data. The data distribution is still blind, however an expected upper limit in the case where no signal is observed is computed to be 3.2 x 10-4 at 95% CL.Une recherche de la désintégration rare B0 -> K*0 tau+ tau- est effectuée à l'aide de 9/fb de données de collision proton-proton recueillies avec l'expérience LHCb au CERN. La désintégration est reconstruite à l'aide de deux états finaux : l'état entièrement hadronique, dans lequel les deux leptons tau se désintègrent dans le canal tau- -> pi- pi+ pi- (pi0) nu, et l'état mixte hadronique-leptonique, dans lequel un tau se désintègre dans le canal précité et l'autre dans le canal tau- -> mu- nu nu. La mesure du rapport d'embranchement est effectuée relativement à celle du mode de normalisation B0 -> D- (-> pi- K+ pi-) Ds+ (-> K+ K- pi+). La sélection des événements utilise des classificateurs d’analyse multivariée Boosted Decision Tree (BDT) basés sur des variables cinématiques et d'isolement afin de réduire la quantité de bruit de fond. Un ajustement sur un dernier BDT est effectué afin d’extraire le nombre d’évènements de signal dans les données. La distribution des données est encore masquée, mais une limite supérieure attendue dans le cas où aucun signal n'est observé est calculée comme étant de 3,2 x 10-4 à 95 % CL

Recent Belle II results on radiative and electroweak penguin decays

International audienceRadiative and electroweak penguin decays are excellent probes for new physics, since they are forbidden at tree level in the Standard Model, and hence any deviation from their predicted branching fractions would be a clear sign of physics processes not accounted for by the theory. In this paper, recent results on radiative and electroweak penguin decays at the Belle II experiment are reported. The results are obtained with a dataset corresponding to an integrated luminosity of $189 \text{ fb}^{−1}$, and include measurements of $B \to X_s \gamma$, $B \to J/\psi(l^+l^-)K$ and $B \to K^*l^+l^-$ decays