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

Search for the lepton-flavour-violating decays B+→K+e±μ∓B^+ \rightarrow K^+ e^{\pm}\mu^{\mp}

The lepton flavour quantum number is conserved in all processes of the Standard Model of particle physics, and tests of this prediction form an important part of todays particle physics. A large number of models that describe physics beyond the Standard Model include lepton flavour violating processes. One of these is the decay $B^+ \to K^+e^\pm\mu^\mp$, which some models predicted up top a measurable magnitude of $10^{-8}$. This poster presents the current status of the search for the lepton flavour violating decay $B^+ \to K^+e^\pm\mu^\mp$ with the LHCb Run 1 data corresponding to 3 fb$^{−1}$. The sensitivity of the measurement is expected to enter the interesting territory

Precision measurements of () with the LHCb experiment

High-precision measurements of observables of the Standard Model of particle physics, like the CKM matrix parameters, are key to answering the open questions of particle physics. The most precise CKM angle sin(2β) can be optimally determined by a decay-time dependent measurement of CP violation in B→ψKS0 decays. In this thesis data from B→J/ψ(→μμ)KS0, B→ψ(2S)(→μμ)KS0 and B→J/ψ(→ee)KS0 decays is analysed with KS0→π+π- collected at a centre-of-mass energy of √s = 13TeV with pp collisions by the LHCb experiment between 2015 and 2018. The data corresponds to an integrated luminosity of 6/fb and results in the combination of all three decays for the CP violation parameters in S(ψKS0) = 0.717 +/- 0.013 (stat.) +/- 0.008 (syst.), C(ψKS0) = 0.008 +/- 0.012 (stat.) +/- 0.003 (syst.), where S corresponds to sin(2β). This is consistent with the Standard Model predictions and with previous measurements. Furthermore, this is the most precise single measurement and more precise than the current world average.Hochpräzessionsmessungen von Observablen des Standardmodells der Teilchenphysik, wie die Parameter der CKM-Matrix, sind entscheidend, um offene Fragen der Teilchenphysik zu beantworten. Der am genauesten gemessene CKM Winkel sin(2β) kann optimal gemessen werden mit Zerfallszeit-abhängigen CP-verletzenden Messungen in B→ψKS0 Zerfällen. In dieser Arbeit wurden Daten von B→J/ψ(→μμ)KS0, B→ψ(2S)(→μμ)KS0 und B→J/ψ(→ee)KS0 Zerfällen mit KS0→π+π- analysiert. Diese wurden aufgenommen bei einer Schwerpunktsenergie von √s = 13TeV mit pp Kollisionen am LHCb-Experiment zwischen 2015 und 2018. Die Daten entsprechen einer integrierten Luminosität von 6/fb und resultieren in der Kombination von allen drei Zerfällen für die CP-verletzenden Parameter in S(ψKS0) = 0.717 +/- 0.013 (stat.) +/- 0.008 (syst.), C(ψKS0) = 0.008 +/- 0.012 (stat.) +/- 0.003 (syst.), wobei S sin(2β) entspricht. Das ist konsistent mit den Vorhersagen des Standardmodells und vorherigen Messungen. Die Messung erreicht die größte Genauigkeit einer Einzelmessung und ist genauer als der Weltmittelwert