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

Development of microlens-enhanced SiPMs for a radiation-hard scintillating fibre tracker at LHCb

The LHCb experiment at CERN’s Large Hadron Collider (LHC) is currently taking data with a newly developed Scintillating Fibre (SciFi) Tracker read out with multichannel silicon pho- tomultipliers (SiPMs). The innermost fibre modules, exposed to the highest radiation, will need to be exchanged at the end of the current run, as part of Upgrade Ib (2026–2028). For this consolidation work and in view of Upgrade II (2032–2034) this thesis work focusses on the development of microlens-enhanced SiPMs with increased photon detection efficiency (PDE). A simulation study comparing the expected increase in light detection between SiPMs without and with microlenses has been conducted to guide possible implementations, and has been validated by a simulation based on a commercial software. Microlenses have been deposited on available, non-customised SiPMs. The light yield of a short fibre mat has been measured and the results of different SiPM surfaces compared. For microlens-enhanced SiPMs with a fill factor of 50.0%, an improvement of 32% at a low overvoltage of $\Delta \text{V}$ = 1V over SiPMs with a residual layer is seen. This increase drops to 19% at a higher overvoltage of $\Delta \text{V}$= 4V. For SiPMs with a larger fill factor of 82.4% no significant difference is observed. For Upgrade II, cryogenic cooling is foreseen to mitigate radiation-induced ageing effects. Irradiated detectors with an advanced technology have been tested, and a reduction in dark count rate of five orders of magnitude between operation temperatures of –40 ◦C and –196 ◦C (liquid nitrogen) has been measured. Customised SiPMs, combining a high PDE and low crosstalk probability in the cryogenic technology have been produced and initial promising results are presented

Preparation of a high-precision X-ray detector for kaonic atom measurements at J-PARC and DAΦNE

Eines der wichtigsten, ungelösten Probleme im Gebiet der Niedrigenergie-QCD der Hadronenphysik ist die Antikaon-Nukleon Wechselwirkung nahe der Produktionsschwelle. Diese Wechselwirkung kann jedoch Licht auf eine der fundamentalsten Fragen der Physik werfen: die Frage der Erzeugung von Hadronenmassen. Zwei Experimente (E57 am J-PARC Beschleuniger und SIDDHARTA-2 am DAFNE Beschleuniger) wurden beantragt um den Beitrag der starken Wechselwirkung am Grundzustand von kaonischem Deuterium zu untersuchen. Der Grundzustand von kaonischem Deuterium ist aufgrund der starken Wechselwirkung zwischen dem Strange-Quark im Kaon und den Quarks im Kern verschoben und verbreitert. Diese Verschiebung und Verbreiterung soll mithilfe von einem neu entwickelten X-ray-Detektorsystem mit einer Präzision von 60 eV beziehungsweise 140 eV bestimmt werden. Das Detektorsystem besteht aus 48 Silizium-Drift-Detektoren (SDDs), welche am Stefan Meyer Institut für Subatomare Physik getestet wurden. Diese Testmessungen beinhalteten Stabilitätsmessungen, eine Bestimmung der Driftzeit, eine Evaluation der Crosstalk-Wahrscheinlichkeit und mehrere Tests an verschiedenen Verstärkerboards um die beste Energieauflösung zu erzielen. Vier dieser SDD-Arrays wurden im Experiment E62 zur Messung von kaonischem Helium am J-PARC verwendet, um die SDDs erstmalig im Umfeld eines Beschleunigers zu testen. Die erzielten Resultate bestätigten den hervorragenden Arbeitsbetrieb der SDDs und unterstrichen, dass die SDDs bereit für den Einsatz in den Experimenten E57 und SIDDHARTA-2 sind.The antikaon-nucleon interaction close to threshold is one of the most important unsolved problems in the field of low-energy QCD in hadron physics. This interaction can shed light on one of the most fundamental questions in physics, namely the creation of hadron masses. Two experiments (E57 at J-PARC and SIDDHARTA-2 at DAFNE) have been proposed to study the contribution of the strong interaction on the 1s ground state of kaonic deuterium. The 1s state of kaonic deuterium should be shifted and broadened due to the strong interaction between the strange quark in the kaon and the quarks in the nucleus. This shift and width will be determined with a newly developed X-ray detector system with a precision of 60 eV and 140 eV, respectively. The X-ray detector system consists of 48 Silicon Drift Detectors (SDDs), which have been thoroughly tested at the Stefan Meyer Institute for Subatomic Physics. These test measurements included a stability analysis, a drift time measurement, a crosstalk probability evaluation and several tests on amplifier settings to achieve the best energy resolution. Four SDD arrays have been tested in the E62 kaonic helium experiment at J-PARC to test the SDDs for the first time in a real beam environment. The obtained results confirmed the SDDs’ excellent operation, and ensured their readiness to be used in the E57 and SIDDHARTA-2 experiments

A New Silicon Drift Detector For Kaonic Deuterium Measurements: On behalf of the E57 collaboration at J-PARC

The interaction of antikaons with nucleons and nuclei in the lowenergy regime is a very active research field in hadron physics. Specially, the antikaon-nucleon interaction close to threshold provides crucial information on the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD and touching one of the fundamental problems in hadron physic today - the still unsolved question of how hadron masses are generated. To study this problem, we have developed a new X–ray detector system and constructed an experimental apparatus to measure the kaonic deuterium 1s ground state shift and width with an accuracy of 60 eV and 140 eV, respectively

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

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

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