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

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

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

First observation of the Λ0 b → Λ+ c D− s K+K− decay and search for pentaquarks in the Λ+ c D− s system

The Λ0 b → Λþ c D− s KþK− decay is observed for the first time using the data sample from proton-proton collisions recorded at a center-of-mass energy of 13 TeV with the LHCb detector, corresponding to an integrated luminosity of 6 fb−1. The ratio of branching fraction to that of Λ0 b → Λþ c D− s decays is measured as 0.0141 0.0019 0.0012, where the first uncertainty is statistical and the second systematic. A search for hidden-charm pentaquarks with strangeness is performed in the Λþ c D− s system. No evidence is found, and upper limits on the production ratio of Pccs¯ ð4338Þ0 and Pccs¯ ð4459Þ0 pentaquarks relative to the Λþ c D− s final state are set at the 95% confidence level as 0.12 and 0.20, respectively

Determination of quantum numbers for several excited charmed mesons observed in B- -> D*(+)pi(-) pi(-) decays

A four-body amplitude analysis of the B − → D * + π − π − decay is performed, where fractions and relative phases of the various resonances contributing to the decay are measured. Several quasi-model-independent analyses are performed aimed at searching for the presence of new states and establishing the quantum numbers of previously observed charmed meson resonances. In particular the resonance parameters and quantum numbers are determined for the D 1 ( 2420 ) , D 1 ( 2430 ) , D 0 ( 2550 ) , D ∗ 1 ( 2600 ) , D 2 ( 2740 ) and D ∗ 3 ( 2750 ) states. The mixing between the D 1 ( 2420 ) and D 1 ( 2430 ) resonances is studied and the mixing parameters are measured. The dataset corresponds to an integrated luminosity of 4.7     fb − 1 , collected in proton-proton collisions at center-of-mass energies of 7, 8 and 13 TeV with the LHCb detector

Updated measurement of decay-time-dependent CP asymmetries in D-0 -> K+ K- and D-0 -> pi(+)pi(-) decays

A search for decay-time-dependent charge-parity (CP) asymmetry in D0 \u2192 K+ K 12 and D0 \u2192 \u3c0+ \u3c0 12 decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 5.4 fb^ 121. The D0 mesons are required to originate from semileptonic decays of b hadrons, such that the charge of the muon identifies the flavor of the neutral D meson at production. The asymmetries in the effective decay widths of D0 and anti-D0 mesons are determined to be A_\u393(K+ K 12) = ( 124.3 \ub1 3.6 \ub1 0.5) 7 10^ 124 and A_\u393(\u3c0+ \u3c0 12) = (2.2 \ub1 7.0 \ub1 0.8) 7 10^ 124 , where the uncertainties are statistical and systematic, respectively. The results are consistent with CP symmetry and, when combined with previous LHCb results, yield A_\u393(K+ K 12) = ( 124.4 \ub1 2.3 \ub1 0.6) 7 10^ 124 and A_\u393(\u3c0+ \u3c0 12) = (2.5 \ub1 4.3 \ub1 0.7) 7 10^ 124

Updated measurement of decay-time-dependent CP asymmetries in D-0 -> K+ K- and D-0 -> pi(+)pi(-) decays

A search for decay-time-dependent charge-parity (CP) asymmetry in D-0 -> K+ K- and D-0 -> pi(+)pi(-) eff decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 5.4 fb(-1). The D-0 mesons are required to originate from semileptonic decays of b hadrons, such that the charge of the muon identifies the flavor of the neutral D meson at production. The asymmetries in the effective decay widths of D-0 and (D) over bar (0) mesons are determined to be A(Gamma)(K+ K-) = (-4.3 +/- 3.6 +/- 0.5) x 10(-4) and A(Gamma) (K+ K- ) = (2.2 +/- 7.0 +/- 0.8) x 10(-4), where the uncertainties are statistical and systematic, respectively. The results are consistent with CP symmetry and, when combined with previous LHCb results, yield A(Gamma) (K+ K-) = (-4.4 +/- 2.3 +/- 0.6) x 10(-4) and A(Gamma) (pi(+)pi(-))= (2.5 +/- 4.3 +/- 0.7) x 10(-4)

MIBAD - An FPGA-based readout system for the LHCb Beam Conditions Monitor

Experiments at particle accelerators, such as the Large Hadron Collider (LHC), are at risk of damage due to the high-energy beams. The Beam Conditions Monitor (BCM) protects the LHCb detector at the LHC. It measures the particle flux with diamond sensors at two positions near the interaction point. If the measured signals exceed safe levels, the BCM automatically triggers a dump of the LHC beams. The LHCb detector was upgraded from 2018 to 2022. Consequently, the BCM needed to be adapted to a five-fold increase in instantaneous luminosity and a new detector geometry. Moreover, the pre-existing BCM hardware card is no longer supported due to an experiment-wide replacement of the readout electronics. This thesis presents the $\textit {Machine Interface Beam Abort Decision (MIBAD)}$ system as the BCM readout for the post-upgrade era. The development of the system, encompassing hardware, firmware, and software, is detailed. The main emphasis of this work is the implementation of the beam abort decision logic. As a vital part of the BCM safety system, the MIBAD continuously evaluates the beam conditions while meeting strict requirements regarding reliability and availability. A review of the testing and commissioning phase, as well as the experiences in the first months of operation, indicate that these goals have been met. The upgraded BCM, equipped with the MIBAD system, has safeguarded the LHCb detector since June 2023

MIBAD - an FPGA-based readout system for the LHCb Beam Conditions Monitor

Experiments at particle accelerators, such as the Large Hadron Collider (LHC), are at risk of damage due to the high-energy beams. The Beam Conditions Monitor protects the LHCb detector at the LHC. It measures the particle flux with diamond sensors at two positions near the interaction point. If the measured signals exceed safe levels, the BCM automatically triggers a dump of the LHC beams. The LHCb detector was upgraded from 2018 to 2022. Consequently, the BCM needed to be adapted to a five-fold increase in instantaneous luminosity and a new detector geometry. Moreover, the pre-existing BCM hardware card is no longer supported due to an experiment-wide replacement of the readout electronics. This thesis presents the Machine Interface Beam Abort (MIBAD) system as the BCM readout for the post-upgrade era. The development of the system, encompassing hardware, firmware, and software, is detailed. The main emphasis of this work is the implementation of the beam abort decision logic. As a vital part of the BCM safety system, the MIBAD continuously evaluates the beam conditions while meeting strict requirements regarding reliability and availability. A review of the testing and commissioning phase, as well as the experiences in the first months of operation, indicate that these goals have been met.The upgraded BCM, equipped with the MIBAD system, has safeguarded the LHCb detector since June 2023.Experimente an Teilchenbeschleunigern wie dem Large Hadron Collider (LHC), sind Beschädigungsrisiken durch die hochenergetischen Strahlen ausgesetzt. Daher wird das LHCb-Experiment am LHC durch den Beam Conditions Monitor (BCM) geschützt. Mithilfe von Diamantsensoren misst dieses Sicherheitssystem den Teilchenfluss an zwei Orten in der Nähe des Interaktionspunkts. Überschreiten die Messwerte ein sicheres Niveau, löst der BCM automatisch eine Extraktion der LHC-Strahlen aus. In den Jahren 2018 bis 2022 hat der LHCb-Detektor ein Upgrade erhalten. Infolgedessen musste der BCM an die verfünffachte instantane Luminosität und die veränderte Detektorgeometrie angepasst werden. Außerdem wird die bestehende Ausleseelektronik des BCM wegen eines experimentweiten Austauschs der Datennahmehardware nicht mehr unterstützt. In dieser Arbeit wird das Machine Interface Beam Abort (MIBAD) System für den Betrieb des BCMs nach dem Upgrade vorgestellt. Alle Aspekte der Entwicklung, also Hardware, Firmware und Software werden behandelt. Den Schwerpunkt der Arbeit bildet die Implementierung der Routine für die Bewertung der Stahlqualität mit programmierbaren Logikbausteinen. Für diese Kernkomponente des Strahlüberwachungssystems werden strenge Anforderungen bezüglich Verlässlichkeit und Verfügbarkeit gestellt. In Hinblick auf die Testphase und die ersten Monate im Produktivbetrieb wurden diese Ziele erreicht. Seit Juni 2023 schützt der BCM mit der MIBAD Ausleseelektronik den LHCb Detektor

Description of Light Guidance in Dual Clad Scintillating Fibres for the LHCb SciFi Tracker

During the LHCb upgrade in 2019/2020, a new detector element will be installed that uses scintillating fibres (SciFi) to detect particle tracks, the so-called SciFi Tracker. To predict its performance, a single fibre simulation has previously been developed with the Geant4 toolkit. The simulation results are compared to measurements in order to tune the simulation parameters and gain an understanding of the underlying fibre properties. This note presents the relevant information obtained so far and new findings concerning the reflection losses in scintillating fibres