The upgraded LHCb detector has started its Run 3 of data taking in 2022, with a completely overhauled DAQ system, reading out and processing the full detector data at every LHC bunch crossing (30 MHz average rate). At the same time, an intense R D activity is taking place, with the aim of further improving the real-time data processing performance of LHCb, in view of "Upgrade II", where luminosity will be increased. In this work, we describe the experience gained with a prototype device for a 30 MHz real-time tracking in the LHCb VELO detector, implemented in state-of-art PCIe-hosted FPGA cards interconnected by fast optical links. The system has been processing live LHCb data opportunistically during physics data taking, thanks to a dedicated TestBed facility fed by the experiment monitoring system. We describe, amongst other things, the system used to organise and optimise the high-speed distribution of data to the components, and the synchronisation with the most updated alignment constants to be used in track reconstruction.

The increasing computing power and bandwidth of FPGAs opens new possibilities in the field of real-time processing of high-energy physics data. The LHCb experiment has implemented a cluster-finder FPGA architecture aimed at reconstructing hits in its innermost silicon-pixel detector onthe-fly during readout. In addition to accelerating the event reconstruction procedure by providing it with higher-level primitives, this system enables further opportunities. LHCb triggerless readout architecture makes these reconstructed hit positions available for every collision, amounting to a flow of 1011 hits per second, that can be used for further analysis. In this work, we have implemented a set of programmable counters, counting the hit rate at many locations in the detector volume simultaneously. We use these data to continuously track the motion of the beams overlap region and the relative position of the detector elements, with precisions of µm and time granularity of (ms). We show that this can be achieved by simple linear combination of data, that can be executed in real time with minimal computational effort. This novel approach allows a fast and precise determination of the beamline position without the need to reconstruct more complex quantities like tracks and vertices. We report results obtained with pp collision data collected in 2024 at LHCb.

The LHCb collaboration is planning an upgrade (LHCb “Upgrade- II”) to collect data during Run 5 at an instantaneous luminosity an order of magnitude larger than the current one (Run 3). LHCb relies on a complete realtime reconstruction of all collision events at LHC-Point 8, which will have to cope with both the luminosity increase and the introduction of correspondingly more granular and complex detectors. After an intensive R&D programme, LHCb approved a FPGA-based system to pre-reconstruct tracks in the SciFi detector at readout level during Run 4, as an intermediate step towards a system that could be extended to other tracking detectors in the future. It is based on the “artificial retina”, an extremely parallel architecture. Using simulated data, the performance of a hardware demonstrator of this architecture has been tested as a function of instantaneous luminosity and system size, and was found to have O(n) complexity, which is a crucial feature for high luminosity applications.

Abstract The first full amplitude analysis of B + → ψ(2S)K + π + π − decays is performed using proton-proton collision data corresponding to an integrated luminosity of 9 fb−1 recorded with the LHCb detector. The rich K + π + π − spectrum is studied and the branching fractions of the resonant substructure associated with the prominent K 1(1270)+ contribution are measured. The data cannot be described by conventional strange and charmonium resonances only. An amplitude model with 53 components is developed comprising 11 hidden-charm exotic hadrons. New production mechanisms for charged charmonium-like states are observed. Significant resonant activity with spin-parity J P = 1+ in the ψ(2S)π + system is confirmed and a multi-pole structure is demonstrated. The spectral decomposition of the ψ(2S)π + π − invariant-mass structure, dominated by X 0 → ψ(2S)ρ(770)0 decays, broadly resembles the J/ψϕ spectrum observed in B + → J/ψϕK + decays. Exotic ψ(2S)K + π − resonances are observed for the first time.

Abstract A time-dependent, flavour-tagged measurement of CP violation is performed with B 0 → D + D − and B s 0 $$ {B}_s^0 $$ → D s + D s − $$ {D}_s^{+}{D}_s^{-} $$ decays, using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 6 fb −1. In B 0 → D + D − decays the CP-violation parameters are measured to be S D + D − = − 0.552 ± 0.100 stat ± 0.010 syst , C D + D − = 0.128 ± 0.103 stat ± 0.010 syst . $$ {\displaystyle \begin{array}{c}{S}_{D^{+}{D}^{-}}=-0.552\pm 0.100\left(\textrm{stat}\right)\pm 0.010\left(\textrm{syst}\right),\\ {}{C}_{D^{+}{D}^{-}}=0.128\pm 0.103\left(\textrm{stat}\right)\pm 0.010\left(\textrm{syst}\right).\end{array}} $$ In B s 0 $$ {B}_s^0 $$ → D s + D s − $$ {D}_s^{+}{D}_s^{-} $$ decays the CP-violating parameter formulation in terms of ϕ s and |λ| results in ϕ s = − 0.086 ± 0.106 stat ± 0.028 syst rad , ∣ λ D s + D s − ∣ = 1.145 ± 0.126 stat ± 0.031 syst . $$ {\displaystyle \begin{array}{c}{\phi}_s=-0.086\pm 0.106\left(\textrm{stat}\right)\pm 0.028\left(\textrm{syst}\right)\textrm{rad},\\ {}\mid {\lambda}_{D_s^{+}{D}_s^{-}}\mid =1.145\pm 0.126\left(\textrm{stat}\right)\pm 0.031\left(\textrm{syst}\right).\end{array}} $$ These results represent the most precise single measurement of the CP-violation parameters in their respective channels. For the first time in a single measurement, CP symmetry is observed to be violated in B 0 → D + D − decays with a significance exceeding six standard deviations.

Measurements are presented of the cross-section for the central exclusive production of J/psi -> mu(+) mu(-) and psi(2S) -> mu(+)mu(-) processes in proton-proton collisions at root s = 13 TeV with 2016-2018 data. They are performed by requiring both muons to be in the LHCb acceptance (with pseudorapidity 2 < eta(mu +/-) < 4.5) and mesons in the rapidity range 2.0 < y < 4.5. The integrated cross-section results are sigma(J/psi ->mu+ mu-) (2.0 < y(J/psi) < 4.5, 2.0 < eta(mu +/-) < 4.5) = 400 +/- 2 +/- 5 +/- 12 pb, sigma(psi(2S)->mu+mu-)(2.0 < y(psi(2S)) < 4.5, 2.0 < eta(mu +/-) < 4.5) = 9.40 +/- 0.15 +/- 0.13 +/- 0.27 pb, where the uncertainties are statistical, systematic and due to the luminosity determination. In addition, a measurement of the ratio of psi(2S) and J/psi cross-sections, at an average photon-proton centre-of-mass energy of 1 TeV, is performed, giving sigma(psi(2S))/sigma(J/psi) = 0.1763 +/- 0.0029 +/- 0.0008 +/- 0.0039, where the first uncertainty is statistical, the second systematic and the third due to the knowledge of the involved branching fractions. For the first time, the dependence of the J/psi and psi(2S) cross-sections on the total transverse momentum transfer is determined in pp collisions and is found consistent with the behaviour observed in electron-proton collisions.

This paper presents the first measurement of $$\psi {(2S)}$$ ψ ( 2 S ) and $$\chi _{c1}(3872)$$ χ c 1 ( 3872 ) meson production within fully reconstructed jets. Each quarkonium state (tag) is reconstructed via its decay to the $${{J \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }} $$ J / ψ ( $$\rightarrow $$ → $$\mu ^+\mu ^-$$ μ + μ - ) $$\pi ^+\pi ^-$$ π + π - final state in the forward region using proton-proton collision data collected by the LHCb experiment at the center-of-mass-energy of $$13\text {TeV} $$ 13 TeV in 2016, corresponding to an integrated luminosity of $$1.64\,\text {\,fb} ^{-1} $$ 1.64 \,fb - 1 . The fragmentation function, presented as the ratio of the quarkonium-tag transverse momentum to the full jet transverse momentum ( $$p_{\textrm{T}} (\text {tag})/p_{\textrm{T}} (\text {jet})$$ p T ( tag ) / p T ( jet ) ), is measured differentially in $$p_{\textrm{T}} (\text {jet})$$ p T ( jet ) and $$p_{\textrm{T}} (\text {tag})$$ p T ( tag ) bins. The distributions are separated into promptly produced quarkonia from proton-proton collisions and quarkonia produced from displaced b -hadron decays. While the displaced quarkonia fragmentation functions are in general well described by parton-shower predictions, the prompt quarkonium distributions differ significantly from fixed-order non-relativistic QCD (NRQCD) predictions followed by a QCD parton shower.

A time-dependent, flavour-tagged measurement of CP violation is performed with B0 → D+D− and B_s^0 → D_s^+D_s^- decays, using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 6 fb−1. In B0 → D+D− decays the CP-violation parameters are measured to be [ S_D^+D^-=-0.552± 0.100(stat)± 0.010(syst),; C_D^+D^-=0.128± 0.103(stat)± 0.010(syst). ] In B_s^0 → D_s^+D_s^- decays the CP-violating parameter formulation in terms of ϕs and |λ| results in [ ϕ_s=-0.086± 0.106(stat)± 0.028(syst)rad,; |λ_D_s^+D_s^-| =1.145± 0.126(stat)± 0.031(syst). ] These results represent the most precise single measurement of the CP-violation parameters in their respective channels. For the first time in a single measurement, CP symmetry is observed to be violated in B0 → D+D− decays with a significance exceeding six standard deviations.

A search for hidden-charm pentaquark states decaying to a range of ΣcD¯ and Λc+D¯ final states, as well as doubly charmed pentaquark states to ΣcD and Λc+D, is made using samples of proton-proton collision data corresponding to an integrated luminosity of 5.7 fb−1 recorded by the LHCb detector at s=13 TeV. Since no significant signals are found, upper limits are set on the pentaquark yields relative to that of the Λc+ baryon in the Λc+→pK−π+ decay mode. The known pentaquark states are also investigated, and their signal yields are found to be consistent with zero in all cases. © 2024 CERN, for the LHCb Collaboration 2024 CERN

The LHCb collaboration measures production of the exotic hadron χ_c1(3872) in proton-nucleus collisions for the first time. Comparison with the charmonium state ψ(2S) suggests that the exotic χ_c1(3872) experiences different dynamics in the nuclear medium than conventional hadrons, and comparison with data from proton-proton collisions indicates that the presence of the nucleus may modify χ_c1(3872) production rates. This is the first measurement of the nuclear modification factor of an exotic hadron.

For accurate determination of particle masses accurate knowledge of the momentum scale of the detectors is crucial. The procedure used to calibrate the momentum scale of the LHCb spectrometer is described and illustrated using the performance obtained with an integrated luminosity of $1.6~ fb^{-1}$ collected during 2016 in $pp$ running. The procedure uses large samples of $J/\psi \rightarrow \mu^+ \mu^-$ and $B^+ \rightarrow J/\psi K^+$ decays and leads to a relative accuracy of $3 \times 10^{-4}$ on the momentum scale.

A comprehensive study of the angular distributions in the bottom-baryon decays Λ^0_b→Λ_c^+ h^-(h=π, K), followed by Λ_c^+→Λ h^+ with Λ→pπ^- or Λ_c^+→pK^0_S decays, is performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of 9 fb^-1 collected by the LHCb experiment at center-of-mass energies of 7, 8 and 13 Te -0.1em V. The decay parameters and the associated charge-parity (CP) asymmetries are measured, with no significant CP violation observed. For the first time, the Λ^0_b →Λ_c^+ h^- decay parameters are measured. The most precise measurements of the decay parameters α, β and γ are obtained for Λ_c^+ decays and an independent measurement of the decay parameters for the strange-baryon Λ decay is provided. The results deepen our understanding of weak decay dynamics in baryon decays.

Abstract The Λ b 0 $$ {\Lambda}_b^0 $$ → D + D − Λ decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.3 fb −1. Using the B 0 → D + D − K S 0 $$ {D}^{+}{D}^{-}{K}_S^0 $$ decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be R = σ Λ b 0 σ B 0 = B Λ b 0 → D + D − Λ B B 0 → D + D − K S 0 = 0.179 ± 0.022 ± 0.014 , $$ \mathcal{R}=\frac{\sigma_{\Lambda_b^0}}{\sigma_{B^0}}=\frac{\mathcal{B}\left({\Lambda}_b^0\to {D}^{+}{D}^{-}\Lambda \right)}{\mathcal{B}\left({B}^0\to {D}^{+}{D}^{-}{K}_{\textrm{S}}^0\right)}=0.179\pm 0.022\pm 0.014, $$ where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, B B 0 → D + D − K S 0 $$ \mathcal{B}\left({B}^0\to {D}^{+}{D}^{-}{K}_{\textrm{S}}^0\right) $$ , and the cross-section ratio, σ Λ b 0 / σ B 0 $$ {\sigma}_{\Lambda_b^0}/{\sigma}_{B^0} $$ , previously measured by LHCb are used to derive the branching fraction of the Λ b 0 $$ {\Lambda}_b^0 $$ → D + D − Λ decay B Λ b 0 → D + D − Λ = 1.24 ± 0.15 ± 0.10 ± 0.28 ± 0.11 × 10 − 4 , $$ \mathcal{B}\left({\Lambda}_b^0\to {D}^{+}{D}^{-}\Lambda \right)=\left(1.24\pm 0.15\pm 0.10\pm 0.28\pm 0.11\right)\times {10}^{-4}, $$ where the third and fourth contributions are due to uncertainties of B B 0 → D + D − K S 0 $$ \mathcal{B}\left({B}^0\to {D}^{+}{D}^{-}{K}_{\textrm{S}}^0\right) $$ and σ Λ b 0 / σ B 0 $$ {\sigma}_{\Lambda_b^0}/{\sigma}_{B^0} $$ , respectively. Inspection of the D +Λ and D + D − invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The Λ b 0 $$ {\Lambda}_b^0 $$ → D *+ D − Λ decay is also observed for the first time as a partially reconstructed component in the D + D − Λ invariant mass spectrum.

The first measurement of the Z boson production cross-section at centre-of-mass energy v s = 5.02TeV in the forward region is reported, using pp collision data collected by the LHCb experiment in year 2017, corresponding to an integrated luminosity of 100 +/- 2 pb-1. The production cross-section is measured for final-state muons in the pseudorapidity range 2.0 <. < 4.5 with transverse momentum pT > 20 GeV/c. The integrated cross-section is determined to be sZ.mu+mu- = 39.6 +/- 0.7(stat) +/- 0.6(syst) +/- 0.8(lumi) pb for the di-muon invariant mass in the range 60 < M mu mu < 120 GeV/c2. This result and the differential cross-section results are in good agreement with theoretical predictions at next-to-next-to-leading order in the strong coupling constant. Based on a previous LHCb measurement of the Z boson production cross-section in pPb collisions at v sNN = 5.02TeV, the nuclear modification factor RpPb is measured for the first time at this energy. The measured values are 1.2+0.5 -0.3(stat) +/- 0.1(syst) in the forward region (1.53 < y* mu < 4.03) and 3.6+1.6 -0.9(stat)+/- 0.2(syst) in the backward region (-4.97 < y* mu < -2.47), where y* mu represents the muon rapidity in the centre-of-mass frame.

Abstract A measurement of CP-violating observables associated with the interference of B0→ D0K⋆(892)0 and $$ {B}^0\to {\overline{D}}^0{K}^{\star }{(892)}^0 $$ B 0 → D ¯ 0 K ⋆ 892 0 decay amplitudes is performed in the D0→ K∓π±(π+π−), D0→ π+π−(π+π−), and D0→ K+K− final states using data collected by the LHCb experiment corresponding to an integrated luminosity of 9 fb−1. CP-violating observables related to the interference of $$ {B}_s^0\to {D}^0{\overline{K}}^{\star }{(892)}^0 $$ B s 0 → D 0 K ¯ ⋆ 892 0 and $$ {B}_s^0\to {\overline{D}}^0{\overline{K}}^{\star }{(892)}^0 $$ B s 0 → D ¯ 0 K ¯ ⋆ 892 0 are also measured, but no evidence for interference is found. The B0 observables are used to constrain the parameter space of the CKM angle γ and the hadronic parameters $$ {r}_{B^0}^{DK\star } $$ r B 0 DK ⋆ and $$ {\delta}_{B^0}^{DK\star } $$ δ B 0 DK ⋆ with inputs from other measurements. In a combined analysis, these measurements allow for four solutions in the parameter space, only one of which is consistent with the world average.

A study of resonant structures in B^{+}→D^{*+}D^{-}K^{+} and B^{+}→D^{*-}D^{+}K^{+} decays is performed, using proton-proton collision data at center-of-mass energies of sqrt[s]=7, 8, and 13 TeV recorded by the LHCb experiment, corresponding to an integrated luminosity of 9  fb^{-1}. A simultaneous amplitude fit is performed to the two channels with contributions from resonances decaying to D^{*-}D^{+} and D^{*+}D^{-} states linked by C parity. This procedure allows the C parities of resonances in the D^{*±}D^{∓} mass spectra to be determined. Four charmonium or charmoniumlike states are observed decaying into D^{*±}D^{∓}: η_{c}(3945), h_{c}(4000), χ_{c1}(4010), and h_{c}(4300), with quantum numbers J^{PC} equal to 0^{-+}, 1^{+-}, 1^{++}, and 1^{+-}, respectively. At least three of these states have not been observed previously. In addition, the existence of the T_{c[over ¯]s[over ¯]0}^{*}(2870)^{0} and T_{c[over ¯]s[over ¯]1}^{*}(2900)^{0} resonances in the D^{-}K^{+} mass spectrum, already observed in the B^{+}→D^{+}D^{-}K^{+} decay, is confirmed in a different production channel.

A comprehensive study of the angular distributions in the bottom-baryon decays Λ_{b}^{0}→Λ_{c}^{+}h^{-}(h=π,K), followed by Λ_{c}^{+}→Λh^{+} with Λ→pπ^{-} or Λ_{c}^{+}→pK_{S}^{0} decays, is performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of 9  fb^{-1} collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. The decay parameters and the associated charge-parity (CP) asymmetries are measured, with no significant CP violation observed. For the first time, the Λ_{b}^{0}→Λ_{c}^{+}h^{-} decay parameters are measured. The most precise measurements of the decay parameters α, β, and γ are obtained for Λ_{c}^{+} decays and an independent measurement of the decay parameters for the strange-baryon Λ decay is provided. The results deepen our understanding of weak decay dynamics in baryon decays.

A study of prompt Xi(+)(c) production in proton-lead collisions is performed with the LHCb experiment at a centerof-mass energy per nucleon pair of 8.16 TeV in 2016 in pPb and Pbp collisions with an estimated integrated luminosity of approximately 12.5 and 17.4 nb(-1), respectively. The Xi(+)(c) roduction cross section, as well as the Xi(+)(c) to Lambda(+)(c) production cross-section ratio, are measured as a function of the transverse momentum and rapidity and compared to the latest theory predictions. The forward-backward asymmetry is also measured as a function of the Xi(+)(c) ransverse momentum. The results provide strong constraints on theoretical calculation and are a unique input for hadronization studies in different collision systems.

A bstract Using a dataset corresponding to 9 fb − 1 of integrated luminosity collected with the LHCb detector between 2011 and 2018 in proton-proton collisions, the decay-time distributions of the decay modes $$ {B}_s^0\to J/{\psi \eta}^{\prime } $$ B s 0 → J / ψη ′ and $$ {B}_s^0\to J/\psi {\pi}^{+}{\pi}^{-} $$ B s 0 → J / ψ π + π − are studied. The decay-width difference between the light and heavy mass eigenstates of the $$ {B}_s^0 $$ B s 0 meson is measured to be ∆Γ s = 0 . 087 ± 0 . 012 ± 0 . 009 ps − 1 , where the first uncertainty is statistical and the second systematic.

A study of B_c^+→χ_cπ^+ decays is reported using proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. The decay B_c^+→χ_c2π^+ is observed for the first time, with a significance exceeding seven standard deviations. The relative branching fraction with respect to the B_c^+→ J/ψπ^+ decay is measured to be ℬ_B_c^+→χ_c2π^+/ℬ_B_c^+→ J/ψπ^+=0.37± 0.06± 0.02± 0.01, where the first uncertainty is statistical, the second is systematic, and the third is due to the knowledge of the χc2 → J/ψγ branching fraction. No significant B_c^+→χ_c1π^+ signal is observed and an upper limit for the relative branching fraction for the B_c^+→χ_c1π^+ and B_c^+→χ_c2π^+ decays of ℬ_B_c^+→χ_c1π^+/ℬ_B_c^+→χ_c2π^+=<0.49 is set at the 90