LHCb Research Articles

{{J}/psi } and {{D}} ^0 production in sqrt{s_{scriptscriptstyle text {NN}}} =68.5,text {GeV} PbNe collisions

The first measurement of {{J}/psi } and {{D}} ^0 production in PbNe collisions by the LHCb experiment in its fixed-target configuration is reported. The production of {{J}/psi } and {{D}} ^0 mesons is studied with a beam of lead ions with an energy of 2.5,text {TeV} per nucleon colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy of sqrt{s_{scriptscriptstyle text {NN}}} =68.5,text {GeV} . The {{J}/psi }/{{D}} ^0 production cross-section ratio is studied as a function of rapidity, transverse momentum and collision centrality. These data are compared with measurements from ptext {Ne} collisions at the same energy and show no difference in the observed {{J}/psi } suppression trend when comparing ptext {Ne} and PbNe peripheral collisions with PbNe central collisions.

Search for the doubly heavy baryon decaying to * *The project support from CERN and from the national agencies: CAPES, CNPq, FAPERJ and FINEP (Brazil); MOST and NSFC (China); CNRS/IN2P3 (France); BMBF, DFG and MPG (Germany); INFN (Italy); NWO (Netherlands); MNiSW and NCN (Poland); MEN/IFA (Romania); MICINN (Spain); SNSF and SER (Switzerland); NASU (Ukraine); STFC (United Kingdom); DOE NP and

A first search for the decay is performed by the LHCb experiment with a data sample of proton-proton collisions, corresponding to an integrated luminosity of 9 fb−1 recorded at centre-of-mass energies of 7, 8, and 13 TeV. Two peaking structures are seen with a local (global) significance of and standard deviations at masses of 6571 and 6694 MeV/, respectively. Upper limits are set on the baryon production cross-section times the branching fraction relative to that of the decay at centre-of-mass energies of 8 and 13 TeV, in the and in the rapidity and transverse-momentum ranges from 2.0 to 4.5 and 0 to , respectively. Upper limits are presented as a function of the mass and lifetime.

Mass predictions of triply heavy hybrid baryons via QCD sum rules

In this article, we study the mass spectrum of the low-lying triply heavy hybrid baryon, which consists of three valence heavy quarks in a color octet and one valence gluon, with spin-parity J^P=(frac{1}{2})^+ via QCD sum rules. This is the first study on the triply heavy hybrid baryons in the framework of QCD sum rules. After performing the QCD sum rule analysis, we find that the mass of cccg hybrid baryon lies in M_{cccg}= 5.91–6.13 GeV. As a byproduct, the mass of the triply bottom hybrid baryon state is extracted to be around M_{bbbg}= 14.62–14.82 GeV. The contributions up to dimension eight at the leading order of alpha _s (LO) in the operator product expansion are taken into account in the calculation. The triply charmed hybrid baryon predicted in this work can decay into one doubly charmed baryon and one charmed meson. Especially, we propose to search for cccg hybrid baryon with J^{P}= (1/2)^+ in the P-wave decay channels Xi _{cc}^{++} D^0, Xi _{cc}^{+} D^+, and Xi _{ccs}^{+} D_s^+, which may be accessible in future BelleII, Super-B, PANDA, and LHCb experiments.

Charmonium production in pNe collisions at sqrt{s_{scriptscriptstyle text {NN}}} =68.5 GeV

The measurement of charmonium states produced in proton-neon (ptext {Ne}) collisions by the LHCb experiment in its fixed-target configuration is presented. The production of {{J} hspace{-1.66656pt}/hspace{-1.111pt}psi } and psi {(2S)} mesons is studied with a beam of 2.5mathrm{,Tehspace{-1.00006pt}V} protons colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy sqrt{s_{scriptscriptstyle text {NN}}} =68.5mathrm{,Gehspace{-1.00006pt}V} . The data sample corresponds to an integrated luminosity of 21.7pm 1.4 nb^{-1}. The {{J} hspace{-1.66656pt}/hspace{-1.111pt}psi } and psi {(2S)} hadrons are reconstructed in mu ^+mu ^- final states. The {{J} hspace{-1.66656pt}/hspace{-1.111pt}psi } production cross-section per target nucleon in the centre-of-mass rapidity range y^star in [-2.29, 0] is found to be 506 pm 8 pm 46 text { nb/nucleon}. The ratio of {{J} hspace{-1.66656pt}/hspace{-1.111pt}psi } and D^0 cross-sections is evaluated to (1.06 pm 0.02 pm 0.09)%. The psi {(2S)} to {{J} hspace{-1.66656pt}/hspace{-1.111pt}psi } relative production rate is found to be (1.67 pm 0.27pm 0.10)% in good agreement with other measurements involving beam and target nuclei of similar sizes.

Observation of the {B}_s^0 → D*+D*− decay

The first observation of the {B}_s^0 → D∗+D∗− decay and the measurement of its branching ratio relative to the B0→ D∗+D∗− decay are presented. The data sample used corresponds to an integrated luminosity of 9 fb−1 of proton-proton collisions recorded by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV between 2011 and 2018. The decay is observed with more than 10 standard deviations and the time-integrated ratio of branching fractions is determined to beBBs0→D∗+D∗−BB0→D∗+D∗−=0.269±0.032±0.011±0.008,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\frac{\\mathcal{B}\\left({B}_s^0\ o {D}^{\\ast +}{D}^{\\ast -}\\right)}{\\mathcal{B}\\left({B}^0\ o {D}^{\\ast +}{D}^{\\ast -}\\right)}=0.269\\pm 0.032\\pm 0.011\\pm 0.008, $$\\end{document}where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the fragmentation fraction ratio fs/fd. The {B}_s^0 → D*+D*− branching fraction is calculated to beBBs0→D∗+D∗−=2.15±0.26±0.09±0.06±0.16×10−4,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{B}\\left({B}_s^0\ o {D}^{\\ast +}{D}^{\\ast -}\\right)=\\left(2.15\\pm 0.26\\pm 0.09\\pm 0.06\\pm 0.16\\right)\ imes {10}^{-4}, $$\\end{document}where the fourth uncertainty is due to the B0→ D*+D*− branching fraction. These results are calculated using the average {B}_s^0 meson lifetime in simulation. Correction factors are reported for scenarios where either a purely heavy or a purely light {B}_s^0 eigenstate is considered.

Observation of the {textrm{B}}_{textrm{s}}^0 → χc1(3872)π+π− decay

The first observation of the {B}_s^0 → (χc1(3872) → J/ψπ+π−)π+π− decay is reported using proton-proton collision data, corresponding to integrated luminosities of 1, 2 and 6 fb−1, collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The ratio of branching fractions relative to the {B}_s^0 → (ψ(2S) → J/ψπ+π−)π+π− decay is measured to beBBs0→χc13872π+π−×Bχc13872→J/ψπ+π−BBs0→ψ2Sπ+π−×Bψ2S→J/ψπ+π−=6.8±1.1±0.2×10−2,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\frac{\\mathcal{B}\\left({B}_s^0\ o {\\chi}_{c1}(3872){\\pi}^{+}{\\pi}^{-}\\right)\ imes \\mathcal{B}\\left({\\chi}_{c1}(3872)\ o J/\\psi {\\pi}^{+}{\\pi}^{-}\\right)}{\\mathcal{B}\\left({B}_s^0\ o \\psi (2S){\\pi}^{+}{\\pi}^{-}\\right)\ imes \\mathcal{B}\\left(\\psi (2S)\ o J/\\psi {\\pi}^{+}{\\pi}^{-}\\right)}=\\left(6.8\\pm 1.1\\pm 0.2\\right)\ imes {10}^{-2}, $$\\end{document}where the first uncertainty is statistical and the second systematic. The mass spectrum of the π+π− system recoiling against the χc1(3872) meson exhibits a large contribution from {B}_s^0 → χc1(3872) (f0(980) → π+π−) decays.

First observation and branching fraction measurement of the {Lambda}_b^0to {D}_s^{-}p decay

The first observation of the {Lambda}_b^0to {D}_s^{-}p decay is presented using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of sqrt{s} = 13 TeV, corresponding to a total integrated luminosity of 6 fb−1. Using the {Lambda}_b^0to {Lambda}_c^{+}{pi}^{-} decay as the normalisation mode, the branching fraction of the {Lambda}_b^0to {D}_s^{-}p decay is measured to be mathcal{B}left({Lambda}_b^0to {D}_s^{-}pright)=left(12.6pm 0.5pm 0.3pm 1.2right)times {10}^{-6} , where the first uncertainty is statistical, the second systematic and the third due to uncertainties in the branching fractions of the {Lambda}_b^0to {Lambda}_c^{+}{pi}^{-} , {D}_s^{-}to {K}^{-}{K}^{+}{pi}^{-} and {Lambda}_c^{+}to p{K}^{-}{pi}^{+} decays.

Towards the precision measurement of CP violation in B → D*μν decays at LHCb

Measurement of CP-violating observables in semileptonic decays is a sensitive null-test of the Standard Model: any CP violation would be an unambiguous sign of New Physics effects. The model-independent technique to measure parity and CP-odd observables in the B → D∗μν decays is proposed, which effectively cancels out parity-even terms in the decay density together with the associated theory uncertainty. The feasibility study is performed with pseudoexperiments, and the sensitivity at the LHCb experiment is estimated. Finally, the most significant systematic effects and the data-driven ways to control them are considered.

Search for CP violation in {D}_{(s)}^{+} → K−K+K+ decays

A search for direct CP violation in the Cabibbo-suppressed decay {D}_s^{+} → K−K+K+ and in the doubly Cabibbo-suppressed decay D+ → K−K+K+ is reported. The analysis is performed with data collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.6 fb−1. The search is conducted by comparing the {D}_{(s)}^{+} and {D}_{(s)}^{-} Dalitz-plot distributions through a model-independent binned technique, based on fits to the K−K+K+ invariant-mass distributions, with a total of 0.97 (1.27) million {D}_s^{+} (D+) signal candidates. The results are given as p-values for the hypothesis of CP conservation and are found to be 13.3% for the {D}_s^{+} → K−K+K+ decay and 31.6% for the D+→ K−K+K+ decay. No evidence for CP violation is observed in these decays.

Measurement of the ratio of branching fractions mathcal{B}left({B}_c^{+}to {B}_s^0{pi}^{+}right)/mathcal{B}left({B}_c^{+}to J/psi {pi}^{+}right)

The ratio of branching fractions of {B}_c^{+}to {B}_s^0{pi}^{+} and {B}_c^{+}to J/psi {pi}^{+} decays is measured with proton-proton collision data of a centre-of-mass energy of 13 TeV. The data were collected with the LHCb experiment during 2016–2018, corresponding to an integrated luminosity of 5.4 fb−1. The {B}_s^0 mesons are reconstructed via the decays {B}_s^0to J/psi phi and {B}_s^0to {D}_s^{-}{pi}^{+} . The ratio of branching fractions is measured to be mathcal{B}left({B}_c^{+}to {B}_s^0{pi}^{+}right)/mathcal{B}left({B}_c^{+}to J/psi {pi}^{+}right)=91pm 10pm 8pm 3 where the first uncertainty is statistical, the second is systematic and the third is due to the knowledge of the branching fractions of the intermediate state decays.

A study of C!P violation in the decays {{B} ^pm } rightarrow [{{K} ^+} {{K} ^-} {{uppi } ^+} {{uppi } ^-} ]_{D} h^{pm } (h = K, pi ) and {{B} ^pm } rightarrow [{{uppi } ^+} {{uppi } ^-} {{uppi } ^+} {{uppi } ^-} ]_{D} h^{pm }

The first study of C!P violation in the decay mode {{B} ^pm } rightarrow [{{K} ^+} {{K} ^-} {{uppi } ^+} {{uppi } ^-} ]_{D} h^pm , with h=K,pi , is presented, exploiting a data sample of proton–proton collisions collected by the LHCb experiment that corresponds to an integrated luminosity of 9text {,fb} ^{-1} . The analysis is performed in bins of phase space, which are optimised for sensitivity to local C!P asymmetries. C!P-violating observables that are sensitive to the angle gamma of the Unitarity Triangle are determined. The analysis requires external information on charm-decay parameters, which are currently taken from an amplitude analysis of LHCb data, but can be updated in the future when direct measurements become available. Measurements are also performed of phase-space integrated observables for {{B} ^pm } rightarrow [{{K} ^+} {{K} ^-} {{uppi } ^+} {{uppi } ^-} ]_{D} h^pm and {{B} ^pm } rightarrow [{{uppi } ^+} {{uppi } ^-} {{uppi } ^+} {{uppi } ^-} ]_{D} h^pm decays.

Controlling refractive index and reducing the Global Warming Potential of Cerenkov gas radiators: a challenge in the era of diminishing fluorocarbon availability

Saturated fluorocarbons (SFCs) of the form CnF(2n+2) are chosen for their optical properties (high transparency in the near UV, adapted refractive index and low chromatic dispersion over wavelength ranges of interest) for use as Cherenkov radiators. The COMPASS and LHCb experiments currently use C4F10 and CF4 gas radiators. SFCs have high Global Warming Potentials (GWPs), however (in the range 5000–9000). There is thus an impetus to reduce their use and wastage through leaks in existing installations.Newer fluids of the form CnF2nO, including the 3M NOVEC® range, can offer similar optical performance to SFCs of the same order, n, but with GWPs equivalent to CO2. These GWPs are, however, geometry-specific: closed molecular rings having an oxygen atom as a link can have GWPs as high as those of SFCs, and should be avoided.While the optical constraints of RICH detectors can motivate a “special case” argument to retain the use of preferred SFCs, legislation and external market forces will limit their future availability, leaving “holes” in the CnFx spectrum that might not be filled by NOVEC equivalents. This situation might require the blending of low molar concentrations of heritage-stock higher-order SFCs and NOVEC vapours with transparent light gases such as nitrogen, and is the subject of this paper.While continuous optical measurement of refractive index in dynamically changing gas mixtures is very demanding, the monitoring of sound velocity has been historically shown to provide simple, reliable and continuous real time mixture information. Indeed the speed of sound is, in itself, a monitor of the speed of light and the Cherenkov threshold in a gas radiator.This ultrasonic (“sonar”) technique was first used for controlling the real-time blending C5F12 with N2 in the SLD CRID at the SLAC linear collider. The technique could become important again in future operation to meet the optical and low GWP constraints of future Cherenkov gas radiators. Some examples are explored in this paper.

Open charm production and asymmetry in pNe collisions at sqrt{s_{scriptscriptstyle {textrm{NN}}}} = 68.5,text {Gehspace{-1.00006pt}V}

A measurement of {{D}} ^0 meson production by the LHCb experiment in its fixed-target configuration is presented. The production of {{D}} ^0 mesons is studied with a beam of 2.5 ,text {Tehspace{-1.00006pt}V} protons colliding on a gaseous neon target at rest, corresponding to a nucleon–nucleon centre-of-mass energy of sqrt{s_{scriptscriptstyle text {NN}}} = 68.5,,text {Gehspace{-1.00006pt}V} . The sum of the {{D}} ^0 and {hspace{0.0pt}overline{hspace{0.0pt}{D}}} {}^0 production cross-section in ptext {Ne} collisions in the centre-of-mass rapidity range y^{star }in [-2.29, 0] is found to be sigma _{D^{0}}^{y^star in [-2.29, 0]} = 48.2 pm 0.3 pm 4.5 ,upmu text {b}/text {nucleon} where the first uncertainty is statistical and the second is systematic. The {{{D}} ^0}-{{hspace{0.0pt}overline{hspace{0.0pt}{D}}} {}^0} production asymmetry is also evaluated and suggests a trend towards negative values at large negative y^{star }. The considered models do not account precisely for all the features observed in the LHCb data, but theoretical predictions including 1% intrinsic charm and 10% recombination contributions better describe the data than the other models considered.

Measurement of antiproton production from antihyperon decays in {p} textrm{He} collisions at sqrt{s_{scriptscriptstyle mathrm NN}} =110,text {Gehspace{-1.00006pt}V}

The interpretation of cosmic antiproton flux measurements from space-borne experiments is currently limited by the knowledge of the antiproton production cross-section in collisions between primary cosmic rays and the interstellar medium. Using collisions of protons with an energy of 6.5,text {Tehspace{-1.00006pt}V} incident on helium nuclei at rest in the proximity of the interaction region of the LHCb experiment, the ratio of antiprotons originating from antihyperon decays to prompt production is measured for antiproton momenta between 12 and 110,text {Gehspace{-1.00006pt}V!/}c . The dominant antihyperon contribution, namely {overline{varLambda }} rightarrow {overline{{p}}} {{pi } ^+} decays from promptly produced overline{varLambda } particles, is also exclusively measured. The results complement the measurement of prompt antiproton production obtained from the same data sample. At the energy scale of this measurement, the antihyperon contributions to antiproton production are observed to be significantly larger than predictions of commonly used hadronic production models.

RMS-R3 – the system for monitoring the region of interactions and background at the LHCB experiment (CERN)

The upgraded Large Hadron Collider beauty (LHCb) detector will provide data taken in Run3 at the instantaneous luminosity of proton-proton collisions increased to 2⋅1033 cm-2s-1 at energies of up to 14 TeV. To ensure the safe operation of the experiment, a new beam and background Radiation Monitoring System (RMS-R3) was built. RMS-R3 is based on metal-foil detector technology developed at the Institute for Nuclear Research, National Academy of Sciences of Ukraine (Kyiv, Ukraine). The system comprises four detector modules with two sensors in each. Their frequency response is proportional to the flux of incident charged particles. The modules are located around the beam pipe at a distance of 2.2 m from the interaction point. The results measured during the Run3 in 2022 testify to the reliable operation of the system. Applying the asymmetry method, high-accuracy data were obtained on the localization of the interactions region and the beam and background contribution.

Study of exclusive photoproduction of charmonium in ultra-peripheral lead-lead collisions

The cross-sections of exclusive (coherent) photoproduction J/ψ and ψ(2S) mesons in ultra-peripheral PbPb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV are measured using a data sample corresponding to an integrated luminosity of 228 ± 10 μb−1, collected by the LHCb experiment in 2018. The differential cross-sections are measured separately as a function of transverse momentum and rapidity in the nucleus-nucleus centre-of-mass frame for J/ψ and ψ(2S) mesons. The integrated cross-sections are measured to be {sigma}_{J/psi}^{textrm{coh}} = 5.965 ± 0.059 ± 0.232 ± 0.262 mb and {sigma}_{psi (2S)}^{textrm{coh}} = 0.923 ± 0.086 ± 0.028 ± 0.040 mb, where the first listed uncertainty is statistical, the second systematic and the third due to the luminosity determination. The cross-section ratio is measured to be {sigma}_{psi (2S)}^{textrm{coh}}/{sigma}_{J/psi}^{textrm{coh}} = 0.155 ± 0.014 ± 0.003, where the first uncertainty is statistical and the second is systematic. These results are compatible with theoretical predictions.

Energy deposition studies for the LHCb insertion region of the CERN Large Hadron Collider

The LHCb (Large Hadron Collider beauty) experiment at CERN LHC aims at achieving a significantly higher luminosity than originally planned by means of two major upgrades: the Upgrade I that took place during the Long Shutdown 2 (LS2) and the Upgrade II proposed for LS4. Such an increase in instantaneous and integrated luminosity with respect to the design values requires to reassess the radiation exposure of LHC magnets, cryogenics, and electronic equipment placed in the insertion region 8 (IR8) around LHCb. Monte Carlo simulations are a powerful tool to understand and predict the interaction between particle showers and accelerator elements, especially in case of future scenarios. For this purpose, their validation through the comparison with available measurements is a relevant step. A detailed IR8 model, including the LHCb detector, has been implemented with the fluka code. The objective of this study is to evaluate radiation levels due to proton-proton collisions and benchmark the predicted dose values against beam loss monitor measurements performed in 2018. Finally, we comment on the upcoming LHC run (Run 3, from 2022 to 2025), featuring a first luminosity jump in LHCb.11 MoreReceived 10 June 2022Revised 8 February 2023Accepted 18 April 2023DOI:https://doi.org/10.1103/PhysRevAccelBeams.26.061002Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeam lossBeam techniquesParticle interactionsParticle phenomenaPhysical SystemsAccelerator subsystemsAccelerators & storage ringsHigh-energy accelerators & collidersAccelerators & BeamsParticles & Fields

The LHCb HLT2 Storage System: A 40-GB/s System Made of Commercial Off-the-Shelf Components and Open-Source Software

The LHCb (Large Hadron Collider beauty) experiment is designed to study differences between particles and anti-particles as well as very rare decays in the charm and beauty sector of the standard model at the LHC. With the major upgrade done in view of Run 3, the detector will read-out all events at the full LHC bunch-crossing frequency of 40 MHz. The LHCb data acquisition system will be subject to a considerably increased data rate, reaching a peak of 40 Tb/s. The second stage of the two-stage filtering consists of more than 10000 multi-threaded processes which simultaneously write output files at an aggregated band-width of 100 Gb/s. At the same time, a small number of file-moving processes will read files from the same storage to copy them over to tape-storage. This whole mechanism must run reliably over months and be able to cope with significant fluctuations. Moreover, for cost reasons, it must be built from off-the-shelf components. In this paper we describe LHCb’s solution to this challenge. We show the design, present reasons for the design choices, the configuration and tuning of the adopted software solution, and present performance figures.

The Real-Time System for Distribution of Clock, Control and Monitoring Commands With Fixed Latency of the LHCb Experiment at CERN

The Large Hadron Collider beauty (LHCb) experiment has gone through a major upgrade for LHC Run 3 at European Organization for Nuclear Research (CERN), scheduled to start in the middle of 2022. The entire readout system of the experiment has been replaced by front-end and back-end electronics that are able to record LHC events at the full LHC bunch crossing rate of 40 MHz. To maintain synchronicity across the full system, clock and control commands are originated from a single readout supervisor (SODIN) and distributed downstream through a passive optical network (PON) infrastructure, reaching all the back-end cards of the readout system, via a two-level hierarchy and using PON splitters. A field programmable gate arrays (FPGA) firmware core, called LHCb-PON and based on the CERN timing, trigger, and control (TTC)-PON, is instantiated on SODIN and all back-end cards and provides the communication protocol while ensuring a stable distribution of control commands within the readout period of 25 ns and a clock signal with fixed and deterministic latency with a precision of a few hundreds of picoseconds. This is achieved by the firmware backbone that provides clock recovery and ensures the transmission of a control word downstream with fixed latency. In addition, the LHCb-PON also provides monitoring functionalities over the upstream link, with less strict timing requirements, connecting multiple back-end cards to the central SODIN. This is achieved by having each back-end card send data upstream through a time-division multiplexing (TDM) scheme. This article describes the implementation, measurements, and results from the usage of the system during the startup of the LHC Run 3.

Design and Commissioning of the First 32-Tbit/s Event-Builder

The LHCb experiment is a forward spectrometer, designed to study beauty and charm quarks Physics at the LHC. To exploit of the higher luminosity that will be delivered during Run3, the full experiment needed a substantial upgrade, from the detector to the Data Acquisition (DAQ) and High Level Trigger (HLT). In this paper, we will focus on the new DAQ system for the LHCb experiment; that represents a substantial paradigm shift compared to the previous one, and to similar systems used by similar experiments in the past and present times. To overcome the inefficiencies introduced by a local selection implemented directly with the readout hardware, the Run3 system is designed to perform a full software reconstruction of all the produced events. To achieve this, both the DAQ and the HLT need to process the ~ 30 MHz full event-rate. In particular, this paper will introduce the final design of the system; it will provide a focus on the hardware and software design of the Event Building (EB) and how we integrated technologies designed for the High Performance Computing (HPC) world - like InfiniBand HDR (200 Gb/s)- into the DAQ system; we will present performance measurements of the full EB system under different operational conditions; and we will provide a feedback from EB operation during the beginning of the data-taking.