LHCb Detector Research Articles

High-density gas target at the LHCb experiment

The recently installed internal gas target at LHCb presents exceptional opportunities for an extensive physics program for heavy-ion, hadron, spin, and astroparticle physics. A storage cell placed in the LHC primary vacuum, an advanced Gas Feed System, the availability of multi-TeV proton and ion beams, and the recent upgrade of the LHCb detector make this project unique worldwide. In this paper, we outline the main components of the system, the physics prospects it offers, and the hardware challenges encountered during its implementation. The commissioning phase has yielded promising results, demonstrating that fixed-target collisions can occur concurrently with the collider mode without compromising efficient data acquisition and high-quality reconstruction of beam-gas and beam-beam interactions. Published by the American Physical Society 2024

Search for the lepton-flavor violating decay Bs0→ϕμ±τ∓

A search for the lepton-flavor violating decays Bs0→ϕμ±τ∓ is presented, using a sample of proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9 fb−1. The τ leptons are selected using decays with three charged pions. No significant excess is observed, and an upper limit on the branching fraction is determined to be B(Bs0→ϕμ±τ∓)<1.0×10−5 at 90% confidence level. © 2024 CERN, for the LHCb Collaboration 2024 CERN

Observation of muonic Dalitz decays of chib mesons and precise spectroscopy of hidden-beauty states

The decays of the χb1(1P), χb2(1P), χb1(2P) and χb2(2P) mesons into the Υ(1S)μ+μ− final state are observed with a high significance using proton-proton collision data collected with the LHCb detector and corresponding to an integrated luminosity of 9 fb−1. The newly observed decays together with the Υ(2S) → Υ(1S)π+π− and Υ(3S) → Υ(2S)π+π− decay modes are used for precision measurements of the mass and mass splittings for the hidden-beauty states.

Exotic Hadrons at LHCb

It has been 5 years since the data sample from the LHCb detector, the first experiment optimized for heavy-flavor physics studies at a hadronic collider, was completed. These data led to many major discoveries in exotic hadron spectroscopy, which we review in this article. We supplement the experimental results with a selection of phenomenological interpretations. As the upgraded LHCb detector is expected to collect a larger data sample starting in 2024, we also discuss the potential of the LHCb program in exotic hadron physics for the near future and beyond.

Upgrade of the LHCb RICH detectors and characterization of the new opto-electronics chain

The LHCb detector has been upgraded to manage a five-fold increase in the instantaneous luminosity delivered to the experiment during LHC Run 3 and to readout data at the full bunch crossing rate of 40 MHz. The enhanced LHCb RICH detectors now feature Multianode Photomultiplier Tubes (MaPMTs), covering a total area of approximately 4 square meters, and brand-new frontend electronics to comply with the trigger-less readout architecture. The opto-electronics chain is capable of detecting single photons at repetition rates of up to 100 MHz/cm2 while maintaining an exceptionally low noise. The RICH upgrade is comprehensively outlined, including details about the characterization and studies on the photon detection system. The stability and uniformity achieved by optimizing the parameters of the opto-electronics chain enable the RICH system to function successfully and to provide excellent charged hadron identification in high occupancy conditions.

First observation of Λb0→Σc(*)++D(*)−K− decays

The four decays, Λb0→Σc(*)++D(*)−K−, are observed for the first time using proton-proton collision data collected with the LHCb detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb−1. By considering the Λb0→Λc+D¯0K− decay as reference channel, the following branching fraction ratios are measured to be B(Λb0→Σc++D−K−)B(Λb0→Λc+D¯0K−)=0.282±0.016±0.016±0.005, B(Λb0→Σc*++D−K−)B(Λb0→Σc++D−K−)=0.460±0.052±0.028, B(Λb0→Σc++D*−K−)B(Λb0→Σc++D−K−)=2.261±0.202±0.129±0.046, B(Λb0→Σc*++D*−K−)B(Λb0→Σc++D−K−)=0.896±0.137±0.066±0.018, where the first uncertainties are statistical, the second are systematic, and the third are due to uncertainties in the branching fractions of intermediate particle decays. These initial observations mark the beginning of pentaquark searches in these modes, with more datasets to become available following the LHCb upgrade. © 2024 CERN, for the LHCb Collaboration 2024 CERN

Amplitude analysis and branching fraction measurement of B+→D∗−Ds+π+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}^{+}\ o {D}^{\\ast -}{D}_s^{+}{\\pi}^{+} $$\\end{document} decays

The decays of the B+ meson to the final state D∗−Ds+π+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {D}^{\\ast -}{D}_s^{+}{\\pi}^{+} $$\\end{document} are studied in proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb−1. The ratio of branching fractions of the B+→D∗−Ds+π+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}^{+}\ o {D}^{\\ast -}{D}_s^{+}{\\pi}^{+} $$\\end{document} and B0→D∗−Ds+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}^0\ o {D}^{\\ast -}{D}_s^{+} $$\\end{document} decays is measured to be 0.173 ± 0.006 ± 0.010, where the first uncertainty is statistical and the second is systematic. Using partially reconstructed Ds∗+→Ds+γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {D}_s^{\\ast +}\ o {D}_s^{+}\\gamma $$\\end{document} and Ds+π0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {D}_s^{+}{\\pi}^0 $$\\end{document} decays, the ratio of branching fractions between the B+→D∗−Ds∗+π+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}^{+}\ o {D}^{\\ast -}{D}_s^{\\ast +}{\\pi}^{+} $$\\end{document} and B+→D∗−Ds+π+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}^{+}\ o {D}^{\\ast -}{D}_s^{+}{\\pi}^{+} $$\\end{document} decays is determined as 1.31 ± 0.07 ± 0.14. An amplitude analysis of the B+→D∗−Ds+π+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}^{+}\ o {D}^{\\ast -}{D}_s^{+}{\\pi}^{+} $$\\end{document} decay is performed for the first time, revealing dominant contributions from known excited charm resonances decaying to the D*−π+ final state. No significant evidence of exotic contributions in the Ds+π+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {D}_s^{+}{\\pi}^{+} $$\\end{document} or D∗−Ds+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {D}^{\\ast -}{D}_s^{+} $$\\end{document} channels is found. The fit fraction of the scalar state Tcs¯0∗2900++\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {T}_{c\\overline{s}0}^{\\ast }{(2900)}^{++} $$\\end{document} observed in the B+→D−Ds+π+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}^{+}\ o {D}^{-}{D}_s^{+}{\\pi}^{+} $$\\end{document} decay is determined to be less than 2.3% at a 90% confidence level.

Функціональні характеристики системи RMS-R3 у третій серії фізичних вимірювань в експерименті LHCb

The upgraded LHCb detector allows the collection of data in the third physics run at instantaneous luminosity up to 2·1033 cm-2s-1 in proton-proton collisions at energy up to 14 TeV. A set of high-speed monitoring systems, including the RMS-R3 system, which monitors the nuclear interactions in the interaction region of the IP-8 (LHCb) experiment and the background, ensures the effective conduct of the experiment. An important functional characteristic of this system is the observation of luminosity stability over a wide dynamic range, which in its upper limit provides a linear response at ten times the nominal luminosity. This paper illustrates a new functionality feature of the RMS-R3, which is its ability to produce highly accurate data on the localization of the physical events of nuclear collisions in the interaction region of the experiment. The data measured in 2022 - 2023 allow us to observe the parameter variation impact of the nucleus-nucleus average number interactions in a single bunch crossing of the beams, the change of the state of the VELO detector and the injection of gaseous target SMOG2 by different gases.

The LHCb VELO Upgrade module construction

The LHCb detector has undergone a major upgrade for LHC Run 3. This Upgrade I detector facilitates operation at higher luminosity and utilises full-detector information at the LHC collision rate, critically including the use of vertex information. A new vertex locator system, the VELO Upgrade, has been constructed. The core element of the new VELO are the double-sided pixelated hybrid silicon detector modules which operate in vacuum close to the LHC beam in a high radiation environment. The construction and quality assurance tests of these modules are described in this paper. The modules incorporate 200 μm thick, n-on-p silicon sensors bump-bonded to 130 nm technology ASICs. These are attached with high precision to a silicon microchannel substrate that uses evaporative CO2 cooling. The ASICs are controlled and read out with flexible printed circuits that are glued to the substrate and wire-bonded to the chips. The mechanical support of the module is given by a carbon fibre plate, two carbon fibre rods and an aluminium plate. The sensor attachment was achieved with an average precision of 21 μm, more than 99.5% of all pixels are fully functional, and a thermal figure of merit of 3 Kcm2W-1 was achieved. The production of the modules was successfully completed in 2021, with the final assembly and installation completed in time for data taking in 2022.

Search for Bc+→π+μ+μ-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{B} _{c} ^+} \\!\\rightarrow {{\\pi } ^+} {\\mu ^+\\mu ^-} $$\\end{document} decays and measurement of the branching fraction ratio B(Bc+→ψ(2S)π+)/B(Bc+→J/ψπ+)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathcal {B}} ({{B} _{c} ^+} \\!\\rightarrow {\\psi {(2S)}} {{\\pi } ^+} )/{\\mathcal {B}} ({{B} _{c} ^+} \\!\\rightarrow {{J \\hspace{-1.66656pt}/\\hspace{-1.111pt}\\psi }} {{\\pi

The first search for nonresonant Bc+→π+μ+μ-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{B} _{c} ^+} \\!\\rightarrow {{\\pi } ^+} {\\mu ^+\\mu ^-} $$\\end{document} decays is reported. The analysis uses proton–proton collision data collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9fb-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\,\ ext {fb} ^{-1}$$\\end{document}. No evidence for an excess of signal events over background is observed and an upper limit is set on the branching fraction ratio B(Bc+→π+μ+μ-)/B(Bc+→J/ψπ+)<2.1×10-4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathcal {B}} ({{B} _{c} ^+} \\!\\rightarrow {{\\pi } ^+} {\\mu ^+\\mu ^-} )/{\\mathcal {B}} ({{B} _{c} ^+} \\!\\rightarrow {{J \\hspace{-1.66656pt}/\\hspace{-1.111pt}\\psi }} {{\\pi } ^+} ) < 2.1\ imes 10^{-4}$$\\end{document} at 90%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$90\\%$$\\end{document} confidence level. Additionally, an updated measurement of the ratio of the Bc+→ψ(2S)π+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{B} _{c} ^+} \\!\\rightarrow {\\psi {(2S)}} {{\\pi } ^+} $$\\end{document} and Bc+→J/ψπ+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{B} _{c} ^+} \\!\\rightarrow {{J \\hspace{-1.66656pt}/\\hspace{-1.111pt}\\psi }} {{\\pi } ^+} $$\\end{document} branching fractions is reported. The ratio B(Bc+→ψ(2S)π+)/B(Bc+→J/ψπ+)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathcal {B}} ({{B} _{c} ^+} \\!\\rightarrow {\\psi {(2S)}} {{\\pi } ^+} )/{\\mathcal {B}} ({{B} _{c} ^+} \\!\\rightarrow {{J \\hspace{-1.66656pt}/\\hspace{-1.111pt}\\psi }} {{\\pi } ^+} )$$\\end{document} is measured to be 0.254±0.018±0.003±0.005\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.254\\pm 0.018 \\pm 0.003 \\pm 0.005$$\\end{document}, where the first uncertainty is statistical, the second systematic, and the third is due to the uncertainties on the branching fractions of the leptonic J/ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${J \\hspace{-1.66656pt}/\\hspace{-1.111pt}\\psi }$$\\end{document} and ψ(2S)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\psi {(2S)}$$\\end{document} decays. This measurement is the most precise to date and is consistent with previous LHCb results.

Recent LHCb results on forward physics and diffraction

The LHCb detector at the LHC offers unique coverage of forward rapidities for studies of Central Exclusive Production (CEP) and soft QCD. CEP measurements allow the investigation of the nature of pomerons, and provide constraints on low-x gluon phenomenology, probing potential saturation effects. Moreover LHCb can test phenomenological models of soft QCD processes, by measuring the production of forward hadrons in pp collisions. In this talk the latest results from the LHCb experiment will be presented.

Fraction of χ_{c} Decays in Prompt J/ψ Production Measured in pPb Collisions at sqrt[s_{NN}]=8.16 TeV.

The fraction of χ_{c1} and χ_{c2} decays in the prompt J/ψ yield, F_{χ_{c}→J/ψ}=σ_{χ_{c}→J/ψ}/σ_{J/ψ}, is measured by the LHCb detector in pPb collisions at sqrt[s_{NN}]=8.16 TeV. The study covers the forward (1.5<y^{*}<4.0) and backward (-5.0<y^{*}<-2.5) rapidity regions, where y^{*} is the J/ψ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of 13.6±0.3 and 20.8±0.5 nb^{-1}, respectively. The result is presented as a function of the J/ψ transverse momentum p_{T,J/ψ} in the range 1<p_{T,J/ψ}<20 GeV/c. The F_{χ_{c}→J/ψ} fraction at forward rapidity is compatible with the LHCb measurement performed in pp collisions at sqrt[s]=7 TeV, whereas the result at backward rapidity is 2.4σ larger than in the forward region for 1<p_{T,J/ψ}<3 GeV/c. The increase of F_{χ_{c}→J/ψ} at low p_{T,J/ψ} at backward rapidity is compatible with the suppression of the ψ(2S) contribution to the prompt J/ψ yield. The lack of in-medium dissociation of χ_{c} states observed in this study sets an upper limit of 180MeV on the free energy available in these pPb collisions to dissociate or inhibit charmonium state formation.

Curvature-bias corrections using a pseudomass method

Momentum measurements for very high momentum charged particles, such as muons from electroweak vector boson decays, are particularly susceptible to charge-dependent curvature biases that arise from misalignments of tracking detectors. Low momentum charged particles used in alignment procedures have limited sensitivity to coherent displacements of such detectors, and therefore are unable to fully constrain these misalignments to the precision necessary for studies of electroweak physics. Additional approaches are therefore required to understand and correct for these effects. In this paper the curvature biases present at the LHCb detector are studied using the pseudomass method in proton-proton collision data recorded at centre of mass energy √(s)=13 TeV during 2016, 2017 and 2018. The biases are determined using Z→μ + μ - decays in intervals defined by the data-taking period, magnet polarity and muon direction. Correcting for these biases, which are typically at the 10-4 GeV-1 level, improves the Z→μ + μ - mass resolution by roughly 18% and eliminates several pathological trends in the kinematic-dependence of the mean dimuon invariant mass.

Impact of the LHCb 8 [formula omitted], [formula omitted], and asymmetry data on the CT14HERA2 PDFs

First, we calculate the total cross-sections and differential cross-sections of the W and Z productions at next-to-leading order QCD using ResBos and CT14HERA2 PDFs, and compare with the measurements from the LHCb detector at a center-of-mass energy of 8 TeV and find good agreement between the experimental data and theoretical predictions. Then, we analyze the impact of LHCb 8 TeV W, Z, and asymmetry data on CT14HERA2 PDFs( g(x,Q), u(x,Q), d(x,Q), ū(x,Q), d̄(x,Q), d(x,Q)/u(x,Q) ) using the Error PDF Updating Method Package. Through this analysis, we find that the LHCb 8 TeV W and Z data prefer softer gloun and d(x,Q) at large x region, but have no significant impacts on u(x,Q) PDF.

Production of η and η′ mesons in pp and pPb collisions

The production of η and η′ mesons is studied in proton-proton and proton-lead collisions collected with the LHCb detector. Proton-proton collisions are studied at center-of-mass energies of 5.02 and 13TeV and proton-lead collisions are studied at a center-of-mass energy per nucleon of 8.16TeV. The studies are performed in center-of-mass (c.m.) rapidity regions 2.5&lt;yc.m.&lt;3.5 (forward rapidity) and −4.0&lt;yc.m.&lt;−3.0 (backward rapidity) defined relative to the proton beam direction. The η and η′ production cross sections are measured differentially as a function of transverse momentum for 1.5&lt;pT&lt;10GeV and 3&lt;pT&lt;10GeV, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for η and η′ mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of η mesons are also used to calculate η/π0 cross-section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass-dependent nuclear effects in heavy-ion collisions, as well as η and η′ meson fragmentation. ©2024 CERN, for the LHCb Collaboration 2024 CERN

Improved Measurement of CP Violation Parameters in B_{s}^{0}→J/ψK^{+}K^{-} Decays in the Vicinity of the ϕ(1020) Resonance.

The decay-time-dependent CP asymmetry in B_{s}^{0}→J/ψ(→μ^{+}μ^{-})K^{+}K^{-} decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 6 fb^{-1}, collected with the LHCb detector at a center-of-mass energy of 13TeV. Using a sample of approximately 349 000 B_{s}^{0} signal decays with an invariant K^{+}K^{-} mass in the vicinity of the ϕ(1020) resonance, the CP-violating phase ϕ_{s} is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the B_{s}^{0}-B[over ¯]_{s}^{0} system, ΔΓ_{s}, and the difference of the average B_{s}^{0} and B^{0} meson decay widths, Γ_{s}-Γ_{d}. The values obtained are ϕ_{s}=-0.039±0.022±0.006 rad, ΔΓ_{s}=0.0845±0.0044±0.0024 ps^{-1}, and Γ_{s}-Γ_{d}=-0.0056_{-0.0015}^{+0.0013}±0.0014 ps^{-1}, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements to date and are consistent with expectations based on the Standard Model and with the previous LHCb analyses of this decay. These results are combined with previous independent LHCb measurements. The phase ϕ_{s} is also measured independently for each polarization state of the K^{+}K^{-} system and shows no evidence for polarization dependence.

Constraining the low-x structure of nuclei with LHCb

The LHCb detector’s forward geometry provides unprecedented access to the very low regions of Bjorken x inside the nucleon. With full particle ID and a fast DAQ, LHCb is able to fully reconstruct plentiful charged particles and neutral mesons, as well as relatively rare probes such as heavy quarks, providing a unique set of constraints on nucleon structure functions. This contribution will discuss recent LHCb measurements sensitive to the low-x structure of nucleons, and discuss the impact of recent LHCb measurements that dramatically reduce nPDF uncertainties.

Fast Inclusive Flavour Tagging at LHCb

The task of identifying B meson flavor at the primary interaction point in the LHCb detector is crucial for measurements of mixing and timedependent CP violation. Flavor tagging is usually done with a small number of expert systems that find important tracks to infer the B meson flavor from. Recent advances show that replacing all of those expert systems with one ML algorithm that considers all tracks in an event yields an increase in tagging power. However, training the current classifier takes a long time and it is not suitable for use in real time triggers. In this work we present a new classifier, based on the DeepSet architecture. With the right inductive bias of permutation invariance, we achieve great speedups in training (multiple hours vs 10 minutes), a factor of 4-5 speed-up in inference for use in real time environments like the trigger and less tagging asymmetry. For the first time we investigate and compare performances of these “Inclusive Flavor Taggers” on simulation of the upgraded LHCb detector for the third run of the LHC.

Event and data persistency models for the LHCb Real Time Analysis System

Starting in 2022, the upgraded LHCb detector is collecting data with a pure software trigger. In its first stage, reducing the rate from 30MHz to about 1MHz, GPUs are used to reconstruct and trigger on B and D meson topologies and high-pT objects in the event. In its second stage, a CPU farm is used to reconstruct the full event and perform candidate selections, which are persisted for offline use with an output rate of about 10GB/s. Fast data processing, flexible and custom-designed data structures tailored for SIMD architectures and efficient storage of the intermediate data at various steps of the processing pipeline onto persistent media, e.g. tapes is essential to guarantee the full physics program of LHCb. We present the event model and data persistency developments for the trigger of LHCb in Run 3. Particular emphasis is given to the novel software-design aspects with respect to the Run 1+2 data taking, the performance improvements which can be achieved and the experience of restructuring a major part of the reconstruction software in a large HEP experiment.

Gpu-based optical photon simulation for the LHCb RICH 1 detector

We present the investigation of the use of Opticks, a GPU-accelerated optical photon interface with the LHCb detector simulation, to improve computation time of optical photon propagation. The hybrid workflow, combining the particle simulation package Geant4 and Opticks, offloads optical photon propagation to GPUs, thereby accelerating the overall simulation process. The consistency of the results obtained from Geant4 and Opticks simulations is verified with a simplified LHCb RICH1 detector geometry, demonstrating the feasibility of the proposed approach. In addition, the ongoing transition to the NVIDIA OptiX 7 API and re-structuring of Opticks code is discussed within the context of HEP simulation workflows, with caveats explored.