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A bstract The W boson mass is measured using proton-proton collision data at s = 13 TeV corresponding to an integrated luminosity of 1.7 fb − 1 recorded during 2016 by the LHCb experiment. With a simultaneous fit of the muon q/p T distribution of a sample of W → μν decays and the ϕ * distribution of a sample of Z → μμ decays the W boson mass is determined to be m w = 80354 ± 23 stat ± 10 exp ± 17 theory ± 9 PDF MeV , where uncertainties correspond to contributions from statistical, experimental systematic, theoretical and parton distribution function sources. This is an average of results based on three recent global parton distribution function sets. The measurement agrees well with the prediction of the global electroweak fit and with previous measurements.

A bstract A measurement of the inelastic proton-proton cross section with the CMS detector at a center-of-mass energy of s = 13 TeV is presented. The analysis is based on events with energy deposits in the forward calorimeters, which cover pseudorapidities of −6 . 6 < η < −3 . 0 and +3 . 0 < η < +5 . 2. An inelastic cross section of 68 . 6 ± 0 . 5(syst) ± 1 . 6(lumi) mb is obtained for events with M X > 4 . 1 GeV and/or M Y > 13 GeV, where M X and M Y are the masses of the diffractive dissociation systems at negative and positive pseudorapidities, respectively. The results are compared with those from other experiments as well as to predictions from high-energy hadron-hadron interaction models.

A bstract The cross section for coherent photonuclear production of J/ ψ is presented as a function of the electromagnetic dissociation (EMD) of Pb. The measurement is performed with the ALICE detector in ultra-peripheral Pb-Pb collisions at a centre-of-mass energy per nucleon pair of s NN = 5.02 TeV. Cross sections are presented in five different J/ ψ rapidity ranges within | y | < 4, with the J/ ψ reconstructed via its dilepton decay channels. In some events the J/ ψ is not accompanied by EMD, while other events do produce neutrons from EMD at beam rapidities either in one or the other beam direction, or in both. The cross sections in a given rapidity range and for different configurations of neutrons from EMD allow for the extraction of the energy dependence of this process in the range 17 < W γ Pb , n < 920 GeV, where W γ Pb , n is the centre-of-mass energy per nucleon of the γ Pb system. This range corresponds to a Bjorken- x interval spanning about three orders of magnitude: 1.1 × 10 − 5 < x < 3.3 × 10 − 2 . In addition to the ultra-peripheral and photonuclear cross sections, the nuclear suppression factor is obtained. These measurements point to a strong depletion of the gluon distribution in Pb nuclei over a broad, previously unexplored, energy range. These results, together with previous ALICE measurements, provide unprecedented information to probe quantum chromodynamics at high energies.

A bstract Machine Learning algorithms have played an important role in hadronic jet classification problems. The large variety of models applied to Large Hadron Collider data has demonstrated that there is still room for improvement. In this context Quantum Machine Learning is a new and almost unexplored methodology, where the intrinsic properties of quantum computation could be used to exploit particles correlations for improving the jet classification performance. In this paper, we present a brand new approach to identify if a jet contains a hadron formed by a b or b ¯ quark at the moment of production, based on a Variational Quantum Classifier applied to simulated data of the LHCb experiment. Quantum models are trained and evaluated using LHCb simulation. The jet identification performance is compared with a Deep Neural Network model to assess which method gives the better performance.

A bstract Production cross-sections of prompt charm mesons are measured with the first data from pp collisions at the LHC at a centre-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 4.98 ± 0.19 pb −1 collected by the LHCb experiment. The production cross-sections of D 0 , D + , D s + , and D *+ mesons are measured in bins of charm meson transverse momentum, p T , and rapidity, y , and cover the range 0 < p T < 15GeV/c and 2.0 < y < 4.5. The inclusive cross-sections for the four mesons, including charge conjugation, within the range of 1 < p T < 8 GeV/c are found to be σ pp → D 0 X = 2460 ± 3 ± 130 μ b σ pp → D + X = 1000 ± 3 ± 110 μ b σ pp → D s + X = 460 ± 13 ± 100 μ b σ pp → D ∗ + X = 880 ± 5 ± 140 μ b where the uncertainties are due to statistical and systematic uncertainties, respectively.

A bstract The process pp → p ℓ + ℓ − p (*) , with ℓ + ℓ − a muon or an electron pair produced at midrapidity with mass larger than 110 GeV, has been observed for the first time at the LHC in pp collisions at s = 13 TeV. One of the two scattered protons is measured in the CMS-TOTEM precision proton spectrometer (CT-PPS), which operated for the first time in 2016. The second proton either remains intact or is excited and then dissociates into a low-mass state p * , which is undetected. The measurement is based on an integrated luminosity of 9.4 fb −1 collected during standard, high-luminosity LHC operation. A total of 12 μ + μ − and 8 e + e − pairs with m ( ℓ + ℓ − ) > 110 GeV, and matching forward proton kinematics, are observed, with expected backgrounds of 1 . 49 ± 0 . 07 (stat) ± 0 . 53 (syst) and 2 . 36 ± 0 . 09 (stat) ± 0 . 47 (syst), respectively. This corresponds to an excess of more than five standard deviations over the expected background. The present result constitutes the first observation of proton-tagged γγ collisions at the electroweak scale. This measurement also demonstrates that CT-PPS performs according to the design specifications.

A bstract Production cross-sections of prompt charm mesons are measured using data from pp collisions at the LHC at a centre-of-mass energy of 5 TeV. The data sample corresponds to an integrated luminosity of 8 . 60 ± 0 . 33 pb −1 collected by the LHCb experiment. The production cross-sections of D 0 , D + , D s + , and D ∗+ mesons are measured in bins of charm meson transverse momentum, p T , and rapidity, y . They cover the rapidity range 2 . 0 < y < 4 . 5 and transverse momentum ranges 0 < p T < 10 GeV /c for D 0 and D + and 1 < p T < 10 GeV /c for D s + and D ∗+ mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of 1 < p T < 8 GeV /c are determined to be σ pp → D 0 X = 1004 ± 3 ± 54 μ b , σ pp → D + X = 402 ± 2 ± 30 μ b , σ pp → D s + X = 170 ± 4 ± 16 μ b , σ pp → D ∗ + X = 421 ± 5 ± 36 μ b , where the uncertainties are statistical and systematic, respectively.

A bstract Measurements are reported of the central exclusive production of J/ψ and ψ (2 S ) mesons in pp collisions at a centre-of-mass energy of 13 TeV. Backgrounds are significantly reduced compared to previous measurements made at lower energies through the use of new forward shower counters. The products of the cross-sections and the branching fractions for the decays to dimuons, where both muons are within the pseudorapidity range 2 . 0 < η < 4 . 5, are measured to be σ J / ψ → μ + μ − = 435 ± 18 ± 11 ± 17 p b σ ψ 2 S → μ + μ − = 11.1 ± 1.1 ± 0.3 ± 0.4 p b . The first uncertainties are statistical, the second are systematic, and the third are due to the luminosity determination. The cross-sections are also measured differentially for meson rapidities between 2.0 and 4.5. Good agreement is observed with theoretical predictions. Photoproduction cross-sections are derived and compared to previous experiments, and a deviation from a pure power-law extrapolation of lower energy data is observed.

A bstract The first FASER search for a light, long-lived particle decaying into a pair of photons is reported. The search uses LHC proton-proton collision data at s = 13 . 6 TeV collected in 2022 and 2023, corresponding to an integrated luminosity of 57 . 7 fb − 1 . A model with axion-like particles (ALPs) dominantly coupled to weak gauge bosons is the primary target. Signal events are characterised by high-energy deposits in the electromagnetic calorimeter and no signal in the veto scintillators. One event is observed, compared to a background expectation of 0 . 44 ± 0 . 39 events, which is entirely dominated by neutrino interactions. World-leading constraints on ALPs are obtained for masses up to 300 MeV and couplings to the Standard Model W gauge boson, g aWW , around 10 − 4 GeV − 1 , testing a previously unexplored region of parameter space. Other new particle models that lead to the same experimental signature, including ALPs coupled to gluons or photons, U(1) B gauge bosons, up-philic scalars, and a Type-I two-Higgs doublet model, are also considered for interpretation, and new constraints on previously viable parameter space are presented in this paper.

A bstract A precision measurement of the Z boson production cross-section at s = 13 TeV in the forward region is presented, using pp collision data collected by the LHCb detector, corresponding to an integrated luminosity of 5.1 fb − 1 . The production cross-section is measured using Z → μ + μ − events within the fiducial region defined as pseudorapidity 2 . 0 < η < 4 . 5 and transverse momentum p T > 20 GeV /c for both muons and dimuon invariant mass 60 < M μμ < 120 GeV /c 2 . The integrated cross-section is determined to be σ Z → μ + μ − = 196.4 ± 0.2 ± 1.6 ± 3.9 pb , where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measured results are in agreement with theoretical predictions within uncertainties.