We provide an update on QCD predictions for top-quark pair production close to threshold including bound state effects at the Large Hadron Collider. We compute the top-quark pair invariant mass distribution dσ/dMtt¯, including Coulomb resummation for bound-state effects, as well as threshold resummation for emissions of soft and collinear gluons. We discuss uncertainty estimates and present a proposal for the use of these predictions in experimental analyses.

Abstract We study the impact of state-of-the-art top-quark data collected at the large hadron collider on parton distribution functions (PDFs). Following the ABMP methodology, the fit extracts simultaneously proton PDFs, the strong coupling $$\alpha _s(M_Z)$$ α s ( M Z ) and heavy-quark masses at next-to-next-to-leading order (NNLO) accuracy in QCD. It includes recent high-statistics data on absolute total inclusive cross sections for $$t\bar{t}+X$$ t t ¯ + X , the sum of $$(t + X)$$ ( t + X ) and $$(\bar{t} + X)$$ ( t ¯ + X ) hadroproduction, and normalized inclusive data double-differential in the invariant mass and rapidity of the $$t\bar{t}$$ t t ¯ pair at $$\sqrt{S}=13$$ S = 13 TeV. The gluon PDF at large x and the top-quark mass value derived from these data are well compatible with the previous ABMP16 results, but with significantly smaller uncertainties, reduced by up to a factor of two. At NNLO in QCD we obtain for the strong coupling the value $$\alpha _s^{(n_f=5)}(M_Z)= 0.1150 \pm 0.0009$$ α s ( n f = 5 ) ( M Z ) = 0.1150 ± 0.0009 and for the top-quark mass in the $${\overline{\text{ MS }}}$$ MS ¯ -scheme $$m_t(m_t) = 160.6 \pm 0.6$$ m t ( m t ) = 160.6 ± 0.6 GeV, corresponding to $$m_t^\textrm{pole} = 170.2 \pm 0.7$$ m t pole = 170.2 ± 0.7 GeV in the on-shell scheme. The new fit, dubbed ABMPtt, is publicly released in grids in LHAPDF format.

We describe the fits of the top-quark mass value at NNLO using as input the double-differential distributions in rapidity and invariant mass of tt̅ pairs obtained by the ATLAS and CMS collaborations from unfolding of their experimental data to the parton level, compared to NNLO theory predictions. We consider different state-of-the-art PDF sets, finding results of the fits compatible among each other within uncertainties. On the other hand, we observe some tension among the fits to different datasets.

We extract the top-quark mass value in the on-shell renormalization scheme from the comparison of theoretical predictions for pp → tt + X at next-to-next-to-leading order (NNLO) QCD accuracy with experimental data collected by the ATLAS and CMS collaborations for absolute total, normalized single-differential and double-differential cross-sections during Run 1, Run 2 and the ongoing Run 3 at the Large Hadron Collider (LHC). For the theory computations of heavy-quark pair-production we use the MATRIX framework, interfaced to PineAPPL for the generation of grids of theory predictions, which can be efficiently used a-posteriori during the fit, performed within xFitter. We take several state-of-the-art parton distribution functions (PDFs) as input for the fit and evaluate their associated uncertainties, as well as the uncertainties arising from renormalization and factorization scale variation. Fit uncertainties related to the datasets are also part of the extracted uncertainty of the top-quark mass and turn out to be of similar size as the combined scale and PDF uncertainty. Fit results from different PDF sets agree among each other within 1σ uncertainty, whereas some datasets related to tt decay in different channels (dileptonic vs. semileptonic) point towards top-quark mass values in slight tension among each other, although still compatible within 2.5 σ accuracy. Our results are compatible with the PDG 2022 top-quark pole-mass value. Our work opens the road towards more complex simultaneous NNLO fits of PDFs, the strong coupling αs(MZ) and the top-quark mass, using the currently most precise experimental data on tt + X total and multi-differential cross sections from the LHC.

The azimuthal correlation angle, Δϕ , between the scattered lepton and the leading jet in deep inelastic e^±p scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of √(s) = 318 GeV , corresponding to an integrated luminosity of 326 pb^-1 . A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality 10 GeV^2< Q^2 < 350 GeV^2 , inelasticity 0.04< y < 0.7 , outgoing lepton energy E_e > 10 GeV , lepton polar angle 140^∘< θ _e < 180^∘ , jet transverse momentum 2.5 GeV< p_T,jet < 30 GeV , and jet pseudorapidity -1.5< η _jet < 1.8 . Jets were reconstructed using the k_T algorithm with the radius parameter R = 1 . The leading jet in an event is defined as the jet that carries the highest p_T,jet . Differential cross sections, dσ /dΔϕ , were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity. Perturbative calculations at 𝒪(α _s^2) accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near Δϕ→π for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD. The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.

We describe our recent NNLO QCD extraction of the top-quark pole mass from fits to experimental data on total inclusive and normalized (multi)-differential cross sections for tt̅ + X hadroproduction, using as input various modern PDF + α_s(M_Z) sets. We find top-quark mass values compatible among each other and with the PDG 2024 preferred value.

The measurement of charmonium states produced in proton-neon ( pNe ) collisions by the LHCb experiment in its fixed-target configuration is presented. The production of J/ψ and ψ(2S) mesons is studied with a beam of 2.5 TeV protons colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy √(s_NN) =68.5 GeV . The data sample corresponds to an integrated luminosity of 21.7± 1.4 nb ^-1 . The J/ψ and ψ(2S) hadrons are reconstructed in μ ^+ μ ^- final states. The J/ψ production cross-section per target nucleon in the centre-of-mass rapidity range y^⋆∈ [-2.29, 0] is found to be 506 ± 8 ± 46 nb/nucleon . The ratio of J/ψ and D^0 cross-sections is evaluated to (1.06 ± 0.02 ± 0.09)% . The ψ(2S) to J/ψ relative production rate is found to be (1.67 ± 0.27± 0.10)% in good agreement with other measurements involving beam and target nuclei of similar sizes.

The decay B- -> Lambda(+)(c)(Lambda) over bar K--(c)- is studied in proton-proton collisions at a center-of-mass energy of root s = 13 TeV using data corresponding to an integrated luminosity of 5 fb(-1) collected by the LHCb experiment. In the Lambda K-+(c)- 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)(2930)(0) = 2924.5 +/- 0.4 +/- 1.1 Mev, m Xi(c)(2930)(0)) = 2938.5 +/- 0.9 +/- 2.3 Mev, Gamma(Xi(c)(2930)(0)) = 4.8 +/- 0.9 +/- 1.5 MeV, Gamma(Xi(c)(2930)(0) - 11.0 +/- 1.9 +/- 7.5 MeV, where the first uncertainties are statistical and the second systematic. The results are consistent with a previous LHCb measurement using a prompt Lambda K-+(c)- sample. Evidence of a new Xi(c)(2930)(0) state is found with a local significance of 3.8 sigma, whose mass and width are measured to be 2881.8 +/- 3.1 +/- 8.5 MeV and 12.4 +/- 5.3 +/- 5.8 MeV, respectively. In addition, evidence of a new decay mode Xi(c)(2930)(0) -> Lambda K-+(c) is found with a significance of 3.7 sigma. The relative branching fraction of B- -> Lambda(+)(c)(Lambda) over bar K--(c)- with respect to the B- -> D+D-K- decay is measured to be 2.36 +/- 0.11 +/- 0.22 +/- 0.25, where the first uncertainty is statistical, the second systematic and the third originates from the branching fractions of charm hadron decays.

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 < pT < 100 GeV and in the pseudorapidity range 2.5 < ? < 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.

A search for K-S(L)(0) -> mu(+) mu(-) mu(+) mu(-) decays is performed 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 5.1 fb(-1). No evidence for signal is found. The 90% confidence level upper limits are the first set for both decays and are B(K-S(0)) -> mu(+) mu(-) mu(+) mu(-)) < 5.1 x 10(-12) and B(K-L(0))-> mu(+) mu(-) mu(+) mu(-)) < 2.3 x 10(-9).

This article presents the first measurement of the differential Z-boson production cross-section in the forward region using proton-lead collisions with the LHCb detector. The dataset was collected at a nucleon-nucleon centre-of-mass energy of √(s_NN) = 8.16 TeV in 2016, corresponding to an integrated luminosity of 30.8 nb−1. The forward-backward ratio and the nuclear modification factors are measured together with the differential cross-section as functions of the Z boson rapidity in the centre-of-mass frame, the transverse momentum of the Z boson and a geometric variable ϕ*. The results are in good agreement with the predictions from nuclear parton distribution functions, providing strong constraining power at small Bjorken-x.

An amplitude analysis of the D+ → π−π+π+ decay is performed with a sample corresponding to 1.5 fb−1 of integrated luminosity of pp collisions at a centre-of-mass energy √(s) = 8 TeV collected by the LHCb detector in 2012. The sample contains approximately six hundred thousand candidates with a signal purity of 95

The CKM angle γ is determined from CP-violating observables measured in B± → D[K∓π±π±π∓]h±, (h = K, π) decays, where the measurements are performed in bins of the decay phase-space of the D meson. Using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 9 fb−1, γ is determined to be γ =(54.8[ +6.0; -5.8 ][ +0.6; -0.6 ][ +6.7; -4.3 ])^∘, where the first uncertainty is statistical, the second systematic and the third from the external inputs on the coherence factors and strong phases of the D-meson decays.

The production cross-sections of Υ mesons, namely Υ(1S), Υ(2S) and Υ(3S), in pp collisions at √(s) = 5 TeV are measured with a data sample corresponding to an integrated luminosity of 9.13 ± 0.18 pb−1 collected by the LHCb detector. The Υ mesons are reconstructed in the decay mode Υ → μ+μ−. Double differential cross-sections times branching fractions, as functions of the transverse momentum pT and the rapidity y of the Υ mesons, are measured in the range pT < 20 GeV/c and 2.0 < y < 4.5. The results integrated over these pT and y ranges are σ(Y(1S))×ℬ(Y(1S)→μ^+μ^-)=2101± 33± 83 pb, σ(Y(2S))×ℬ(Y(2S)→μ^+μ^-)=526± 20± 21 pb, σ(Y(3S))×ℬ(Y(3S)→μ^+μ^-)=242± 16± 10 pb, where the first uncertainties are statistical and the second are systematic. The ratios of cross-sections between measurements of two different Υ states and between measurements at different centre-of-mass energies are determined. The nuclear modification factor of Υ(1S) at √(s) = 5 TeV is updated as well using the directly measured cross-section results from this analysis.

A study of the B → KS0K+K-π+ and B → KS0K+K+π- decays is performed using proton-proton collisions at center-of-mass energies of 7, 8 and 13 TeV at the LHCb experiment. The KS0K±π± invariant mass spectra from both decay modes reveal a rich content of charmonium resonances, such as ηc, J/ψ, ηc(2S) and χc1. Precise measurements of their parameters and branching fractions are obtained. Dalitz plot analyses of ηc → KS0K±π± and ηc(2S) → KS0K±π± decays are performed.

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 TeV protons colliding on a gaseous neon target at rest, corresponding to a nucleon–nucleon centre-of-mass energy of √(s_NN) = 68.5 GeV . The sum of the D ^0 and D^0 production cross-section in pNe collisions in the centre-of-mass rapidity range y^⋆∈ [-2.29, 0] is found to be σ _D^0^y^⋆∈ [-2.29, 0] = 48.2 ± 0.3 ± 4.5 b/nucleon where the first uncertainty is statistical and the second is systematic. The D ^0-D^0 production asymmetry is also evaluated and suggests a trend towards negative values at large negative y^⋆ . 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.

Searches for CP violation in the decays D_(s)^+→ηπ^+ and D_(s)^+→η^'π^+ are performed using pp collision data corresponding to 6 fb−1 of integrated luminosity collected by the LHCb experiment. The calibration channels D_(s)^+→ϕπ^+ are used to remove production and detection asymmetries. The resulting CP-violating asymmetries are [ 𝒜^CP=(D^+→ηπ^+)=(0.34± 0.66± 0.16± 0.05)%,; 𝒜^CP=(D_s^+→ηπ^+)=(0.32± 0.51± 0.12)%,; [ 𝒜^CP=(D^+→η^'π^+)=(0.49± 0.18± 0.06± 0.05)%,; 𝒜^CP=(D_s^+→η^'π^+)=(0.01± 0.12± 0.08)%, ] ] where the first uncertainty is statistical, the second is systematic and the third, relevant for the D+ channels, is due to the uncertainty on 𝒜^CP=(D^+→ϕπ^+) . These measurements, currently the most precise for three of the four channels considered, are consistent with the absence of CP violation. A combination of these results with previous LHCb measurements is presented.

A measurement of charm mixing and CP-violating parameters is reported, using B over bar -> D0(-> K0S pi+pi-)x mu- nu over bar mu X decays reconstructed in proton-proton collisions collected by the LHCb experiment during the years 2016 to 2018, corresponding to an integrated luminosity of 5.4 fb-1. The measured mixing and CP-violating parameters are xCP = [4.29 1 1.48(stat) 1 0.26(syst)] x 10-3, yCP = [12.61 1 3.12(stat) 1 0.83(syst)] x 10-3, Ax = [-0.77 1 0.93(stat) 1 0.28(syst)] x 10-3, Ay = [3.01 1 1.92(stat) 1 0.26(syst)] x 10-3. The results are complementary to and consistent with previous measurements. A combination with the recent LHCb analysis of D*+ -> D0(-> K0S pi+ pi-)pi+ decays is reported.