Abstract: The production of a W boson in association with a single charm quark is studied using 4.6 fb(-1) of pp collision data at root s = 7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96(-0.30)(+0.26) at Q (2) = 1.9 GeV2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio sigma(W (+) +)/sigma(W (-) + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s-(s) over bar quark asymmetry.

Abstract: The lifetimes of the Omega(0)(c) and Xi(0)(c) baryons are measured using a pp collision dataset collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). The charm baryons are produced in the fully reconstructed decay chains Omega(-)(b) -> Omega(0)(c)(-> pK(-)K(-)pi(+))pi(-) and Xi(-)(b) -> Xi(0)(c)(-> pK(-)K(-)pi(+))pi(-). The measurement uses topologically and kinematically similar B- -> D-0(-> K-K+pi(-)pi(+))pi(-) decays for normalisation. The measured lifetimes are tau(Omega c0) = 276.3 +/- 19.4 (stat) +/- 1.8 (syst) +/- 0.7(tau(D0))fs, tau(Xi c0) = 149.2 +/- 2.5 (stat) +/- 0.9 (syst) +/- 0.4(tau(D0))fs, where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the D-0 lifetime. These results are consistent with previous measurements performed by the LHCb experiment.

Abstract: An amplitude analysis of the D-s1(2460)(+) -> D-s(+)pi(+)pi(-) transition is performed simultaneously in B-0 -> D-Ds+pi(+)pi(-), B+ -> (D) over bar D-0(s)+pi(+)pi(-), and B-0 -> D*D--(s)+pi(+)pi(-) decays. The study is based on a data sample of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of root s = 7,8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb(-1). A clear double-peak structure is observed in the m(pi(+)pi(-)) spectrum of the D-s1(2460)(+) -> D-s(+)pi(+)pi(-) decay. The data can be described either with a model including f(0)(500), f(0)(980), and f(2)(1270) resonances, in which the contributions of f(0)(980) and f(2)(1270) are unexpectedly large, or with a model including f(0)(500), a doubly charged open-charm tetraquark state T-c (s) over bar(++) and its isospin partner T-c (s) over bar(0). If the former is considered implausible, the T-c (s) over bar states are observed with high significance, and the data are consistent with isospin symmetry. When imposing isospin constraints between the two T-c (s) over bar states, their mass and width are determined to be (2327 +/- 13 +/- 13) MeV and (96 +/- 16(-23)(+170)) MeV, respectively, where the first uncertainty is statistical and the second is systematic. The mass is slightly below the DK threshold, and a spin-parity of 0(+) is favoured with high significance. (c) 2025 The Authors. Published by Elsevier B.V. and Science China Press.

Abstract: The resonant structure of the doubly Cabibbo-suppressed decay D+-> K-K+K+ is studied for the first time. The measurement is based on a sample of pp-collision data, collected at a centre-of-mass energy of 8 TeV with the LHCb detector and corresponding to an integrated luminosity of 2 fb(-1). The amplitude analysis of this decay is performed with the isobar model and a phenomenological model based on an effective chiral Lagrangian. In both models the S-wave component in the K-K+ system is dominant, with a small contribution of the phi(1020) meson and a negligible contribution from tensor resonances. The K+K- scattering amplitudes for the considered combinations of spin (0,1) and isospin (0,1) of the two-body system are obtained from the Dalitz plot fit with the phenomenological decay amplitude.

Abstract: The doubly Cabibbo- suppressed decay Xi(+)(c) -> p phi with ! K+K is observed for the fi rst time, with a statistical signi fi cance of more than fi fteen standard deviations. The data sample used in this analysis corresponds to an integrated luminosity of 2 fb recorded with the LHCb detector in pp collisions at a centre- of- mass energy of 8TeV. The ratio of branching fractions between the decay + c ! p and the singly Cabibbo- suppressed decay + c ! pK is measured to be B (Xi(+)(c) -> p phi) B (Xi(+)(c) -> p phi) = (19 : 8 0 : 7 0 : 9 0 : 2) 10 where the fi rst uncertainty is statistical, the second systematic and the third due to the knowledge of the Xi(+)(c) -> pK(+)pi(+) branching fraction.