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This talk presents a survey of ATLAS measurements at the LHC that are sensitive in various ways to the parton distribution functions of the proton.

A bstract The exclusive photoproduction reactions γp → J/ψ (1 S ) p and γp → ψ (2 S ) p have been measured at an ep centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 373 pb − 1 . The measurement was made in the kinematic range 30 < W < 180 GeV, Q 2 < 1 GeV 2 and | t | < 1 GeV 2 , where W is the photon-proton centre-of-mass energy, Q 2 is the photon virtuality and t is the squared four-momentum transfer at the proton vertex. The decay channels used were J/ψ (1 S ) → μ + μ − , ψ (2 S ) → μ + μ − and ψ (2 S ) → J/ψ (1 S ) π + π − with subsequent decay J/ψ (1 S ) → μ + μ − . The ratio of the production cross sections, R = σ ψ (2 S ) /σ J/ψ (1 S ) , has been measured as a function of W and | t | and compared to previous data in photoproduction and deep inelastic scattering and with predictions of QCD-inspired models of exclusive vector-meson production, which are in reasonable agreement with the data.

A summary is given of recent ATLAS results at the LHC, covering a number of areas that reflect the Collaboration's work in low energy physical observables in multiparticle events, elastic photon-photon scattering, proton-proton scattering and the tagging of diffractive events.

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current ... scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb... and span six orders of magnitude in negative four-momentum-transfer squared, ..., and Bjorken x. The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixed-flavour-number schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in ... An extraction of ... and results on electroweak unification and scaling violations are also presented.

The azimuthal correlation angle,$$\\Delta \\phi $$Δ ϕ , between the scattered lepton and the leading jet in deep inelastic$$e^{\\pm }p$$e ± p scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of$$\\sqrt{s} = 318 {\\,\\text {Ge}\\hspace{-0.66666pt}\\text {V}}$$s = 318 Ge V , corresponding to an integrated luminosity of$$326 \\,\\text {pb}^{-1}$$326 pb - 1 . A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality$$10 {\\,\\text {Ge}\\hspace{-0.66666pt}\\text {V}}^2< Q^2 < 350 {\\,\\text {Ge}\\hspace{-0.66666pt}\\text {V}}^2$$10 Ge V 2 < Q 2 < 350 Ge V 2 , inelasticity$$0.04< y < 0.7$$0.04 < y < 0.7 , outgoing lepton energy$$E_e > 10 {\\,\\text {Ge}\\hspace{-0.66666pt}\\text {V}}$$E e > 10 Ge V , lepton polar angle$$140^\\circ< \\theta _e < 180^\\circ $$140 ∘ < θ e < 180 ∘ , jet transverse momentum$$2.5 {\\,\\text {Ge}\\hspace{-0.66666pt}\\text {V}}< p_\\textrm{T,jet} < 30 {\\,\\text {Ge}\\hspace{-0.66666pt}\\text {V}}$$2.5 Ge V < p T,jet < 30 Ge V , and jet pseudorapidity$$-1.5< \\eta _\\textrm{jet} < 1.8$$- 1.5 < η jet < 1.8 . Jets were reconstructed using the$$k_\\textrm{T}$$k T algorithm with the radius parameter$$R = 1$$R = 1 . The leading jet in an event is defined as the jet that carries the highest$$p_\\textrm{T,jet}$$p T,jet . Differential cross sections,$$d\\sigma /d\\Delta \\phi $$d σ / d Δ ϕ , 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$$\\mathcal {O}(\\alpha _{s}^2)$$O ( α s 2 ) accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near$$\\Delta \\phi \\rightarrow \\pi $$Δ ϕ → 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.

A new measurement of inclusive-jet cross sections in the Breit frame in neutral current deep inelastic scattering using the ZEUS detector at the HERA collider is presented. The data were taken in the years 2004 to 2007 at a centre-of-mass energy of \\(318\\,GeV\\) and correspond to an integrated luminosity of \\(347\\,pb^-1\\). Massless jets, reconstructed using the \\(k_t\\)-algorithm in the Breit reference frame, have been measured as a function of the squared momentum transfer, \\(Q^2\\), and the transverse momentum of the jets in the Breit frame, \\(p_ Breit\\). The measured jet cross sections are compared to previous measurements and to perturbative QCD predictions. The measurement has been used in a next-to-next-to-leading-order QCD analysis to perform a simultaneous determination of parton distribution functions of the proton and the strong coupling, resulting in a value of \\(_s(M_Z^2) = 0.1142 0.0017~(experimental/fit)\\) \\(^+0.0006_-0.0007~(model/parameterisation)\\) \\(^+0.0006_-0.0004~(scale)\\), whose accuracy is improved compared to similar measurements. In addition, the running of the strong coupling is demonstrated using data obtained at different scales.

The azimuthal correlation angle, Δ ϕ , 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 Ge V , 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 Ge V 2 < Q 2 < 350 Ge V 2 , inelasticity 0.04 < y < 0.7 , outgoing lepton energy E e > 10 Ge V , lepton polar angle 140 ∘ < θ e < 180 ∘ , jet transverse momentum 2.5 Ge V < p T,jet < 30 Ge V , 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, d σ / d Δ ϕ , 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 Δ ϕ → 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.

Production of exclusive dijets in diffractive deep inelastic [Formula omitted] scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 372 pb [Formula omitted]. The measurement was performed for [Formula omitted]-p centre-of-mass energies in the range [Formula omitted] and for photon virtualities [Formula omitted]. Energy flows around the jet axis are presented. The cross section is presented as a function of [Formula omitted] and [Formula omitted], where [Formula omitted], x is the Bjorken variable and [Formula omitted] is the proton fractional longitudinal momentum loss. The angle [Formula omitted] is defined by the [Formula omitted]-dijet plane and the [Formula omitted]- [Formula omitted] plane in the rest frame of the diffractive final state. The [Formula omitted] cross section is measured in bins of [Formula omitted]. The results are compared to predictions from models based on different assumptions about the nature of the diffractive exchange.

Abstract The exclusive photoproduction reactions γp → J/ψ(1S)p and γp → ψ(2S)p have been measured at an ep centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 373 pb −1. The measurement was made in the kinematic range 30 < W < 180 GeV, Q 2 < 1 GeV2 and |t| < 1 GeV2, where W is the photon-proton centre-of-mass energy, Q 2 is the photon virtuality and t is the squared four-momentum transfer at the proton vertex. The decay channels used were J/ψ(1S) → μ + μ − , ψ(2S) → μ + μ − and ψ(2S) → J/ψ(1S)π + π − with subsequent decay J/ψ(1S) → μ + μ − . The ratio of the production cross sections, R = σ ψ(2S) /σ J/ψ(1S), has been measured as a function of W and |t| and compared to previous data in photoproduction and deep inelastic scattering and with predictions of QCD-inspired models of exclusive vector-meson production, which are in reasonable agreement with the data.