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A bstract We compute the exclusive electroproduction, γ * p → Vp , of heavy quarkonia V to NLO in the collinear factorisation scheme, which has been formally proven for this process. The inclusion of an off-shell virtuality Q 2 carried by the photon extends the photoproduction phase space of the exclusive heavy quarkonia observable to electroproduction kinematics. This process is relevant for diffractive scattering at HERA and the upcoming EIC, as well as at the proposed LHeC and FCC.

We propose a method which allows the inclusion of exclusive heavy vector-meson production data at low x in future global parton analyses. As an example we perform a study within xFitter to determine the gluon parton distribution function (PDF) at next-to-leading order (NLO) at moderate-to-low x using the measurements of exclusive J / ψ production in ep and pp collisions from HERA and LHC. We further study the constraints from the corresponding Υ production process. We finish by discussing the possible effects at next-to-next-to-leading order (NNLO) through incorporation of a K factor for the exclusive heavy vector-meson coefficient function at NLO.

A bstract New, more precise data on diffractive J/ψ photoproduction and on exclusive J/ψ production in the process pp → p + J/ψ + p at the LHC allow a better constraint on the low- x gluon distribution in the domain of relatively low scales Q 2 ~ 2–6 GeV 2 . We account for the ‘skewed’ effect and for the real part of the amplitude, as well as for the absorptive corrections in the case of the exclusive process pp → p + J/ψ + p . The predictions for exclusive J/ψ production at = 8 and 14 TeV and for exclusive (1 S ) production at 7, 8 and 14 TeV are also given. We present results at leading and next-to-leading order.

We present the achievements of the last years of the experimental and theoretical groups working on hadronic cross section measurements at the low-energy e + e − colliders in Beijing, Frascati, Ithaca, Novosibirsk, Stanford and Tsukuba and on τ decays. We sketch the prospects in these fields for the years to come. We emphasise the status and the precision of the Monte Carlo generators used to analyse the hadronic cross section measurements obtained as well with energy scans as with radiative return, to determine luminosities and τ decays. The radiative corrections fully or approximately implemented in the various codes and the contribution of the vacuum polarisation are discussed.

We present a measurement of the doubly radiative decay η → π0γγ based ona sample of 82 million η mesons produced in the e+e− → ϕ → ηγ process at the Frascatiϕ-factory DAΦNE. From the data analysis, 1246 ± 133 signal events were observed. Bynormalising the signal to the well-known η → 3π0 decay the branching fraction B(η → π0γγ) ismeasured to be (0.98 ± 0.11stat ± 0.14syst) × 10−4. This result agrees with a preliminary KLOEmeasurement, but is a factor of two smaller than the current world average. Results for dΓ(η →π0γγ)/dM 2(γγ) are also presented and compared with the latest theoretical predictions.

The perturbative QCD expansion for [Formula omitted] photoproduction appears to be unstable: the NLO correction is large (and of opposite sign) to the LO contribution. Moreover, the predictions are very sensitive to the choice of factorisation and renormalisation scales. Here we show that perturbative stability is greatly improved by imposing a [Formula omitted] cut' on the NLO coefficient functions; a cut which is required to avoid double counting. [Formula omitted] is the input scale used in the parton DGLAP evolution. This result opens the possibility of high precision exclusive [Formula omitted] data in the forward direction at the LHC being able to determine the low x gluon distribution at low scales.

A brief status report on the hadronic contributions to the running of the electromagnetic coupling and the anomalous magnetic moment of the muon is given.

We justify the practical use of the Shuvaev integral transform approach to calculate the skewed distributions, needed to describe diffractive processes, directly from the conventional diagonal global parton distributions. We address doubts which have been raised about this procedure. We emphasise that the approach, on the one hand, satisfies all theoretical requirements, and, on the other hand, is consistent with DVCS data at NLO. We construct an easily accessible package for the computation of these skewed distributions.

We perform a parton analysis within𝚡𝙵𝚒𝚝𝚝𝚎𝚛to determine the gluon parton distribution function (PDF) at next-to-leading order (NLO) at moderate-to-lowxusing the measurements of exclusiveJ/ψproduction inepandppcollisions from HERA and LHC. We further study the constraints from the correspondingΥproduction process and finish by discussing the possible effects at next-to-next-to-leading order (NNLO) through incorporation of aKfactor for the exclusive heavy vector-meson coefficient function at NLO.

The perturbative QCD expansion for J / ψ photoproduction appears to be unstable: the NLO correction is large (and of opposite sign) to the LO contribution. Moreover, the predictions are very sensitive to the choice of factorisation and renormalisation scales. Here we show that perturbative stability is greatly improved by imposing a ` Q 0 cut’ on the NLO coefficient functions; a cut which is required to avoid double counting. Q 0 is the input scale used in the parton DGLAP evolution. This result opens the possibility of high precision exclusive J / ψ data in the forward direction at the LHC being able to determine the low x gluon distribution at low scales.