Isolated photons with high transverse energy have been studied in deep inelastic \(ep\) scattering with the ZEUS detector at HERA, using an integrated luminosity of \(326\,\) pb\(^{-1}\) in the range ...of exchanged-photon virtuality \(10 - 350\) GeV\(^2\). Outgoing isolated photons with transverse energy \(4<E_T^\gamma< 15\) GeV and pseudorapidity \(-0.7 <\eta^\gamma< 0.9\) were measured with accompanying jets having transverse energy and pseudorapidity \(2.5 <E_T^{jet}<35\) GeV and \(-1.5<\eta^{jet}< 1.8\), respectively. Differential cross sections are presented for the following variables: the fraction of the incoming photon energy and momentum that is transferred to the outgoing photon and the leading jet; the fraction of the incoming proton energy transferred to the photon and leading jet; the differences in azimuthal angle and pseudorapidity between the outgoing photon and the leading jet and between the outgoing photon and the scattered electron. Comparisons are made with theoretical predictions: a leading-logarithm Monte Carlo simulation, a next-to-leading-order QCD prediction, and a prediction using the \(k_T\)-factorisation approach.
The exclusive deep inelastic electroproduction of \(\psi(2S)\) and \(J/\psi(1S)\) at an \(ep\) centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range ...\(2 < Q^2 < 80\) GeV\(^2\), \(30 < W < 210\) GeV and \(|t| < 1\) GeV\(^2\), where \(Q^2\) is the photon virtuality, \(W\) is the photon-proton centre-of-mass energy and \(t\) is the squared four-momentum transfer at the proton vertex. The data for \(2 < Q^2 < 5\) GeV\(^2\) were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb\(^{-1}\). The data for \(5 < Q^2 < 80\) GeV\(^2\) are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb\(^{-1}\). The decay modes analysed were \(\mu^+\mu^-\) and \(J/\psi(1S) \pi^+\pi^-\) for the \(\psi(2S)\) and \(\mu^+\mu^-\) for the \(J/\psi(1S)\). The cross-section ratio \(\sigma_{\psi(2S)}/\sigma_{J/\psi(1S)}\) has been measured as a function of \(Q^2, W\) and \(t\). The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.
The high-precision HERA data allows searches up to TeV scales for Beyond the
Standard Model contributions to electron-quark scattering. Combined
measurements of the inclusive deep inelastic cross ...sections in neutral and
charged current $ep$ scattering corresponding to a luminosity of around 1
fb$^{-1}$ have been used in this analysis. A new approach to the beyond the
Standard Model analysis of the inclusive $ep$ data is presented; simultaneous
fits of parton distribution functions together with contributions of "new
physics" processes were performed. Results are presented considering a finite
radius of quarks within the quark form-factor model. The resulting 95% C.L.
upper limit on the effective quark radius is $0.43\cdot 10^{-16}$ cm.
The exclusive deep inelastic electroproduction of \(\psi(2S)\) and \(J/\psi(1S)\) at an \(ep\) centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range ...\(2 < Q^2 < 80\) GeV\(^2\), \(30 < W < 210\) GeV and \(|t| < 1\) GeV\(^2\), where \(Q^2\) is the photon virtuality, \(W\) is the photon-proton centre-of-mass energy and \(t\) is the squared four-momentum transfer at the proton vertex. The data for \(2 < Q^2 < 5\) GeV\(^2\) were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb\(^{-1}\). The data for \(5 < Q^2 < 80\) GeV\(^2\) are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb\(^{-1}\). The decay modes analysed were \(\mu^+\mu^-\) and \(J/\psi(1S) \,\pi^+\pi^-\) for the \(\psi(2S)\) and \(\mu^+\mu^-\) for the \(J/\psi(1S)\). The cross-section ratio \(\sigma_{\psi(2S)}/\sigma_{J/\psi(1S)}\) has been measured as a function of \(Q^2, W\) and \(t\). The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.
Production of exclusive dijets in diffractive deep inelastic \(e^\pm p\) scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 372 pb\(^{-1}\). The measurement ...was performed for \(\gamma^*-p\) centre-of-mass energies in the range \(90 < W < 250\) GeV and for photon virtualities \(Q^2 > 25\) GeV\(^2\). Energy and transverse-energy flows around the jet axis are presented. The cross section is presented as a function of \(\beta\) and \(\phi\), where \(\beta=x/x_{\rm I\!P}\), \(x\) is the Bjorken variable and \(x_{\rm I\!P}\) is the proton fractional longitudinal momentum loss. The angle \(\phi\) is defined by the \(\gamma^*-\)dijet plane and the \(\gamma^*-e^\pm\) plane in the rest frame of the diffractive final state. The \(\phi\) cross section is measured in bins of \(\beta\). The results are compared to predictions from models based on different assumptions about the nature of the diffractive exchange.
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