Combined HERA data on charm production in deep-inelastic scattering have previously been used to determine the charm-quark running mass mc(mc) in the MS‾ renormalisation scheme. Here, the same data ...are used as a function of the photon virtuality Q2 to evaluate the charm-quark running mass at different scales to one-loop order, in the context of a next-to-leading order QCD analysis. The scale dependence of the mass is found to be consistent with QCD expectations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
At large values of x , the parton distribution functions (PDFs) of the proton are poorly constrained and there are considerable variations between different global fits. Data at such high x have ...already been published by the ZEUS Collaboration, but not yet used in PDF extractions. A technique for comparing predictions based on different PDF sets to the observed number of events in the ZEUS data is presented. It is applied to compare predictions from the most commonly used PDFs to published ZEUS data at high Bjorken x . A wide variation is found in the ability of the PDFs to predict the observed results. A scheme for including the ZEUS highx data in future PDF extractions is discussed.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
A simultaneous fit of parton distribution functions (PDFs) and electroweak parameters to HERA data on deep inelastic scattering is presented. The input data are the neutral current and charged ...current inclusive cross sections which were previously used in the QCD analysis leading to the HERAPDF2.0 PDFs. In addition, the polarization of the electron beam was taken into account for the ZEUS data recorded between 2004 and 2007. Results on the vector and axial-vector couplings of the Z boson to u- and d-type quarks, on the value of the electroweak mixing angle and the mass of the W boson are presented. The values obtained for the electroweak parameters are in agreement with Standard Model predictions.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
The proton-dissociative diffractive photoproduction of
J
/
ψ
mesons has been studied in ep collisions with the ZEUS detector at HERA using an integrated luminosity of 112 pb
−1
. The cross section is ...presented as a function of the photon-proton centre-of-mass energy and of the squared four-momentum transfer at the proton vertex. The results are compared to perturbative QCD calculations.
The azimuthal correlation angle, \(\Delta\phi\), between the scattered lepton and the leading jet in deep inelastic \(e^{\pm}p\) scattering at HERA has been studied using data collected with the ZEUS ...detector at a centre-of-mass energy of \(\sqrt{s} = 318 \;\mathrm{GeV}\), corresponding to an integrated luminosity of \(326 \;\mathrm{pb}^{-1}\). A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality \(10 \;\mathrm{GeV}^2 < Q^2 < 350 \;\mathrm{GeV}^2\), inelasticity \(0.04 < y < 0.7\), outgoing lepton energy \(E_e > 10 \;\mathrm{GeV}\), lepton polar angle \(140^\circ < \theta_e < 180^\circ\), jet transverse momentum \(2.5 \;\mathrm{GeV} < p_\mathrm{T,jet} < 30 \;\mathrm{GeV}\), and jet pseudorapidity \(-1.5 < \eta_\mathrm{jet} < 1.8\). Jets were reconstructed using the \(k_\mathrm{T}\) algorithm with the radius parameter \(R = 1\). The leading jet in an event is defined as the jet that carries the highest \(p_\mathrm{T,jet}\). Differential cross sections, \(d\sigma/d\Delta\phi\), 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 \(\mathcal{O}(\alpha_{s}^2)\) accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near \(\Delta\phi \rightarrow \pi\) 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 \(318\,\text{GeV}\) and correspond to an integrated luminosity of \(347\,\text{pb}^{-1}\). 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, \(p_{\perp,\text{Breit}}\). 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 \(\alpha_s(M_Z^2) = 0.1142 \pm 0.0017~\text{(experimental/fit)}\) \({}^{+0.0006}_{-0.0007}~\text{(model/parameterisation)}\) \({}^{+0.0006}_{-0.0004}~\text{(scale)}\), whose accuracy is improved compared to similar measurements. In addition, the running of the strong coupling is demonstrated using data obtained at different scales.
Lorentz and CPT symmetry in the quark sector of the Standard Model are studied in the context of an effective field theory using ZEUS \(e^{\pm} p\) data. Symmetry-violating effects can lead to ...time-dependent oscillations of otherwise time-independent observables, including scattering cross sections. An analysis using five years of inclusive neutral-current deep inelastic scattering events corresponding to an integrated HERA luminosity of \(372\; \text{pb}^{-1}\) at \(\sqrt{s} = 318\) Gev has been performed. No evidence for oscillations in sidereal time has been observed within statistical and systematic uncertainties. Constraints, most for the first time, are placed on 42 coefficients parameterising dominant CPT-even dimension-four and CPT-odd dimension-five spin-independent modifications to the propagation and interaction of light quarks.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract The photoproduction of D ^sup ±^ mesons has been measured with the ZEUS detector at HERA at three different ep ...centre-of-mass energies, ..., of 318, 251 and 225 GeV. For each data set, D ^sup ±^ mesons were required to have transverse momentum, p ^sub T^^sup D^, and pseudo-rapidity, eta ^sup D^, in the ranges 1.9 < p ^sub T^^sup D^ < 20 GeV and |eta ^sup D^| < 1.6. The events were required to have a virtuality of the incoming photon, Q ^sup 2^, of less than 1 GeV^sup 2^. The dependence on ... was studied by normalising to the high-statistics measurement at ... GeV. This led to the cancellation of a number of systematic effects both in data and theory. Predictions from next-to-leading-order QCD describe the ... dependence of the data well.
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