Plasma-based accelerators offer the possibility to drive future compact light sources and high-energy physics applications. Achieving good beam quality, especially a small beam energy spread, is still one of the major challenges. Here, we propose to use a periodically modulated plasma density to shape the longitudinal fields acting on an electron bunch in the linear wakefield regime. With simulations, we demonstrate an on-average flat accelerating field that maintains a small beam energy spread.

The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(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

The FLASHForward project at DESY is a pioneering plasma-wakefield acceleration experiment that aims to produce, in a few centimetres of ionised hydrogen, beams with energy of order GeV that are of quality sufficient to be used in a free-electron laser. The plasma is created by ionising a gas in a gas cell with a multi-TW laser system. The plasma wave will be driven by high-current-density electron beams from the FLASH linear accelerator. The laser system can also be used to provide optical diagnostics of the plasma and electron beams due to the <30fs synchronisation between the laser and the driving electron beam. The project will explore both external and internal witness-beam injection techniques. The operation parameters of the experiment are discussed, as well as the scientific programme.

The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(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 μ^+μ^- and J/ψ(1S) π^+π^- for the ψ(2S) and μ^+μ^- for the J/ψ(1S). The cross-section ratio σ_ψ(2S)/σ_J/ψ(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.

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 \(e^{\pm }p\) 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\(^{-1}\) and span six orders of magnitude in negative four-momentum-transfer squared, \(Q^2\), 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 \(\alpha _s(M_Z^2)=0.1183 \pm 0.0009 \mathrm{(exp)} \pm 0.0005\mathrm{(model/parameterisation)} \pm 0.0012\mathrm{(hadronisation)} ^{+0.0037}_{-0.0030}\mathrm{(scale)}\). An extraction of \(xF_3^{\gamma Z}\) and results on electroweak unification and scaling violations are also presented.

Generation of ultra-short electron bunches with a few femtoseconds arrival-time jitter is the major challenge in plasma acceleration with external injection. Meanwhile, peak current stability is also one of the crucial factors for user experiments when the electron bunch is used for free-electron laser (FEL) generation. ARES (Accelerator Research Experiment at SINBAD) will consist of a compact S-band normal-conducting photo-injector providing ultra-short electron bunches of 100 MeV. We present bunch arrival-time jitter studies for two different compression schemes, velocity bunching and magnetic compression with a slit, at ARES with start-to-end simulations. Contributions from various jitter sources are quantified.

H1 and ZEUS have published single-differential cross sections for inclusive D ∗±-meson production in deep-inelastic ep scattering at HERA from their respective final data sets. These cross sections are combined in the common visible phase-space region of photon virtuality Q 2 > 5 GeV2, electron inelasticity 0.02 < y < 0.7 and the D ∗± meson’s transverse momentum p T(D ∗) > 1.5 GeV and pseudorapidity |η(D ∗)| < 1.5. The combination procedure takes into account all correlations, yielding significantly reduced experimental uncertainties. Double-differential cross sections d2 σ/dQ 2dy are combined with earlier D ∗± data, extending the kinematic range down to Q 2 > 1.5 GeV2. Perturbative next-to-leading-order QCD predictions are compared to the results.

ARES is a planned linear accelerator for research and development in the field of production of ultra-short electron bunches. The goal of ARES is to produce low charge (0.2 50 pC), ultra-short (from few fs to sub-fs) bunches, with improved arrival time stability (less than 10 fs) for various applications, such as external injection for Laser Plasma Wake-Field acceleration. The ARES layout will allow to perform and compare different kind of conventional e-bunch compression techniques, such as pure velocity bunching, hybrid velocity bunching (i.e. velocity bunching plus magnetic compression) and pure magnetic compression with the slit insertion. This flexibility will allow to directly compare the different methods in terms of arrival time stability and local peak current. In this paper we present simulation results for the compression of an electron bunch with 0.5 pC charge. We compare the case of pure velocity bunching compression to the one of a hybrid compression using velocity bunching plus a magnetic compressor.

The photoproduction of isolated photons, both inclusive and together with a jet, has been measured with the ZEUS detector at HERA using an integrated luminosity of 374 pb(-1). Differential cross sections are presented in the isolated-photon transverse-energy and pseudorapidity ranges 6 < E-T(gamma) < 15 GeV and -0.7 < eta(gamma) < 0.9, and for jet transverse-energy and pseudorapidity ranges 4 < E-T(jet) < 35 GeV and -1.5 < eta(jet) < 1.8, for exchanged-photon virtualities Q(2) < 1 GeV2. Differential cross sections are also presented for inclusive isolated-photon production as functions of the transverse energy and pseudorapidity of the photon. Higher-order theoretical calculations are compared to the results. (C) 2014 The Authors. Published by Elsevier B.V.

The reduced cross sections for e(+)p deep inelastic scattering have been measured with the ZEUS detector at HERA at three different center-of-mass energies, 318, 251 and 225 GeV. The cross sections, measured double differentially in Bjorken x and the virtuality, Q(2), were obtained in the region 0.13 <= y <= 0.75, where y denotes the inelasticity and 5 <= Q(2) <= 110 GeV2. The proton structure functions F-2 and F-L were extracted from the measured cross sections.

The production of beauty and charm quarks in ep interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared 5 < Q 2 < 1000 GeV2 using an integrated luminosity of 354 pb−1. The beauty and charm content in events with at least one jet have been extracted using the invariant mass of charged tracks associated with secondary vertices and the decay-length significance of these vertices. Differential cross sections as a function of Q 2, Bjorken x, jet trans- verse energy and pseudorapidity were measured and compared with next-to-leading-order QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the double-differential cross section as a function of x and Q 2. The running beauty-quark mass, m b at the scale m b , was determined from a QCD fit at next-to-leading order to HERA data for the first time and found to be m b (m b ) = 4.07 ± 0.14 (fit) − 0.07 + 0.01 (mod.) − 0.00 + 0.05 (param.) − 0.05 + 0.08 (theo.) GeV.

The photoproduction of D ∗± mesons has been measured with the ZEUS detector at HERA at three different ep centre-of-mass energies, \( \sqrt{s} \), of 318, 251 and 225 GeV. For each data set, D ∗± mesons were required to have transverse momentum, p T D ∗ , and pseudo-rapidity, η D∗, in the ranges 1.9 < p T D ∗ < 20 GeV and |η D∗| < 1.6. The events were required to have a virtuality of the incoming photon, Q 2, of less than 1 GeV2. The dependence on \( \sqrt{s} \) was studied by normalising to the high-statistics measurement at \( \sqrt{s}=318 \) 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 \( \sqrt{s} \) dependence of the data well.

SINBAD (Short INnovative Bunches and Accelerators at DESY) is a proposed dedicated accelerator research and development facility at DESY where amongst other topics laser-driven wakefield acceleration (LWFA) with external injection of ultra-short bunches will be exploited. At SINBAD we aim to demonstrate externally-injected bunch acceleration inside a plasma wake with minimal degradation of its energy spread and emittance at low plasma densities. To minimise induced energy spread, the bunch should occupy a small fraction of the plasma wavelength and has to be longitudinally synchronised with the laser driver to high accuracy. To avoid emittance growth the transport lattice for the incoming beam has to be matched to the intrinsic beta-function of the plasma. We present a preparatory feasibility study for future plasma experiments at SINBAD using simulations with the particle-in-cell code OSIRIS [1].

In this extended analysis using the ZEUS detector at HERA, the photoproduction of isolated photons together with a jet is measured for different ranges of the fractional photon energy, x γ meas , contributing to the photon-jet final state. Cross sections are evaluated in the photon transverse-energy and pseudorapidity ranges 6 < E T γ < 15 GeV and −0.7 < η γ < 0.9, and for jet transverse-energy and pseudorapidity ranges 4 < E T jet < 35 GeV and −1.5 < η jet < 1.8, for an integrated luminosity of 374 pb−1. The kinematic observables studied comprise the transverse energy and pseudorapidity of the photon and the jet, the azimuthal difference between them, the fraction of proton energy taking part in the interaction, and the difference between the pseudorapidities of the photon and the jet. Higher-order theoretical calculations are compared to the results.

The production of Z(0) bosons in the reaction ep -> eZ(0)p((*)), where p((*)) stands for a proton or a low-mass nucleon resonance, has been studied in ep collisions at HERA using the ZEUS detector. The analysis is based on a data sample collected between 1996 and 2007, amounting to 496 pb(-1) of integrated luminosity. The Z(0) was measured in the hadronic decay mode. The elasticity of the events was ensured by a cut on eta(max) <3.0, where eta(ma)x is the maximum pseudorapidity of energy deposits in the calorimeter defined with respect to the proton beam direction. A signal was observed at the Z(0) mass. The cross section of the reaction ep -> eZ(0)p((*)) was measured to be sigma(ep -> eZ(0)p((*))) = 0.13 +/- 0.06(stat.) +/- 0.01(syst) pb, in agreement with the Standard Model prediction of 0.16 pb. Thfs is the first measurement of Z(0) production in ep collisions. (C) 2012 Elsevier B.V. All rights reserved.

The production of D *± mesons in deep inelastic ep scattering has been measured for exchanged photon virtualities 5 < Q 2 < 1000 GeV 2 , using an integrated luminosity of 363 pb −1 with the ZEUS detector at HERA. Differential cross sections have been measured and compared to next-to-leading-order QCD calculations. The cross-sections are used to extract the charm contribution to the proton structure functions, expressed in terms of the reduced charm cross section, σ_red^cc . Theoretical calculations based on fits to inclusive HERA data are compared to the results.

The production of D 0, D *+, D +, \( D_s^{+} \) and \( \Lambda_c^{+} \) charm hadrons and their antiparticles in ep scattering at HERA has been studied with the ZEUS detector, using a total integrated luminosity of 372 pb−1. The fractions of charm quarks hadronising into a particular charm hadron were derived. In addition, the ratio of neutral to charged D-meson production rates, the fraction of charged D mesons produced in a vector state, and the stangeness-suppression factor have been determined. The measurements have been performed in the photoproduction regime. The charm hadrons were reconstructed in the range of transverse momentum p T > 3.8 GeV and pseudorapidity |η| < 1.6. The charm fragmentation fractions are compared to previous results from HERA and from e + e − experiments. The data support the hypothesis that fragmentation is independent of the production process.