Olaf Deppe

University of Hamburg, Medicine, Faculty Member

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Eskandar Sadeghi-Boroujerdi

University of York

Noah Gardiner

University of South Carolina

Tzvi Langermann

Bar-Ilan University

Qais Assef

Ecole Pratique des Hautes Etudes

Jawad Qureshi

Zaytuna College

Hassan Ansari

Institute for Advanced Study

Mohammad Suhail E.M al-Hudawi

University of Hyderabad

Viacheslav Kuleshov

Stockholm University

Frank Griffel

University of Oxford

Armando Marques-Guedes

UNL - New University of Lisbon

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Papers by Olaf Deppe

Semi-automated fiducial marker registration reduces target registration error

International Congress Series, 2004

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Observation of events with an energetic forward neutron in deep inelastic scattering at HERA

Physics Letters B, 1996

In deep inelastic neutral current scattering of positrons and protons at the center of mass energ... more In deep inelastic neutral current scattering of positrons and protons at the center of mass energy of 300 GeV, we observe, with the ZEUS detector, events with a high energy neutron produced at very small scattering angles with respect to the proton direction. The events constitute a fixed fraction of the deep inelastic, neutral current event sample independent of Bjorken x and Q 2 in the range 3 • 10 −4 < x BJ < 6 • 10 −3 and 10 < Q 2 < 100 GeV 2 .

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High- $E_T$ inclusive jet cross sections in photoproduction at HERA

The European Physical Journal C, 1998

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Measurement of the proton structure function F-2 and sigma(gamma*p)(tot) at low Q(2) and very low x at HERA

Physics Letters B, 1997

A small electromagnetic sampling calorimeter, installed in the ZEUS experiment in 1995, significa... more A small electromagnetic sampling calorimeter, installed in the ZEUS experiment in 1995, significantly enhanced the acceptance for very low x and low Q 2 inelastic neutral current scattering, e + p → e + X, at HERA. A measurement of the proton structure function F 2 and the total virtual photon-proton (γ * p) cross-section is

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$Research paper thumbnail of Search for resonance decays to an $\overline v$-neutrino plus jet in $\mathrm{e^+ p}$ scattering at DESY HERA$

Search for resonance decays to an $\overline v$-neutrino plus jet in $\mathrm{e^+ p}$ scattering at DESY HERA

Physical Review D, Particles and fields, 2001

A study of the antineutrino-jet mass spectrum in e^+p -> antineutrino+X events at center-of-ma... more A study of the antineutrino-jet mass spectrum in e^+p -> antineutrino+X events at center-of-mass energy 300 GeV has been performed with the ZEUS detector at HERA using an integrated luminosity of 47.7 pb^-1. The mass spectrum is in good agreement with that expected from Standard Model processes over the antineutrino -jet mass range studied. No significant excess attributable to the decay of a narrow resonance is observed. By using both e^+p -> e^+ X and e^+p -> antineutrino X data, mass-dependent limits are set on the s-channel production of scalar and vector resonant states. Couplings to first-generation quarks are considered and limits are presented as a function of the e^+q and antineutrino-q branching ratios. These limits are used to constrain the production of leptoquarks and R-parity violating squarks.

Exclusive ρ^0 production in deep inelastic electron-proton scattering at HERA

The exclusive production of ρ^0 mesons in deep inelastic electron-proton scattering has been stud... more The exclusive production of ρ^0 mesons in deep inelastic electron-proton scattering has been studied using the ZEUS detector. Cross sections have been measured in the range 7 < Q^2 < 25 GeV^2 for γ^*p centre of mass (c.m.) energies from 40 to 130 GeV. The γ^*p →ρ^0 p cross section exhibits a Q^-(4.2 ± 0.8 ^+1.4_-0.5) dependence and both longitudinally and transversely polarised ρ^0's are observed. The γ^*p →ρ^0 p cross section rises strongly with increasing c.m. energy, when compared with NMC data at lower energy, which cannot be explained by production through soft pomeron exchange. The data are compared with perturbative QCD calculations where the rise in the cross section reflects the increase in the gluon density at low x. the gluon density at low x.

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Measurement of the reaction y * p-+ dpp in deep inelastic e + p scattering at HERA ZEUS Collaboration

The production of ~b mesons in the reaction e+p --+ e+~bp (qb ~ K + K ) , for 7 < Q2 < 25 G... more The production of ~b mesons in the reaction e+p --+ e+~bp (qb ~ K + K ) , for 7 < Q2 < 25 GeV 2 and for virtual photon-proton centre of mass energies (W) in the range 42-134 GeV, has been studied with the ZEUS detector at HERA. When compared to lower energy data at similar Q2, the results show that the 7*P --~ ~bp cross section rises strongly with W. This behaviour is similar to that previously found for the y*p ~ pOp cross section. This strong dependence cannot be explained by production through soft pomeron exchange. It is, however, consistent with perturbative QCD expectations, where it reflects the rise of the gluon momentum density in the proton at small x. The ratio of tr(qb)fir(p°), which has previously been determined by ZEUS to be 0.065 + 0.013 (stat.) in photoproduction at a mean W of 70 GeV, is measured to be 0.18 + 0.05 (stat.) -40.03 (syst.) at a mean Q2 of 12.3 GeV 2 and mean W of ~ 100 GeV and is thus approaching at large Q2 the value of 2 / 9 predicted from the...

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Measurement of the F-2 structure function in deep inelastic e(+)p scattering using 1994 data from the ZEUS detector at HERA

Zeitschrift Fur Physik C-Particles and Fields, 1996

We present measurements of the structure function F 2 in e + p scattering at HERA in the range 3.... more We present measurements of the structure function F 2 in e + p scattering at HERA in the range 3.5 GeV 2 < Q 2 < 5000 GeV 2. A new reconstruction method has allowed a significant improvement in the resolution of the kinematic variables and an extension of the kinematic region covered by the experiment. At Q 2 < 35 GeV 2 the range in x now spans 6.3 • 10 −5 < x < 0.08 providing overlap with measurements from fixed target experiments. At values of Q 2 above 1000 GeV 2 the x range extends to 0.5. Systematic errors below 5% have been achieved for most of the kinematic region. The structure function rises as x decreases; the rise becomes more pronounced as Q 2 increases. The behaviour of the structure function data is well described by next-to-leading order perturbative QCD as implemented in the DGLAP evolution equations.

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A search for excited fermions in e(+)p collisions at HERA

Zeitschrift Fur Physik C-Particles and Fields, 1997

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Search for selectron and squark production in e(+)p collisions at HERA

Physics Letters B, 1998

We have searched for the production of a selectron and a squark in e + p collisions at a center-o... more We have searched for the production of a selectron and a squark in e + p collisions at a center-of-mass energy of 300 GeV using the ZEUS detector at HERA. The selectron and squark are sought in the direct decay into the lightest neutralino in the framework of supersymmetric extensions to the Standard Model which conserve R-parity. No evidence for the production of supersymmetric particles has been found in a data sample corresponding to 46.6 pb −1 of integrated luminosity. We express upper limits on the product of the cross section times the decay branching ratios as excluded regions in the parameter space of the Minimal Supersymmetric Standard Model.

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Measurement of elastic φ photoproduction at HERA

Physics Letters B, 1996

The production of φ mesons in the reaction e + p → e + φp (φ → K + K −) at a median Q 2 of 10 −4 ... more The production of φ mesons in the reaction e + p → e + φp (φ → K + K −) at a median Q 2 of 10 −4 GeV 2 has been studied with the ZEUS detector at HERA. The differential φ photoproduction cross section dσ/dt has an exponential shape and has been determined in the kinematic range 0.1 < |t| < 0.5 GeV 2 and 60 < W < 80 GeV. An integrated cross section of σ γp→φp = 0.96 ± 0.19 +0.21 −0.18 µb has been obtained by extrapolating to t = 0. When compared to lower energy data, the results show a weak energy dependence of both σ γp→φp and the slope of the t distribution. The φ decay angular distributions are consistent with s-channel helicity conservation. From lower energies to HERA energies, the features of φ photoproduction are compatible with those of a soft diffractive process.

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Measurement of the ET,jet2/Q2 dependence of forward-jet production at HERA

Physics Letters B, 2000

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The Q2 dependence of dijet cross sections in γp interactions at HERA

Physics Letters B, 2000

The dependence of the photon structure on the photon virtuality, Q 2 , is studied by measuring th... more The dependence of the photon structure on the photon virtuality, Q 2 , is studied by measuring the reaction e + p → e + + jet+ jet+ X at photon-proton centre-of-mass energies 134 < W < 223 GeV. Events have been selected in the Q 2 ranges ≈ 0 GeV 2 , 0.1-0.55 GeV 2 , and 1.5-4.5 GeV 2 , having two jets with transverse energy E jet T > 5.5 GeV in the final state. The dijet cross section has been measured as a function of the fractional momentum of the photon participating in the hard process, x OBS γ. The ratio of the dijet cross section with x OBS γ < 0.75 to that with x OBS γ > 0.75 decreases as Q 2 increases. The data are compared with the predictions of NLO pQCD and leading-order Monte Carlo programs using various parton distribution functions of the photon. The measurements can be interpreted in terms of a resolved photon component that falls with Q 2 but remains present at values of Q 2 up to 4.5 GeV 2. However, none of the models considered gives a good description of the data.

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Measurement of elastic ϒ photoproduction at HERA

Physics Letters B, 1998

The photoproduction reaction γp → µ + µ − p has been studied in ep interactions using the ZEUS de... more The photoproduction reaction γp → µ + µ − p has been studied in ep interactions using the ZEUS detector at HERA. The data sample corresponds to an integrated luminosity of 43.2 pb −1. The Υ meson has been observed in photoproduction for the first time. The sum of the products of the elastic Υ(1S), Υ(2S), Υ(3S) photoproduction cross sections with their respective branching ratios is determined to be 13.3 ± 6.0(stat.) +2.7 −2.3 (syst.) pb at a mean photon-proton centre of mass energy of 120 GeV. The cross section is above the prediction of a perturbative QCD model.

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Differential cross sections of photoproduction in ep collisions at HERA

Physics Letters B, 1997

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Event shape analysis of deep inelastic scattering events with a large rapidity gap at HERA

Physics Letters B, 1998

A global event shape analysis of the multihadronic final states observed in neutral current deep ... more A global event shape analysis of the multihadronic final states observed in neutral current deep inelastic scattering events with a large rapidity gap with respect to the proton direction is presented. The analysis is performed in the range 5 ≤ Q 2 ≤ 185 GeV 2 and 160 ≤ W ≤ 250 GeV, where Q 2 is the virtuality of the photon and W is the virtual-photon proton centre of mass energy. Particular emphasis is placed on the dependence of the shape variables, measured in the γ * −pomeron rest frame, on the mass of the hadronic final state, M X. With increasing M X the multihadronic final state becomes more collimated and planar. The experimental results are compared with several models which attempt to describe diffractive events. The broadening effects exhibited by the data require in these models a significant gluon component of the pomeron.

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Measurement of the reaction in deep inelastic e+p scattering at HERA

Physics Letters B, 1996

The production of φ mesons in the reaction e + p → e + φp (φ → K + K −), for 7 < Q 2 < 25 GeV 2 a... more The production of φ mesons in the reaction e + p → e + φp (φ → K + K −), for 7 < Q 2 < 25 GeV 2 and for virtual photon-proton centre of mass energies (W) in the range 42-134 GeV, has been studied with the ZEUS detector at HERA. When compared to lower energy data at similar Q 2 , the results show that the γ * p → φp cross section rises strongly with W. This behaviour is similar to that previously found for the γ * p → ρ 0 p cross section. This strong dependence cannot be explained by production through soft pomeron exchange. It is, however, consistent with perturbative QCD expectations, where it reflects the rise of the gluon momentum density in the proton at small x. The ratio of σ(φ)/σ(ρ 0), which has previously been determined by ZEUS to be 0.065 ± 0.013 (stat.) in photoproduction at a mean W of 70 GeV, is measured to be 0.18 ± 0.05 (stat.) ± 0.03 (syst.) at a mean Q 2 of 12.3 GeV 2 and mean W of ≈ 100 GeV and is thus approaching at large Q 2 the value of 2/9 predicted from the quark charges of the vector mesons and a flavour independent production mechanism.

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Exclusive ϱ0 production in deep inelastic electron-proton scattering at HERA

Physics Letters B, 1995

The exclusive production of p" mesons in deep inelastic electron-proton scattering has been studi... more The exclusive production of p" mesons in deep inelastic electron-proton scattering has been studied using the ZEUS detector. Cross sections have been measured in the range 7 < Q2 < 25 GeV* for y*p centre of mass (c.m.) energies from 40 to 130 GeV. The y*p-f pup cross section exhibits a Q-~4~2*0~8~~~) dependence and both longitudinally and transversely polarised p"'s are observed. The y*p-+ p"p cross section rises strongly with increasing c.m. energy, when compared with NMC data at lower energy, which cannot be explained by production through soft pomeron exchange. The data are compared with perturbative QCD calculations where the rise in the cross section reflects the increase in the gluon density at low X.

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Observation of isolated high-E photons in photoproduction at HERA

Physics Letters B, 1997

Events containing an isolated prompt photon with high transverse energy, together with a balancin... more Events containing an isolated prompt photon with high transverse energy, together with a balancing jet, have been observed for the first time in photoproduction at HERA. The data were taken with the ZEUS detector, in a γp centre of mass energy range 120-250 GeV. The fraction of the incoming photon energy participating in the production of the prompt photon and the jet, x γ , shows a strong peak near unity, consistent with LO QCD Monte Carlo predictions. In the transverse energy and pseudorapidity range 5 ≤ E γ T < 10 GeV, −0.7 ≤ η γ < 0.8, E jet T ≥ 5 GeV, and −1.5 ≤ η jet ≤ 1.8, with x OBS γ > 0.8, the measured cross section is 15.3±3.8±1.8 pb, in good agreement with a recent NLO calculation.

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Measurement of exclusive ω electroproduction at HERA

Physics Letters B, 2000

The exclusive electroproduction of ω mesons, ep → eωp, has been studied in the kinematic range 3 ... more The exclusive electroproduction of ω mesons, ep → eωp, has been studied in the kinematic range 3 < Q 2 < 20 GeV 2 , 40 < W < 120 GeV and |t| < 0.6 GeV 2 with the ZEUS detector at HERA using an integrated luminosity of 37.7 pb −1. The ω mesons were identified via the decay ω → π + π − π 0. The exclusive cross section in the above kinematic region is σ ep→eωp = 0.108 ± 0.014(stat.) ± 0.026(syst.) nb. The reaction ep → eφp, φ → π + π − π 0 , has also been measured. The cross sections, as well as the ratios σ γ * p→ωp /σ γ * p→ρ 0 p and σ γ * p→ωp /σ γ * p→φp , are presented as a function of W and Q 2. Thus, for the first time, the properties of ω electroproduction can be compared to those of ρ 0 , φ and J/ψ electroproduction at high W .

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Semi-automated fiducial marker registration reduces target registration error

International Congress Series, 2004

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Observation of events with an energetic forward neutron in deep inelastic scattering at HERA

Physics Letters B, 1996

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High- $E_T$ inclusive jet cross sections in photoproduction at HERA

The European Physical Journal C, 1998

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Measurement of the proton structure function F-2 and sigma(gamma*p)(tot) at low Q(2) and very low x at HERA

Physics Letters B, 1997