H Meyer

Publications (596)339.57 Total impact

• Source

  Available from: Christian Gauthier

  Article: Analysis of local properties during a scratch test on a polymeric surface using molecular dynamics simulations.

  M Solar, H Meyer, C Gauthier
  [show abstract] [hide abstract]
  ABSTRACT: This work demonstrates a possible route to connect a particle (chain) based understanding with continuum mechanical questions about contact mechanics. The bond orientation, chain conformation and stress field of a polymer film were analyzed during scratch tests (tangential contact) using a molecular dynamics (MD) simulation approach. Scratch tests with a conical tip at constant scratching velocity were simulated on linear amorphous polymer surfaces at various temperatures and roughnesses of the tip and for various interactions between the tip and the particles of the polymer chains. The second Legendre polynomial (computed for small domains around the tip) gave the bond orientation inside the polymer film during sliding of the tip. The gyration tensor (layer-resolved in the direction of the polymer film thickness) provided information about the conformation of the polymer chains. These results allowed us to argue in favor of Briscoe's hypothesis (thin film sheared vs. "bulk" compressive behavior) concerning the friction properties of the polymer surfaces. Finally, the first stress measurements of the virial stress tensor (in sub-boxes placed in the MD cell) revealed a complex combination between compressive hydrostatic pressure and shear stress, which may be interpreted as a complex sheared domain at the interface.
  The European Physical Journal E 03/2013; 36(3):9843. · 1.94 Impact Factor
• Article: Anomalous Dynamics in 2D Polymer Melts.

  H Meyer, A N Semenov
  [show abstract] [hide abstract]
  ABSTRACT: The dynamics in polymer monolayers where chains are strongly confined and adopt 2D conformations are drastically different to those in the bulk. It is shown that viscoelastic hydrodynamic interactions play a major role defining the anomalous chain diffusion properties in such systems where chains cannot cross each other. We developed a quantitative analytical theory of polymer subdiffusion in 2D systems revealing a complex behavior controlled by a delicate interplay of inertial, viscoelastic hydrodynamic interactions, finite-box-size and frictional effects. The theory is fully supported by extensive momentum-conserving and Langevin molecular-dynamics simulation data explaining the highly cooperative character of 2D polymer motions.
  Physical Review Letters 12/2012; 109(24):248304. · 7.37 Impact Factor
• Article: Combination and QCD Analysis of Charm Production Cross Section Measurements in Deep-Inelastic ep Scattering at HERA

  H. Abramowicz, I. Abt, L. Adamczyk, M. Adamus, R. Aggarwal, C. Alexa, V. Andreev, S. Antonelli, P. Antonioli, A. Antonov, [......], W. Zeuner, Z. Zhang, B. O. Zhautykov, N. Zhmak, A. Zichichi, R. Žlebčík, H. Zohrabyan, Z. Zolkapli, F. Zomer, D. S. Zotkin
  [show abstract] [hide abstract]
  ABSTRACT: Measurements of open charm production cross sections in deep-inelastic ep scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections sigma_red^{c\bar{c}} for charm production are obtained in the kinematic range of photon virtuality 2.5<Q2<2000 GeV2 and Bjorken scaling variable 0.00003<x<0.05. The combination method accounts for the correlations of the systematic uncertainties among the different data sets. The combined charm data together with the combined inclusive deep-inelastic scattering cross sections from HERA are used as input for a detailed NLO QCD analysis to study the influence of different heavy flavour schemes on the parton distribution functions. The optimal values of the charm mass as a parameter in these different schemes are obtained. The implications on the NLO predictions for W^{\pm} and Z production cross sections at the LHC are investigated. Using the fixed flavour number scheme, the running mass of the charm quark is determined.
  11/2012;
• Article: Hydrodynamic and viscoelastic effects in polymer diffusion.

  J Farago, H Meyer, J Baschnagel, A N Semenov
  [show abstract] [hide abstract]
  ABSTRACT: We develop a fluctuating hydrodynamics approach to study the impact of the hydrodynamic and viscoelastic interactions on the motion of the center of mass of a polymer as well as on the relaxation of Rouse modes, either in a Θ solvent or in a melt of identical unentangled chains. We show that this method allows us to describe the effect of hydrodynamic interactions beyond the Zimm (for a single chain in a Θ solvent) or the Rouse models (for an unentangled melt). In the latter case, we recover the same important effect of the viscoelastic hydrodynamic interactions on the center-of-mass diffusion, first described in Farago et al (2011 Phys. Rev. Lett. 107 178301).
  Journal of Physics Condensed Matter 07/2012; 24(28):284105. · 2.55 Impact Factor
• Article: Length-scale dependent relaxation shear modulus and viscoelastic hydrodynamic interactions in polymer liquids.

  A N Semenov, J Farago, H Meyer
  [show abstract] [hide abstract]
  ABSTRACT: A quantitative theory of hydrodynamic interactions in unentangled polymer melts and concentrated solutions is presented. The study is focussed on the pre-Rouse transient time regimes (t < τ(R), the Rouse relaxation time) where the hydrodynamic response is governed mainly by the viscoelastic effects. It is shown that transient viscoelastic hydrodynamic interactions are not suppressed (screened) at large distances and are virtually independent of polymer molecular mass. A number of transient regimes of unusual and qualitatively different behavior of isotropic and anisotropic hydrodynamic response functions are elucidated. The regimes are characterized in terms of two main length-scale dependent characteristic times: momentum spreading time τ(i) ∝ r(4∕3) and viscoelastic time τ(∗) ∝ r(4). It is shown that for t > τ(i) the viscoelastic hydrodynamic interactions can be described in terms of the time or length scale dependent effective viscosity which, for t < τ(R) and/or for r < R(coil), turns out to be much lower than the macroscopic "polymer" viscosity η(m). The theory also involves a quantitative analysis of the length-scale dependent stress relaxation in polymer melts. The general predictions for hydrodynamic interactions in thermostated systems with Langevin friction are obtained as well.
  The Journal of chemical physics 06/2012; 136(24):244905. · 3.09 Impact Factor
• Article: Überbrückung bis zur Herztransplantation bei Kindern und Jugendlichen mit 2 pneumatisch betriebenen Unterstützungssystemen

  N. Reiß, A. El-Banayosy, T. Breymann, U. Blanz, H. Meyer, K. Minami, R. Körfer
  [show abstract] [hide abstract]
  ABSTRACT: Überbrückungsmöglichkeiten. Lange Zeit standen für die Überbrückung bis zur Herztransplantation bei Kindern und Jugendlichen ausschließlich die bei Erwachsenen etablierten Systeme zur Verfügung. Wir haben das Thoratec-System (Schlagvolumen 65ml) bei 8 Kindern und Jugendlichen eingesetzt. 7 der 8 Patienten konnten letztendlich erfolgreich transplantiert werden. Für kleinere Kinder wurde inzwischen ein Unterstützungssystem vom Typ Medos mit einer Ventrikelgröße von 25 bzw. 10ml entwickelt. Ergebnisse mit Unterstützungssystem vom Typ Medos. Mit dem Unterstützungssystem Typ Medos konnte bei 3 Kleinkindern eine suffiziente Kreislaufunterstützung erreicht werden, jedoch kam es bei den beiden ersten Kindern zu Blutungskomplikationen und Massentransfusion. Beide Kinder verstarben an Multiorganversagen. Bei dem 3. Kind (Implantation ohne Herz-Lungen-Maschine) traten keine Blutungskomplikationen auf, es kam zur Erholung der Organsysteme. Leider verstarb das Kind aufgrund eines technischen Fehlers. Schlussfolgerung. Das Thoratec-System stellt ein sicheres Überbrückungssystem zur Herztransplantation für Kinder und Jugendliche mit einem Körpergewicht über 25kg dar. Für kleine Kinder steht seit einigen Jahren das Medos-System zur Verfügung. Mit zunehmender Erfahrung und Implantation ohne extrakorporale Zirkulation dürften bei den Kleinkindern ähnliche Ergebnisse erzielt werden wie bei größeren Kindern. Bridging procedure. For a long time only the in adults established systems (e.g. Thoratec) are available for the bridging procedure in the paediatric population. We have implanted the Thoratec device (volume 65ml) for uni- or biventricular support in 8 children or adolescents. 7 of the 8 included patients underwent successful heart transplantation. 1 of the 8 patients (previous Mustard-OP in the early childhood) died after 2 month, because of multiorgan failure. Medos system. Recently the Medos system (volume 10ml, 25ml) was implanted in 3 small infants (body weight 4,5kg – 20kg). In the last case implantation was carried out without heart-lung-machine. All three patients had sufficient haemodynamic conditions. Nevertheless, the two first patients had bleeding complications with consequent polytransfusion and they finally died because of multiorgan failure. In the third infant no bleeding complication occurred, all organs systems recovered. Unfortunately the infant died because of technical failure. Conclusion. Summarized, the Thoratec device represents a safe mechanical circulatory support system for bridging procedure in children with a body weight more than 25kg. For smaller infants the Medos-system is available. With increasing experiences (e.g. implantation without HLM) the results may similar to those in greater children.
  Monatsschrift Kinderheilkunde 04/2012; 151(11):1188-1193. · 0.27 Impact Factor
• Source

  Available from: Andreas Werner Jung

  Article: Search for squarks in R-parity violating supersymmetry in ep collisions at HERA

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, S. Backovic, A. Baghdasaryan, S. Baghdasaryan, E. Barrelet, W. Bartel, K. Begzsuren, [......], Y. Vazdik, M. von den Driesch, D. Wegener, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, H. Zohrabyan, F. Zomer
  [show abstract] [hide abstract]
  ABSTRACT: A search for squarks in R-parity violating supersymmetry is performed in e ± p collisions at HERA using the H1 detector. The full data sample taken at a centre-of-mass energy Ös=319\sqrt{s}=319GeV is used for the analysis, corresponding to an integrated luminosity of 255pb−1 of e + p and 183pb−1 of e − p collision data. The resonant production of squarks via a Yukawa coupling λ′ is considered, taking into account direct and indirect R-parity violating decay modes. Final states with jets and leptons are investigated. No evidence for squark production is found and mass dependent limits on λ′ are obtained in the framework of the Minimal Supersymmetric Standard Model and in the Minimal Supergravity Model. In the considered part of the parameter space, for a Yukawa coupling of electromagnetic strength λ′=0.3, squarks of all flavours are excluded up to masses of 275GeV at 95% confidence level, with down-type squarks further excluded up to masses of 290GeV.
  European Physical Journal C 04/2012; 71(3):1-16. · 3.63 Impact Factor
• Article: Inclusive D*± meson and associated dijet production in deep-inelastic scattering at HERA

  A. Aktas, V. Andreev, T. Anthonis, B. Antunovic, S. Aplin, A. Asmone, A. Astvatsatourov, A. Babaev, S. Backovic, A. Baghdasaryan, [......], J. Zálešák, Z. Zhang, A. Zhelezov, A. Zhokin, Y.C. Zhu, J. Zimmermann, T. Zimmermann, H. Zohrabyan, F. Zomer, The Collaboration
  [show abstract] [hide abstract]
  ABSTRACT: Inclusive D*± production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D*± meson is investigated. The analysis covers values of photon virtuality 2 ≤ Q2 ≤ 100GeV2 and of inelasticity 0.05≤y≤0.7. Differential cross sections are measured as a function of Q2 and x and of various D*± meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon–gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the kT-unintegrated gluon distribution of the proton.
  European Physical Journal C 04/2012; 51(2):271-287. · 3.63 Impact Factor
• Article: Measurement of the inclusive e±p scattering cross section at high inelasticity y and of the structure function FL

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, S. Backovic, A. Baghdasaryan, S. Baghdasaryan, E. Barrelet, W. Bartel, O. Behrend, [......], Y. Vazdik, M. von den Driesch, D. Wegener, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, H. Zohrabyan, F. Zomer
  [show abstract] [hide abstract]
  ABSTRACT: A measurement is presented of the inclusive neutral current e ± p scattering cross section using data collected by the H1 experiment at HERA during the years 2003 to 2007 with proton beam energies E p of 920, 575, and 460GeV. The kinematic range of the measurement covers low absolute four-momentum transfers squared, 1.5GeV2<Q 2<120GeV2, small values of Bjorken x, 2.9⋅10−5<x<0.01, and extends to high inelasticity up to y=0.85. The structure function F L is measured by combining the new results with previously published H1 data at E p =920GeV and E p =820GeV. The new measurements are used to test several phenomenological and QCD models applicable in this low Q 2 and low x kinematic domain.
  European Physical Journal C 04/2012; 71(3):1-50. · 3.63 Impact Factor
• Source

  Available from: Andreas Werner Jung

  Article: Measurement of leading neutron production in deep-inelastic scattering at HERA

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, B. Antunovic, S. Backovic, A. Baghdasaryan, E. Barrelet, W. Bartel, K. Begzsuren, [......], D. Wegener, C. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer
  [show abstract] [hide abstract]
  ABSTRACT: The production of leading neutrons, where the neutron carries a large fraction x L of the incoming proton’s longitudinal momentum, is studied in deep-inelastic positron-proton scattering at HERA. The data were taken with the H1 detector in the years 2006 and 2007 and correspond to an integrated luminosity of 122pb−1. The semi-inclusive cross section is measured in the phase space defined by the photon virtuality 6<Q 2<100GeV2, Bjorken scaling variable 1.5⋅10−4<x<3⋅10−2, longitudinal momentum fraction 0.32<x L <0.95 and neutron transverse momentum p T <0.2GeV. The leading neutron structure function, F2LN(3)(Q2,x,xL)F_{2}^{LN(3)}(Q^{2},x,x_{L}), and the fraction of deep-inelastic scattering events containing a leading neutron are studied as a function of Q 2, x and x L . Assuming that the pion exchange mechanism dominates leading neutron production, the data provide constraints on the shape of the pion structure function.
  European Physical Journal C 04/2012; 68(3):381-399. · 3.63 Impact Factor
• Article: Three- and four-jet production at low x at HERA

  F.D. Aaron, A. Aktas, C. Alexa, V. Andreev, B. Antunovic, S. Aplin, A. Asmone, A. Astvatsatourov, S. Backovic, A. Baghdasaryan, [......], J. Žáček, J. Zálešák, Z. Zhang, A. Zhelezov, A. Zhokin, Y.C. Zhu, T. Zimmermann, H. Zohrabyan, F. Zomer, The Collaboration
  [show abstract] [hide abstract]
  ABSTRACT: Three- and four-jet production is measured in deep-inelastic ep scattering at low x and Q2 with the H1 detector using an integrated luminosity of 44.2pb-1. Several phase space regions are selected for the three-jet analysis in order to study the underlying parton dynamics from global topologies to the more restrictive regions of forward jets close to the proton direction. The measurements of cross sections for events with at least three jets are compared to fixed order QCD predictions of O(a\texts2){\mathcal{O}}(\alpha_{{\text{s}}}^2) and O(a\texts3){\mathcal{O}}(\alpha_{{\text{s}}}^3) and with Monte Carlo simulation programs where higher order effects are approximated by parton showers. A good overall description is provided by the O(a\texts3){\mathcal{O}}(\alpha_{{\text{s}}}^3) calculation. Too few events are predicted at the lowest x∼10-4, especially for topologies with two forward jets. This hints to large contributions at low x from initial state radiation of gluons close to the proton direction and unordered in transverse momentum. The Monte Carlo program in which gluon radiation is generated by the colour dipole model gives a good description of both the three- and the four-jet data in absolute normalisation and shape.
  European Physical Journal C 04/2012; 54(3):389-409. · 3.63 Impact Factor
• Article: Measurement of charm and beauty jets in deep inelastic scattering at HERA

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, S. Backovic, A. Baghdasaryan, E. Barrelet, W. Bartel, K. Begzsuren, A. Belousov, [......], Y. Vazdik, M. von den Driesch, D. Wegener, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, H. Zohrabyan, F. Zomer
  [show abstract] [hide abstract]
  ABSTRACT: Measurements of cross sections for events with charm and beauty jets in deep inelastic scattering at HERA are presented. Events with jets of transverse energy $E_{T}^{\mathrm{jet}}>6$E_{T}^{\mathrm{jet}}>6GeV and pseudorapidity −1.0<η jet<1.5 in the laboratory frame are selected in the kinematic region of photon virtuality Q 2>6GeV2 and inelasticity variable 0.07<y<0.625. Measurements are also made requiring a jet in the Breit frame with $E_{T}^{*{\mathrm{jet}}}>6$E_{T}^{*{\mathrm{jet}}}>6GeV. The data were collected with the H1 detector in the years 2006 and 2007 corresponding to an integrated luminosity of 189pb−1. The numbers of charm and beauty jets are determined using variables reconstructed using the H1 vertex detector with which the impact parameters of the tracks to the primary vertex and the position of secondary vertices are measured. The measurements are compared with QCD predictions and with previous measurements where heavy flavours are identified using muons.
  European Physical Journal C 04/2012; 71(1):1-21. · 3.63 Impact Factor
• Article: Jet production in ep collisions at high Q2 and determination of αs

  The Collaboration, F. D. Aaron, C. Alexa, K. Alimujiang, V. Andreev, B. Antunovic, A. Asmone, S. Backovic, A. Baghdasaryan, E. Barrelet, [......], Ch. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer, R. Zus
  [show abstract] [hide abstract]
  ABSTRACT: The production of jets is studied in deep-inelastic e ± p scattering at large negative four momentum transfer squared 150<Q 2<15000GeV2 using HERA data taken in 1999–2007, corresponding to an integrated luminosity of 395pb−1. Inclusive jet, 2-jet and 3-jet cross sections, normalised to the neutral current deep-inelastic scattering cross sections, are measured as functions of Q 2, jet transverse momentum and proton momentum fraction. The measurements are well described by perturbative QCD calculations at next-to-leading order corrected for hadronisation effects. The strong coupling as determined from these measurements is as(MZ)=0.1168±0.0007(exp.)+0.0046-0.0030(th.)±0.0016\alpha_{s}(M_{Z})=0.1168\pm0.0007\,\mathrm{(exp.)}{}^{+0.0046}_{-0.0030}\,\mathrm{(th.)}\pm 0.0016 (PDF).
  European Physical Journal C 04/2012; 65(3):363-383. · 3.63 Impact Factor
• Article: Drinking-Water Production in Urban Environments – Bank Filtration in Berlin

  G. Massmann, A. Pekdeger, T. Heberer, G. Grützmacher, U. Dünnbier, A. Knappe, H. Meyer, A. Mechlinski
  [show abstract] [hide abstract]
  ABSTRACT: Das Berliner Trinkwasser wird überwiegend durch induzierte Uferfiltration entlang der Oberflächengewässer gewonnen. Durch die geringen Durchlässigkeiten der Seesedimente findet eine Infiltration nur an den besser durchlässigen Uferzonen statt, und es kommt zu einer Unterströmung der Seen. Durch die Kombination verschiedener Umwelttracer konnte eine starke vertikale Altersdifferenzierung des Uferfiltrats nachgewiesen werden. Die Fließzeiten betragen in den flacheren Grundwasserleiterbereichen einige Monate, in den tieferen Bereichen sogar mehrere Jahre. Das den Abbau redox-sensitiver Substanzen beeinflussende, vorherrschende Redoxmilieu weist ebenfalls eine starke vertikale Differenzierung auf, die Infiltration erfolgt überwiegend anoxisch, und das Uferfiltrat wird mit der Tiefe reduzierender. Da das Oberflächenwasser einen variablen Anteil geklärten Abwassers enthält, konnten einige abwasserbürtige Substanzen (z. B. pharmazeutische Rückstände) in Oberflächenwasser- und im Uferfiltrat nachgewiesen werden. Obwohl der überwiegende Teil pharmazeutischer Rückstände effizient während der Untergrundpassage entfernt wird, erwiesen sich einige Substanzen als äußerst persistent (AMDOPH, Primidon und Carbamazepin). Berlin relies on induced bank filtration from a broad-scale, lake-type surface water system. Because the hydraulic conductivity of the lake sediments is low, infiltration only occurs close to the more permeable shore zones. Using multiple environmental tracer methods, a strong vertical age stratification of the bank filtrate could be shown. Travel times are generally long and vary throughout the upper aquifers from a few months near the ground surface to several decades in greater depth. Infiltration is mostly anoxic and redox zones were found to be vertically stratified too, becoming more reducing with depth. Because Berlin’s watercourses contain a proportion of treated municipal sewage a number of wastewater residues, e. g. pharmaceutical residues, were detected in surface water and groundwater. While the majority of the pharmaceutical residues studied were efficiently removed during underground passage, some substances (AMDOPH, primidone and carbamazepine) were found to be very persistent.
  Grundwasser 04/2012; 12(3):232-245. · 0.91 Impact Factor
• Article: Diffractive electroproduction of ρ and ϕ mesons at HERA

  The Collaboration, F. D. Aaron, M. Aldaya Martin, C. Alexa, V. Andreev, B. Antunovic, A. Asmone, S. Backovic, A. Baghdasaryan, E. Barrelet, [......], Ch. Wissing, E. Wünsch, J. Žáček, J. Záleák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer, R. Zus
  [show abstract] [hide abstract]
  ABSTRACT: Diffractive electroproduction of ρ and ϕ mesons is measured at HERA with the H1 detector in the elastic and proton dissociative channels. The data correspond to an integrated luminosity of 51 pb−1. About 10500 ρ and 2000 φ events are analysed in the kinematic range of squared photon virtuality 2.5 ≤ Q 2 ≤ 60 GeV2, photon-proton centre of mass energy 35 ≤ W ≤ 180 GeV and squared four-momentum transfer to the proton |t| ≤ 3 GeV2. The total, longitudinal and transverse cross sections are measured as a function of Q 2, W and |t|. The measurements show a transition to a dominantly “hard” behaviour, typical of high gluon densities and small q[`(q)] q\overline q dipoles, for Q 2 larger than 10 to 20 GeV2. They support flavour independence of the diffractive exchange, expressed in terms of the scaling variable (Q 2+M 2 V )/4, and proton vertex factorisation. The spin density matrix elements are measured as a function of kinematic variables. The ratio of the longitudinal to transverse cross sections, the ratio of the helicity amplitudes and their relative phases are extracted. Several of these measurements have not been performed before and bring new information on the dynamics of diffraction in a QCD framework. The measurements are discussed in the context of models using generalised parton distributions or universal dipole cross sections. KeywordsLepton-Nucleon Scattering
  Journal of High Energy Physics 04/2012; 2010(5):1-111. · 5.83 Impact Factor
• Article: Strangeness production at low Q2 in deep-inelastic ep scattering at HERA

  Collaboration, F. D. Aaron, C. Alexa, V. Andreev, B. Antunovic, S. Aplin, A. Asmone, A. Astvatsatourov, A. Bacchetta, S. Backovic, [......], V. Yeganov, J. Žáček, J. Zálešák, Z. Zhang, A. Zhelezov, A. Zhokin, Y. C. Zhu, T. Zimmermann, H. Zohrabyan, F. Zomer
  [show abstract] [hide abstract]
  ABSTRACT: The production of neutral strange hadrons is investigated using deep-inelastic scattering events measured with the H1 detector at HERA. The measurements are made in the phase space defined by the negative four-momentum transfer squared of the photon 2<Q 2<100 GeV2 and the inelasticity 0.1<y<0.6. The K s 0 and \varLambda([`\varLambda])\varLambda(\bar{\varLambda}) production cross sections and their ratios are determined. K s 0 production is compared to the production of charged particles in the same region of phase space. The Λ– [`\varLambda]\bar{\varLambda} asymmetry is also measured and found to be consistent with zero. Predictions of leading order Monte Carlo programs are compared to the data.
  European Physical Journal C 04/2012; 61(2):185-205. · 3.63 Impact Factor
• Article: Prompt photons in photoproduction at HERA

  The Collaboration, F. D. Aaron, M. Aldaya Martin, C. Alexa, V. Andreev, B. Antunovic, S. Backovic, A. Baghdasaryan, E. Barrelet, W. Bartel, [......], Ch. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer, R. Zus
  [show abstract] [hide abstract]
  ABSTRACT: The production of prompt photons is measured in the photoproduction regime of electron–proton scattering at HERA. The analysis is based on a data sample corresponding to a total integrated luminosity of 340pb−1 collected by the H1 experiment. Cross sections are measured for photons with transverse momentum and pseudorapidity in the range 6 < ETg < 156
  European Physical Journal C 04/2012; 66(1):17-33. · 3.63 Impact Factor
• Article: Measurement of the charm and beauty structure functions using the H1 vertex detector at HERA

  The Collaboration, F. D. Aaron, M. Aldaya Martin, C. Alexa, K. Alimujiang, V. Andreev, B. Antunovic, A. Asmone, S. Backovic, A. Baghdasaryan, [......], C. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer, R. Zus
  [show abstract] [hide abstract]
  ABSTRACT: Inclusive charm and beauty cross sections are measured in e − p and e + p neutral current collisions at HERA in the kinematic region of photon virtuality 5≤Q 2≤2000GeV2 and Bjorken scaling variable 0.0002≤x≤0.05. The data were collected with the H1 detector in the years 2006 and 2007 corresponding to an integrated luminosity of 189pb−1. The numbers of charm and beauty events are determined using variables reconstructed by the H1 vertex detector including the impact parameter of tracks to the primary vertex and the position of the secondary vertex. The measurements are combined with previous data and compared to QCD predictions.
  European Physical Journal C 04/2012; 65(1):89-109. · 3.63 Impact Factor
• Article: Search for baryonic resonances decaying to Ξπ in deep-inelastic scattering at HERA

  A. Aktas, C. Alexa, V. Andreev, T. Anthonis, B. Antunovic, S. Aplin, A. Asmone, A. Astvatsatourov, S. Backovic, A. Baghdasaryan, [......], J. Žáček, J. Zálešák, Z. Zhang, A. Zhelezov, A. Zhokin, Y.C. Zhu, T. Zimmermann, H. Zohrabyan, F. Zomer, The Collaboration
  [show abstract] [hide abstract]
  ABSTRACT: A search for narrow baryonic resonances decaying into Ξ-π- or Ξ-π+ and their antiparticles is carried out with the H1 detector using deep inelastic scattering events at HERA in the range of negative photon four-momentum transfer squared 2 < Q2 < 100GeV2. No signal is observed for a new baryonic state in the mass range 1600–2300MeV in either the doubly charged or the neutral decay channels. The known Ξ(1530)0 is observed through its decay mode into Ξ-π+. Upper limits are given on the ratio of the production rates of new baryonic states, such as the hypothetical pentaquark states Ξ– 5q or Ξ0 5q, relative to the Ξ(1530)0 baryon state.
  European Physical Journal C 04/2012; 52(3):507-514. · 3.63 Impact Factor
• Article: Inelastic production of J/ψ mesons in photoproduction and deep inelastic scattering at HERA

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, B. Antunovic, S. Backovic, A. Baghdasaryan, E. Barrelet, W. Bartel, K. Begzsuren, [......], D. Wegener, Ch. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer
  [show abstract] [hide abstract]
  ABSTRACT: A measurement is presented of inelastic photo- and electroproduction of J/ψ mesons in ep scattering at HERA. The data were recorded with the H1 detector in the period from 2004 to 2007. Single and double differential cross sections are determined and the helicity distributions of the J/ψ mesons are analysed. The results are compared to theoretical predictions in the colour singlet model and in the framework of non-relativistic QCD. Calculations in the colour singlet model using ak T factorisation ansatz are able to give a good description of the data, while colour singlet model calculations to next-to-leading order in collinear factorisation underestimate the data.
  European Physical Journal C 04/2012; 68(3):401-420. · 3.63 Impact Factor