The diffractive photoproduction of J/psi mesons is measured with the H1 detector at the ep collider HERA using an integrated luminosity of 78 pb^-1. The differential cross section d sigma(gamma p -> J/psi Y) / d t is studied in the range 2 < |t| < 30 GeV^2, where t is the square of the four-momentum transferred at the proton vertex. The cross section is also presented as a function of the photon-proton centre-of-mass energy W in three t intervals, spanning the range 50 < W < 200 GeV. A fast rise of the cross section with W is observed for each t range and the slope for the effective linear Pomeron trajectory is measured to be alpha^\prime= -0.0135 \pm 0.0074 (stat.) \pm 0.0051 (syst.) GeV^-2. The measurements are compared with perturbative QCD models based on BFKL and DGLAP evolution. The data are found to be compatible with s-channel helicity conservation.

Perturbative QCD

Pomeron

Helicity

Momentum transfer

10.1016/j.physletb.2003.06.056

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Citations (55)

Search for bosonic stop decays in R-parity violating supersymmetry in e+p collisions at HERA

Physics Letters B (2004)

Å. Aktas V. Andreev T. Anthonis A. Asmone A. Babaev

Yukawa potential

R-parity

Parity (physics)

10.1016/j.physletb.2004.08.032

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Citations (13)

Photoproduction of dijets with high transverse momenta at HERA

Physics Letters B (2006)

Å. Aktas V. Andreev T. Anthonis B. Antunović S. Aplin

10.1016/j.physletb.2006.05.060

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Citations (23)

Reactively Sputtered Iridium Oxide

Journal of The Electrochemical Society (2007)

B. Wessling Astrid Besmehn W. Mokwa Uwe Schnakenberg

Iridium oxide is reactively sputtered onto cold and heated substrates using radio frequency (rf) as well as dc plasma excitation. Oxygen integration rates into the growing film follow similar patterns for all investigated deposition conditions; differences can be explained on the grounds of plasma characteristics. X-ray photoelectron spectroscopy and scanning electron microscopy show that the type of plasma excitation as well as substrate heating have little effect on the deposited films' chemical compositions but a remarkable effect on their morphologies. The thin films are characterized regarding their use as electrode coatings for neural stimulation, where dc sputtering delivers the best results. Here, the most porous structures are deposited, enabling ion insertion into the material to sites of charge transfer. Repeated potential cycling of in physiological electrolyte toward higher electrochemical activity strongly changes film composition as well as morphology. Activation transforms iridium oxides to hydroxides, leaving a noncompact matrix, easily permeable for water and ionic species.

10.1149/1.2713691

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Citations (36)

Forward $\pi^\circ$ production and associated transverse energy flow in deep-inelastic scattering at HERA

The European Physical Journal C (2004)

Å. Aktas H. Henschel W. Erdmann R. Weber P. Dixon

Energy Flow

10.1140/epjc/s2004-01983-1

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Citations (21)

Search for doubly-charged Higgs boson production at HERA

Physics Letters B (2006)

Å. Aktas V. Andreev T. Anthonis B. Antunović S. Aplin

A search for the single production of doubly-charged Higgs bosons H^{\pm \pm} in ep collisions is presented. The signal is searched for via the Higgs decays into a high mass pair of same charge leptons, one of them being an electron. The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment at HERA. No evidence for doubly-charged Higgs production is observed and mass dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only decays into an electron and a muon via a coupling of electromagnetic strength h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3, masses below 112 GeV are ruled out.

Yukawa potential

Pair production

10.1016/j.physletb.2006.05.061

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Citations (31)

Sputtered Ir Films Evaluated for Electrochemical Performance I. Experimental Results

Journal of The Electrochemical Society (2008)

B. Wessling W. Mokwa Uwe Schnakenberg

The present work deals with the microstructure and electrochemical characteristics of sputtered metallic iridium thin films. The thin films are characterized regarding their electrochemical performance in cyclic voltammetry. Distinct morphologies and microstructures of Ir thin films are generated by altering the process parameters of power, pressure, and target-to-substrate distance. Growth of films with high specific surface and high electroactivity can be fostered by process conditions that deliver a low surface mobility of the deposited atoms. The anodically delivered charge can be varied by factors of more than 30, merely determined by film morphology. Electrochemical characteristics of the thin films are strongly tied to crystallographic orientation. The development of preferred orientation over adatom kinetic energy inversely correlates with the development of electrochemical activity. Enhanced shadowing effects during growth can be used to further increase the specific surface available for charge transfer. This is illustrated by changes in film thickness. Using a process supplying low-mobility Ir atoms to the surface, the thickest evaluated Ir film, at almost 3000 nm, delivers an anodic charge of after 100-fold potential cycling.

10.1149/1.2844805

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Citations (36)