Low Q^2 Jet Production at HERA and Virtual Photon Structure

The transition between photoproduction and deep-inelastic scattering is investigated in jet production at the HERA ep collider, using data collected by the H1 experiment. Measurements of the differential inclusive jet cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the transverse energy and the pseudorapidity of the jets in the virtual photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3 < y < 0.6. The interpretation of the results in terms of the structure of the virtual photon is discussed. The data are best described by QCD calculations which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure

A Search for Selectrons and Squarks at HERA

Data from electron-proton collisions at a center-of-mass energy of 300 GeV are used for a search for selectrons and squarks within the framework of the minimal supersymmetric model. The decays of selectrons and squarks into the lightest supersymmetric particle lead to final states with an electron and hadrons accompanied by large missing energy and transverse momentum. No signal is found and new bounds on the existence of these particles are derived. At 95% confidence level the excluded region extends to 65 GeV for selectron and squark masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure

A Measurement of the Proton Structure Function F ⁣2(x,Q2)F_{\!2}(x,Q^2)

A measurement of the proton structure function $F_{\!2}(x,Q^2)$ is reported for momentum transfer squared $Q^2$ between 4.5 $GeV^2$ and 1600 $GeV^2$ and for Bjorken $x$ between $1.8\cdot10^{-4}$ and 0.13 using data collected by the HERA experiment H1 in 1993. It is observed that $F_{\!2}$ increases significantly with decreasing $x$, confirming our previous measurement made with one tenth of the data available in this analysis. The $Q^2$ dependence is approximately logarithmic over the full kinematic range covered. The subsample of deep inelastic events with a large pseudo-rapidity gap in the hadronic energy flow close to the proton remnant is used to measure the "diffractive" contribution to $F_{\!2}$.Comment: 32 pages, ps, appended as compressed, uuencoded fil

Fabrication and efficiency measurement of a Mo/C/Si/C three material system multilayer Laue lens

In this letter, we report on the manufacturing of a multilayer Laue lens (MLL) consisting of a multilayer stack with three materials: molybdenum and silicon as the absorber and spacer layer, respectively, and carbon as transition layers. The design has four layers per period: Mo/C/Si/C. It yields 6000 zones and provides an aperture of 50 μm. This allows the MLL structure to accept a large portion of the coherent part of the beam and to achieve a small spot size. The MLL deposition was made by magnetron sputtering at the Fraunhofer IWS, and the sectioning was done by laser cutting and subsequent focused ion beam milling to a thickness that provides a good efficiency for a photon energy of 12 keV. The diffraction efficiency as a function of the tilting angle has been measured at beamline 1-BM of the Advanced Photon Source. An efficiency of almost 40% has been achieved. This shows that the material system performs well compared to MLLs made of two-materials and that it is in excellent agreement with the numerically calculated efficiency for a comparable molybdenum/silicon bilayer system lens. We conclude that the three material system offers high efficiencies and is advantageous for stress reduction in MLLs