Virtual Photon Structure from Jet Production at HERA

The feasibility of measuring parton distribution functions of of virtual photons via the jet production at HERA is investigated.Comment: Contribution to the Workshop on "Future Physics at HERA", eds. G. Ingelman, A. De Roeck, R. Klanner,4 pages, 3 figures, epsfi

Deep-inelastic production of heavy quarks

Deep-inelastic production of heavy quarks at HERA, especially charm, is an excellent signal to measure the gluon distribution in the proton at small $x$ values. By measuring various differential distributions of the heavy quarks this reaction permits additional more incisive QCD analyses due to the many scales present. Furthermore, the relatively small mass of the charm quark, compared to the typical momentum transfer $Q$, allows one to study whether and when to treat this quark as a parton. This reaction therefore sheds light on some of the most fundamental aspects of perturbative QCD. We discuss the above issues and review the feasibility of their experimental investigation in the light of a large integrated luminosity.Comment: 10 pages, uses epsfig.sty, five ps figures included. To appear in the proceedings of the workshop Future Physics at HERA, eds. G. Ingelman, A. De Roeck and R. Klanner, DESY, Hamburg, 199

Design and First Tests of a Radiation-Hard Pixel Sensor for the European X-Ray Free-Electron Laser

The high intensity and high repetition rate of the European X-ray Free-Electron Laser, presently under construction in Hamburg, requires silicon sensors which can stand X-ray doses of up to 1 GGy for 3 years of operation at high bias voltage. Within the AGIPD Collaboration the X-ray-radiation damage in MOS Capacitors and Gate-Controlled Diodes fabricated by four vendors on high-ohmic n-type silicon with two crystal orientations and dif- ferent technological parameters, has been studied for doses between 1 kGy and 1 GGy. The extracted values of oxide-charge and surface-current densi- ties have been used in TCAD simulations, and the layout and technological parameters of the AGIPD pixel sensor optimized. It is found that the op- timized layout for high X-ray doses is significantly different from the one for non-irradiated sensors. First sensors and test structures have been de-livered in early 2013. Measurement results for X-ray doses of 0 to 10 MGy and their comparison to simulations are presented. They demonstrate that the optimization has been successful and that the sensors fulfill the required specifications

Future ep Physics: The Outlook for HERA

The luminosity of the electron-proton collider, HERA, will be increased by a factor of five during the long shutdown in the year 2000. At the same time longitudinal lepton beam polarisation will be provided for the collider experiments H1 and ZEUS. These far reaching upgrades to the machine will be matched by upgrades to the detectors. The result will be a unique facility for the study of the structure of the proton and the nature of the strong and electroweak interactions. The physics potential of the upgraded accelerator is discussed here together with a brief description of the HERA machine and collider detector upgrades.Comment: 13 pages, Late

On the low x behaviour of nuclear shadowing

We calculate the x dependence of nuclear shadowing at moderate values of Q^2 by using HERA diffractive data and, for consistency, F2 parameterization of ZEUS. We show that no decrease of shadowing occurs down to very low x (x = 10^-4).Comment: 9 pages, submitted on june for publicatio

Study of X-ray Radiation Damage in Silicon Sensors

The European X-ray Free Electron Laser (XFEL) will deliver 30,000 fully coherent, high brilliance X-ray pulses per second each with a duration below 100 fs. This will allow the recording of diffraction patterns of single complex molecules and the study of ultra-fast processes. Silicon pixel sensors will be used to record the diffraction images. In 3 years of operation the sensors will be exposed to doses of up to 1 GGy of 12 keV X-rays. At this X-ray energy no bulk damage in silicon is expected. However fixed oxide charges in the insulating layer covering the silicon and interface traps at the Si-SiO2 interface will be introduced by the irradiation and build up over time. We have investigated the microscopic defects in test structures and the macroscopic electrical properties of segmented detectors as a function of the X-ray dose. From the test structures we determine the oxide charge density and the densities of interface traps as a function of dose. We find that both saturate (and even decrease) for doses between 10 and 100 MGy. For segmented sensors the defects introduced by the X-rays increase the full depletion voltage, the surface leakage current and the inter-pixel capacitance. We observe that an electron accumulation layer forms at the Si-SiO2 interface. Its width increases with dose and decreases with applied bias voltage. Using TCAD simulations with the dose dependent parameters obtained from the test structures, we are able to reproduce the observed results. This allows us to optimize the sensor design for the XFEL requirements

g_1 at low x and low Q^2 with Polarized ep Colliders

Measurements of g_1 at low x and low Q^2 are expected to provide a sensitive probe of the transition from Regge to perturbative QCD dynamics, offering a new testing ground for models of small x physics. We discuss the potential of polarized ep colliders (Polarized HERA and eRHIC) to investigate this physics --- varying Q^2 between 0.01 and 1 GeV^2 --- and to constrain the high-energy part of the Drell-Hearn-Gerasimov sum-rule for polarized photoproduction.Comment: 18 pages, 2 figure