Omega Meson Production in the p n -> d omega Reaction at ANKE

In the framework of this thesis a first measurement of the p n -> d omega total cross section has been performed at mean excess energies of Q ~= 26 and 60 MeV. The motivation, apparatus, analysis, results and their tentative interpretation are discussed in the following. The comparison of the cross sections for meson production in proton-proton and proton-neutron collisions close to threshold, constrain theoretical models describing the production mechanisms. For eta production the observed cross section ratio R = sigma( p n -> p n eta ) / sigma( p p -> p p eta) ~= 6.5 is generally attributed to isovector dominance in model calculations based on meson exchange. It is therefore interesting to investigate whether a similar isospin dependence is found also for the omega, the next heavier isoscalar meson. Relatively few experiments were performed for the p p -> p p omega reaction, but in proton-neutron collisions no data whatsoever are available. The p n -> d omega reaction was studied in the p d -> pSP d omega reaction at four proton beam momenta between 2.6 and 2.9 GeV/c at the ANKE spectrometer of COSY-JAülich. A deuterium cluster-jet target was used as an effective neutron target, detecting the low momentum recoil protons (pSP), which have momenta of about 80 MeV/c, in a silicon telescope placed close to the target. These recoil protons can be treated as "spectators" that influence the reaction only through their modification of the kinematics. By variation of angle and momentum of the spectator protons, a certain range in excess energy Q is selected experimentally. This range is used to extract results in p-n collisions for the corresponding Q values. The deuterons emitted at angles below 8 degree with a momenta around 2 GeV/c were detected in the forward system of the ANKE spectrometer. Inclined Cerenkov counters in combination with two layers of scintillation counters enabled us to identify these deuterons despite a two orders of magnitude higher proton background. Their momenta were reconstructed using the information from two multi-wire proportional chambers. The p n -> d omega reaction was then identified via the missing mass technique. In order to normalise the data, first the efficiencies of all detectors were evaluated. Secondly the absolute luminosity was determined by the p-d elastic scattering reaction, employing the possibility to identify slow deuterons simultaneously in the silicon telescope. Measurements in p p -> p p omega at SATURNE show there to be a strong contribution from multi-pion production below the omega peak in the missing mass spectrum. This can only be reliably estimated by comparing data above and below the omega threshold. Used are the experimental data at 2.6, 2.7, 2.8 and 2.9 GeV/c beam momentum, which correspond to mean Q values in p n -> d omega of -40, -5, 26 and 60 MeV respectively. At the highest energy, there is clear evidence for an omega peak, whereas at 2.8 GeV/c the residual omega signal depends much more sensitively upon the background description. The cross sections extracted for p n -> d omega at Q ~= 26 MeV and 60 MeV are significantly smaller than theoretical predictions. This suggests that the reaction mechanism for omega production differs from the one for the eta, possibly implying a relatively larger contribution from isoscalar meson exchange. Measurements with higher precision in both Q and in cross section are scheduled already for August 2003. The results are expected to shed even further light on the basic production mechanisms

Role of tumor size in the pre-operative management of rectal cancer patients

Clinical management of rectal cancer patients relies on pre-operative staging. Studies however continue to report moderate degrees of over/understaging as well as inter-observer variability. The aim of this study was to determine the sensitivity, specificity and accuracy of tumor size for predicting T and N stages in pre-operatively untreated rectal cancers

Effect of EpCAM, CD44, CD133 and CD166 expression on patient survival in tumours of the ampulla of Vater

Carcinomas of the Vaterian system are rare and presumably arise from pre-existing adenomas. According to the cancer stem cell (CSC) hypothesis, only a small subset of tumor cells has the ability to initiate and develop tumor growth. In colorectal cancer, CD44, CD133, CD166 and EpCAM have been proposed to represent CSC marker proteins and their expression has been shown to correlate with patient survival