Measurement of Scaled Momentum Distributions in the Breit Frame at HERA Using the ZEUS Detector

[摘要] Charged particle production has been studied in Deep Inelastic Scattering (DIS) events using the ZEUS detector. The Central Tracking Detector (CTD) has been a principal component in this analysis. Results from a method developed to measure the hit efficiency of the CTD were used to determine its optimum operating conditions during the data taking period. Scaled momentum distributions of charged particles have been measured in the current fragmentation region of the Breit frame over a large range of Q2from 10 to 1280 GeV2. In this region, the fragmentation properties of the struck quark in DIS are expected to be similar to those of the quarks produced in e+e- annihilation experiments. Transformation from the HERA laboratory frame to the Breit system is shown to be accomplished experimentally. The required Lorentz boost, however, limits the resolution with which the scaled momentum distributions can be measured. The evolution with Q of the scaled momentum distributions is used to study QCD coherence effects in DIS by comparing to a variety of Monte Carlo models. This comparison reveals that the best description of the data is achieved using models which incorporate coherence effects. The data are compared with theoretical predictions in order to extract a value of LambdaEFF, an effective QCD scale. A comparison between the DIS data and corresponding data from e+e- annihilation experiments is made in order to investigate the similarity between the fragmentation properties of quarks in the two distinct processes. A clear agreement is observed between the Q-evolution of the scaled momenta in DIS and e+e- annihilation and thereby provides evidence for the universality of quark fragmentation.

[发布机构] University:University of Glasgow

[关键词] High energy physics