Measurement of Jet Fragmentation Properties in $p\bar{p}$ Collisions at $\sqrt{s}$ = 1.8-TeV
[report]
Shun-ichi Kanda
1990
unpublished
The fragmentation properties of jets in jjp collisions at ..(i = 1.8 TeV have been studied by the CDF experiment at Fermilab. A method based on the QCD-inspired fragmentation models is proposed for the experimental distinction of two types of partons-quarks and gluons. A number of variables, such as mechanical/electric moments, multiplicity, and EM fraction, are calculated for Monte Carlo (reference) jets. Their resulting distributions suggest that gluon jets are softer and broader than quark
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... ts, reflecting the nature of the double color charge of the gluon. The reference jets are compared with real dijet events of the CDF experiment. The real data show strong preference for gluon-like behaviour. This is consistent with the QCD prediction: The gluon jet is dominant at the CDF energy. In order to integrate the information on variables of jets, each jet is characterized in global likelihood which is a simple sum of all log-likelihood functions derived from 30 different variables. This results in a bigger quarkfgluon discrimination power than that of a single mOBt effective variable. The global likelihood for real dijet events are distributed much like gluons, and that for l'cand+jet events, in which the jet is associated with a photon candidate, are distributed like the mixture of gluons and quarks. The gluon fraction in a given sample is determined by fitting its global likelihood distribution to the superposition of two distributions for quark and gluon samples. The CDF dijet data shows approximately 80% gluon fraction, and the l'cond+jet data shows about 40% gluon fraction in the jet transverse energy (Et) range of 10-30 GeV. These results agree within the error with the gluon fraction determined from theoretical prediction and the expected 1r 0 h ratio in the CDF photon candidates, except that some disagreement for dijet event is observed at low energy. ii To my father =d mother iii Acknowledgement I would like to acknowledge to University of Tsukuba High Energy Physics group for their help. In particular I would like to thank my advisor, Prof. Kondo, for giving me the opportunity to work on CDF and suggesting the topic of this analysis. He has excited my acadelnic curiosity and always guided me in the right direction. Without his support and encouragement, this thesis would not have been possible. There is Dr. Kim who got me involved in the PEM calorimeter works and jet physics. He taught me not only how to build and test chambers and also how to play hooky from school. I also thank Dr. Mishina and Dr. Fukui for their great help in maintenance and beam test of chambers.
doi:10.2172/1372879
fatcat:qhcckxd2f5elpc4xsc6tg3i6wu