Observation of jet photoproduction and comparison to Monte Carlo simulation

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Title: Observation of jet photoproduction and comparison to Monte Carlo simulation
Author: Lincoln, Donald W.
Advisor: Corcoran, Marjorie D.
Degree: Doctor of Philosophy thesis
Abstract: The photon is the carrier of the electromagnetic force. However in addition to its well known nature, the theories of QCD and quantum mechanics would indicate that the photon can also for brief periods of time split into a $q\overline{q}$ pair (an extended photon). How these constituents share energy and momentum is an interesting question and such a measurement was investigated by scattering photons off protons. The post collision kinematics should reveal pre-collision information. Unfortunately, when these constituents exit the collision point, they undergo subsequent interactions (gluon radiation, fragmentation, etc.) which scramble their kinematics. An algorithm was explored which was shown via Monte Carlo techniques to partially disentangle these post collision interactions and reveal the collision kinematics. The presence or absence of large transverse momenta internal ($k\sb\bot$) to the photon has a significant impact on the ability to reconstruct the kinematics of the leading order calculation hard scatter system. Reconstruction of the next to leading order high $E\sb\bot$ partons is more straightforward. Since the photon exhibits this unusual behavior only part of the time, many of the collisions recorded will be with a non-extended (or direct) photon. Unless a method for culling only the extended photons out can be invented, this contamination of direct photons must be accounted for. No such culling method is currently known, and so any measurement will necessarily contain both photon types. Theoretical predictions using Monte Carlo methods are compared with the data and are found to reproduce many experimentally measured distributions quite well. Overall the LUND Monte Carlo reproduces the data better than the HERWIG Monte Carlo. As expected at low jet $E\sb\bot$, the data set seems to be dominated by extended photons, with the mix becoming nearly equal at Jet $E\sb\bot$ $>$ 4 GeV. The existence of a large photon $k\sb\bot$ appears to be favored.
Citation: Lincoln, Donald W.. (1994) "Observation of jet photoproduction and comparison to Monte Carlo simulation." Doctoral Thesis, Rice University.
Date: 1994

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