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Title:Angular distributions of high-mass dilepton production in hadron collisions
Author(s):McClellan, Randall Evan
Director of Research:Peng, Jen-Chieh
Doctoral Committee Chair(s):Grosse-Perdekamp, Matthias
Doctoral Committee Member(s):Willenbrock, Scott; Eckstein, James
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Abstract:The SeaQuest experiment is a fixed-target dimuon experiment currently running at the Fermi National Accelerator Laboratory (FNAL). By utilizing the high-intensity, 120GeV proton beam delivered by the FNAL Main Injector (MI), SeaQuest is able to measure proton-induced Drell-Yan dimuon production off of various nuclear targets in kinematic regions inaccessible to previous similar experiments. A suitably large fraction of the final dataset has been recorded, reconstructed, and analyzed. Very preliminary results from light-sea flavor asymmetry, nuclear dependence, and partonic energy loss analyses have been presented at numerous international conferences. A novel, FPGA-based trigger system has been designed, implemented, and optimized for the SeaQuest experiment. By implementing the trigger decision logic in FPGA firmware, it is more adaptable to changing experimental conditions. Additionally, the peripheral tasks of timing alignment, "trigger matrix" generation, and firmware uploading have been mostly automated, reducing the likelihood of user error in the maintenance and operation of the trigger system. Significant upgrades to hardware and firmware have greatly improved the performance of the trigger system since the 2012 commissioning run of SeaQuest. Four additional v1495 modules were added to facilitate thorough pulser testing of the firmware designs and in-situ pulser tests of all compiled firmware. These pulser tests proved crucial for diagnosing many errors that may have otherwise gone unnoticed. A significant change to the internal clocking of the trigger system eliminated a subtle source of rate-dependent trigger efficiency. With this upgrade, the trigger finally meets the "dead-time free" design specification. Drell-Yan dimuon data have been collected and analyzed for central θCS, with nearly flat acceptance in ϕCS, in the mass range 5.0GeV < M_ɣ* < 10.0 GeV at forward x_F with the SeaQuest spectrometer at FNAL. A very preliminary extraction of ƛ has been performed, and the remaining difficulties in extracting ν have been evaluated. Although the results are not yet publishable, significant progress has been made in developing this very challenging angular distributions analysis. A simple scheme for correcting for the angular acceptances of the spectrometer, trigger, and reconstruction has been developed and demonstrated. A generally applicable correction for the kinematically-dependent, rate-dependent reconstruction efficiency has been developed and applied to all current analyses on SeaQuest data. This rate-dependence correction was the first major hurdle in the path to publication of many preliminary SeaQuest results. The last remaining major correction for all analyses, but especially important for the angular parameter extraction, is the full characterization, rate-dependence correction, and subtraction of the combinatoric background contribution to the reconstructed dimuon sample. Independently, an intuitive, kinematic derivation of the single-event definitions of the Drell-Yan angular parameters has been developed under the assumption of unpolarized annihilating quarks within unpolarized nuclei. At O(α_s), where the quarks remain co-planar with the hadrons in the photon rest frame, this kinematic method reproduces the Lam-Tung relation and derives an additional equality for μ^2, which is only interpretable for single-event parameters. This method has been extended to the case of quark non-coplanarity, and the coplanar equalities become inequalities. A new equality was discovered, which should be obeyed by single-event parameters even in the case of a non-coplanar quark axis. The non-coplanar parameter relations have been used to derive constraints on the experimentally accessible values of ƛ and v. These constraints are compared with existing data and have been found consistent, except in the cases where significant contributions from non-zero Boer-Mulders functions are expected. Finally, the kinematically-derived parameter definitions have been applied to high-precision CMS data. The relative contributions of the q(bar q) and qg processes to the Z-boson "Drell-Yan" cross-section have been extracted. Further, an average measure of non-coplanarity, likely caused by O(α_s^2) and higher processes, has been extracted.
Issue Date:2016-07-07
Rights Information:Copyright 2016 by Randall Evan McClellan. All rights reserved.
Date Available in IDEALS:2016-11-10
Date Deposited:2016-08

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