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oai:www.ideals.illinois.edu:2142/88073 2023-07-11 col_2142_5131 col_2142_8859 com_2142_5130 com_2142_8858 com_2142_234

Grosse Perdekamp, Matthias Makins, Naomi Stack, John Willenbrock, Scott S. McKinney, Cameron Palmer 2015-09-29T20:38:36Z 2015-09-29T20:38:36Z 2015-08 2015-07-17 In the 1980s, polarized deep inelastic lepton-nucleon scattering experiments revealed that only about a third of the proton's spin of $\frac{1}{2}\hbar$ is carried by the quarks and antiquarks, leaving physicists with the puzzle of how to account for the remaining spin. As gluons carry roughly 50\% of the proton's momentum, it seemed most logical to look to the gluon spin as another significant contributor. However, lepton-nucleon scattering experiments only access the gluon helicity distribution, $\Delta g$, through effects on the quark distributions via scaling violations. Constraining $\Delta g$ through scaling violations requires experiments that together cover a large range of $Q^{2}$. Such experiments had been carried out with unpolarized beams, leaving $g(x)$ (the unpolarized gluon distribution) relatively well-known, but the polarized experiments have only thus far provided weak constraints on $\Delta g$ in a limited momentum fraction range. With the commissioning in 2000 of the Relativistic Heavy Ion Collider, the first polarized proton-proton ($pp$) collider, and the first polarized $pp$ running in 2002, the gluon distributions could be accessed directly by studying quark-gluon and gluon-gluon interactions. In 2009, data from measurements of double longitudinal spin asymmetries, $A_{LL},$ at the STAR and PHENIX experiments through 2006 were included in a QCD global analysis performed by Daniel de Florian, Rodolfo Sassot, Marco Stratmann, and Werner Vogelsang (DSSV), yielding the first direct constraints on the gluon helicity. The DSSV group found that the contribution of the gluon spin to the proton spin was consistent with zero, but the data provided by PHENIX and STAR was all at mid-rapidity, meaning $\Delta g$ was constrained by data only a range in $x$ from 0.05 to 0.2, leaving out helicity contributions from the huge number of low-$x$ gluons. A more recent analysis by DSSV from 2014 including RHIC data through 2009 for the first time points to significant gluon polarization at intermediate momentum fractions, meaning gluon polarization measurements may be more interesting than anticipated, especially at momentum fractions where no constraints exist as of yet. A forward detector upgrade in PHENIX, the Muon Piston Calorimeter (MPC), was designed with the purpose of extending the sensitivity to $\Delta g$ to lower $x$. Monte Carlo simulations indicate that measurements of hadrons in the MPC's pseudorapidity of range $3.1<\eta<3.9$ probe asymmetric collisions between high-$x$ quarks and low-$x$ gluons, with the $x$ of the gluons reaching below 0.01 at a collision energy $\sqrt{s}=500\,GeV$. We access $\Delta g$ through measurements of $A_{LL}$ for electromagnetic clusters in the MPC; this thesis details the measurement from the Run 11 (2011) data set at $\sqrt{s}=500\,GeV$. We find $A_{LL}\approx0$, but the statistical uncertainties from this measurement mean we likely cannot resolve the small expected asymmetries. However, improved techniques for determining the relative luminosity between bunch crossings with different helicity configurations will allow data from a much larger data set in Run 13 to be most impactful in constraining $\Delta g,$ whereas previous measurements of $A_{LL}$ have had difficulties limiting the systematic uncertainty from relative luminosity. In this thesis, we begin by presenting an overview of the physics motivation for this experiment. Then, we discuss the experimental apparatus at RHIC and PHENIX, with a focus on those systems integral to our analysis. The analysis sections of the thesis cover calibration of the Muon Piston Calorimeter, a careful examination of the relative luminosity systematic uncertainty, and the process of obtaining a final physics result. Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2015-09-29 without embargo terms The student, Cameron McKinney, accepted the attached license on 2015-07-17 at 12:19. The student, Cameron McKinney, submitted this Dissertation for approval on 2015-07-17 at 12:28. This Dissertation was approved for publication on 2015-07-17 at 13:29. DSpace SAF Submission Ingestion Package generated from Vireo submission #8530 on 2015-09-29 at 13:23:02 Made available in DSpace on 2015-09-29T20:38:36Z (GMT). No. of bitstreams: 2 MCKINNEY-DISSERTATION-2015.pdf: 8954381 bytes, checksum: b36ca6730cbebf706d6e76720ccf1616 (MD5) LICENSE.txt: 4213 bytes, checksum: c1c74e45adc8f0f84d02c94081d1d94f (MD5) Previous issue date: 2015-07-17 application/pdf http://hdl.handle.net/2142/88073 en Copyright 2015 by Cameron Palmer McKinney PHENIX proton spin gluon polarization double spin asymmetry Delta G Gluon polarization in the proton: constraints at low x from the measurement of the double longitudinal spin asymmetry for forward-rapidity hadrons with the PHENIX detector at RHIC text text 2015-8 Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.