ABSTRACT Title of dissertation: ELLIPTIC FLOW AT FORWARD RAPIDITY IN psNN = 200 GeV Au+Au COLLISIONS Eric Michael Richardson, Doctor of Philosophy, 2012 Dissertation directed by: Professor Alice C. Mignerey Department of Chemistry and Biochemistry Forward rapidity elliptic flow (v2) of both unidentified charged hadrons and decay muons has been measured from psNN = 200 GeV Au+Au collisions as a func- tion of pseudorapidity (η), transverse momentum, and number of nucleon collision participants. The measurements were performed at Brookhaven National Labora- tory's Relativistic Heavy Ion Collider using the PHENIX experiment's Muon Arm spectrometers, located at 1.2 < η 2.4. To identify hadrons, which consist mostly j j . of pions, kaons, and protons, a longitudinal momentum cut was applied to tracks stopping in the shallow steel layers of the Muon Arms. Those particles traversing completely through the Muon Arms consist of mostly muons from pion and kaon decays. The standard event plane (EP) method was used to measure v2, whose accuracy was improved 20-25% by combining the measured EP angles of several ∼ detectors, instead of using the measured EP from a single detector. Additionally, a hit swapping technique was devised to optimize track cuts, estimate background, and apply a background correction. To investigate the ability of the Muon Arms to accurately measure unidentified hadron v2, a GEANT simulation was also under- taken. The forward rapidity v2 results show good agreement with mid-rapidity mea- surements for central collisions (. 20-30% centrality), indicating a longitudinally extended thermalized medium with similar eccentricity, at least out to the Muon Arm η region. Only when compared to very forward BRAHMS measurements (η ≈ 3) is a v2 suppression seen for central collisions. For increasingly peripheral col- lisions, a growing suppression in v2 is observed for the Muon Arm measurements compared to mid-rapidity, indicating increased changes in the medium properties of ever smaller systems. For peripheral collisions of the same/similar centralities, an increased suppression is observed toward forward η. ELLIPTIC FLOW AT FORWARD RAPIDITY IN psNN = 200 GeV Au+Au COLLISIONS by Eric Michael Richardson Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2012 Advisory Committee: Professor Alice C. Mignerey, Chair/Advisor Professor Thomas D. Cohen Professor Christopher Jarzynski Professor Sang Bok Lee Professor William B. Walters c Copyright by Eric Michael Richardson 2012 Acknowledgments To paraphrase a famous metaphor, the work presented in this dissertation would not have been possible without \standing on the shoulders of giants." How- ever, to mention all the people, living or deceased, who made this analysis possible would require an additional dissertation or two that I will spare both of us from. Instead I will focus on those who most directly aided me in my dissertation research and graduate career while at the University of Maryland and Brookhaven National Laboratory. I must first thank the best sailor I know, my advisor Alice Mignerey, for navigating me through the treacherous waters of graduate school. Thanks to her guidance and advice I found the lighthouse through the fog. I am also very grateful to ShinIchi Esumi for teaching me the ins-and-outs of azimuthal anisotropy. Taking as much time as he did in answering my many questions was extremely generous and invaluable for my education. I can't stress my appreciation enough. I also need to thank Chris Pinkenburg and Carla Vale for their computing ex- pertise. Without their help many aspects of this analysis would not have been pos- sible, including producing the background reconstruction data, correcting the SMD channel swap, and performing the PISA simulation. Additionally, both openly wel- comed my general computing questions, and Chris specifically welcomed questions about the RXNP online monitoring and my analysis modules when they wouldn't compile. The background reconstruction data would also not have been possible without the guidance of Hugo Pereira Da Costa who helped me modify the Muon ii Arm reconstruction code. My appreciation further extends to several past and present Mignerey group members including Abigail Bickley, who introduced me to PHENIX and its analysis computing framework. While she was at Brookhaven she was a great mentor who set a steller example of how to lead and get things done. And I thank my good friend Richard Bindel for introducing me to C++, ROOT, and heavy-ion collisions. He showed great unselfishness in answering my questions when he could have been working on his own analysis. Our spirited conversations about physics or otherwise were also very enjoyable. I am further grateful to Marguerite Tonjes for not only introducing me to heavy-ion physics, but also providing computing and logistical support to the Mignerey group. I also thank Robert Pak for his watchful eye on my progress at Brookhaven as well as his guidance and advice. Additionally, I am appreciative of Matt Wysocki for our informative conversations and pointing me to some of his code, which I used as a blueprint for writing some of my own. And I thank John Koster and Seishi Dairaku for their help in correcting the SMD channel swap, and Kohei Shoji for providing me with the physical dimensions of the MuID. I am further grateful to those members of the RXNP detector group not yet mentioned who helped me along the way, including Wei Xie who was instrumental in all aspects of the RXNP's success, along with Chun Zhang who wrote much of the software. Also critical was Jiangyong Jia who, along with his student Rui Wei, provided me their code for combining event plane angles, which I adapted for this analysis. Thanks also to Yoshimasa Ikeda for his work in constructing, maintaining, iii and operating the RXNP. And of course no detector upgrade would be successful without the tireless work of the DAQ team, which was lead by John Haggerty and Martin Purschke. Of course none of this would be possible without the love and support of my extraordinary family, especially my father and mother, Cody and Margaret Richardson. They provided me with a wonderful childhood along the St. Lawrence River that set the foundation for any past or future success I may achieve. Their enthusiastic interest in all of my endeavors, whether they be sports, hobbies, or academics, has always provided me great comfort. I also want to thank my friends Robert and Kay Smith for their generosity and encouragement in helping me broaden my horizons. I am forever in their debt. iv Table of Contents Acknowledgements ii List of Tables viii List of Figuresx Glossary of Terms xv Prologue xix 1 Introduction1 1.1 The Standard Model...........................1 1.1.1 Fundamental Particles......................1 1.1.2 Quantum Chromodynamics...................6 1.2 Heavy Ion Collisions........................... 11 1.2.1 Event Evolution.......................... 13 1.2.2 Event Characterization...................... 17 1.3 Azimuthal Anisotropy.......................... 23 2 Experimental Overview 34 2.1 Relativistic Heavy Ion Collider...................... 34 2.2 PHENIX Detector............................ 38 2.2.1 Global Detectors......................... 42 2.2.1.1 Beam Beam Counter.................. 42 2.2.1.2 Zero Degree Calorimeter Shower Maximum Detector 44 2.2.1.3 Muon Piston Calorimeter−............... 47 2.2.2 Muon Arm Detectors....................... 48 2.2.2.1 Muon Tracker...................... 49 2.2.2.2 Muon Identifier..................... 52 2.2.2.3 Muon Arm Absorber.................. 54 3 Reaction Plane Detector Upgrade. 61 3.1 Overview.................................. 61 3.2 Design and Geometry........................... 64 3.3 Simulations and Testing......................... 69 3.4 Online Performance............................ 78 3.5 Calibrations................................ 80 3.6 Event Plane Resolution.......................... 81 3.7 Summary................................. 87 v 4 Data Acquisition and Offline Computing 89 4.1 Data Acquisition............................. 89 4.2 Offline Computing............................ 91 4.2.1 Overview............................. 91 4.2.2 Centrality Determination..................... 92 4.2.3 Track Reconstruction in Muon Arms.............. 97 5 Analysis 102 5.1 Event Plane Method........................... 102 5.2 Track Sources............................... 106 5.3 Quality Assurance............................ 111 5.3.1 Global QA............................. 111 5.3.2 Event Plane QA......................... 112 5.3.2.1 EP Flatness....................... 112 5.3.2.2 EP Stability....................... 114 5.3.2.3 EP Resolution..................... 114 5.3.3 Muon Arm QA.......................... 115 5.3.4 Shift Leader Comment QA.................... 117 5.4 Event and Track Requirements..................... 117 5.4.1 Variable Definitions........................ 118 5.4.2 Variable Requirements...................... 120 5.4.3 Effectiveness of Variable Requirements............. 121 5.5 Background Estimation.......................... 126 5.5.1 Swap Half-octant Method.................... 126 5.5.2 Variable Distributions...................... 129 5.6 Correcting SMD Swapped Channels................... 130 5.7 Combining Event Planes (EPs)..................... 141 5.7.1 Method.............................. 141 5.7.2 Non-flow Effects on EP Resolution..............