BOSTON UNIVERSITY GRADUATE SCHOOL OF ARTS AND SCIENCES Dissertation MEASUREMENT OF THE TOTAL AND DIFFERENTIAL CROSS SECTION OF Z BOSON PRODUCTION IN ASSOCIATION WITH JETS IN PROTON-PROTON COLLISIONS AT SQRT(S) = 13 TEV by DANIEL J. ARCARO B.S., Boston University, 2013 CERN-THESIS-2020-208 Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2020 c 2020 by DANIEL J. ARCARO All rights reserved Approved by First Reader Lawrence R. Sulak, PhD Professor of Physics Second Reader John M. Butler, PhD Professor of Physics Acknowledgments I would like to thank Larry Sulak for his wisdom and guidance in the world of ex- perimental physics. I will carry the knowledge passed down from him throughout my life and future careers. This thesis would not have been possible without the Boston University CMS group and many CMS collaborators elsewhere. Thank you to my friends and family for their support throughout my education and graduate career. I am especially lucky to have Clover for her collaboration and support during this journey. iv MEASUREMENT OF THE TOTAL AND DIFFERENTIAL CROSS SECTION OF Z BOSON PRODUCTION IN ASSOCIATION WITH JETS IN PROTON-PROTON COLLISIONS AT SQRT(S) = 13 TEV DANIEL J. ARCARO Boston University, Graduate School of Arts and Sciences, 2020 Major Professor: Lawrence R. Sulak, PhD Professor of Physics ABSTRACT Z boson production in association with jets at the LHC is a major source of background to standard model searches and it provides a sensitive evaluation of the accuracy of perturbative QCD predictions. The production of a Z boson, decaying to two charged muons (µ+µ−), in association with jets in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. The cross sections and their ratios are measured with data recorded by the CMS experiment at the LHC in 2016, corre- sponding to an integrated luminosity of 35.9 fb−1. The cross sections are measured as a function of observables including the transverse momentum and rapidity of the Z boson, the jet transverse momentum and rapidity for the five highest momentum jets, and jet multiplicity. The measurements are compared with predictions from a multi- leg next-to-leading-order Monte Carlo generator and a next-to-next-to-leading order calculation with next-to-next-to-leading logarithm resummation and parton shower- ing. v Contents 1 Introduction and Theoretical Overview 1 1.1 Introduction . .1 1.2 The Standard Model . .1 1.3 Proton-proton collisions at the LHC . .3 1.3.1 Parton distribution functions . .3 1.3.2 Drell-Yan process . .4 1.3.3 Jet formation . .8 1.4 Drell-Yan at the LHC . .9 2 The Compact Muon Solenoid 12 2.1 The CMS Detector . 12 2.2 The CMS Hadron Calorimeter . 14 2.2.1 Calorimeter Design . 14 2.2.2 Signal Transducers . 16 2.2.3 Digitization and Readout . 18 2.3 Back End Electronics . 18 2.3.1 Introduction to FPGA’s . 18 2.3.2 Micro Telecommunications Crate . 19 2.3.3 HCAL Trigger and Readout Card . 20 2.3.4 AMC13 . 20 2.3.5 AMC13 Software . 25 3 Z+jets Measurement 28 3.1 Data and Simulated Samples . 28 3.2 Event Reconstruction . 32 3.2.1 Muons Reconstruction . 34 vi 3.3 Sample Corrections . 35 3.3.1 Rochester Correction . 35 3.3.2 Muon Scale Factors . 35 3.3.3 Pileup . 36 3.3.4 L1 Prefire Weights . 38 3.4 Object Selections . 41 3.4.1 Muon Selection . 41 3.4.2 Jet Selections . 42 3.4.3 Particle Level Objects . 44 3.5 Background Estimation . 44 3.6 Observables . 47 3.7 Phenomenological Models and Theoretical Calculations . 56 3.8 Unfolding Procedure . 59 3.9 Systematical Uncertainties . 65 3.10 Software . 70 3.11 Results . 72 4 Conclusions 101 A Appendix 103 A.1 Systematic Tables . 103 References 129 Curriculum Vitae 134 vii List of Tables 2.1 AMC13 Trigger Throttling State . 22 3.1 Single Muon Data Samples . 29 3.2 Single Muon Triggers . 29 3.3 Monte Carlo Signal Samples. Both inclusive and binned samples are combined. 30 3.4 DY npNLO Weights . 30 3.5 Monte Carlo Resonant Samples . 31 3.6 Monte Carlo Non-Resonant Samples with T* = TuneCUETP8M1. 32 3.7 Loose Jet ID Parameters . 42 3.8 Unfolding Numbers . 76 st A.1 Differential cross section in 1 jet jηj (Njets ≥ 1)............ 104 st A.2 Differential cross section in 1 jet pT (Njets ≥ 1)............ 104 nd A.3 Differential cross section in 2 jet jηj (Njets ≥ 2)............ 105 nd A.4 Differential cross section in 2 jet pT (Njets ≥ 2)............ 105 rd A.5 Differential cross section in 3 jet jηj (Njets ≥ 3)............ 106 rd A.6 Differential cross section in 3 jet pT (Njets ≥ 3)............ 106 th A.7 Differential cross section in 4 jet jηj (Njets ≥ 4)............ 107 th A.8 Differential cross section in 4 jet pT (Njets ≥ 4)............ 107 A.9 Differential cross section in HT (Njets ≥ 1)............... 108 A.10 Differential cross section in HT (Njets ≥ 2)............... 108 A.11 Differential cross section in HT (Njets ≥ 3)............... 109 A.12 Differential cross section in dijet mass Mjj (Njets ≥ 2)......... 109 A.13 Differential cross section in Exclusive jet multiplicity . 110 viii A.14 Differential cross section in Inclusive jet multiplicity . 110 Z A.15 Differential cross section in pT ...................... 111 Z A.16 Differential cross section in pT ...................... 112 A.17 Differential cross section in jyZj (Njets ≥ 1)............... 113 A.18 Differential cross section in ydiff(jet1,jet2) (Njets ≥ 2)........... 113 A.19 Differential cross section in ysum(jet1,jet2) (Njets ≥ 2)........... 114 A.20 Differential cross section in ydiff(Z,jet1) (Njets ≥ 1)............ 114 A.21 Differential cross section in ysum(Z,jet1) (Njets ≥ 1)............ 115 A.22 Differential cross section in ydiff(Z,jet1) (Njets ≥ 2)............ 115 A.23 Differential cross section in ysum(Z,jet1) (Njets ≥ 2)............ 116 A.24 Differential cross section in ydiff(Z,jet2) (Njets ≥ 2)............ 116 A.25 Differential cross section in ysum(Z,jet2) (Njets ≥ 2)............ 117 A.26 Differential cross section in ydiff(Z,jet1+jet2) (Njets ≥ 2).......... 117 A.27 Differential cross section in ysum(Z,jet1+jet2) (Njets ≥ 2)......... 118 A.28 Differential cross section in ∆φZ,jet1 (Njets ≥ 1)............. 118 A.29 Differential cross section in ∆φZ,jet1 (Njets ≥ 2)............. 119 A.30 Differential cross section in ∆φZ,jet1 (Njets ≥ 3)............. 120 A.31 Differential cross section in ∆φZ,jet2 (Njets ≥ 2)............. 121 A.32 Differential cross section in ∆φZ,jet2 (Njets ≥ 3)............. 122 A.33 Differential cross section in ∆φZ,jet3 (Njets ≥ 3)............. 123 A.34 Differential cross section in ∆φjet1,jet2 (Njets ≥ 2)............ 124 A.35 Differential cross section in ∆φjet1,jet2 (Njets ≥ 3)............ 125 A.36 Differential cross section in ∆φjet1,jet3 (Njets ≥ 3)............ 126 A.37 Differential cross section in ∆φjet2,jet3 (Njets ≥ 3)............ 127 ix List of Figures 1·1 Standard Model of Elementary Particles. .2 1·2 Feynman diagrams for the Drell-Yan process . .6 2·1 HCAL layout and segmentation in the Z-η plane. 15 2·2 HCAL layout and segmentation in the Z-η plane. 21 2·3 AMC13 data format with detailed header information. 24 3·1 Jet multiplicity for the inclusive and binned samples. 31 3·2 Tag and Probe Fit . 36 3·3 Data Trigger Efficiency and SFs . 37 3·4 Number of vertices in data and MC . 39 3·5 Number of vertices in era B-F and G-H . 40 3·6 Dimuon mass and Z candidate jyj background comparison . 46 3·7 Jet multiplicity background comparison . 46 3·8 Z candidate pT background comparison . 47 3·9 First, second, and third jet y background comparison . 48 3·10 First, second, and third jet pT background comparison . 49 3·11 Invariant mass of leading and subleading jet background comparison . 50 3·12 Total hadronic pT background comparison . 51 3·13 Muon pT and η .............................. 52 3·14 Z pT and jyj ................................ 53 3·15 Jet Multiplicity . 54 3·16 Jet pT and jyj ............................... 55 3·17 Invariant mass of leading and subleading jet. 56 3·18 Total hadronic pT one, two, and three jets inclusive. 57 x 3·19 Difference in azimuthal angle between the Z boson and leading jet . 58 3·20 Construction of a response matrix . 61 3·21 Leading jet pT and jyj response matrices . 62 3·22 Second jet pT and jyj response matrices . 63 3·23 Dijet mass, Z pT , and jet multiplicity response matrix . 64 3·24 Total correlations of the Z pT and leading jet pT ............ 69 3·25 Leading jet pT and jyj differential cross section . 73 3·26 Second jet pT and jyj differential cross section . 74 3·27 Third jet pT and jyj differential cross section . 75 3·28 Fourth jet pT and jyj differential cross section . 78 3·29 Fifth jet pT and jyj differential cross section . 79 3·30 Double differential as a function of leading jet pT and jyj ....... 80 3·31 Total hadronic pT differential cross section . 81 3·32 Dijet mass differential cross section . 82 3·33 Jet multiplicity differential cross section . 83 3·34 Z pT and jyj differential cross section . 85 3·35 Z jyj differential cross section . 86 3·36 Double differential as a function of Z pT and jyj ............ 88 3·37 Double differential as a function of leading jet jyj and Z jyj ...... 89 3·38 ∆y leading and sub-leading jet . 90 3·39 ∆y Z and leading jet (≥ 1jet).....................