Higgs collider phenomenology: important backgrounds, naturalness probes and the electroweak phase transition. A Dissertation presented by Harikrishnan Ramani to The Graduate School in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Physics and Astronomy Stony Brook University August 2017 (include this copyright page only if you are selecting copyright through ProQuest, which is optional) Copyright by Harikrishnan Ramani 2017 Stony Brook University The Graduate School Harikrishnan Ramani We, the dissertation committee for the above candidate for the Doctor of Philosophy degree, hereby recommend acceptance of this dissertation Patrick Meade - Dissertation Advisor Associate Professor, Department of Physics and Astronomy George Sterman - Chairperson of Defense Distinguished Professor, Department of Physics and Astronomy Dmitri Tsybychev - Committee Member Associate Professor, Department of Physics and Astronomy Eder Izaguirre - Outside Member Assistant Physicist, Department of Physics, Brookhaven National Laboratory This dissertation is accepted by the Graduate School Charles Taber Dean of the Graduate School ii Abstract of the Dissertation Higgs collider phenomenology: important backgrounds, naturalness probes and the electroweak phase transition. by Harikrishnan Ramani Doctor of Philosophy in Physics and Astronomy Stony Brook University 2017 The Higgs boson discovered in 2012, might be the portal to new physics. With the Higgs as the common theme we present the following research arcs. In order to study the Higgs, it is important to have a very good handle on Standard model(SM) backgrounds. One such background process is SM WW production, which reported routine 3 sigma excesses in early run 1 of the LHC. However, experiments use Parton Showers for theoreti- cal prediction and this might be inadequate for exclusive cross-sections. We show that taking into account higher order Sudakov logarithms through transverse momentum and jet-veto resummation predicts a larger cross-section than parton showers and reduces the theory-experiment disagree- ment. iii Next, improvements are suggested to the state-of-the-art finite temperature field theory cal- culations that can predict the nature of the electroweak phase transitions in beyond-the-standard model scenarios. We find that relaxing the high-temperature approximation and resumming logs of temperature to super-daisy order can have significant changes in the order of the phase transition. This in turn can have important consequences for the possibility of creating the baryon anti-baryon asymmetry across this phase transition. Our improved calculation in general predicts weaker phase transitions, and hence smaller baryon-anti baryon asymmetry. This strengthens the case for build- ing future colliders in the form of a no-lose theorem; absence of deviation from the Standard model in Higgs precision physics can falsify the possibility of Electroweak Baryogenesis. Finally, we present another consequence of Higgs precision studies, constraining new physics invented to ameliorate the hierarchy problem. These theories generically predict top partners at the electroweak scale, which are connected with the top quark through a symmetry. However these top partners have not been detected at colliders making the electroweak scale severely fine-tuned. We find that generically, top-partner mass limits will reach a TeV just from Higgs precision at future colliders. iv Dedication Page To my grandfather, who taught me to ask questions. v Contents 1 Introduction 1 1.1 Standard Model of Particle Physics . 1 1.2 Problems from Astronomical / Cosmological Observations . 2 1.3 Small or Arbitrary parameter problems . 4 1.4 The Hierarchy Problem . 5 1.5 Baryogenesis . 7 1.6 Colliders: Past, Current and Future State of Experiments . 9 1.7 Outline of Thesis . 11 + 2 Transverse momentum resummation effects in W W − measurements 13 2.1 Introduction . 13 + 2.2 W W − transverse momentum resummation . 18 2.3 Numerical results . 21 2.4 Transverse Momentum Reweighting and Fiducial Cross Sections . 24 2.5 Reweighting Results . 27 2.6 Jet Veto . 30 2.7 Discussion . 32 3 Precision diboson measurements and the interplay of pT and jet-veto resummations 36 3.1 Introduction . 36 3.2 Jet-Veto and pT Resummation Theory . 40 3.3 Reweighting MC events and Applications . 43 vi 3.4 Results and Comparison . 47 3.5 Jet Definitions and other QCD effects . 48 3.6 Discussion . 50 3 + 4 Resummation of jet veto logarithms at N LLa + NNLO for W W − production at the LHC 55 4.1 Introduction . 55 4.2 fixed order . 56 4.3 Jet veto resummation . 58 4.3.1 Hard function . 59 4.3.2 Beam function . 61 4.3.3 Rapidity Renormalization Group . 64 4.4 Results . 65 5 Thermal Resummation and Phase Transitions 71 5.1 Introduction . 71 5.2 Review: Calculating the Electroweak Phase Transition . 77 5.2.1 Tree-level Potential . 77 5.2.2 Coleman Weinberg Potential . 78 5.2.3 Finite Temperature . 79 5.2.4 Resummation of the Thermal Mass: Truncated Full Dressing (TFD) . 81 5.2.5 Types of Electroweak Phase Transitions . 84 5.2.6 Problems with the standard one-loop TFD calculation of the phase transition 88 5.3 Formal aspects of finite-temperature mass resummation . 91 5.3.1 Tadpole resummation in φ4 theories . 92 5.3.2 A general resummation procedure for BSM theories . 98 5.3.3 Future Directions . 100 5.4 Computing the the Strength of the Phase Transition . 102 5.4.1 Zero-Temperature Calculation . 102 vii 5.4.2 Finite-Temperature Calculation . 104 5.4.3 Comparing Resummation Schemes . 112 5.5 Physical Consequences . 114 5.6 Conclusions . 119 6 Higgs Precision Constraints on Colored Naturalness 122 6.1 Introduction . 122 6.2 Naturalness and Higgs Couplings . 125 6.3 Higgs Precision Constraints & Colored Top Partners . 127 6.3.1 Definitions for non-Standard Model Higgs couplings . 128 6.3.2 How to Constrain and Hide Top Partners . 130 6.4 Data Sets and Fitting Procedure . 133 6.4.1 Current and future proton collider data . 133 6.4.2 Future lepton collider data . 135 6.5 Canonical Top Partner Models and Extensions . 137 6.5.1 Spin-0 . 137 6.5.2 Spin-1/2 . 144 6.5.3 Spin-1 . 148 6.6 Results and Discussions . 150 6.6.1 Constraints on top partners that only affect hgg, hγγ loops . 151 6.6.2 Constraints on top-partners with modified SM Higgs couplings . 154 6.6.3 Constraints on canonical models and extensions . 157 6.7 Conclusions . 161 Appendices 164 A Instruction Manual for Optimized Partial Dressing Calculation of Phase Transition 165 B Future Complementary Higgs Precision Probes 168 C Loop-induced Higgs Couplings 173 viii D Cross-check with HiggsSignals 175 E Data Tables 177 ix List of Figures + 2.1 Plot of resummed, finite (matching) and fixed-order W W − transverse momen- tum distributions from 8 TeV proton collisions. Note that the LO pT distribution has the same ↵s order as the NLO total cross section. 21 + 2.2 Plot of renormalization, factorization and resummation scale variations of the W W − transverse momentum distribution for 8 TeV collisions. 22 + 2.3 NNLO+LO predictions, with error bands, for the W W − transverse momentum distribution for 7,8 and 14 TeV collisions. 22 2.4 NNLL+LO prediction for the WW transverse momentum distribution at 8 TeV, with and without the non-perturbative Gaussian smearing factor exp 1GeV2 b2 . 23 − 2.5 Comparision of our resummed WW pT distribution with a SCET-based⇥ resumma-⇤ tion calculation, with error bands shown for both. 24 + 2.6 Plot of Resummation predicted and MC+shower predictions for W W − trans- verse momentum distributions at 8 TeV. The shaded region represents the scale Q variation by a factor of 2 relative to the central scale choice Q = mW for the resummation prediction. 26 + 2.7 aMC@NLO+Herwig++ observables histogrammed for W W − transverse mo- mentum distribution for 7 TeV collisions and including the reweighting correction. ............................................ 30 x 2.8 The top row shows the reweighting correction for left (Powheg+Pythia8), center miss (aMC@NLO+Herwig++), right (Powheg+Herwig++) to the pT (ll + ET ) ob- servable. The bottom row has bin-by-bin percentage difference in events between reweighting and the MC + PS. 31 2.9 Events before the Jet veto. The number of 0 jet events or events with 1 or more jets is shown as a function of the pT of the diboson system. Since 1 or more jet - events are vetoed, this sculpts the pT -shape. 32 j 3.1 For ps =8TeV and R =0.4 anti-kT jet algorithm, in the left hand panel dσ/dpT is plotted. For the distribution shown in blue, errors come from scale variations without NP factors, in red ⇤NP =500MeVuncertainties are included. In the right j hand panel, the fractional uncertainty of dσ/dpT from scale variation relative to the central scale choice is shown with and without NP uncertainties. 46 a........................................46 b........................................46 WW 3.2 correlation variable ⇢ as a function of pT ..................... 47 WW 3.3 Comparison of jet-veto efficiency and pT in the zero jet bin, from jet veto re- summation and pT resummation for R=0.4 at 8 TeV (top) and 13 TeV (bottom). 50 a 8TeV..................................... 50 b 13TeV .................................... 50 3.4 Comparison of jet veto efficiencies for 8 TeV for R=0.4, 0.5 and 1. 51 3.5 Comparison of jet veto efficiencies for 8 TeV using pT reweighting method with MPI off vs on for R =0.4, 0.5 and 1. 51 + 3.6 The pT (` `− +MET)distribution after a parametrized smearing of MET.....52 + 4.1 Summary of jet veto resummation results for qq¯ W W −. We include results at ! 8 TeV and 13 TeV, under ATLAS or CMS jet veto cuts.