Session R14: Electroweak Physics

Measuring Higgs Boson Pair Production in the 4b Final State at the ATLAS Experiment

Measuring the production of pairs of Higgs bosons, or di-Higgs production, offers physicists insight into how the Higgs boson interacts with itself. These self-interactions determine the shape of the Higgs potential. Variations of this potential beyond the Standard Model could explain big mysteries, such as the imbalance between matter and anti-matter in our universe. We'll present recent results from the ATLAS Experiment at the LHC measuring Higgs boson pairs in an especially challenging final state where each Higgs boson decays to two b-quarks.   

ttHH production in multilepton final states with the ATLAS experiment

Higgs boson pair production in association with a top-quark pair, ttHH, is a rare and unexplored process in the Standard Model with an expected cross-section 0.8 fb at 13 TeV. It is sensitive to BSM physics in the Higgs sector due to the Yukawa coupling of the Top quark. In addition, ttHH production provides a signature to probe Higgs self-coupling. A new analysis using ATLAS Run-2 and Run-3 data studies the ttHH sensitivity and the Higgs self-coupling constraints. In this talk, the sensitivity for an integrated luminosity of 140 fb−1 in Run2 will be presented. The ttHH decay final states containing either a pair of same-sign leptons or multi-lepton (SSML) are considered. Analysis strategies with novel techniques on multivariate analysis (ex. BDT, transformer), background modeling, and ttHH sensitivity will be discussed.   

Search for Higgs boson decays to two bottom and charm quarks at ATLAS

The Higgs boson, the mass mediator in the Standard Model (SM) of particle physics, was discovered at the Large Hadron Collider (LHC) in 2012. Since then, measuring the decay from the Higgs boson to fermions and validating the SM prediction has been one of the main physics goals of the LHC. The Higgs boson to bottom quark decay (H->bb) has been observed by the ATLAS collaboration during the LHC second data run (Run 2). Similarly, upper limits have been set on the probability of Higgs bosons decaying to charm quarks (H->cc) using ATLAS Run 2 data. In this talk, we present the latest ATLAS combined measurement of the Higgs boson decays to bottom and charm quarks (H->bb,cc). Novel machine learning techniques are used to improve signal purity. This final ATLAS Run 2 combined measurement sets the most stringent upper limit on H->cc to date. In addition, this combined measurement orthogonalizes the event selection between H->bb and H->cc and correlates their modeling uncertainties. With the cancellation of uncertainties, the measurement sets the most stringent ratio between the charm and bottom Yukawa coupling modifiers (k_c/k_b) as well.    

Heavy Mass Estimator in Resonant Higgs pair production in single lepton bbWW channel

In the study of searching for a new heavy resonanse that decays into a pair of Higgs bosons, specifically X → HH → bbWW → bblνqq (bblvlv), the critical components requiring precise measurement are the leptons (electrons and muons), jets, and neutrinos. The conventional method for determining neutrino energy, using Missing Transverse Momentum, relies on balancing the detected energy in the transverse plane of all reconstructed particles in the event. To address inaccuracies in neutrino energy measurement and to deal with the cancellation of momenta of two neutrinos in the final state, a new technique called the Heavy Mass Estimator (HME) was introduced in the CMS Run 2 analysis in the dilepton final state. This technique aims to calculate the most probable mass of X by maximizing the likelihood function using experimental observables in the final state. We are currently exploring the extension of HME to the single lepton final state, anticipating a significant improvement in sensitivity.   

Search for light pseudoscalar Higgs bosons with boosted di-mu di-tau topologies

A search is performed for a light pseudoscalar Higgs boson (a) motivated by the theoretical framework of two Higgs doublet plus singlet models (2HDM+S). This search uses Run II LHC data collected at 13 TeV by the CMS experiment and analyzes the decay channel H->a a->mu mu tau tau, with H being either the 125 GeV state or a more massive Higgs boson. Final state taus have a boosted and collimated topology due to the large mass difference between the H and a. Thus, a novel algorithm for this non-standard final state is designed to increase the identification efficiency, and a dedicated machine learning technique is used for the case of overlapping hadronic tau decays. Limits are derived in the context of four types of 2HDM+S models.   

Entangled Top Quarks at the LHC measured with the CMS Detector at √s = 13 TeV

Measurements of the entanglement of top quark pairs utilizing spin correlations are presented using events containing two leptons produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were recorded by the CMS experiment at the CERN LHC in 2016 and correspond to an integrated luminosity of 35.9 fb^-1. The extent to which top quarks are entangled is measured by an entanglement proxy, which is optimized to have maximal sensitivity.