Session B18: Higgs Yukawas

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Shown is a measurement of the ttH process, in which a 125 GeV Higgs boson is produced along with a pair of top quarks. The Higgs boson is required to decay to all hadronic tau leptons, while all top quarks are required to decay to jets. This final state allows for full reconstruction of the Higgs boson, permitting differential measurements. Proton-proton collision data with a center-of-mass energy of 13 TeV collected by the ATLAS experiment at CERN's Large Hadron Collider are used.   

Live

The Large Hadron Collider (LHC) is a “top quark factory”. It allows for precise measurements of several top quark properties. In addition to this, for the first time ever it is now possible to measure rare processes involving top quarks. Associated production of top and anti-top quarks along with Higgs boson or with electro-weak gauge bosons like W or Z has been observed at the LHC. Precise measurements of these processes have implications on the Standard Model of particle physics and even in cosmology. Recent results from measurements of these rare top quarks processes at the ATLAS experiment in $pp$ collisions at $\sqrt{s}=$ 13 TeV will be discussed   

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We will present our recent calculation of matching NLO QCD corrections to the production of a top-quark pair in association with a W boson using the POWHEG-BOX framework. We compare our results with other Monte Carlo generators for the two same-sign lepton signature commonly used by the experiments. Special focus will be put on the assessment of the importance of subleading electroweak contributions in the modelling of the production process. In addition, We will discuss theoretical uncertainties of our predictions, which are estimated by variations of the renormalization and factorization scales, also matching uncertainties are estimated.   

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The CMS collaboration recently presented their results on the Higgs decay to a pair of muons with 137 fb$^{-1}$ of data at $\sqrt s$ = 13 TeV. The analysis targeted four different production modes, the gluon fusion (ggH), the vector boson fusion (VBF), the Higgs-strahlung process (VH) and the production in association with a pair of top quarks (ttH). Each of these categories had developed it's own dedicated boosted decision tree (BDT) or a deep neural-network (DNN) to efficiently separate the signal from the major background processes. The VBF category used a template-based fit to the DNN score whereas the remaining categories performed data-driven fits to the dimuon mass spectrum. A combined fit from all these categories sees a slight excess in the data corresponding to 3.0 standard deviations at M$_{H}$ = 125.38 GeV (the most precise measurement of the Higgs boson mass to date). This is the first evidence for the Higgs Boson decay to second-generation fermions and is thus an exciting result.   

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The CMS collaboration recently published their result of the search for the Higgs boson decay to two muons using the full LHC Run 2 data set (137fb$^{-1}$). In comparison with previous searches, the analysis sensitivity was substantially enhanced by splitting the data into four exclusive channels, corresponding to different Higgs production modes. The channel targeting the vector boson fusion (VBF) mode used a Monte-Carlo (MC) based strategy, not previously implemented in $H\rightarrow\mu\mu$ searches. In this approach, the background and expected signal were predicted from MC simulation, and a deep neural network (DNN) was trained to maximize the signal-background separation. The signal strength was then extracted by fitting the MC templates of the DNN output score to the observed data. The VBF category significantly contributed to the overall sensitivity of the analysis, with the observed (expected) excess of data corresponding to 2.4 (1.8) standard deviations. A combination of this result with other channels allowed to achieve observed significance of 3.0 standard deviations, which presents the first evidence of the Higgs boson decay to muons.   

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One of the predictions of the Standard Model is that the Higgs boson is even under charge-parity inversion. In this study, we discuss the first direct measurement of the CP nature of the Yukawa coupling between the Higgs boson and tau leptons which is performed on the $H\to\tau\tau$ events. The analysis is based on a p-p collision data set corresponding to $137 \text{ fb}^{-1}$ integrated luminosity recorded by the CMS experiment at CERN during 2016-2018. This is a combined analysis of the $\mu\tau_h$ and $\tau_h\tau_h$ final states in which $\tau_h$ shows the decay of a tau to hadron(s). The angle between the two planes spanned by each of the tau decays is sensitive to the CP of the coupling. Different optimizations are performed to increase the CP sensitivity while retaining enough statistics. The result disfavors a pure CP-odd coupling by $3.2$ standard deviations.   

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A search is presented for the production of the Standard Model Higgs boson in association with a high-energy photon. With a focus on the vector boson fusion process and the dominant Higgs boson decay to $b$-quark pairs, the search benefits from a large reduction of multijet background compared to more inclusive searches. Results are reported from the analysis of $\SI{132}$ fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=\SI{13}$ TeV collected with the ATLAS detector at the Large Hadron Collider. The measured Higgs boson signal yield in this final state signature is $1.3 \pm 1.0$ times the Standard Model prediction. The observed significance of the Higgs boson signal above the background is 1.3 standard deviations, compared to an expected significance of 1.0 standard deviations.   

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With the observation of the $H\rightarrow b\bar{b}$ decay process, the Higgs Yukawa coupling to massive 3rd generation particles have all been measured and our heads now turn towards the 2nd generation. A direct search for the decay of a Higgs boson to charm quarks was originally thought to be beyond the scope of the LHC due to low the $H\rightarrow c\bar{c}$ branching fraction and the difficulty of correctly identifying jets originating from the hadronization of charm quarks. However, through the use of modern machine learning and advanced analysis techniques the potential reach of such a search continues to increase. In this talk I will present a study which looks for a Higgs bosons produced in conjunction with a vector boson (the so-called VH production mode) with the Higgs boson decaying to a pair of charm quarks. The analysis focuses on events where the charm quarks hadronize into two distinct jets, and is split into multiple channels based on the decay of the W and Z boson. Events were produced in $\sqrt{s}=13$ TeV proton-proton collisions and collected during the Run 2 data collection period of the CMS detector.