Proceedings Series

Vol. 11 (2018), No. 2, pp. 211 – 407

The Final HiggsTools Meeting


Acta Phys. Pol. B Proc. Suppl. 11, 217 (2018)

page 217

\(\mathcal {CP}\)-violating Effects on MSSM Higgs Searches

Acta Phys. Pol. B Proc. Suppl. 11, 223 (2018)

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We study the effects of \(\mathcal {CP}\)-violating phases on the phenomenology of the Higgs sector of the MSSM. Complex parameters in the MSSM lead to \(\mathcal {CP}\)-violating mixing between the tree-level \(\mathcal {CP}\)-even and \(\mathcal {CP}\)-odd neutral Higgs states, leading to three new loop-corrected mass eigenstates \(h_a\), \(a \in \lbrace 1,2,3\rbrace \). For scenarios where a light Higgs boson at about 125 GeV can be identified with the observed signal and where the other Higgs states are significantly heavier, a large admixture of the heavy neutral Higgs bosons occurs as a generic feature if \(\mathcal {CP}\)-violating effects are taken into account. Including interference contributions in the predictions for cross sections times branching ratios of the Higgs bosons is essential in this case. As a first step, we present the gluon-fusion and bottom-quark annihilation cross sections for \(h_a\) for the general case of arbitrary complex parameters, and we demonstrate that squark effects strongly depend on the phases of the complex parameters. We then study the effects of interference between \(h_2\) and \(h_3\) for the example of the process \(b\bar {b} \to \tau ^+\tau ^-\). We show that large destructive interference effects modify the LHC exclusion bounds such that parts of the parameter space that would be excluded by MSSM Higgs searches under the assumption of \(\mathcal {CP}\)-conservation open up when the possibility of \(\mathcal {CP}\)-violation in the Higgs sector is accounted for.

Vector Boson Scattering Studies in CMS: The \(pp \to ZZ jj\) Channel

Acta Phys. Pol. B Proc. Suppl. 11, 239 (2018)

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In these proceedings, we discuss the family of Vector Boson Scattering (VBS) processes, in particular, we look at a very recent result from the CMS Collaboration. In this analysis, a search was performed for VBS in the four-lepton and two-jet final state using proton–proton collisions at 13 TeV. The electroweak production of two \(Z\) bosons in association with two jets was measured with an observed (expected) significance of 2.7 (1.6) standard deviations, using a multivariate classifier. Additionally, an expected significance of 1.2 standard deviations was found using matrix elements techniques. Here, we will discuss the latter approach in detail.

Search for \(t\bar {t}H\), \(H \rightarrow b\bar {b}\) at the CMS Experiment in 2016 Using 12.9 fb\(^{-1}\) of \(pp\) Collision Data

Acta Phys. Pol. B Proc. Suppl. 11, 249 (2018)

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We present an overview of the search for \(t\bar {t}H\) in the CMS experiment using up to 12.9 fb\(^{-1}\) of data collected during 2016. The analysis is carried out in the \(H \rightarrow b\bar {b}\) final state with at least one of the top quarks decaying leptonically, resulting in a multi-parton final state with a combinatorial self-background. Discriminators based on machine learning and the direct computation of matrix elements from observed jet and lepton properties are used to distinguish between the \(t\bar {t}H\) signal and the \({t}\bar {t} + \mathrm {jets}\) background. Using a combined fit of the multivariate discriminants in several event categories, we find an observed (expected) upper limit of \(\mu \lt 1.5~(1.7)\) at the 95% confidence level. We further discuss how this analysis can be extended to the full Run 2 dataset.

Search for a Higgs Boson in Association with a Pair of Top Quarks with the ATLAS Detector

Acta Phys. Pol. B Proc. Suppl. 11, 257 (2018)

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The production of a Higgs boson in association with a pair of top quarks (\(t\bar {t}H\)) is one of the main Higgs production channels at the LHC which is yet unobserved. In the recent publications, the ATLAS Collaboration claims evidence for the process using the data collected in 2015 and 2016 at the LHC. The process offers direct sensitivity to the top-Yukawa coupling which is the largest fermion coupling to the Higgs. Any deviation of the top-Yukawa coupling measured directly and compared to indirect constraints would provide a hint towards new physics. In the context of \(t\bar {t}H\), the \(H \to b\bar {b}\) decay is of particular interest due to the large branching ratio and it is, therefore, potentially offering high sensitivity to the top-Yukawa coupling. The goal of this paper is to summarize the recent progress in \(t\bar {t}H(b\bar {b})\) analysis contrasting the strategy employed by ATLAS in 2016 with the new publication in 2017.

Measuring the Top-quark Pole Mass Using \(t\bar t + 1\) Jet Events

Acta Phys. Pol. B Proc. Suppl. 11, 267 (2018)

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The top quark is the heaviest particle discovered so far. Its mass, \(m_t\), is a fundamental parameter of the Standard Model (SM) and its values is an input of many theoretical calculations. Since top quarks are not free-particles, \(m_t\) is not an observable and has to be inferred from other distributions. With the Large Hadron Collider (LHC) entering the precision era, an accurate measurement of the top-quark mass which takes into account all sources of error is important in consistency tests of the SM and in constraining new physics (NP) scenarios through precise electroweak fits. The \(pp\rightarrow t\bar t + 1\) jet process is interesting since the extra-jet radiation depends on the value of \(m_t\). A study of the normalized differential cross section as a function of the invariant mass of the \(t\bar {t} + 1\) jet system is presented, which aims to reduce the total uncertainty on the extraction of \(m_t\).

Higgs Production at NNLO in VBF

Acta Phys. Pol. B Proc. Suppl. 11, 277 (2018)

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This paper expands on recently published results for the factorising next-to-next-to-leading order (NNLO) QCD corrections to Higgs production in the vector boson fusion (VBF) channel. The calculation is fully differential in the kinematics of the Higgs boson and the final-state jets, and is implemented in the NNLOjet framework for computing higher order QCD corrections. We find the NNLO corrections to be limited in magnitude to about \(\pm 5\)% with a weak kinematical dependence in the transverse momenta and rapidity separation of the two tagging jets.

NLO Corrections to \(h \to WW/ZZ \to 4\) Fermions in a Singlet Extension of the Standard Model

Acta Phys. Pol. B Proc. Suppl. 11, 285 (2018)

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At the LHC, the properties of the Higgs boson are investigated to search for traces of physics beyond the Standard Model (SM), with the aim of making discoveries via precision measurements. To this end, theoretical predictions at the highest possible accuracy are required, both within the SM and its extensions. Singlet extensions (SESMs) supplement the SM by a scalar SU(2)\(_W\) gauge singlet, replacing the single Higgs boson of the SM by two CP-even Higgs bosons. The SM coupling strength is shared by the two Higgs bosons, i.e. the Higgs bosons couple with the SM strength weighted by the sine or cosine of a mixing angle. The mass of the additional Higgs boson, the mixing angle, and possibly one or more couplings of the scalar self-interactions parametrize the extended sector. The program Prophecy4f, which calculates decay observables for \(h \to WW/ZZ \to 4\) fermions with EW and QCD corrections in the SM, has been upgraded to an SESM and used to quantify the deviations induced by the extension. We summarize the basic features of the considered extension and the most important numerical results on the predictions for the Higgs decays to four fermions.

Higgs Boson Pair Production: Monte Carlo Generator Interface and Parton Shower

Acta Phys. Pol. B Proc. Suppl. 11, 295 (2018)

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We discuss the combination of the NLO QCD matrix element for double Higgs boson production with a parton shower, including the full top-quark mass dependence. Since the 2-loop double Higgs boson production amplitude is currently known only numerically, in order to produce a fast and stable code for the evaluation of the virtual matrix element, we construct a grid based on a fixed number of precomputed phase-space points. Results are generated in both the POWHEG-BOX and MadGraph5_aMC@NLO Monte Carlo frameworks and showered with Pythia. We investigate the sensitivity of showered predictions of the Higgs boson pair transverse momentum distribution to the parameters of the POWHEG matching scheme.

Modeling BSM Effects on the Higgs Transverse-momentum Spectrum in an EFT Approach

Acta Phys. Pol. B Proc. Suppl. 11, 307 (2018)

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After the discovery of the Higgs boson in 2012, LHC is currently studying its properties. The measurements of small deviations from the SM predictions can be the only way to access new physics, if no new resonances will be found. The bottom-up Effective Field Theory offers a consistent approach, with new higher dimension operators built of Standard Model fields (SMEFT). We discuss how this approach works in the case of the transverse momentum spectrum of the Higgs particle. In our calculation, we augmented the Standard Model with three additional dimension-six operators corresponding to modifications of the top and bottom Yukawa couplings, and a point-like Higgs coupling to gluons. We also discuss the inclusion of the chromomagnetic operator. We present and discuss the impact of these three operators on the \(p_{\rm T}\) spectra at the NLL+NLO accuracy, and show how it can be approximately extended to the NNLL+NNLO level. We find that such modifications, while affecting the total rate within the current uncertainties, can lead to significant distortions in the spectrum shape.

\(b\) Quark Mass Effects in Associated Production

Acta Phys. Pol. B Proc. Suppl. 11, 323 (2018)

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In this work, we study an extension of the commonly used 5F scheme, where \(b\) quarks are treated as massless partons, in which full mass effects are retained in both the initial and in the final state. We name this scheme 5F massive scheme (5FMS). We implement this scheme in the Sherpa Monte Carlo event generator at MePs@Nlo accuracy, and we compare it for two relevant cases for the LHC: \(b\bar {b} \rightarrow H\) and \(pp\rightarrow Zb\).

PDF Dependence on Parameter Fits from Hadronic Data

Acta Phys. Pol. B Proc. Suppl. 11, 329 (2018)

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We present a discussion on the methods for extracting a given parameter from measurements of hadronic data, with particular focus on determinations of the strong coupling constant. We show that when the PDF dependency on the determination is adequately taken into account, the dispersion between the results from different measurements is significantly reduced. We speculatively propose the concept of preferred value of a parameter from a particular dataset.

Developments of TauSpinner Prepared for Production of \(\tau \) Lepton Pairs with High \(p_{\rm T}\) Jets for the Spin-2 Case

Acta Phys. Pol. B Proc. Suppl. 11, 339 (2018)

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In the recently published paper, a new version of TauSpinner tool ver.2.0.0 has been presented. It introduces non-standard states and couplings in the case of spin-2 state (as an example), and study their effects in the vector-boson-fusion processes by exploiting the spin correlations of \(\tau \)-lepton pair decay products in processes where final states include also two hard jets. The implementation is prepared as the external routine. Consistency tests of the implemented matrix elements, reweighting algorithm and numerical results for observables sensitive to \(\tau \) polarization are presented.

Deep Learning Approach to Measurement of Higgs Boson CP in the \(H\rightarrow \tau \tau \) Decay Channel

Acta Phys. Pol. B Proc. Suppl. 11, 349 (2018)

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The measurement of the Higgs boson CP is amongst the most vital measurements in establishing the nature of the Higgs boson. Of the many decay channels, the ditau final state is one of the most sensitive channels due to the Yukawa coupling allowing access to a potential mixing between CP-even and CP-odd Higgs bosons. While decay modes such as the \(\tau \to \rho ^{\pm }\nu \) are well-established in literature, modes such as the \(\tau \to a_1^{\pm }\nu \) are not so. A new approach to encompass many decay modes has been developed using deep learning neural networks. This article summarises work done in assessing the robustness of the approach with respect to detector resolution effects and potential modelling issues. Also discussed is the Drell–Yan background.

Higgs Production, Decay, and Related Mathematical Objects

Acta Phys. Pol. B Proc. Suppl. 11, 365 (2018)

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In these proceedings and the talk on which it is based, the author reviews the work he has participated in, during the last three years while being an ESR under the HiggsTools network. It is based on four peer-reviewed papers as well as some unpublished work. The paper is framed around the calculation of the planar Feynman integrals contributing to the two-loop correction to \(H\!+\!j\) production in hadron colliders. That project (which had the calculation of the two-loop contribution to the decay width for \(H\!\rightarrow \!Z\gamma \) as a spin-off) resulted in analytical expressions, of which some were expressible in terms of the function class of generalized polylogarithms, for which methods of reduction and evaluation will be discussed. Yet some of the the master integrals were not expressible in terms of that function class, for those elliptic integrals were needed, and a method useful to identify such cases, that of \(d\)-dimensional unitarity cuts, is discussed as well.

full authors' list

S. Borowka, G. Heinrich, S. Jahn, S.P. Jones, M. Kerner, J. Schlenk

Numerical Evaluation of Two-loop Integrals with pySecDec

Acta Phys. Pol. B Proc. Suppl. 11, 375 (2018)

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We describe the program pySecDec, which factorises endpoint singularities from multi-dimensional parameter integrals and can serve to calculate integrals occurring in higher order perturbative calculations numerically. We focus on the new features and on frequently asked questions about the usage of the program.

Computing Radiative Corrections in Four Dimensions

Acta Phys. Pol. B Proc. Suppl. 11, 387 (2018)

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I comment and summarize the principles underlying the Four Dimensional Regularization/Renormalization (FDR) approach to the UV and IR infinities. A few recent results are also reviewed.

Physics After the Discovery of the Higgs Boson

Acta Phys. Pol. B Proc. Suppl. 11, 397 (2018)

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I show that with the discovery of the Higgs boson, we have entered a new phase of our understanding of nature. This leads us towards a paradigm shift in the search for possible new physics, away from major extensions like supersymmetry towards minimalistic extensions, that largely preserve the structure of the Standard Model. To discover such new physics, precision may be more important than energy. Precision \(=\) Discovery! A possible path for the future is sketched.


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